From 68a58f255ac7b7487769667fdd5fe2536f952c15 Mon Sep 17 00:00:00 2001
From: Ross Smyth <crs2017@gmail.com>
Date: Thu, 15 Feb 2024 19:54:35 -0500
Subject: [PATCH 01/22] Add postfix-match experimental feature

Co-authored-by: Josh Stone <jistone@redhat.com>
---
 compiler/rustc_ast_passes/src/feature_gate.rs |  1 +
 compiler/rustc_feature/src/unstable.rs        |  2 +
 compiler/rustc_parse/src/parser/expr.rs       | 19 +++++-
 compiler/rustc_span/src/symbol.rs             |  1 +
 .../src/language-features/postfix-match.md    | 22 +++++++
 .../feature-gate-postfix_match.rs             | 17 +++++
 .../feature-gate-postfix_match.stderr         | 23 +++++++
 .../ui/match/postfix-match/pf-match-chain.rs  | 16 +++++
 .../postfix-match/pf-match-exhaustiveness.rs  |  7 +++
 .../pf-match-exhaustiveness.stderr            | 21 +++++++
 .../ui/match/postfix-match/pf-match-types.rs  | 15 +++++
 .../match/postfix-match/pf-match-types.stderr | 21 +++++++
 tests/ui/match/postfix-match/postfix-match.rs | 62 +++++++++++++++++++
 13 files changed, 226 insertions(+), 1 deletion(-)
 create mode 100644 src/doc/unstable-book/src/language-features/postfix-match.md
 create mode 100644 tests/ui/feature-gates/feature-gate-postfix_match.rs
 create mode 100644 tests/ui/feature-gates/feature-gate-postfix_match.stderr
 create mode 100644 tests/ui/match/postfix-match/pf-match-chain.rs
 create mode 100644 tests/ui/match/postfix-match/pf-match-exhaustiveness.rs
 create mode 100644 tests/ui/match/postfix-match/pf-match-exhaustiveness.stderr
 create mode 100644 tests/ui/match/postfix-match/pf-match-types.rs
 create mode 100644 tests/ui/match/postfix-match/pf-match-types.stderr
 create mode 100644 tests/ui/match/postfix-match/postfix-match.rs

diff --git a/compiler/rustc_ast_passes/src/feature_gate.rs b/compiler/rustc_ast_passes/src/feature_gate.rs
index a28fcb0077948..296f237763eb2 100644
--- a/compiler/rustc_ast_passes/src/feature_gate.rs
+++ b/compiler/rustc_ast_passes/src/feature_gate.rs
@@ -565,6 +565,7 @@ pub fn check_crate(krate: &ast::Crate, sess: &Session, features: &Features) {
     gate_all!(generic_const_items, "generic const items are experimental");
     gate_all!(unnamed_fields, "unnamed fields are not yet fully implemented");
     gate_all!(fn_delegation, "functions delegation is not yet fully implemented");
+    gate_all!(postfix_match, "postfix match is experimental");
 
     if !visitor.features.never_patterns {
         if let Some(spans) = spans.get(&sym::never_patterns) {
diff --git a/compiler/rustc_feature/src/unstable.rs b/compiler/rustc_feature/src/unstable.rs
index 17c4d81474e27..89f471d21bb07 100644
--- a/compiler/rustc_feature/src/unstable.rs
+++ b/compiler/rustc_feature/src/unstable.rs
@@ -555,6 +555,8 @@ declare_features! (
     (unstable, offset_of_nested, "1.77.0", Some(120140)),
     /// Allows using `#[optimize(X)]`.
     (unstable, optimize_attribute, "1.34.0", Some(54882)),
+    /// Allows postfix match `expr.match { ... }`
+    (unstable, postfix_match, "CURRENT_RUSTC_VERSION", Some(121618)),
     /// Allows macro attributes on expressions, statements and non-inline modules.
     (unstable, proc_macro_hygiene, "1.30.0", Some(54727)),
     /// Allows `&raw const $place_expr` and `&raw mut $place_expr` expressions.
diff --git a/compiler/rustc_parse/src/parser/expr.rs b/compiler/rustc_parse/src/parser/expr.rs
index 6cc358db9fcae..02ff452473dd0 100644
--- a/compiler/rustc_parse/src/parser/expr.rs
+++ b/compiler/rustc_parse/src/parser/expr.rs
@@ -1375,6 +1375,12 @@ impl<'a> Parser<'a> {
             return Ok(self.mk_await_expr(self_arg, lo));
         }
 
+        if self.eat_keyword(kw::Match) {
+            let match_span = self.prev_token.span;
+            self.psess.gated_spans.gate(sym::postfix_match, match_span);
+            return self.parse_match_block(lo, match_span, self_arg);
+        }
+
         let fn_span_lo = self.token.span;
         let mut seg = self.parse_path_segment(PathStyle::Expr, None)?;
         self.check_trailing_angle_brackets(&seg, &[&token::OpenDelim(Delimiter::Parenthesis)]);
@@ -2889,8 +2895,19 @@ impl<'a> Parser<'a> {
     /// Parses a `match ... { ... }` expression (`match` token already eaten).
     fn parse_expr_match(&mut self) -> PResult<'a, P<Expr>> {
         let match_span = self.prev_token.span;
-        let lo = self.prev_token.span;
         let scrutinee = self.parse_expr_res(Restrictions::NO_STRUCT_LITERAL, None)?;
+
+        self.parse_match_block(match_span, match_span, scrutinee)
+    }
+
+    /// Parses a `match expr { ... }` or a `expr.match { ... }` expression.
+    /// This is after the match token and scrutinee are eaten
+    fn parse_match_block(
+        &mut self,
+        lo: Span,
+        match_span: Span,
+        scrutinee: P<Expr>,
+    ) -> PResult<'a, P<Expr>> {
         if let Err(mut e) = self.expect(&token::OpenDelim(Delimiter::Brace)) {
             if self.token == token::Semi {
                 e.span_suggestion_short(
diff --git a/compiler/rustc_span/src/symbol.rs b/compiler/rustc_span/src/symbol.rs
index 3784a08b1b720..2474189fef6e1 100644
--- a/compiler/rustc_span/src/symbol.rs
+++ b/compiler/rustc_span/src/symbol.rs
@@ -1319,6 +1319,7 @@ symbols! {
         poll,
         poll_next,
         post_dash_lto: "post-lto",
+        postfix_match,
         powerpc_target_feature,
         powf128,
         powf16,
diff --git a/src/doc/unstable-book/src/language-features/postfix-match.md b/src/doc/unstable-book/src/language-features/postfix-match.md
new file mode 100644
index 0000000000000..cd6b6a7442c5a
--- /dev/null
+++ b/src/doc/unstable-book/src/language-features/postfix-match.md
@@ -0,0 +1,22 @@
+# `postfix-match`
+
+`postfix-match` adds the feature for matching upon values postfix
+the expressions that generate the values.
+
+```rust,edition2021
+#![feature(postfix_match)]
+
+enum Foo {
+    Bar,
+    Baz
+}
+
+fn get_foo() -> Foo {
+    Foo::Bar
+}
+
+get_foo().match {
+    Foo::Bar => {},
+    Foo::Baz => panic!(),
+}
+```
diff --git a/tests/ui/feature-gates/feature-gate-postfix_match.rs b/tests/ui/feature-gates/feature-gate-postfix_match.rs
new file mode 100644
index 0000000000000..dce7e81a9ae44
--- /dev/null
+++ b/tests/ui/feature-gates/feature-gate-postfix_match.rs
@@ -0,0 +1,17 @@
+// Testing that postfix match doesn't work without enabling the feature
+
+fn main() {
+    let val = Some(42);
+
+    val.match { //~ ERROR postfix match is experimental
+        Some(42) => "the answer to life, the universe, and everything",
+        _ => "might be the answer to something"
+    };
+
+    // Test that the gate works behind a cfg
+    #[cfg(FALSE)]
+    val.match { //~ ERROR postfix match is experimental
+        Some(42) => "the answer to life, the universe, and everything",
+        _ => "might be the answer to something"
+    };
+}
diff --git a/tests/ui/feature-gates/feature-gate-postfix_match.stderr b/tests/ui/feature-gates/feature-gate-postfix_match.stderr
new file mode 100644
index 0000000000000..136838788dd29
--- /dev/null
+++ b/tests/ui/feature-gates/feature-gate-postfix_match.stderr
@@ -0,0 +1,23 @@
+error[E0658]: postfix match is experimental
+  --> $DIR/feature-gate-postfix_match.rs:6:9
+   |
+LL |     val.match {
+   |         ^^^^^
+   |
+   = note: see issue #121618 <https://github.com/rust-lang/rust/issues/121618> for more information
+   = help: add `#![feature(postfix_match)]` to the crate attributes to enable
+   = note: this compiler was built on YYYY-MM-DD; consider upgrading it if it is out of date
+
+error[E0658]: postfix match is experimental
+  --> $DIR/feature-gate-postfix_match.rs:13:9
+   |
+LL |     val.match {
+   |         ^^^^^
+   |
+   = note: see issue #121618 <https://github.com/rust-lang/rust/issues/121618> for more information
+   = help: add `#![feature(postfix_match)]` to the crate attributes to enable
+   = note: this compiler was built on YYYY-MM-DD; consider upgrading it if it is out of date
+
+error: aborting due to 2 previous errors
+
+For more information about this error, try `rustc --explain E0658`.
diff --git a/tests/ui/match/postfix-match/pf-match-chain.rs b/tests/ui/match/postfix-match/pf-match-chain.rs
new file mode 100644
index 0000000000000..80546e1963bb6
--- /dev/null
+++ b/tests/ui/match/postfix-match/pf-match-chain.rs
@@ -0,0 +1,16 @@
+//@ run-pass
+
+#![feature(postfix_match)]
+
+fn main() {
+    1.match {
+        2 => Some(0),
+        _ => None,
+    }.match {
+        None => Ok(true),
+        Some(_) => Err("nope")
+    }.match {
+        Ok(_) => (),
+        Err(_) => panic!()
+    }
+}
diff --git a/tests/ui/match/postfix-match/pf-match-exhaustiveness.rs b/tests/ui/match/postfix-match/pf-match-exhaustiveness.rs
new file mode 100644
index 0000000000000..f4cac46f7cd64
--- /dev/null
+++ b/tests/ui/match/postfix-match/pf-match-exhaustiveness.rs
@@ -0,0 +1,7 @@
+#![feature(postfix_match)]
+
+fn main() {
+    Some(1).match { //~ non-exhaustive patterns
+        None => {},
+    }
+}
diff --git a/tests/ui/match/postfix-match/pf-match-exhaustiveness.stderr b/tests/ui/match/postfix-match/pf-match-exhaustiveness.stderr
new file mode 100644
index 0000000000000..f458218bb5d67
--- /dev/null
+++ b/tests/ui/match/postfix-match/pf-match-exhaustiveness.stderr
@@ -0,0 +1,21 @@
+error[E0004]: non-exhaustive patterns: `Some(_)` not covered
+  --> $DIR/pf-match-exhaustiveness.rs:4:5
+   |
+LL |     Some(1).match {
+   |     ^^^^^^^ pattern `Some(_)` not covered
+   |
+note: `Option<i32>` defined here
+  --> $SRC_DIR/core/src/option.rs:LL:COL
+  ::: $SRC_DIR/core/src/option.rs:LL:COL
+   |
+   = note: not covered
+   = note: the matched value is of type `Option<i32>`
+help: ensure that all possible cases are being handled by adding a match arm with a wildcard pattern or an explicit pattern as shown
+   |
+LL ~         None => {},
+LL ~         Some(_) => todo!(),
+   |
+
+error: aborting due to 1 previous error
+
+For more information about this error, try `rustc --explain E0004`.
diff --git a/tests/ui/match/postfix-match/pf-match-types.rs b/tests/ui/match/postfix-match/pf-match-types.rs
new file mode 100644
index 0000000000000..af205926fb610
--- /dev/null
+++ b/tests/ui/match/postfix-match/pf-match-types.rs
@@ -0,0 +1,15 @@
+#![feature(postfix_match)]
+
+fn main() {
+    Some(10).match {
+    //~^ NOTE `match` arms have incompatible types
+        Some(5) => false,
+        //~^ NOTE this is found to be of type `bool`
+        Some(2) => true,
+        //~^ NOTE this is found to be of type `bool`
+        None    => (),
+        //~^ ERROR `match` arms have incompatible types
+        //~| NOTE expected `bool`, found `()`
+        _       => true
+    }
+}
diff --git a/tests/ui/match/postfix-match/pf-match-types.stderr b/tests/ui/match/postfix-match/pf-match-types.stderr
new file mode 100644
index 0000000000000..0cfc1363d5f1e
--- /dev/null
+++ b/tests/ui/match/postfix-match/pf-match-types.stderr
@@ -0,0 +1,21 @@
+error[E0308]: `match` arms have incompatible types
+  --> $DIR/pf-match-types.rs:10:20
+   |
+LL | /     Some(10).match {
+LL | |
+LL | |         Some(5) => false,
+   | |                    ----- this is found to be of type `bool`
+LL | |
+LL | |         Some(2) => true,
+   | |                    ---- this is found to be of type `bool`
+LL | |
+LL | |         None    => (),
+   | |                    ^^ expected `bool`, found `()`
+...  |
+LL | |         _       => true
+LL | |     }
+   | |_____- `match` arms have incompatible types
+
+error: aborting due to 1 previous error
+
+For more information about this error, try `rustc --explain E0308`.
diff --git a/tests/ui/match/postfix-match/postfix-match.rs b/tests/ui/match/postfix-match/postfix-match.rs
new file mode 100644
index 0000000000000..03c4e8ab5451f
--- /dev/null
+++ b/tests/ui/match/postfix-match/postfix-match.rs
@@ -0,0 +1,62 @@
+//@ run-pass
+
+#![feature(postfix_match)]
+
+struct Bar {
+    foo: u8,
+    baz: u8,
+}
+
+pub fn main() {
+    let thing = Some("thing");
+
+    thing.match {
+        Some("nothing") => {},
+        Some(text) if text.eq_ignore_ascii_case("tapir")  => {},
+        Some("true") | Some("false") => {},
+        Some("thing") => {},
+        Some(_) => {},
+        None => {}
+    };
+
+    let num = 2u8;
+
+    num.match {
+        0 => {},
+        1..=5 => {},
+        _ => {},
+    };
+
+    let slic = &[1, 2, 3, 4][..];
+
+    slic.match {
+        [1] => {},
+        [2, _tail @ ..] => {},
+        [1, _] => {},
+        _ => {},
+    };
+
+    slic[0].match {
+        1 => 0,
+        i => i,
+    };
+
+    let out = (1, 2).match {
+        (1, 3) => 0,
+        (_, 1) => 0,
+        (1, i) => i,
+        _ => 3,
+    };
+    assert!(out == 2);
+
+    let strct = Bar {
+        foo: 3,
+        baz: 4
+    };
+
+    strct.match {
+        Bar { foo: 1, .. } => {},
+        Bar { baz: 2, .. } => {},
+        _ => (),
+    };
+}

From 78b3bf98c3425d139b42a6326701573ff98b1a1f Mon Sep 17 00:00:00 2001
From: Ross Smyth <crs2017@gmail.com>
Date: Sat, 17 Feb 2024 12:43:54 -0500
Subject: [PATCH 02/22] Add MatchKind member to the Match expr for pretty
 printing & fmt

---
 compiler/rustc_ast/src/ast.rs                 | 11 +++++++++-
 compiler/rustc_ast/src/mut_visit.rs           |  2 +-
 compiler/rustc_ast/src/visit.rs               |  2 +-
 compiler/rustc_ast_lowering/src/expr.rs       |  2 +-
 .../rustc_ast_pretty/src/pprust/state/expr.rs | 20 +++++++++++++-----
 .../src/assert/context.rs                     |  2 +-
 .../src/deriving/cmp/partial_ord.rs           |  2 +-
 .../src/deriving/debug.rs                     |  3 +--
 compiler/rustc_expand/src/build.rs            |  4 ++--
 compiler/rustc_lint/src/unused.rs             |  4 ++--
 compiler/rustc_parse/src/parser/expr.rs       | 18 +++++++++-------
 .../clippy/clippy_lints/src/redundant_else.rs |  2 +-
 .../src/suspicious_operation_groupings.rs     |  2 +-
 .../clippy/clippy_utils/src/ast_utils.rs      |  2 +-
 src/tools/rustfmt/src/expr.rs                 |  8 +++----
 src/tools/rustfmt/src/matches.rs              |  4 +++-
 tests/pretty/postfix-match.rs                 | 21 +++++++++++++++++++
 17 files changed, 76 insertions(+), 33 deletions(-)
 create mode 100644 tests/pretty/postfix-match.rs

diff --git a/compiler/rustc_ast/src/ast.rs b/compiler/rustc_ast/src/ast.rs
index 13b1a589d9ba9..6ffb3d65abcad 100644
--- a/compiler/rustc_ast/src/ast.rs
+++ b/compiler/rustc_ast/src/ast.rs
@@ -1436,7 +1436,7 @@ pub enum ExprKind {
     /// `'label: loop { block }`
     Loop(P<Block>, Option<Label>, Span),
     /// A `match` block.
-    Match(P<Expr>, ThinVec<Arm>),
+    Match(P<Expr>, ThinVec<Arm>, MatchKind),
     /// A closure (e.g., `move |a, b, c| a + b + c`).
     Closure(Box<Closure>),
     /// A block (`'label: { ... }`).
@@ -1761,6 +1761,15 @@ pub enum StrStyle {
     Raw(u8),
 }
 
+/// The kind of match expression
+#[derive(Clone, Copy, Encodable, Decodable, Debug, PartialEq)]
+pub enum MatchKind {
+    /// match expr { ... }
+    Prefix,
+    /// expr.match { ... }
+    Postfix,
+}
+
 /// A literal in a meta item.
 #[derive(Clone, Encodable, Decodable, Debug, HashStable_Generic)]
 pub struct MetaItemLit {
diff --git a/compiler/rustc_ast/src/mut_visit.rs b/compiler/rustc_ast/src/mut_visit.rs
index bbbb34f7f2f48..f9b519b307921 100644
--- a/compiler/rustc_ast/src/mut_visit.rs
+++ b/compiler/rustc_ast/src/mut_visit.rs
@@ -1423,7 +1423,7 @@ pub fn noop_visit_expr<T: MutVisitor>(
             visit_opt(label, |label| vis.visit_label(label));
             vis.visit_span(span);
         }
-        ExprKind::Match(expr, arms) => {
+        ExprKind::Match(expr, arms, _kind) => {
             vis.visit_expr(expr);
             arms.flat_map_in_place(|arm| vis.flat_map_arm(arm));
         }
diff --git a/compiler/rustc_ast/src/visit.rs b/compiler/rustc_ast/src/visit.rs
index 9efb87e53cde9..64c2cbd297d0f 100644
--- a/compiler/rustc_ast/src/visit.rs
+++ b/compiler/rustc_ast/src/visit.rs
@@ -919,7 +919,7 @@ pub fn walk_expr<'a, V: Visitor<'a>>(visitor: &mut V, expression: &'a Expr) -> V
             visit_opt!(visitor, visit_label, opt_label);
             try_visit!(visitor.visit_block(block));
         }
-        ExprKind::Match(subexpression, arms) => {
+        ExprKind::Match(subexpression, arms, _kind) => {
             try_visit!(visitor.visit_expr(subexpression));
             walk_list!(visitor, visit_arm, arms);
         }
diff --git a/compiler/rustc_ast_lowering/src/expr.rs b/compiler/rustc_ast_lowering/src/expr.rs
index 85b599902b959..b4515ea3a9bac 100644
--- a/compiler/rustc_ast_lowering/src/expr.rs
+++ b/compiler/rustc_ast_lowering/src/expr.rs
@@ -181,7 +181,7 @@ impl<'hir> LoweringContext<'_, 'hir> {
                     )
                 }),
                 ExprKind::TryBlock(body) => self.lower_expr_try_block(body),
-                ExprKind::Match(expr, arms) => hir::ExprKind::Match(
+                ExprKind::Match(expr, arms, _) => hir::ExprKind::Match(
                     self.lower_expr(expr),
                     self.arena.alloc_from_iter(arms.iter().map(|x| self.lower_arm(x))),
                     hir::MatchSource::Normal,
diff --git a/compiler/rustc_ast_pretty/src/pprust/state/expr.rs b/compiler/rustc_ast_pretty/src/pprust/state/expr.rs
index 433ef03b6e544..8bd8b6ac14475 100644
--- a/compiler/rustc_ast_pretty/src/pprust/state/expr.rs
+++ b/compiler/rustc_ast_pretty/src/pprust/state/expr.rs
@@ -1,6 +1,6 @@
 use crate::pp::Breaks::Inconsistent;
 use crate::pprust::state::{AnnNode, PrintState, State, INDENT_UNIT};
-use ast::ForLoopKind;
+use ast::{ForLoopKind, MatchKind};
 use itertools::{Itertools, Position};
 use rustc_ast::ptr::P;
 use rustc_ast::token;
@@ -589,12 +589,22 @@ impl<'a> State<'a> {
                 self.word_nbsp("loop");
                 self.print_block_with_attrs(blk, attrs);
             }
-            ast::ExprKind::Match(expr, arms) => {
+            ast::ExprKind::Match(expr, arms, match_kind) => {
                 self.cbox(0);
                 self.ibox(0);
-                self.word_nbsp("match");
-                self.print_expr_as_cond(expr);
-                self.space();
+
+                match match_kind {
+                    MatchKind::Prefix => {
+                        self.word_nbsp("match");
+                        self.print_expr_as_cond(expr);
+                        self.space();
+                    }
+                    MatchKind::Postfix => {
+                        self.print_expr_as_cond(expr);
+                        self.word_nbsp(".match");
+                    }
+                }
+
                 self.bopen();
                 self.print_inner_attributes_no_trailing_hardbreak(attrs);
                 for arm in arms {
diff --git a/compiler/rustc_builtin_macros/src/assert/context.rs b/compiler/rustc_builtin_macros/src/assert/context.rs
index 56c56b2704b00..92efeab08ebea 100644
--- a/compiler/rustc_builtin_macros/src/assert/context.rs
+++ b/compiler/rustc_builtin_macros/src/assert/context.rs
@@ -245,7 +245,7 @@ impl<'cx, 'a> Context<'cx, 'a> {
             ExprKind::Let(_, local_expr, _, _) => {
                 self.manage_cond_expr(local_expr);
             }
-            ExprKind::Match(local_expr, _) => {
+            ExprKind::Match(local_expr, ..) => {
                 self.manage_cond_expr(local_expr);
             }
             ExprKind::MethodCall(call) => {
diff --git a/compiler/rustc_builtin_macros/src/deriving/cmp/partial_ord.rs b/compiler/rustc_builtin_macros/src/deriving/cmp/partial_ord.rs
index 6eccd67f8af19..60dbdf8b54460 100644
--- a/compiler/rustc_builtin_macros/src/deriving/cmp/partial_ord.rs
+++ b/compiler/rustc_builtin_macros/src/deriving/cmp/partial_ord.rs
@@ -132,7 +132,7 @@ fn cs_partial_cmp(
                 // Reference: https://github.com/rust-lang/rust/pull/103659#issuecomment-1328126354
 
                 if !tag_then_data
-                    && let ExprKind::Match(_, arms) = &mut expr1.kind
+                    && let ExprKind::Match(_, arms, _) = &mut expr1.kind
                     && let Some(last) = arms.last_mut()
                     && let PatKind::Wild = last.pat.kind
                 {
diff --git a/compiler/rustc_builtin_macros/src/deriving/debug.rs b/compiler/rustc_builtin_macros/src/deriving/debug.rs
index b11a1b6cda154..108c1078eaa5b 100644
--- a/compiler/rustc_builtin_macros/src/deriving/debug.rs
+++ b/compiler/rustc_builtin_macros/src/deriving/debug.rs
@@ -2,8 +2,7 @@ use crate::deriving::generic::ty::*;
 use crate::deriving::generic::*;
 use crate::deriving::path_std;
 
-use ast::EnumDef;
-use rustc_ast::{self as ast, MetaItem};
+use rustc_ast::{self as ast, EnumDef, MetaItem};
 use rustc_expand::base::{Annotatable, ExtCtxt};
 use rustc_span::symbol::{sym, Ident, Symbol};
 use rustc_span::Span;
diff --git a/compiler/rustc_expand/src/build.rs b/compiler/rustc_expand/src/build.rs
index 989b7b485c992..159640163579b 100644
--- a/compiler/rustc_expand/src/build.rs
+++ b/compiler/rustc_expand/src/build.rs
@@ -1,6 +1,6 @@
 use crate::base::ExtCtxt;
 use rustc_ast::ptr::P;
-use rustc_ast::{self as ast, AttrVec, BlockCheckMode, Expr, LocalKind, PatKind, UnOp};
+use rustc_ast::{self as ast, AttrVec, BlockCheckMode, Expr, LocalKind, MatchKind, PatKind, UnOp};
 use rustc_ast::{attr, token, util::literal};
 use rustc_span::source_map::Spanned;
 use rustc_span::symbol::{kw, sym, Ident, Symbol};
@@ -524,7 +524,7 @@ impl<'a> ExtCtxt<'a> {
     }
 
     pub fn expr_match(&self, span: Span, arg: P<ast::Expr>, arms: ThinVec<ast::Arm>) -> P<Expr> {
-        self.expr(span, ast::ExprKind::Match(arg, arms))
+        self.expr(span, ast::ExprKind::Match(arg, arms, MatchKind::Prefix))
     }
 
     pub fn expr_if(
diff --git a/compiler/rustc_lint/src/unused.rs b/compiler/rustc_lint/src/unused.rs
index 3481c66da702e..32b45f865e942 100644
--- a/compiler/rustc_lint/src/unused.rs
+++ b/compiler/rustc_lint/src/unused.rs
@@ -865,7 +865,7 @@ trait UnusedDelimLint {
                 (iter, UnusedDelimsCtx::ForIterExpr, true, None, Some(body.span.lo()), true)
             }
 
-            Match(ref head, _) if Self::LINT_EXPR_IN_PATTERN_MATCHING_CTX => {
+            Match(ref head, ..) if Self::LINT_EXPR_IN_PATTERN_MATCHING_CTX => {
                 let left = e.span.lo() + rustc_span::BytePos(5);
                 (head, UnusedDelimsCtx::MatchScrutineeExpr, true, Some(left), None, true)
             }
@@ -1133,7 +1133,7 @@ impl EarlyLintPass for UnusedParens {
                 }
                 return;
             }
-            ExprKind::Match(ref _expr, ref arm) => {
+            ExprKind::Match(ref _expr, ref arm, _) => {
                 for a in arm {
                     if let Some(body) = &a.body {
                         self.check_unused_delims_expr(
diff --git a/compiler/rustc_parse/src/parser/expr.rs b/compiler/rustc_parse/src/parser/expr.rs
index 02ff452473dd0..e9c1bc7ad5666 100644
--- a/compiler/rustc_parse/src/parser/expr.rs
+++ b/compiler/rustc_parse/src/parser/expr.rs
@@ -11,7 +11,7 @@ use crate::errors;
 use crate::maybe_recover_from_interpolated_ty_qpath;
 use ast::mut_visit::{noop_visit_expr, MutVisitor};
 use ast::token::IdentIsRaw;
-use ast::{CoroutineKind, ForLoopKind, GenBlockKind, Pat, Path, PathSegment};
+use ast::{CoroutineKind, ForLoopKind, GenBlockKind, MatchKind, Pat, Path, PathSegment};
 use core::mem;
 use rustc_ast::ptr::P;
 use rustc_ast::token::{self, Delimiter, Token, TokenKind};
@@ -1375,10 +1375,11 @@ impl<'a> Parser<'a> {
             return Ok(self.mk_await_expr(self_arg, lo));
         }
 
+        // Post-fix match
         if self.eat_keyword(kw::Match) {
             let match_span = self.prev_token.span;
             self.psess.gated_spans.gate(sym::postfix_match, match_span);
-            return self.parse_match_block(lo, match_span, self_arg);
+            return self.parse_match_block(lo, match_span, self_arg, MatchKind::Postfix);
         }
 
         let fn_span_lo = self.token.span;
@@ -2897,16 +2898,17 @@ impl<'a> Parser<'a> {
         let match_span = self.prev_token.span;
         let scrutinee = self.parse_expr_res(Restrictions::NO_STRUCT_LITERAL, None)?;
 
-        self.parse_match_block(match_span, match_span, scrutinee)
+        self.parse_match_block(match_span, match_span, scrutinee, MatchKind::Prefix)
     }
 
-    /// Parses a `match expr { ... }` or a `expr.match { ... }` expression.
-    /// This is after the match token and scrutinee are eaten
+    /// Parses the block of a `match expr { ... }` or a `expr.match { ... }`
+    /// expression. This is after the match token and scrutinee are eaten
     fn parse_match_block(
         &mut self,
         lo: Span,
         match_span: Span,
         scrutinee: P<Expr>,
+        match_kind: MatchKind,
     ) -> PResult<'a, P<Expr>> {
         if let Err(mut e) = self.expect(&token::OpenDelim(Delimiter::Brace)) {
             if self.token == token::Semi {
@@ -2950,7 +2952,7 @@ impl<'a> Parser<'a> {
                     });
                     return Ok(self.mk_expr_with_attrs(
                         span,
-                        ExprKind::Match(scrutinee, arms),
+                        ExprKind::Match(scrutinee, arms, match_kind),
                         attrs,
                     ));
                 }
@@ -2958,7 +2960,7 @@ impl<'a> Parser<'a> {
         }
         let hi = self.token.span;
         self.bump();
-        Ok(self.mk_expr_with_attrs(lo.to(hi), ExprKind::Match(scrutinee, arms), attrs))
+        Ok(self.mk_expr_with_attrs(lo.to(hi), ExprKind::Match(scrutinee, arms, match_kind), attrs))
     }
 
     /// Attempt to recover from match arm body with statements and no surrounding braces.
@@ -3967,7 +3969,7 @@ impl MutVisitor for CondChecker<'_> {
             | ExprKind::While(_, _, _)
             | ExprKind::ForLoop { .. }
             | ExprKind::Loop(_, _, _)
-            | ExprKind::Match(_, _)
+            | ExprKind::Match(_, _, _)
             | ExprKind::Closure(_)
             | ExprKind::Block(_, _)
             | ExprKind::Gen(_, _, _)
diff --git a/src/tools/clippy/clippy_lints/src/redundant_else.rs b/src/tools/clippy/clippy_lints/src/redundant_else.rs
index fb434fb7450a7..3bdf13dbbea65 100644
--- a/src/tools/clippy/clippy_lints/src/redundant_else.rs
+++ b/src/tools/clippy/clippy_lints/src/redundant_else.rs
@@ -105,7 +105,7 @@ impl<'ast> Visitor<'ast> for BreakVisitor {
     fn visit_expr(&mut self, expr: &'ast Expr) {
         self.is_break = match expr.kind {
             ExprKind::Break(..) | ExprKind::Continue(..) | ExprKind::Ret(..) => true,
-            ExprKind::Match(_, ref arms) => arms.iter().all(|arm|
+            ExprKind::Match(_, ref arms, _) => arms.iter().all(|arm|
                 arm.body.is_none() || arm.body.as_deref().is_some_and(|body| self.check_expr(body))
             ),
             ExprKind::If(_, ref then, Some(ref els)) => self.check_block(then) && self.check_expr(els),
diff --git a/src/tools/clippy/clippy_lints/src/suspicious_operation_groupings.rs b/src/tools/clippy/clippy_lints/src/suspicious_operation_groupings.rs
index 60e9d262e7e09..ab1b3043f0c38 100644
--- a/src/tools/clippy/clippy_lints/src/suspicious_operation_groupings.rs
+++ b/src/tools/clippy/clippy_lints/src/suspicious_operation_groupings.rs
@@ -552,7 +552,7 @@ fn ident_difference_expr_with_base_location(
         | (Gen(_, _, _), Gen(_, _, _))
         | (Block(_, _), Block(_, _))
         | (Closure(_), Closure(_))
-        | (Match(_, _), Match(_, _))
+        | (Match(_, _, _), Match(_, _, _))
         | (Loop(_, _, _), Loop(_, _, _))
         | (ForLoop { .. }, ForLoop { .. })
         | (While(_, _, _), While(_, _, _))
diff --git a/src/tools/clippy/clippy_utils/src/ast_utils.rs b/src/tools/clippy/clippy_utils/src/ast_utils.rs
index 3b3939da7b6bc..eb916a37f6ea5 100644
--- a/src/tools/clippy/clippy_utils/src/ast_utils.rs
+++ b/src/tools/clippy/clippy_utils/src/ast_utils.rs
@@ -198,7 +198,7 @@ pub fn eq_expr(l: &Expr, r: &Expr) -> bool {
         },
         (AssignOp(lo, lp, lv), AssignOp(ro, rp, rv)) => lo.node == ro.node && eq_expr(lp, rp) && eq_expr(lv, rv),
         (Field(lp, lf), Field(rp, rf)) => eq_id(*lf, *rf) && eq_expr(lp, rp),
-        (Match(ls, la), Match(rs, ra)) => eq_expr(ls, rs) && over(la, ra, eq_arm),
+        (Match(ls, la, lkind), Match(rs, ra, rkind)) => (lkind == rkind) && eq_expr(ls, rs) && over(la, ra, eq_arm),
         (
             Closure(box ast::Closure {
                 binder: lb,
diff --git a/src/tools/rustfmt/src/expr.rs b/src/tools/rustfmt/src/expr.rs
index c500b30b99826..e04290ce87c69 100644
--- a/src/tools/rustfmt/src/expr.rs
+++ b/src/tools/rustfmt/src/expr.rs
@@ -3,7 +3,7 @@ use std::cmp::min;
 
 use itertools::Itertools;
 use rustc_ast::token::{Delimiter, Lit, LitKind};
-use rustc_ast::{ast, ptr, token, ForLoopKind};
+use rustc_ast::{ast, MatchKind, ptr, token, ForLoopKind};
 use rustc_span::{BytePos, Span};
 
 use crate::chains::rewrite_chain;
@@ -170,8 +170,8 @@ pub(crate) fn format_expr(
                 }
             }
         }
-        ast::ExprKind::Match(ref cond, ref arms) => {
-            rewrite_match(context, cond, arms, shape, expr.span, &expr.attrs)
+        ast::ExprKind::Match(ref cond, ref arms, kind) => {
+            rewrite_match(context, cond, arms, shape, expr.span, &expr.attrs, kind)
         }
         ast::ExprKind::Path(ref qself, ref path) => {
             rewrite_path(context, PathContext::Expr, qself, path, shape)
@@ -625,7 +625,7 @@ pub(crate) fn rewrite_cond(
     shape: Shape,
 ) -> Option<String> {
     match expr.kind {
-        ast::ExprKind::Match(ref cond, _) => {
+        ast::ExprKind::Match(ref cond, _, MatchKind::Prefix) => {
             // `match `cond` {`
             let cond_shape = match context.config.indent_style() {
                 IndentStyle::Visual => shape.shrink_left(6).and_then(|s| s.sub_width(2))?,
diff --git a/src/tools/rustfmt/src/matches.rs b/src/tools/rustfmt/src/matches.rs
index 5a00984d4c00e..63e3162be2c89 100644
--- a/src/tools/rustfmt/src/matches.rs
+++ b/src/tools/rustfmt/src/matches.rs
@@ -2,7 +2,7 @@
 
 use std::iter::repeat;
 
-use rustc_ast::{ast, ptr};
+use rustc_ast::{ast, MatchKind, ptr};
 use rustc_span::{BytePos, Span};
 
 use crate::comment::{combine_strs_with_missing_comments, rewrite_comment};
@@ -72,6 +72,8 @@ pub(crate) fn rewrite_match(
     shape: Shape,
     span: Span,
     attrs: &[ast::Attribute],
+    // TODO: Use this
+    _: MatchKind,
 ) -> Option<String> {
     // Do not take the rhs overhead from the upper expressions into account
     // when rewriting match condition.
diff --git a/tests/pretty/postfix-match.rs b/tests/pretty/postfix-match.rs
new file mode 100644
index 0000000000000..5bb54e15275ba
--- /dev/null
+++ b/tests/pretty/postfix-match.rs
@@ -0,0 +1,21 @@
+#![feature(postfix_match)]
+
+fn main() {
+    let val = Some(42);
+
+    val.match {
+        Some(_) => 2,
+        _ => 1
+    };
+
+
+    Some(2).match {
+        Some(_) => true,
+        None => false
+    }.match {
+        false => "ferris is cute",
+        true => "I turn cats in to petted cats",
+    }.match {
+        _ => (),
+    }
+}

From d4ba888787aa5062f5a8f804be3563881b516f2c Mon Sep 17 00:00:00 2001
From: Ross Smyth <crs2017@gmail.com>
Date: Sat, 17 Feb 2024 14:01:02 -0500
Subject: [PATCH 03/22] Add basic rustfmt implementation & test

---
 src/tools/rustfmt/src/expr.rs                 |  2 +-
 src/tools/rustfmt/src/matches.rs              | 35 ++++++++++++-------
 .../tests/source/postfix-match/pf-match.rs    | 20 +++++++++++
 .../tests/target/postfix-match/pf-match.rs    | 20 +++++++++++
 4 files changed, 64 insertions(+), 13 deletions(-)
 create mode 100644 src/tools/rustfmt/tests/source/postfix-match/pf-match.rs
 create mode 100644 src/tools/rustfmt/tests/target/postfix-match/pf-match.rs

diff --git a/src/tools/rustfmt/src/expr.rs b/src/tools/rustfmt/src/expr.rs
index e04290ce87c69..053afcc52d4c0 100644
--- a/src/tools/rustfmt/src/expr.rs
+++ b/src/tools/rustfmt/src/expr.rs
@@ -3,7 +3,7 @@ use std::cmp::min;
 
 use itertools::Itertools;
 use rustc_ast::token::{Delimiter, Lit, LitKind};
-use rustc_ast::{ast, MatchKind, ptr, token, ForLoopKind};
+use rustc_ast::{ast, ptr, token, ForLoopKind, MatchKind};
 use rustc_span::{BytePos, Span};
 
 use crate::chains::rewrite_chain;
diff --git a/src/tools/rustfmt/src/matches.rs b/src/tools/rustfmt/src/matches.rs
index 63e3162be2c89..e68903c871576 100644
--- a/src/tools/rustfmt/src/matches.rs
+++ b/src/tools/rustfmt/src/matches.rs
@@ -2,7 +2,7 @@
 
 use std::iter::repeat;
 
-use rustc_ast::{ast, MatchKind, ptr};
+use rustc_ast::{ast, ptr, MatchKind};
 use rustc_span::{BytePos, Span};
 
 use crate::comment::{combine_strs_with_missing_comments, rewrite_comment};
@@ -72,8 +72,7 @@ pub(crate) fn rewrite_match(
     shape: Shape,
     span: Span,
     attrs: &[ast::Attribute],
-    // TODO: Use this
-    _: MatchKind,
+    match_kind: MatchKind,
 ) -> Option<String> {
     // Do not take the rhs overhead from the upper expressions into account
     // when rewriting match condition.
@@ -133,15 +132,27 @@ pub(crate) fn rewrite_match(
         }
     } else {
         let span_after_cond = mk_sp(cond.span.hi(), span.hi());
-        Some(format!(
-            "match {}{}{{\n{}{}{}\n{}}}",
-            cond_str,
-            block_sep,
-            inner_attrs_str,
-            nested_indent_str,
-            rewrite_match_arms(context, arms, shape, span_after_cond, open_brace_pos)?,
-            shape.indent.to_string(context.config),
-        ))
+
+        match match_kind {
+            MatchKind::Prefix => Some(format!(
+                "match {}{}{{\n{}{}{}\n{}}}",
+                cond_str,
+                block_sep,
+                inner_attrs_str,
+                nested_indent_str,
+                rewrite_match_arms(context, arms, shape, span_after_cond, open_brace_pos)?,
+                shape.indent.to_string(context.config),
+            )),
+            MatchKind::Postfix => Some(format!(
+                "{}.match{}{{\n{}{}{}\n{}}}",
+                cond_str,
+                block_sep,
+                inner_attrs_str,
+                nested_indent_str,
+                rewrite_match_arms(context, arms, shape, span_after_cond, open_brace_pos)?,
+                shape.indent.to_string(context.config),
+            )),
+        }
     }
 }
 
diff --git a/src/tools/rustfmt/tests/source/postfix-match/pf-match.rs b/src/tools/rustfmt/tests/source/postfix-match/pf-match.rs
new file mode 100644
index 0000000000000..b2366723631ed
--- /dev/null
+++ b/src/tools/rustfmt/tests/source/postfix-match/pf-match.rs
@@ -0,0 +1,20 @@
+#![feature(postfix_match)]
+
+fn main() {
+    let val = Some(42);
+
+    val.match {
+        Some(_) => 2,
+        _ => 1
+    };
+
+    Some(2).match {
+        Some(_) => true,
+        None => false
+    }.match {
+        false => "ferris is cute",
+        true => "I turn cats in to petted cats",
+    }.match {
+        _ => (),
+    }
+}
\ No newline at end of file
diff --git a/src/tools/rustfmt/tests/target/postfix-match/pf-match.rs b/src/tools/rustfmt/tests/target/postfix-match/pf-match.rs
new file mode 100644
index 0000000000000..f439f2726235e
--- /dev/null
+++ b/src/tools/rustfmt/tests/target/postfix-match/pf-match.rs
@@ -0,0 +1,20 @@
+#![feature(postfix_match)]
+
+fn main() {
+    let val = Some(42);
+
+    val.match {
+        Some(_) => 2,
+        _ => 1,
+    };
+
+    Some(2).match {
+        Some(_) => true,
+        None => false,
+    }.match {
+        false => "ferris is cute",
+        true => "I turn cats in to petted cats",
+    }.match {
+        _ => (),
+    }
+}

From 567c98b30f75b8f18bef7dc62e48111aa683e236 Mon Sep 17 00:00:00 2001
From: Ross Smyth <crs2017@gmail.com>
Date: Sat, 2 Mar 2024 20:55:48 -0500
Subject: [PATCH 04/22] Add postfix match MatchSource to HIR

---
 compiler/rustc_ast_lowering/src/expr.rs                  | 7 +++++--
 compiler/rustc_hir/src/hir.rs                            | 3 +++
 compiler/rustc_mir_build/src/thir/pattern/check_match.rs | 1 +
 compiler/rustc_passes/src/check_const.rs                 | 2 +-
 4 files changed, 10 insertions(+), 3 deletions(-)

diff --git a/compiler/rustc_ast_lowering/src/expr.rs b/compiler/rustc_ast_lowering/src/expr.rs
index b4515ea3a9bac..0a196f2fafc28 100644
--- a/compiler/rustc_ast_lowering/src/expr.rs
+++ b/compiler/rustc_ast_lowering/src/expr.rs
@@ -181,10 +181,13 @@ impl<'hir> LoweringContext<'_, 'hir> {
                     )
                 }),
                 ExprKind::TryBlock(body) => self.lower_expr_try_block(body),
-                ExprKind::Match(expr, arms, _) => hir::ExprKind::Match(
+                ExprKind::Match(expr, arms, kind) => hir::ExprKind::Match(
                     self.lower_expr(expr),
                     self.arena.alloc_from_iter(arms.iter().map(|x| self.lower_arm(x))),
-                    hir::MatchSource::Normal,
+                    match kind {
+                        MatchKind::Prefix => hir::MatchSource::Normal,
+                        MatchKind::Postfix => hir::MatchSource::Postfix,
+                    },
                 ),
                 ExprKind::Await(expr, await_kw_span) => self.lower_expr_await(*await_kw_span, expr),
                 ExprKind::Closure(box Closure {
diff --git a/compiler/rustc_hir/src/hir.rs b/compiler/rustc_hir/src/hir.rs
index 3dac6880f17e1..9cec42c91c152 100644
--- a/compiler/rustc_hir/src/hir.rs
+++ b/compiler/rustc_hir/src/hir.rs
@@ -2004,6 +2004,8 @@ pub enum LocalSource {
 pub enum MatchSource {
     /// A `match _ { .. }`.
     Normal,
+    /// A `expr.match { .. }`.
+    Postfix,
     /// A desugared `for _ in _ { .. }` loop.
     ForLoopDesugar,
     /// A desugared `?` operator.
@@ -2020,6 +2022,7 @@ impl MatchSource {
         use MatchSource::*;
         match self {
             Normal => "match",
+            Postfix => ".match",
             ForLoopDesugar => "for",
             TryDesugar(_) => "?",
             AwaitDesugar => ".await",
diff --git a/compiler/rustc_mir_build/src/thir/pattern/check_match.rs b/compiler/rustc_mir_build/src/thir/pattern/check_match.rs
index 2685bae4d09c8..080d45a1ae279 100644
--- a/compiler/rustc_mir_build/src/thir/pattern/check_match.rs
+++ b/compiler/rustc_mir_build/src/thir/pattern/check_match.rs
@@ -481,6 +481,7 @@ impl<'p, 'tcx> MatchVisitor<'p, 'tcx> {
             // when the iterator is an uninhabited type. unreachable_code will trigger instead.
             hir::MatchSource::ForLoopDesugar if arms.len() == 1 => {}
             hir::MatchSource::ForLoopDesugar
+            | hir::MatchSource::Postfix
             | hir::MatchSource::Normal
             | hir::MatchSource::FormatArgs => report_arm_reachability(&cx, &report),
             // Unreachable patterns in try and await expressions occur when one of
diff --git a/compiler/rustc_passes/src/check_const.rs b/compiler/rustc_passes/src/check_const.rs
index 02792491f5ed0..de123a16859ea 100644
--- a/compiler/rustc_passes/src/check_const.rs
+++ b/compiler/rustc_passes/src/check_const.rs
@@ -48,7 +48,7 @@ impl NonConstExpr {
             Self::Match(TryDesugar(_)) => &[sym::const_try],
 
             // All other expressions are allowed.
-            Self::Loop(Loop | While) | Self::Match(Normal | FormatArgs) => &[],
+            Self::Loop(Loop | While) | Self::Match(Normal | Postfix | FormatArgs) => &[],
         };
 
         Some(gates)

From 7be47b219df42cba96560a97de707967cca8c762 Mon Sep 17 00:00:00 2001
From: Ralf Jung <post@ralfj.de>
Date: Fri, 15 Mar 2024 11:59:38 +0100
Subject: [PATCH 05/22] interpret/allocation: fix aliasing issue in interpreter
 and refactor getters a bit

- rename mutating functions to be more scary
- add a new raw bytes getter
---
 .../rustc_const_eval/src/interpret/memory.rs  | 17 ++++++--
 .../src/mir/interpret/allocation.rs           | 42 ++++++++++++++-----
 2 files changed, 45 insertions(+), 14 deletions(-)

diff --git a/compiler/rustc_const_eval/src/interpret/memory.rs b/compiler/rustc_const_eval/src/interpret/memory.rs
index 86aad2e1642d6..9e6776ab55f74 100644
--- a/compiler/rustc_const_eval/src/interpret/memory.rs
+++ b/compiler/rustc_const_eval/src/interpret/memory.rs
@@ -1157,11 +1157,11 @@ impl<'mir, 'tcx: 'mir, M: Machine<'mir, 'tcx>> InterpCx<'mir, 'tcx, M> {
         };
 
         // Side-step AllocRef and directly access the underlying bytes more efficiently.
-        // (We are staying inside the bounds here so all is good.)
+        // (We are staying inside the bounds here and all bytes do get overwritten so all is good.)
         let alloc_id = alloc_ref.alloc_id;
         let bytes = alloc_ref
             .alloc
-            .get_bytes_mut(&alloc_ref.tcx, alloc_ref.range)
+            .get_bytes_unchecked_for_overwrite(&alloc_ref.tcx, alloc_ref.range)
             .map_err(move |e| e.to_interp_error(alloc_id))?;
         // `zip` would stop when the first iterator ends; we want to definitely
         // cover all of `bytes`.
@@ -1182,6 +1182,11 @@ impl<'mir, 'tcx: 'mir, M: Machine<'mir, 'tcx>> InterpCx<'mir, 'tcx, M> {
         self.mem_copy_repeatedly(src, dest, size, 1, nonoverlapping)
     }
 
+    /// Performs `num_copies` many copies of `size` many bytes from `src` to `dest + i*size` (where
+    /// `i` is the index of the copy).
+    ///
+    /// Either `nonoverlapping` must be true or `num_copies` must be 1; doing repeated copies that
+    /// may overlap is not supported.
     pub fn mem_copy_repeatedly(
         &mut self,
         src: Pointer<Option<M::Provenance>>,
@@ -1243,8 +1248,9 @@ impl<'mir, 'tcx: 'mir, M: Machine<'mir, 'tcx>> InterpCx<'mir, 'tcx, M> {
             (dest_alloc_id, dest_prov),
             dest_range,
         )?;
+        // Yes we do overwrite all bytes in `dest_bytes`.
         let dest_bytes = dest_alloc
-            .get_bytes_mut_ptr(&tcx, dest_range)
+            .get_bytes_unchecked_for_overwrite_ptr(&tcx, dest_range)
             .map_err(|e| e.to_interp_error(dest_alloc_id))?
             .as_mut_ptr();
 
@@ -1278,6 +1284,9 @@ impl<'mir, 'tcx: 'mir, M: Machine<'mir, 'tcx>> InterpCx<'mir, 'tcx, M> {
                     }
                 }
             }
+            if num_copies > 1 {
+                assert!(nonoverlapping, "multi-copy only supported in non-overlapping mode");
+            }
 
             let size_in_bytes = size.bytes_usize();
             // For particularly large arrays (where this is perf-sensitive) it's common that
@@ -1290,6 +1299,8 @@ impl<'mir, 'tcx: 'mir, M: Machine<'mir, 'tcx>> InterpCx<'mir, 'tcx, M> {
             } else if src_alloc_id == dest_alloc_id {
                 let mut dest_ptr = dest_bytes;
                 for _ in 0..num_copies {
+                    // Here we rely on `src` and `dest` being non-overlapping if there is more than
+                    // one copy.
                     ptr::copy(src_bytes, dest_ptr, size_in_bytes);
                     dest_ptr = dest_ptr.add(size_in_bytes);
                 }
diff --git a/compiler/rustc_middle/src/mir/interpret/allocation.rs b/compiler/rustc_middle/src/mir/interpret/allocation.rs
index 4047891d7697b..00faa21185371 100644
--- a/compiler/rustc_middle/src/mir/interpret/allocation.rs
+++ b/compiler/rustc_middle/src/mir/interpret/allocation.rs
@@ -37,9 +37,16 @@ pub trait AllocBytes:
     /// Create a zeroed `AllocBytes` of the specified size and alignment.
     /// Returns `None` if we ran out of memory on the host.
     fn zeroed(size: Size, _align: Align) -> Option<Self>;
+
+    /// Gives direct access to the raw underlying storage.
+    ///
+    /// Crucially this pointer is compatible with:
+    /// - other pointers retunred by this method, and
+    /// - references returned from `deref()`, as long as there was no write.
+    fn as_mut_ptr(&mut self) -> *mut u8;
 }
 
-// Default `bytes` for `Allocation` is a `Box<[u8]>`.
+/// Default `bytes` for `Allocation` is a `Box<u8>`.
 impl AllocBytes for Box<[u8]> {
     fn from_bytes<'a>(slice: impl Into<Cow<'a, [u8]>>, _align: Align) -> Self {
         Box::<[u8]>::from(slice.into())
@@ -51,6 +58,11 @@ impl AllocBytes for Box<[u8]> {
         let bytes = unsafe { bytes.assume_init() };
         Some(bytes)
     }
+
+    fn as_mut_ptr(&mut self) -> *mut u8 {
+        // Carefully avoiding any intermediate references.
+        ptr::addr_of_mut!(**self).cast()
+    }
 }
 
 /// This type represents an Allocation in the Miri/CTFE core engine.
@@ -399,10 +411,6 @@ impl<Prov: Provenance, Extra, Bytes: AllocBytes> Allocation<Prov, Extra, Bytes>
 
 /// Byte accessors.
 impl<Prov: Provenance, Extra, Bytes: AllocBytes> Allocation<Prov, Extra, Bytes> {
-    pub fn base_addr(&self) -> *const u8 {
-        self.bytes.as_ptr()
-    }
-
     /// This is the entirely abstraction-violating way to just grab the raw bytes without
     /// caring about provenance or initialization.
     ///
@@ -452,13 +460,14 @@ impl<Prov: Provenance, Extra, Bytes: AllocBytes> Allocation<Prov, Extra, Bytes>
         Ok(self.get_bytes_unchecked(range))
     }
 
-    /// Just calling this already marks everything as defined and removes provenance,
-    /// so be sure to actually put data there!
+    /// This is the entirely abstraction-violating way to just get mutable access to the raw bytes.
+    /// Just calling this already marks everything as defined and removes provenance, so be sure to
+    /// actually overwrite all the data there!
     ///
     /// It is the caller's responsibility to check bounds and alignment beforehand.
     /// Most likely, you want to use the `PlaceTy` and `OperandTy`-based methods
     /// on `InterpCx` instead.
-    pub fn get_bytes_mut(
+    pub fn get_bytes_unchecked_for_overwrite(
         &mut self,
         cx: &impl HasDataLayout,
         range: AllocRange,
@@ -469,8 +478,9 @@ impl<Prov: Provenance, Extra, Bytes: AllocBytes> Allocation<Prov, Extra, Bytes>
         Ok(&mut self.bytes[range.start.bytes_usize()..range.end().bytes_usize()])
     }
 
-    /// A raw pointer variant of `get_bytes_mut` that avoids invalidating existing aliases into this memory.
-    pub fn get_bytes_mut_ptr(
+    /// A raw pointer variant of `get_bytes_unchecked_for_overwrite` that avoids invalidating existing immutable aliases
+    /// into this memory.
+    pub fn get_bytes_unchecked_for_overwrite_ptr(
         &mut self,
         cx: &impl HasDataLayout,
         range: AllocRange,
@@ -479,10 +489,19 @@ impl<Prov: Provenance, Extra, Bytes: AllocBytes> Allocation<Prov, Extra, Bytes>
         self.provenance.clear(range, cx)?;
 
         assert!(range.end().bytes_usize() <= self.bytes.len()); // need to do our own bounds-check
+        // Cruciall, we go via `AllocBytes::as_mut_ptr`, not `AllocBytes::deref_mut`.
         let begin_ptr = self.bytes.as_mut_ptr().wrapping_add(range.start.bytes_usize());
         let len = range.end().bytes_usize() - range.start.bytes_usize();
         Ok(ptr::slice_from_raw_parts_mut(begin_ptr, len))
     }
+
+    /// This gives direct mutable access to the entire buffer, just exposing their internal state
+    /// without reseting anything. Directly exposes `AllocBytes::as_mut_ptr`. Only works if
+    /// `OFFSET_IS_ADDR` is true.
+    pub fn get_bytes_unchecked_raw_mut(&mut self) -> *mut u8 {
+        assert!(Prov::OFFSET_IS_ADDR);
+        self.bytes.as_mut_ptr()
+    }
 }
 
 /// Reading and writing.
@@ -589,7 +608,8 @@ impl<Prov: Provenance, Extra, Bytes: AllocBytes> Allocation<Prov, Extra, Bytes>
         };
 
         let endian = cx.data_layout().endian;
-        let dst = self.get_bytes_mut(cx, range)?;
+        // Yes we do overwrite all the bytes in `dst`.
+        let dst = self.get_bytes_unchecked_for_overwrite(cx, range)?;
         write_target_uint(endian, dst, bytes).unwrap();
 
         // See if we have to also store some provenance.

From 3c70d60c4fe818879ba953530edd4a902b5d9a05 Mon Sep 17 00:00:00 2001
From: Gurinder Singh <frederick.the.fool@gmail.com>
Date: Tue, 19 Mar 2024 09:20:23 +0530
Subject: [PATCH 06/22] Gracefully handle AnonConst in
 diagnostic_hir_wf_check()

when it is the default value of a generic param
---
 .../rustc_hir_analysis/src/hir_wf_check.rs    | 10 ++++
 ...ce-hir-wf-check-anon-const-issue-122199.rs | 12 ++++
 ...ir-wf-check-anon-const-issue-122199.stderr | 60 +++++++++++++++++++
 3 files changed, 82 insertions(+)
 create mode 100644 tests/ui/wf/ice-hir-wf-check-anon-const-issue-122199.rs
 create mode 100644 tests/ui/wf/ice-hir-wf-check-anon-const-issue-122199.stderr

diff --git a/compiler/rustc_hir_analysis/src/hir_wf_check.rs b/compiler/rustc_hir_analysis/src/hir_wf_check.rs
index 2a9101b3808fa..18848702fea69 100644
--- a/compiler/rustc_hir_analysis/src/hir_wf_check.rs
+++ b/compiler/rustc_hir_analysis/src/hir_wf_check.rs
@@ -163,6 +163,16 @@ fn diagnostic_hir_wf_check<'tcx>(
                 kind: hir::GenericParamKind::Type { default: Some(ty), .. },
                 ..
             }) => vec![*ty],
+            hir::Node::AnonConst(_)
+                if let Some(const_param_id) =
+                    tcx.hir().opt_const_param_default_param_def_id(hir_id)
+                    && let hir::Node::GenericParam(hir::GenericParam {
+                        kind: hir::GenericParamKind::Const { ty, .. },
+                        ..
+                    }) = tcx.hir_node_by_def_id(const_param_id) =>
+            {
+                vec![*ty]
+            }
             ref node => bug!("Unexpected node {:?}", node),
         },
         WellFormedLoc::Param { function: _, param_idx } => {
diff --git a/tests/ui/wf/ice-hir-wf-check-anon-const-issue-122199.rs b/tests/ui/wf/ice-hir-wf-check-anon-const-issue-122199.rs
new file mode 100644
index 0000000000000..107cfbb9ff699
--- /dev/null
+++ b/tests/ui/wf/ice-hir-wf-check-anon-const-issue-122199.rs
@@ -0,0 +1,12 @@
+trait Trait<const N: Trait = bar> {
+//~^ ERROR cannot find value `bar` in this scope
+//~| ERROR cycle detected when computing type of `Trait::N`
+//~| ERROR cycle detected when computing type of `Trait::N`
+//~| ERROR `(dyn Trait<{const error}> + 'static)` is forbidden as the type of a const generic parameter
+//~| WARN trait objects without an explicit `dyn` are deprecated
+//~| WARN this is accepted in the current edition (Rust 2015) but is a hard error in Rust 2021!
+    fn fnc(&self) {
+    }
+}
+
+fn main() {}
diff --git a/tests/ui/wf/ice-hir-wf-check-anon-const-issue-122199.stderr b/tests/ui/wf/ice-hir-wf-check-anon-const-issue-122199.stderr
new file mode 100644
index 0000000000000..2d5a0ede962b2
--- /dev/null
+++ b/tests/ui/wf/ice-hir-wf-check-anon-const-issue-122199.stderr
@@ -0,0 +1,60 @@
+error[E0425]: cannot find value `bar` in this scope
+  --> $DIR/ice-hir-wf-check-anon-const-issue-122199.rs:1:30
+   |
+LL | trait Trait<const N: Trait = bar> {
+   |                              ^^^ not found in this scope
+
+warning: trait objects without an explicit `dyn` are deprecated
+  --> $DIR/ice-hir-wf-check-anon-const-issue-122199.rs:1:22
+   |
+LL | trait Trait<const N: Trait = bar> {
+   |                      ^^^^^
+   |
+   = warning: this is accepted in the current edition (Rust 2015) but is a hard error in Rust 2021!
+   = note: for more information, see <https://doc.rust-lang.org/nightly/edition-guide/rust-2021/warnings-promoted-to-error.html>
+   = note: `#[warn(bare_trait_objects)]` on by default
+help: if this is an object-safe trait, use `dyn`
+   |
+LL | trait Trait<const N: dyn Trait = bar> {
+   |                      +++
+
+error[E0391]: cycle detected when computing type of `Trait::N`
+  --> $DIR/ice-hir-wf-check-anon-const-issue-122199.rs:1:22
+   |
+LL | trait Trait<const N: Trait = bar> {
+   |                      ^^^^^
+   |
+   = note: ...which immediately requires computing type of `Trait::N` again
+note: cycle used when computing explicit predicates of trait `Trait`
+  --> $DIR/ice-hir-wf-check-anon-const-issue-122199.rs:1:1
+   |
+LL | trait Trait<const N: Trait = bar> {
+   | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+   = note: see https://rustc-dev-guide.rust-lang.org/overview.html#queries and https://rustc-dev-guide.rust-lang.org/query.html for more information
+
+error[E0391]: cycle detected when computing type of `Trait::N`
+  --> $DIR/ice-hir-wf-check-anon-const-issue-122199.rs:1:13
+   |
+LL | trait Trait<const N: Trait = bar> {
+   |             ^^^^^^^^^^^^^^^^^^^^
+   |
+   = note: ...which immediately requires computing type of `Trait::N` again
+note: cycle used when computing explicit predicates of trait `Trait`
+  --> $DIR/ice-hir-wf-check-anon-const-issue-122199.rs:1:1
+   |
+LL | trait Trait<const N: Trait = bar> {
+   | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+   = note: see https://rustc-dev-guide.rust-lang.org/overview.html#queries and https://rustc-dev-guide.rust-lang.org/query.html for more information
+
+error: `(dyn Trait<{const error}> + 'static)` is forbidden as the type of a const generic parameter
+  --> $DIR/ice-hir-wf-check-anon-const-issue-122199.rs:1:22
+   |
+LL | trait Trait<const N: Trait = bar> {
+   |                      ^^^^^
+   |
+   = note: the only supported types are integers, `bool` and `char`
+
+error: aborting due to 4 previous errors; 1 warning emitted
+
+Some errors have detailed explanations: E0391, E0425.
+For more information about an error, try `rustc --explain E0391`.

From 4250216663331fc4efcbd4bb2e5f93caa1b4d2b8 Mon Sep 17 00:00:00 2001
From: Zachary S <zasample18+github@gmail.com>
Date: Wed, 20 Mar 2024 17:44:26 -0500
Subject: [PATCH 07/22] Add `NonNull::<[T]>::is_empty` as insta-stable.

---
 library/core/src/ptr/non_null.rs | 21 +++++++++++++++++++++
 1 file changed, 21 insertions(+)

diff --git a/library/core/src/ptr/non_null.rs b/library/core/src/ptr/non_null.rs
index 9c0236c172a93..8bb87734eb31f 100644
--- a/library/core/src/ptr/non_null.rs
+++ b/library/core/src/ptr/non_null.rs
@@ -1575,6 +1575,27 @@ impl<T> NonNull<[T]> {
         self.as_ptr().len()
     }
 
+    /// Returns `true` if the non-null raw slice has a length of 0.
+    ///
+    /// # Examples
+    ///
+    /// ```rust
+    /// use std::ptr::NonNull;
+    ///
+    /// let slice: NonNull<[i8]> = NonNull::slice_from_raw_parts(NonNull::dangling(), 3);
+    /// assert!(!slice.is_empty());
+    /// ```
+    #[stable(feature = "slice_ptr_is_empty_nonnull", since = "CURRENT_RUSTC_VERSION")]
+    #[rustc_const_stable(
+        feature = "const_slice_ptr_is_empty_nonnull",
+        since = "CURRENT_RUSTC_VERSION"
+    )]
+    #[must_use]
+    #[inline]
+    pub const fn is_empty(self) -> bool {
+        self.len() == 0
+    }
+
     /// Returns a non-null pointer to the slice's buffer.
     ///
     /// # Examples

From 1cf345e10abec509b708eaa4c0458577624013d9 Mon Sep 17 00:00:00 2001
From: Oli Scherer <git-spam-no-reply9815368754983@oli-obk.de>
Date: Thu, 21 Mar 2024 10:04:20 +0000
Subject: [PATCH 08/22] Remove unnecessary Partial/Ord impl

---
 compiler/rustc_middle/src/mir/consts.rs | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/compiler/rustc_middle/src/mir/consts.rs b/compiler/rustc_middle/src/mir/consts.rs
index 214297b98695f..02185cbeacf9e 100644
--- a/compiler/rustc_middle/src/mir/consts.rs
+++ b/compiler/rustc_middle/src/mir/consts.rs
@@ -456,7 +456,7 @@ impl<'tcx> Const<'tcx> {
 }
 
 /// An unevaluated (potentially generic) constant used in MIR.
-#[derive(Copy, Clone, Debug, Eq, PartialEq, PartialOrd, Ord, TyEncodable, TyDecodable)]
+#[derive(Copy, Clone, Debug, Eq, PartialEq, TyEncodable, TyDecodable)]
 #[derive(Hash, HashStable, TypeFoldable, TypeVisitable, Lift)]
 pub struct UnevaluatedConst<'tcx> {
     pub def: DefId,

From cda209bf433605c0dcd08f4bd04057e6b5623a79 Mon Sep 17 00:00:00 2001
From: Oli Scherer <git-spam-no-reply9815368754983@oli-obk.de>
Date: Thu, 21 Mar 2024 10:11:44 +0000
Subject: [PATCH 09/22] Stop `ConstraintCategory` `Ord` impl from relying on
 `Ty`'s `Ord` impl.

---
 Cargo.lock                                    |  1 +
 compiler/rustc_middle/Cargo.toml              |  1 +
 compiler/rustc_middle/src/mir/query.rs        | 12 +++++++++--
 ...er-to-static-comparing-against-free.stderr | 19 ++++++++---------
 .../user-annotations/adt-nullary-enums.stderr | 21 ++++++++++---------
 5 files changed, 32 insertions(+), 22 deletions(-)

diff --git a/Cargo.lock b/Cargo.lock
index 3110f32ade968..680cb500421d5 100644
--- a/Cargo.lock
+++ b/Cargo.lock
@@ -4236,6 +4236,7 @@ name = "rustc_middle"
 version = "0.0.0"
 dependencies = [
  "bitflags 2.4.2",
+ "derivative",
  "either",
  "field-offset",
  "gsgdt",
diff --git a/compiler/rustc_middle/Cargo.toml b/compiler/rustc_middle/Cargo.toml
index 96c58ef411b71..9e8ee92b5d982 100644
--- a/compiler/rustc_middle/Cargo.toml
+++ b/compiler/rustc_middle/Cargo.toml
@@ -6,6 +6,7 @@ edition = "2021"
 [dependencies]
 # tidy-alphabetical-start
 bitflags = "2.4.1"
+derivative = "2.2.0"
 either = "1.5.0"
 field-offset = "0.3.5"
 gsgdt = "0.1.2"
diff --git a/compiler/rustc_middle/src/mir/query.rs b/compiler/rustc_middle/src/mir/query.rs
index 8bd872c1b19e1..731e050ca9b76 100644
--- a/compiler/rustc_middle/src/mir/query.rs
+++ b/compiler/rustc_middle/src/mir/query.rs
@@ -284,8 +284,15 @@ rustc_data_structures::static_assert_size!(ConstraintCategory<'_>, 16);
 /// order of the category, thereby influencing diagnostic output.
 ///
 /// See also `rustc_const_eval::borrow_check::constraints`.
-#[derive(Copy, Clone, Debug, Eq, PartialEq, PartialOrd, Ord, Hash)]
+#[derive(Copy, Clone, Debug, Eq, PartialEq, Hash)]
 #[derive(TyEncodable, TyDecodable, HashStable, TypeVisitable, TypeFoldable)]
+#[derive(derivative::Derivative)]
+#[derivative(
+    PartialOrd,
+    Ord,
+    PartialOrd = "feature_allow_slow_enum",
+    Ord = "feature_allow_slow_enum"
+)]
 pub enum ConstraintCategory<'tcx> {
     Return(ReturnConstraint),
     Yield,
@@ -295,6 +302,7 @@ pub enum ConstraintCategory<'tcx> {
     Cast {
         /// Whether this is an unsizing cast and if yes, this contains the target type.
         /// Region variables are erased to ReErased.
+        #[derivative(PartialOrd = "ignore", Ord = "ignore")]
         unsize_to: Option<Ty<'tcx>>,
     },
 
@@ -304,7 +312,7 @@ pub enum ConstraintCategory<'tcx> {
     ClosureBounds,
 
     /// Contains the function type if available.
-    CallArgument(Option<Ty<'tcx>>),
+    CallArgument(#[derivative(PartialOrd = "ignore", Ord = "ignore")] Option<Ty<'tcx>>),
     CopyBound,
     SizedBound,
     Assignment,
diff --git a/tests/ui/nll/closure-requirements/propagate-approximated-shorter-to-static-comparing-against-free.stderr b/tests/ui/nll/closure-requirements/propagate-approximated-shorter-to-static-comparing-against-free.stderr
index 9feb2a7320d1d..d7933a39eaacf 100644
--- a/tests/ui/nll/closure-requirements/propagate-approximated-shorter-to-static-comparing-against-free.stderr
+++ b/tests/ui/nll/closure-requirements/propagate-approximated-shorter-to-static-comparing-against-free.stderr
@@ -53,17 +53,16 @@ LL | fn case2() {
 error[E0597]: `a` does not live long enough
   --> $DIR/propagate-approximated-shorter-to-static-comparing-against-free.rs:30:26
    |
-LL |       let a = 0;
-   |           - binding `a` declared here
-LL |       let cell = Cell::new(&a);
-   |                            ^^ borrowed value does not live long enough
+LL |     let a = 0;
+   |         - binding `a` declared here
+LL |     let cell = Cell::new(&a);
+   |                ----------^^-
+   |                |         |
+   |                |         borrowed value does not live long enough
+   |                argument requires that `a` is borrowed for `'static`
 ...
-LL | /     foo(cell, |cell_a, cell_x| {
-LL | |         cell_x.set(cell_a.get()); // forces 'a: 'x, implies 'a = 'static -> borrow error
-LL | |     })
-   | |______- argument requires that `a` is borrowed for `'static`
-LL |   }
-   |   - `a` dropped here while still borrowed
+LL | }
+   | - `a` dropped here while still borrowed
 
 error: aborting due to 2 previous errors
 
diff --git a/tests/ui/nll/user-annotations/adt-nullary-enums.stderr b/tests/ui/nll/user-annotations/adt-nullary-enums.stderr
index 5b385feeedc72..644fc94f73087 100644
--- a/tests/ui/nll/user-annotations/adt-nullary-enums.stderr
+++ b/tests/ui/nll/user-annotations/adt-nullary-enums.stderr
@@ -1,16 +1,17 @@
 error[E0597]: `c` does not live long enough
   --> $DIR/adt-nullary-enums.rs:33:41
    |
-LL |       let c = 66;
-   |           - binding `c` declared here
-LL | /     combine(
-LL | |         SomeEnum::SomeVariant(Cell::new(&c)),
-   | |                                         ^^ borrowed value does not live long enough
-LL | |         SomeEnum::SomeOtherVariant::<Cell<&'static u32>>,
-LL | |     );
-   | |_____- argument requires that `c` is borrowed for `'static`
-LL |   }
-   |   - `c` dropped here while still borrowed
+LL |     let c = 66;
+   |         - binding `c` declared here
+LL |     combine(
+LL |         SomeEnum::SomeVariant(Cell::new(&c)),
+   |                               ----------^^-
+   |                               |         |
+   |                               |         borrowed value does not live long enough
+   |                               argument requires that `c` is borrowed for `'static`
+...
+LL | }
+   | - `c` dropped here while still borrowed
 
 error[E0597]: `c` does not live long enough
   --> $DIR/adt-nullary-enums.rs:41:41

From d8470bb00b5ed2dff50a9bff26854cb75478bf0e Mon Sep 17 00:00:00 2001
From: Oli Scherer <git-spam-no-reply9815368754983@oli-obk.de>
Date: Thu, 21 Mar 2024 10:26:45 +0000
Subject: [PATCH 10/22] Sorting arbitrary constants should not be done, as it
 relies on `DefId` ordering, which breaks incremental compilation.

---
 compiler/rustc_middle/src/ty/layout.rs        | 67 +-------------
 tests/ui/const-generics/transmute-fail.rs     | 75 +++++++++++++++
 tests/ui/const-generics/transmute-fail.stderr | 91 ++++++++++++++++++-
 tests/ui/const-generics/transmute.rs          | 69 --------------
 4 files changed, 164 insertions(+), 138 deletions(-)

diff --git a/compiler/rustc_middle/src/ty/layout.rs b/compiler/rustc_middle/src/ty/layout.rs
index 11fd73c909417..595ef71cc3229 100644
--- a/compiler/rustc_middle/src/ty/layout.rs
+++ b/compiler/rustc_middle/src/ty/layout.rs
@@ -2,7 +2,7 @@ use crate::error::UnsupportedFnAbi;
 use crate::middle::codegen_fn_attrs::CodegenFnAttrFlags;
 use crate::query::TyCtxtAt;
 use crate::ty::normalize_erasing_regions::NormalizationError;
-use crate::ty::{self, ConstKind, Ty, TyCtxt, TypeVisitableExt};
+use crate::ty::{self, Ty, TyCtxt, TypeVisitableExt};
 use rustc_error_messages::DiagMessage;
 use rustc_errors::{
     Diag, DiagArgValue, DiagCtxt, Diagnostic, EmissionGuarantee, IntoDiagArg, Level,
@@ -356,21 +356,10 @@ impl<'tcx> SizeSkeleton<'tcx> {
                                 .ok_or_else(|| &*tcx.arena.alloc(LayoutError::SizeOverflow(ty)))?;
                             return Ok(SizeSkeleton::Known(Size::from_bytes(size)));
                         }
-                        let len = tcx.expand_abstract_consts(len);
-                        let prev = ty::Const::from_target_usize(tcx, s.bytes());
-                        let Some(gen_size) = mul_sorted_consts(tcx, param_env, len, prev) else {
-                            return Err(tcx.arena.alloc(LayoutError::SizeOverflow(ty)));
-                        };
-                        Ok(SizeSkeleton::Generic(gen_size))
+                        Err(tcx.arena.alloc(LayoutError::Unknown(ty)))
                     }
                     SizeSkeleton::Pointer { .. } => Err(err),
-                    SizeSkeleton::Generic(g) => {
-                        let len = tcx.expand_abstract_consts(len);
-                        let Some(gen_size) = mul_sorted_consts(tcx, param_env, len, g) else {
-                            return Err(tcx.arena.alloc(LayoutError::SizeOverflow(ty)));
-                        };
-                        Ok(SizeSkeleton::Generic(gen_size))
-                    }
+                    SizeSkeleton::Generic(_) => Err(tcx.arena.alloc(LayoutError::Unknown(ty))),
                 }
             }
 
@@ -468,56 +457,6 @@ impl<'tcx> SizeSkeleton<'tcx> {
     }
 }
 
-/// When creating the layout for types with abstract consts in their size (i.e. [usize; 4 * N]),
-/// to ensure that they have a canonical order and can be compared directly we combine all
-/// constants, and sort the other terms. This allows comparison of expressions of sizes,
-/// allowing for things like transmuting between types that depend on generic consts.
-/// This returns `None` if multiplication of constants overflows.
-fn mul_sorted_consts<'tcx>(
-    tcx: TyCtxt<'tcx>,
-    param_env: ty::ParamEnv<'tcx>,
-    a: ty::Const<'tcx>,
-    b: ty::Const<'tcx>,
-) -> Option<ty::Const<'tcx>> {
-    use crate::mir::BinOp::Mul;
-
-    let mut work = vec![a, b];
-    let mut done = vec![];
-    while let Some(n) = work.pop() {
-        if let ConstKind::Expr(ty::Expr::Binop(Mul, l, r)) = n.kind() {
-            work.push(l);
-            work.push(r)
-        } else {
-            done.push(n);
-        }
-    }
-    let mut k = 1;
-    let mut overflow = false;
-    done.retain(|c| {
-        let Some(c) = c.try_eval_target_usize(tcx, param_env) else {
-            return true;
-        };
-        let Some(next) = c.checked_mul(k) else {
-            overflow = true;
-            return false;
-        };
-        k = next;
-        false
-    });
-    if overflow {
-        return None;
-    }
-    if k != 1 {
-        done.push(ty::Const::from_target_usize(tcx, k));
-    } else if k == 0 {
-        return Some(ty::Const::from_target_usize(tcx, 0));
-    }
-    done.sort_unstable();
-
-    // create a single tree from the buffer
-    done.into_iter().reduce(|acc, n| ty::Const::new_expr(tcx, ty::Expr::Binop(Mul, n, acc), n.ty()))
-}
-
 pub trait HasTyCtxt<'tcx>: HasDataLayout {
     fn tcx(&self) -> TyCtxt<'tcx>;
 }
diff --git a/tests/ui/const-generics/transmute-fail.rs b/tests/ui/const-generics/transmute-fail.rs
index d7bf1b47fb5a7..90afd23253465 100644
--- a/tests/ui/const-generics/transmute-fail.rs
+++ b/tests/ui/const-generics/transmute-fail.rs
@@ -32,4 +32,79 @@ fn overflow(v: [[[u32; 8888888]; 9999999]; 777777777]) -> [[[u32; 9999999]; 7777
   }
 }
 
+fn transpose<const W: usize, const H: usize>(v: [[u32;H]; W]) -> [[u32; W]; H] {
+  unsafe {
+    std::mem::transmute(v)
+    //~^ ERROR: cannot transmute between types of different sizes, or dependently-sized types
+  }
+}
+
+fn ident<const W: usize, const H: usize>(v: [[u32; H]; W]) -> [[u32; H]; W] {
+  unsafe {
+    std::mem::transmute(v)
+  }
+}
+
+fn flatten<const W: usize, const H: usize>(v: [[u32; H]; W]) -> [u32; W * H] {
+  unsafe {
+    std::mem::transmute(v)
+    //~^ ERROR: cannot transmute between types of different sizes, or dependently-sized types
+  }
+}
+
+fn coagulate<const W: usize, const H: usize>(v: [u32; H*W]) -> [[u32; W];H] {
+  unsafe {
+    std::mem::transmute(v)
+    //~^ ERROR: cannot transmute between types of different sizes, or dependently-sized types
+  }
+}
+
+fn flatten_3d<const W: usize, const H: usize, const D: usize>(
+  v: [[[u32; D]; H]; W]
+) -> [u32; D * W * H] {
+  unsafe {
+    std::mem::transmute(v)
+    //~^ ERROR: cannot transmute between types of different sizes, or dependently-sized types
+  }
+}
+
+fn flatten_somewhat<const W: usize, const H: usize, const D: usize>(
+  v: [[[u32; D]; H]; W]
+) -> [[u32; D * W]; H] {
+  unsafe {
+    std::mem::transmute(v)
+    //~^ ERROR: cannot transmute between types of different sizes, or dependently-sized types
+  }
+}
+
+fn known_size<const L: usize>(v: [u16; L]) -> [u8; L * 2] {
+  unsafe {
+    std::mem::transmute(v)
+    //~^ ERROR: cannot transmute between types of different sizes, or dependently-sized types
+  }
+}
+
+fn condense_bytes<const L: usize>(v: [u8; L * 2]) -> [u16; L] {
+  unsafe {
+    std::mem::transmute(v)
+    //~^ ERROR: cannot transmute between types of different sizes, or dependently-sized types
+  }
+}
+
+fn singleton_each<const L: usize>(v: [u8; L]) -> [[u8;1]; L] {
+  unsafe {
+    std::mem::transmute(v)
+    //~^ ERROR: cannot transmute between types of different sizes, or dependently-sized types
+  }
+}
+
+fn transpose_with_const<const W: usize, const H: usize>(
+  v: [[u32; 2 * H]; W + W]
+) -> [[u32; W + W]; 2 * H] {
+  unsafe {
+    std::mem::transmute(v)
+    //~^ ERROR: cannot transmute between types of different sizes, or dependently-sized types
+  }
+}
+
 fn main() {}
diff --git a/tests/ui/const-generics/transmute-fail.stderr b/tests/ui/const-generics/transmute-fail.stderr
index 397e3be768a1e..1b0d1ea50d086 100644
--- a/tests/ui/const-generics/transmute-fail.stderr
+++ b/tests/ui/const-generics/transmute-fail.stderr
@@ -4,8 +4,8 @@ error[E0512]: cannot transmute between types of different sizes, or dependently-
 LL |     std::mem::transmute(v)
    |     ^^^^^^^^^^^^^^^^^^^
    |
-   = note: source type: `[[u32; H+1]; W]` (generic size (H + 1) * 4 * W)
-   = note: target type: `[[u32; W+1]; H]` (generic size (W + 1) * 4 * H)
+   = note: source type: `[[u32; H+1]; W]` (size can vary because of [u32; H+1])
+   = note: target type: `[[u32; W+1]; H]` (size can vary because of [u32; W+1])
 
 error[E0512]: cannot transmute between types of different sizes, or dependently-sized types
   --> $DIR/transmute-fail.rs:16:5
@@ -22,8 +22,8 @@ error[E0512]: cannot transmute between types of different sizes, or dependently-
 LL |     std::mem::transmute(v)
    |     ^^^^^^^^^^^^^^^^^^^
    |
-   = note: source type: `[[u32; H]; W]` (generic size 4 * H * W)
-   = note: target type: `[u32; W * H * H]` (generic size 4 * H * H * W)
+   = note: source type: `[[u32; H]; W]` (size can vary because of [u32; H])
+   = note: target type: `[u32; W * H * H]` (this type does not have a fixed size)
 
 error[E0512]: cannot transmute between types of different sizes, or dependently-sized types
   --> $DIR/transmute-fail.rs:30:5
@@ -34,6 +34,87 @@ LL |     std::mem::transmute(v)
    = note: source type: `[[[u32; 8888888]; 9999999]; 777777777]` (values of the type `[[u32; 8888888]; 9999999]` are too big for the current architecture)
    = note: target type: `[[[u32; 9999999]; 777777777]; 8888888]` (values of the type `[[u32; 9999999]; 777777777]` are too big for the current architecture)
 
+error[E0512]: cannot transmute between types of different sizes, or dependently-sized types
+  --> $DIR/transmute-fail.rs:37:5
+   |
+LL |     std::mem::transmute(v)
+   |     ^^^^^^^^^^^^^^^^^^^
+   |
+   = note: source type: `[[u32; H]; W]` (size can vary because of [u32; H])
+   = note: target type: `[[u32; W]; H]` (size can vary because of [u32; W])
+
+error[E0512]: cannot transmute between types of different sizes, or dependently-sized types
+  --> $DIR/transmute-fail.rs:50:5
+   |
+LL |     std::mem::transmute(v)
+   |     ^^^^^^^^^^^^^^^^^^^
+   |
+   = note: source type: `[[u32; H]; W]` (size can vary because of [u32; H])
+   = note: target type: `[u32; W * H]` (this type does not have a fixed size)
+
+error[E0512]: cannot transmute between types of different sizes, or dependently-sized types
+  --> $DIR/transmute-fail.rs:57:5
+   |
+LL |     std::mem::transmute(v)
+   |     ^^^^^^^^^^^^^^^^^^^
+   |
+   = note: source type: `[u32; H*W]` (this type does not have a fixed size)
+   = note: target type: `[[u32; W]; H]` (size can vary because of [u32; W])
+
+error[E0512]: cannot transmute between types of different sizes, or dependently-sized types
+  --> $DIR/transmute-fail.rs:66:5
+   |
+LL |     std::mem::transmute(v)
+   |     ^^^^^^^^^^^^^^^^^^^
+   |
+   = note: source type: `[[[u32; D]; H]; W]` (size can vary because of [u32; D])
+   = note: target type: `[u32; D * W * H]` (this type does not have a fixed size)
+
+error[E0512]: cannot transmute between types of different sizes, or dependently-sized types
+  --> $DIR/transmute-fail.rs:75:5
+   |
+LL |     std::mem::transmute(v)
+   |     ^^^^^^^^^^^^^^^^^^^
+   |
+   = note: source type: `[[[u32; D]; H]; W]` (size can vary because of [u32; D])
+   = note: target type: `[[u32; D * W]; H]` (size can vary because of [u32; D * W])
+
+error[E0512]: cannot transmute between types of different sizes, or dependently-sized types
+  --> $DIR/transmute-fail.rs:82:5
+   |
+LL |     std::mem::transmute(v)
+   |     ^^^^^^^^^^^^^^^^^^^
+   |
+   = note: source type: `[u16; L]` (this type does not have a fixed size)
+   = note: target type: `[u8; L * 2]` (this type does not have a fixed size)
+
+error[E0512]: cannot transmute between types of different sizes, or dependently-sized types
+  --> $DIR/transmute-fail.rs:89:5
+   |
+LL |     std::mem::transmute(v)
+   |     ^^^^^^^^^^^^^^^^^^^
+   |
+   = note: source type: `[u8; L * 2]` (this type does not have a fixed size)
+   = note: target type: `[u16; L]` (this type does not have a fixed size)
+
+error[E0512]: cannot transmute between types of different sizes, or dependently-sized types
+  --> $DIR/transmute-fail.rs:96:5
+   |
+LL |     std::mem::transmute(v)
+   |     ^^^^^^^^^^^^^^^^^^^
+   |
+   = note: source type: `[u8; L]` (this type does not have a fixed size)
+   = note: target type: `[[u8; 1]; L]` (this type does not have a fixed size)
+
+error[E0512]: cannot transmute between types of different sizes, or dependently-sized types
+  --> $DIR/transmute-fail.rs:105:5
+   |
+LL |     std::mem::transmute(v)
+   |     ^^^^^^^^^^^^^^^^^^^
+   |
+   = note: source type: `[[u32; 2 * H]; W + W]` (size can vary because of [u32; 2 * H])
+   = note: target type: `[[u32; W + W]; 2 * H]` (size can vary because of [u32; W + W])
+
 error[E0308]: mismatched types
   --> $DIR/transmute-fail.rs:12:53
    |
@@ -46,7 +127,7 @@ error[E0308]: mismatched types
 LL | fn bar<const W: bool, const H: usize>(v: [[u32; H]; W]) -> [[u32; W]; H] {
    |                                                                   ^ expected `usize`, found `bool`
 
-error: aborting due to 6 previous errors
+error: aborting due to 15 previous errors
 
 Some errors have detailed explanations: E0308, E0512.
 For more information about an error, try `rustc --explain E0308`.
diff --git a/tests/ui/const-generics/transmute.rs b/tests/ui/const-generics/transmute.rs
index 245fcf5670e25..e8ab8637932dd 100644
--- a/tests/ui/const-generics/transmute.rs
+++ b/tests/ui/const-generics/transmute.rs
@@ -3,81 +3,12 @@
 #![feature(transmute_generic_consts)]
 #![allow(incomplete_features)]
 
-fn transpose<const W: usize, const H: usize>(v: [[u32;H]; W]) -> [[u32; W]; H] {
-  unsafe {
-    std::mem::transmute(v)
-  }
-}
-
 fn ident<const W: usize, const H: usize>(v: [[u32; H]; W]) -> [[u32; H]; W] {
   unsafe {
     std::mem::transmute(v)
   }
 }
 
-fn flatten<const W: usize, const H: usize>(v: [[u32; H]; W]) -> [u32; W * H] {
-  unsafe {
-    std::mem::transmute(v)
-  }
-}
-
-fn coagulate<const W: usize, const H: usize>(v: [u32; H*W]) -> [[u32; W];H] {
-  unsafe {
-    std::mem::transmute(v)
-  }
-}
-
-fn flatten_3d<const W: usize, const H: usize, const D: usize>(
-  v: [[[u32; D]; H]; W]
-) -> [u32; D * W * H] {
-  unsafe {
-    std::mem::transmute(v)
-  }
-}
-
-fn flatten_somewhat<const W: usize, const H: usize, const D: usize>(
-  v: [[[u32; D]; H]; W]
-) -> [[u32; D * W]; H] {
-  unsafe {
-    std::mem::transmute(v)
-  }
-}
-
-fn known_size<const L: usize>(v: [u16; L]) -> [u8; L * 2] {
-  unsafe {
-    std::mem::transmute(v)
-  }
-}
-
-fn condense_bytes<const L: usize>(v: [u8; L * 2]) -> [u16; L] {
-  unsafe {
-    std::mem::transmute(v)
-  }
-}
-
-fn singleton_each<const L: usize>(v: [u8; L]) -> [[u8;1]; L] {
-  unsafe {
-    std::mem::transmute(v)
-  }
-}
-
-fn transpose_with_const<const W: usize, const H: usize>(
-  v: [[u32; 2 * H]; W + W]
-) -> [[u32; W + W]; 2 * H] {
-  unsafe {
-    std::mem::transmute(v)
-  }
-}
-
 fn main() {
-  let _ = transpose([[0; 8]; 16]);
-  let _ = transpose_with_const::<8,4>([[0; 8]; 16]);
   let _ = ident([[0; 8]; 16]);
-  let _ = flatten([[0; 13]; 5]);
-  let _: [[_; 5]; 13] = coagulate([0; 65]);
-  let _ = flatten_3d([[[0; 3]; 13]; 5]);
-  let _ = flatten_somewhat([[[0; 3]; 13]; 5]);
-  let _ = known_size([16; 13]);
-  let _: [u16; 5] = condense_bytes([16u8; 10]);
-  let _ = singleton_each([16; 10]);
 }

From 60891cab33c99c0be933ddd54008513af7e49cd9 Mon Sep 17 00:00:00 2001
From: Jubilee Young <workingjubilee@gmail.com>
Date: Thu, 21 Mar 2024 13:35:34 -0700
Subject: [PATCH 11/22] Use less hacky STACK_SIZE

---
 compiler/rustc_interface/src/util.rs | 33 +++++++++++++++-------------
 1 file changed, 18 insertions(+), 15 deletions(-)

diff --git a/compiler/rustc_interface/src/util.rs b/compiler/rustc_interface/src/util.rs
index 7d48f90db3625..7ecd7166d1c56 100644
--- a/compiler/rustc_interface/src/util.rs
+++ b/compiler/rustc_interface/src/util.rs
@@ -48,12 +48,20 @@ pub fn add_configuration(cfg: &mut Cfg, sess: &mut Session, codegen_backend: &dy
     }
 }
 
-const STACK_SIZE: usize = 8 * 1024 * 1024;
-
-fn get_stack_size() -> Option<usize> {
-    // FIXME: Hacks on hacks. If the env is trying to override the stack size
-    // then *don't* set it explicitly.
-    env::var_os("RUST_MIN_STACK").is_none().then_some(STACK_SIZE)
+static STACK_SIZE: OnceLock<usize> = OnceLock::new();
+const DEFAULT_STACK_SIZE: usize = 8 * 1024 * 1024;
+
+fn init_stack_size() -> usize {
+    // Obey the environment setting or default
+    *STACK_SIZE.get_or_init(|| {
+        env::var_os("RUST_MIN_STACK")
+            .map(|os_str| os_str.to_string_lossy().into_owned())
+            // ignore if it is set to nothing
+            .filter(|s| s.trim() != "")
+            .map(|s| s.trim().parse::<usize>().unwrap())
+            // otherwise pick a consistent default
+            .unwrap_or(DEFAULT_STACK_SIZE)
+    })
 }
 
 pub(crate) fn run_in_thread_with_globals<F: FnOnce() -> R + Send, R: Send>(
@@ -66,10 +74,7 @@ pub(crate) fn run_in_thread_with_globals<F: FnOnce() -> R + Send, R: Send>(
     // the parallel compiler, in particular to ensure there is no accidental
     // sharing of data between the main thread and the compilation thread
     // (which might cause problems for the parallel compiler).
-    let mut builder = thread::Builder::new().name("rustc".to_string());
-    if let Some(size) = get_stack_size() {
-        builder = builder.stack_size(size);
-    }
+    let builder = thread::Builder::new().name("rustc".to_string()).stack_size(init_stack_size());
 
     // We build the session globals and run `f` on the spawned thread, because
     // `SessionGlobals` does not impl `Send` in the non-parallel compiler.
@@ -120,7 +125,7 @@ pub(crate) fn run_in_thread_pool_with_globals<F: FnOnce() -> R + Send, R: Send>(
         });
     }
 
-    let mut builder = rayon::ThreadPoolBuilder::new()
+    let builder = rayon::ThreadPoolBuilder::new()
         .thread_name(|_| "rustc".to_string())
         .acquire_thread_handler(jobserver::acquire_thread)
         .release_thread_handler(jobserver::release_thread)
@@ -144,10 +149,8 @@ pub(crate) fn run_in_thread_pool_with_globals<F: FnOnce() -> R + Send, R: Send>(
                     on_panic.disable();
                 })
                 .unwrap();
-        });
-    if let Some(size) = get_stack_size() {
-        builder = builder.stack_size(size);
-    }
+        })
+        .stack_size(init_stack_size());
 
     // We create the session globals on the main thread, then create the thread
     // pool. Upon creation, each worker thread created gets a copy of the

From 542533865aa2d828665d96047ed575267eed7ac6 Mon Sep 17 00:00:00 2001
From: Jubilee Young <workingjubilee@gmail.com>
Date: Thu, 21 Mar 2024 14:16:07 -0700
Subject: [PATCH 12/22] Suggest using RUST_MIN_STACK if rustc overflowed

---
 compiler/rustc_driver_impl/src/signal_handler.rs | 6 +++++-
 compiler/rustc_interface/src/util.rs             | 4 ++--
 2 files changed, 7 insertions(+), 3 deletions(-)

diff --git a/compiler/rustc_driver_impl/src/signal_handler.rs b/compiler/rustc_driver_impl/src/signal_handler.rs
index deca108222150..441219eec90dc 100644
--- a/compiler/rustc_driver_impl/src/signal_handler.rs
+++ b/compiler/rustc_driver_impl/src/signal_handler.rs
@@ -1,6 +1,7 @@
 //! Signal handler for rustc
 //! Primarily used to extract a backtrace from stack overflow
 
+use rustc_interface::util::{DEFAULT_STACK_SIZE, STACK_SIZE};
 use std::alloc::{alloc, Layout};
 use std::{fmt, mem, ptr};
 
@@ -100,7 +101,10 @@ extern "C" fn print_stack_trace(_: libc::c_int) {
         written += 1;
     }
     raw_errln!("note: we would appreciate a report at https://github.com/rust-lang/rust");
-    written += 1;
+    // get the current stack size WITHOUT blocking and double it
+    let new_size = STACK_SIZE.get().copied().unwrap_or(DEFAULT_STACK_SIZE) * 2;
+    raw_errln!("help: you can increase rustc's stack size by setting RUST_MIN_STACK={new_size}");
+    written += 2;
     if written > 24 {
         // We probably just scrolled the earlier "we got SIGSEGV" message off the terminal
         raw_errln!("note: backtrace dumped due to SIGSEGV! resuming signal");
diff --git a/compiler/rustc_interface/src/util.rs b/compiler/rustc_interface/src/util.rs
index 7ecd7166d1c56..d09f8d7d7cf75 100644
--- a/compiler/rustc_interface/src/util.rs
+++ b/compiler/rustc_interface/src/util.rs
@@ -48,8 +48,8 @@ pub fn add_configuration(cfg: &mut Cfg, sess: &mut Session, codegen_backend: &dy
     }
 }
 
-static STACK_SIZE: OnceLock<usize> = OnceLock::new();
-const DEFAULT_STACK_SIZE: usize = 8 * 1024 * 1024;
+pub static STACK_SIZE: OnceLock<usize> = OnceLock::new();
+pub const DEFAULT_STACK_SIZE: usize = 8 * 1024 * 1024;
 
 fn init_stack_size() -> usize {
     // Obey the environment setting or default

From 1b95760e41bed110ea20b44f85193fe900b13242 Mon Sep 17 00:00:00 2001
From: Zachary S <zasample18+github@gmail.com>
Date: Thu, 21 Mar 2024 17:00:41 -0500
Subject: [PATCH 13/22] Not insta-stable

---
 library/core/src/ptr/non_null.rs | 8 +++-----
 1 file changed, 3 insertions(+), 5 deletions(-)

diff --git a/library/core/src/ptr/non_null.rs b/library/core/src/ptr/non_null.rs
index 8bb87734eb31f..2ac42e20d43b2 100644
--- a/library/core/src/ptr/non_null.rs
+++ b/library/core/src/ptr/non_null.rs
@@ -1580,16 +1580,14 @@ impl<T> NonNull<[T]> {
     /// # Examples
     ///
     /// ```rust
+    /// #![feature(slice_ptr_is_empty_nonnull)]
     /// use std::ptr::NonNull;
     ///
     /// let slice: NonNull<[i8]> = NonNull::slice_from_raw_parts(NonNull::dangling(), 3);
     /// assert!(!slice.is_empty());
     /// ```
-    #[stable(feature = "slice_ptr_is_empty_nonnull", since = "CURRENT_RUSTC_VERSION")]
-    #[rustc_const_stable(
-        feature = "const_slice_ptr_is_empty_nonnull",
-        since = "CURRENT_RUSTC_VERSION"
-    )]
+    #[unstable(feature = "slice_ptr_is_empty_nonnull", issue = "71146")]
+    #[rustc_const_unstable(feature = "const_slice_ptr_is_empty_nonnull", issue = "71146")]
     #[must_use]
     #[inline]
     pub const fn is_empty(self) -> bool {

From 861e47000f8bb35c76290c28f86757a4f5463c6c Mon Sep 17 00:00:00 2001
From: Jubilee Young <workingjubilee@gmail.com>
Date: Thu, 21 Mar 2024 17:28:32 -0700
Subject: [PATCH 14/22] Fix Itanium mangling usizes

Arrays, surprisingly, are not sized to u64 on all platforms.
---
 .../src/typeid/typeid_itanium_cxx_abi.rs                      | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/compiler/rustc_symbol_mangling/src/typeid/typeid_itanium_cxx_abi.rs b/compiler/rustc_symbol_mangling/src/typeid/typeid_itanium_cxx_abi.rs
index 51e2c96120caa..c5ae08e284e8a 100644
--- a/compiler/rustc_symbol_mangling/src/typeid/typeid_itanium_cxx_abi.rs
+++ b/compiler/rustc_symbol_mangling/src/typeid/typeid_itanium_cxx_abi.rs
@@ -525,8 +525,8 @@ fn encode_ty<'tcx>(
                 "{}",
                 &len.try_to_scalar()
                     .unwrap()
-                    .to_u64()
-                    .unwrap_or_else(|_| panic!("failed to convert length to u64"))
+                    .to_target_usize(&tcx.data_layout)
+                    .expect("Array lens are defined in usize")
             );
             s.push_str(&encode_ty(tcx, *ty0, dict, options));
             compress(dict, DictKey::Ty(ty, TyQ::None), &mut s);

From 1bcbed19d1629d8a67f322c76b8fc4a29e51539f Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Matthias=20Kr=C3=BCger?= <matthias.krueger@famsik.de>
Date: Fri, 22 Mar 2024 08:13:54 +0100
Subject: [PATCH 15/22] add test for #110696

Fixes #110696
---
 ...e-failed-to-resolve-instance-for-110696.rs | 52 +++++++++++++++++++
 ...iled-to-resolve-instance-for-110696.stderr |  9 ++++
 2 files changed, 61 insertions(+)
 create mode 100644 tests/ui/type-alias-impl-trait/ice-failed-to-resolve-instance-for-110696.rs
 create mode 100644 tests/ui/type-alias-impl-trait/ice-failed-to-resolve-instance-for-110696.stderr

diff --git a/tests/ui/type-alias-impl-trait/ice-failed-to-resolve-instance-for-110696.rs b/tests/ui/type-alias-impl-trait/ice-failed-to-resolve-instance-for-110696.rs
new file mode 100644
index 0000000000000..840be25dd2e02
--- /dev/null
+++ b/tests/ui/type-alias-impl-trait/ice-failed-to-resolve-instance-for-110696.rs
@@ -0,0 +1,52 @@
+// test for #110696
+// failed to resolve instance for <Scope<()> as MyIndex<()>>::my_index
+// ignore-tidy-linelength
+
+#![feature(type_alias_impl_trait)]
+
+use std::marker::PhantomData;
+
+
+trait MyIndex<T> {
+    type O;
+    fn my_index(self) -> Self::O;
+}
+trait MyFrom<T>: Sized {
+    type Error;
+    fn my_from(value: T) -> Result<Self, Self::Error>;
+}
+
+
+trait F {}
+impl F for () {}
+type DummyT<T> = impl F;
+fn _dummy_t<T>() -> DummyT<T> {}
+
+struct Phantom1<T>(PhantomData<T>);
+struct Phantom2<T>(PhantomData<T>);
+struct Scope<T>(Phantom2<DummyT<T>>);
+
+impl<T> Scope<T> {
+    fn new() -> Self {
+        unimplemented!()
+    }
+}
+
+impl<T> MyFrom<Phantom2<T>> for Phantom1<T> {
+    type Error = ();
+    fn my_from(_: Phantom2<T>) -> Result<Self, Self::Error> {
+        unimplemented!()
+    }
+}
+
+impl<T: MyFrom<Phantom2<DummyT<U>>>, U> MyIndex<DummyT<T>> for Scope<U> {
+    //~^ ERROR the type parameter `T` is not constrained by the impl trait, self type, or predicates
+    type O = T;
+    fn my_index(self) -> Self::O {
+        MyFrom::my_from(self.0).ok().unwrap()
+    }
+}
+
+fn main() {
+    let _pos: Phantom1<DummyT<()>> = Scope::new().my_index();
+}
diff --git a/tests/ui/type-alias-impl-trait/ice-failed-to-resolve-instance-for-110696.stderr b/tests/ui/type-alias-impl-trait/ice-failed-to-resolve-instance-for-110696.stderr
new file mode 100644
index 0000000000000..a39f77ce17f61
--- /dev/null
+++ b/tests/ui/type-alias-impl-trait/ice-failed-to-resolve-instance-for-110696.stderr
@@ -0,0 +1,9 @@
+error[E0207]: the type parameter `T` is not constrained by the impl trait, self type, or predicates
+  --> $DIR/ice-failed-to-resolve-instance-for-110696.rs:42:6
+   |
+LL | impl<T: MyFrom<Phantom2<DummyT<U>>>, U> MyIndex<DummyT<T>> for Scope<U> {
+   |      ^ unconstrained type parameter
+
+error: aborting due to 1 previous error
+
+For more information about this error, try `rustc --explain E0207`.

From 4d9ce7a1a2f78e26b58c4464f43aab21100ea1f3 Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Matthias=20Kr=C3=BCger?= <matthias.krueger@famsik.de>
Date: Fri, 22 Mar 2024 08:19:44 +0100
Subject: [PATCH 16/22] add test for ice #121472

Fixes #121472
---
 .../underef-index-out-of-bounds-121472.rs     | 16 +++++++++++++
 .../underef-index-out-of-bounds-121472.stderr | 23 +++++++++++++++++++
 2 files changed, 39 insertions(+)
 create mode 100644 tests/ui/type-alias-impl-trait/underef-index-out-of-bounds-121472.rs
 create mode 100644 tests/ui/type-alias-impl-trait/underef-index-out-of-bounds-121472.stderr

diff --git a/tests/ui/type-alias-impl-trait/underef-index-out-of-bounds-121472.rs b/tests/ui/type-alias-impl-trait/underef-index-out-of-bounds-121472.rs
new file mode 100644
index 0000000000000..37e0d89efc752
--- /dev/null
+++ b/tests/ui/type-alias-impl-trait/underef-index-out-of-bounds-121472.rs
@@ -0,0 +1,16 @@
+// test for ICE #121472 index out of bounds un_derefer.rs
+#![feature(type_alias_impl_trait)]
+
+trait T {}
+
+type Alias<'a> = impl T;
+
+struct S;
+impl<'a> T for &'a S {}
+
+fn with_positive(fun: impl Fn(Alias<'_>)) {}
+
+fn main() {
+    with_positive(|&n| ());
+    //~^ ERROR mismatched types
+}
diff --git a/tests/ui/type-alias-impl-trait/underef-index-out-of-bounds-121472.stderr b/tests/ui/type-alias-impl-trait/underef-index-out-of-bounds-121472.stderr
new file mode 100644
index 0000000000000..a224bab0705ef
--- /dev/null
+++ b/tests/ui/type-alias-impl-trait/underef-index-out-of-bounds-121472.stderr
@@ -0,0 +1,23 @@
+error[E0308]: mismatched types
+  --> $DIR/underef-index-out-of-bounds-121472.rs:14:20
+   |
+LL | type Alias<'a> = impl T;
+   |                  ------ the expected opaque type
+...
+LL |     with_positive(|&n| ());
+   |                    ^^
+   |                    |
+   |                    expected opaque type, found `&_`
+   |                    expected due to this
+   |
+   = note: expected opaque type `Alias<'_>`
+                found reference `&_`
+help: consider removing `&` from the pattern
+   |
+LL -     with_positive(|&n| ());
+LL +     with_positive(|n| ());
+   |
+
+error: aborting due to 1 previous error
+
+For more information about this error, try `rustc --explain E0308`.

From 2b5740371c42c632efb3dbe46150798baf56a8d1 Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Matthias=20Kr=C3=BCger?= <matthias.krueger@famsik.de>
Date: Fri, 22 Mar 2024 08:27:14 +0100
Subject: [PATCH 17/22] add test for
 https://github.com/rust-lang/rust/issues/112823

Fixes #112823
---
 ...-type-whensubstituting-in-region-112823.rs | 30 ++++++++++++++++++
 ...e-whensubstituting-in-region-112823.stderr | 31 +++++++++++++++++++
 2 files changed, 61 insertions(+)
 create mode 100644 tests/ui/impl-trait/ice-unexpected-param-type-whensubstituting-in-region-112823.rs
 create mode 100644 tests/ui/impl-trait/ice-unexpected-param-type-whensubstituting-in-region-112823.stderr

diff --git a/tests/ui/impl-trait/ice-unexpected-param-type-whensubstituting-in-region-112823.rs b/tests/ui/impl-trait/ice-unexpected-param-type-whensubstituting-in-region-112823.rs
new file mode 100644
index 0000000000000..d6fa56663a3f0
--- /dev/null
+++ b/tests/ui/impl-trait/ice-unexpected-param-type-whensubstituting-in-region-112823.rs
@@ -0,0 +1,30 @@
+// test for ICE #112823
+// Unexpected parameter Type(Repr) when substituting in region
+
+#![feature(impl_trait_in_assoc_type)]
+
+use std::future::Future;
+
+trait Stream {}
+
+trait X {
+    type LineStream<'a, Repr>
+    where
+        Self: 'a;
+    type LineStreamFut<'a, Repr>
+    where
+        Self: 'a;
+}
+
+struct Y;
+
+impl X for Y {
+    type LineStream<'c, 'd> = impl Stream;
+    //~^ ERROR type `LineStream` has 0 type parameters but its trait declaration has 1 type parameter
+    type LineStreamFut<'a, Repr> = impl Future<Output = Self::LineStream<'a, Repr>>;
+    fn line_stream<'a, Repr>(&'a self) -> Self::LineStreamFut<'a, Repr> {}
+    //~^ ERROR `()` is not a future
+    //~^^ method `line_stream` is not a member of trait `X`
+}
+
+pub fn main() {}
diff --git a/tests/ui/impl-trait/ice-unexpected-param-type-whensubstituting-in-region-112823.stderr b/tests/ui/impl-trait/ice-unexpected-param-type-whensubstituting-in-region-112823.stderr
new file mode 100644
index 0000000000000..28a0f7461e2d5
--- /dev/null
+++ b/tests/ui/impl-trait/ice-unexpected-param-type-whensubstituting-in-region-112823.stderr
@@ -0,0 +1,31 @@
+error[E0407]: method `line_stream` is not a member of trait `X`
+  --> $DIR/ice-unexpected-param-type-whensubstituting-in-region-112823.rs:25:5
+   |
+LL |     fn line_stream<'a, Repr>(&'a self) -> Self::LineStreamFut<'a, Repr> {}
+   |     ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ not a member of trait `X`
+
+error[E0049]: type `LineStream` has 0 type parameters but its trait declaration has 1 type parameter
+  --> $DIR/ice-unexpected-param-type-whensubstituting-in-region-112823.rs:22:21
+   |
+LL |     type LineStream<'a, Repr>
+   |                     --  ----
+   |                     |
+   |                     expected 1 type parameter
+...
+LL |     type LineStream<'c, 'd> = impl Stream;
+   |                     ^^  ^^
+   |                     |
+   |                     found 0 type parameters
+
+error[E0277]: `()` is not a future
+  --> $DIR/ice-unexpected-param-type-whensubstituting-in-region-112823.rs:25:43
+   |
+LL |     fn line_stream<'a, Repr>(&'a self) -> Self::LineStreamFut<'a, Repr> {}
+   |                                           ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ `()` is not a future
+   |
+   = help: the trait `Future` is not implemented for `()`
+
+error: aborting due to 3 previous errors
+
+Some errors have detailed explanations: E0049, E0277, E0407.
+For more information about an error, try `rustc --explain E0049`.

From d7e166d408c6c9f86ef2087c5a013c1600ca94f3 Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Matthias=20Kr=C3=BCger?= <matthias.krueger@famsik.de>
Date: Fri, 22 Mar 2024 08:31:01 +0100
Subject: [PATCH 18/22] add test for ice "type mismatching when copying!"

Fixes #112824
---
 .../ice-type-mismatch-when-copying-112824.rs  | 20 +++++++++++++
 ...e-type-mismatch-when-copying-112824.stderr | 29 +++++++++++++++++++
 2 files changed, 49 insertions(+)
 create mode 100644 tests/ui/const_prop/ice-type-mismatch-when-copying-112824.rs
 create mode 100644 tests/ui/const_prop/ice-type-mismatch-when-copying-112824.stderr

diff --git a/tests/ui/const_prop/ice-type-mismatch-when-copying-112824.rs b/tests/ui/const_prop/ice-type-mismatch-when-copying-112824.rs
new file mode 100644
index 0000000000000..dc9782295c136
--- /dev/null
+++ b/tests/ui/const_prop/ice-type-mismatch-when-copying-112824.rs
@@ -0,0 +1,20 @@
+// test for #112824 ICE type mismatching when copying!
+
+pub struct Opcode(pub u8);
+
+pub struct Opcode2(&'a S);
+//~^ ERROR use of undeclared lifetime name `'a`
+//~^^ ERROR cannot find type `S` in this scope
+
+impl Opcode2 {
+    pub const OP2: Opcode2 = Opcode2(Opcode(0x1));
+}
+
+pub fn example2(msg_type: Opcode2) -> impl FnMut(&[u8]) {
+    move |i| match msg_type {
+        Opcode2::OP2 => unimplemented!(),
+        //~^ ERROR could not evaluate constant pattern
+    }
+}
+
+pub fn main() {}
diff --git a/tests/ui/const_prop/ice-type-mismatch-when-copying-112824.stderr b/tests/ui/const_prop/ice-type-mismatch-when-copying-112824.stderr
new file mode 100644
index 0000000000000..9442eac0cf54a
--- /dev/null
+++ b/tests/ui/const_prop/ice-type-mismatch-when-copying-112824.stderr
@@ -0,0 +1,29 @@
+error[E0261]: use of undeclared lifetime name `'a`
+  --> $DIR/ice-type-mismatch-when-copying-112824.rs:5:21
+   |
+LL | pub struct Opcode2(&'a S);
+   |                   - ^^ undeclared lifetime
+   |                   |
+   |                   help: consider introducing lifetime `'a` here: `<'a>`
+
+error[E0412]: cannot find type `S` in this scope
+  --> $DIR/ice-type-mismatch-when-copying-112824.rs:5:24
+   |
+LL | pub struct Opcode2(&'a S);
+   |                        ^ not found in this scope
+   |
+help: you might be missing a type parameter
+   |
+LL | pub struct Opcode2<S>(&'a S);
+   |                   +++
+
+error: could not evaluate constant pattern
+  --> $DIR/ice-type-mismatch-when-copying-112824.rs:15:9
+   |
+LL |         Opcode2::OP2 => unimplemented!(),
+   |         ^^^^^^^^^^^^
+
+error: aborting due to 3 previous errors
+
+Some errors have detailed explanations: E0261, E0412.
+For more information about an error, try `rustc --explain E0261`.

From b0e10083f3f0300fda3cce292edd7b3cce5f7284 Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Matthias=20Kr=C3=BCger?= <matthias.krueger@famsik.de>
Date: Fri, 22 Mar 2024 08:38:26 +0100
Subject: [PATCH 19/22] add test for ice #113017 no entry found for key in
 generics_of.rs

Fixes #113017
---
 ...nerics_of-no-entry-found-for-key-113017.rs | 20 ++++
 ...cs_of-no-entry-found-for-key-113017.stderr | 92 +++++++++++++++++++
 2 files changed, 112 insertions(+)
 create mode 100644 tests/ui/const-generics/generic_const_exprs/ice-generics_of-no-entry-found-for-key-113017.rs
 create mode 100644 tests/ui/const-generics/generic_const_exprs/ice-generics_of-no-entry-found-for-key-113017.stderr

diff --git a/tests/ui/const-generics/generic_const_exprs/ice-generics_of-no-entry-found-for-key-113017.rs b/tests/ui/const-generics/generic_const_exprs/ice-generics_of-no-entry-found-for-key-113017.rs
new file mode 100644
index 0000000000000..36e552ed88d1a
--- /dev/null
+++ b/tests/ui/const-generics/generic_const_exprs/ice-generics_of-no-entry-found-for-key-113017.rs
@@ -0,0 +1,20 @@
+// test for ICE "no entry found for key" in generics_of.rs #113017
+
+#![feature(generic_const_exprs)]
+#![allow(incomplete_features)]
+
+pub fn String<V>(elem)
+//~^ ERROR expected one of `:`, `@`, or `|`, found `)`
+where
+    V: 'a,
+    //~^ ERROR use of undeclared lifetime name `'a`
+    for<const N: usize = { || {}}> V: 'a,
+    //~^ ERROR use of undeclared lifetime name `'a`
+    //~^^ ERROR only lifetime parameters can be used in this context
+    //~^^^ ERROR defaults for generic parameters are not allowed in `for<...>` binders
+    for<C2: , R2, R3: > <&str as IntoIterator>::Item: 'static,
+    //~^ ERROR `&` without an explicit lifetime name cannot be used here
+    //~^^ ERROR only lifetime parameters can be used in this context
+{}
+
+pub fn main() {}
diff --git a/tests/ui/const-generics/generic_const_exprs/ice-generics_of-no-entry-found-for-key-113017.stderr b/tests/ui/const-generics/generic_const_exprs/ice-generics_of-no-entry-found-for-key-113017.stderr
new file mode 100644
index 0000000000000..54794022ebdb8
--- /dev/null
+++ b/tests/ui/const-generics/generic_const_exprs/ice-generics_of-no-entry-found-for-key-113017.stderr
@@ -0,0 +1,92 @@
+error: expected one of `:`, `@`, or `|`, found `)`
+  --> $DIR/ice-generics_of-no-entry-found-for-key-113017.rs:6:22
+   |
+LL | pub fn String<V>(elem)
+   |                      ^ expected one of `:`, `@`, or `|`
+   |
+   = note: anonymous parameters are removed in the 2018 edition (see RFC 1685)
+help: if this is a `self` type, give it a parameter name
+   |
+LL | pub fn String<V>(self: elem)
+   |                  +++++
+help: if this is a parameter name, give it a type
+   |
+LL | pub fn String<V>(elem: TypeName)
+   |                      ++++++++++
+help: if this is a type, explicitly ignore the parameter name
+   |
+LL | pub fn String<V>(_: elem)
+   |                  ++
+
+error[E0261]: use of undeclared lifetime name `'a`
+  --> $DIR/ice-generics_of-no-entry-found-for-key-113017.rs:9:8
+   |
+LL |     V: 'a,
+   |        ^^ undeclared lifetime
+   |
+   = note: for more information on higher-ranked polymorphism, visit https://doc.rust-lang.org/nomicon/hrtb.html
+help: consider making the bound lifetime-generic with a new `'a` lifetime
+   |
+LL |     for<'a> V: 'a,
+   |     +++++++
+help: consider introducing lifetime `'a` here
+   |
+LL | pub fn String<'a, V>(elem)
+   |               +++
+
+error[E0261]: use of undeclared lifetime name `'a`
+  --> $DIR/ice-generics_of-no-entry-found-for-key-113017.rs:11:39
+   |
+LL |     for<const N: usize = { || {}}> V: 'a,
+   |                                       ^^ undeclared lifetime
+   |
+help: consider making the bound lifetime-generic with a new `'a` lifetime
+   |
+LL |     for<'a, const N: usize = { || {}}> V: 'a,
+   |         +++
+help: consider introducing lifetime `'a` here
+   |
+LL | pub fn String<'a, V>(elem)
+   |               +++
+
+error[E0637]: `&` without an explicit lifetime name cannot be used here
+  --> $DIR/ice-generics_of-no-entry-found-for-key-113017.rs:15:26
+   |
+LL |     for<C2: , R2, R3: > <&str as IntoIterator>::Item: 'static,
+   |                          ^ explicit lifetime name needed here
+   |
+help: consider introducing a higher-ranked lifetime here
+   |
+LL |     for<'a> for<C2: , R2, R3: > <&'a str as IntoIterator>::Item: 'static,
+   |     +++++++                       ++
+
+error[E0658]: only lifetime parameters can be used in this context
+  --> $DIR/ice-generics_of-no-entry-found-for-key-113017.rs:11:15
+   |
+LL |     for<const N: usize = { || {}}> V: 'a,
+   |               ^
+   |
+   = note: see issue #108185 <https://github.com/rust-lang/rust/issues/108185> for more information
+   = help: add `#![feature(non_lifetime_binders)]` to the crate attributes to enable
+   = note: this compiler was built on YYYY-MM-DD; consider upgrading it if it is out of date
+
+error[E0658]: only lifetime parameters can be used in this context
+  --> $DIR/ice-generics_of-no-entry-found-for-key-113017.rs:15:9
+   |
+LL |     for<C2: , R2, R3: > <&str as IntoIterator>::Item: 'static,
+   |         ^^    ^^  ^^
+   |
+   = note: see issue #108185 <https://github.com/rust-lang/rust/issues/108185> for more information
+   = help: add `#![feature(non_lifetime_binders)]` to the crate attributes to enable
+   = note: this compiler was built on YYYY-MM-DD; consider upgrading it if it is out of date
+
+error: defaults for generic parameters are not allowed in `for<...>` binders
+  --> $DIR/ice-generics_of-no-entry-found-for-key-113017.rs:11:9
+   |
+LL |     for<const N: usize = { || {}}> V: 'a,
+   |         ^^^^^^^^^^^^^^^^^^^^^^^^^
+
+error: aborting due to 7 previous errors
+
+Some errors have detailed explanations: E0261, E0637, E0658.
+For more information about an error, try `rustc --explain E0261`.

From bd2d70dd0a0756027724da853784a0f4cf30d926 Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Matthias=20Kr=C3=BCger?= <matthias.krueger@famsik.de>
Date: Fri, 22 Mar 2024 08:44:01 +0100
Subject: [PATCH 20/22] add test for ice #119275 "no entry found for key" in
 predicates_of.rs

fixes #119275
---
 ...icates-of-no-entry-found-for-key-119275.rs | 18 ++++++++
 ...es-of-no-entry-found-for-key-119275.stderr | 46 +++++++++++++++++++
 2 files changed, 64 insertions(+)
 create mode 100644 tests/ui/const-generics/generic_const_exprs/ice-predicates-of-no-entry-found-for-key-119275.rs
 create mode 100644 tests/ui/const-generics/generic_const_exprs/ice-predicates-of-no-entry-found-for-key-119275.stderr

diff --git a/tests/ui/const-generics/generic_const_exprs/ice-predicates-of-no-entry-found-for-key-119275.rs b/tests/ui/const-generics/generic_const_exprs/ice-predicates-of-no-entry-found-for-key-119275.rs
new file mode 100644
index 0000000000000..4ba696f4ae080
--- /dev/null
+++ b/tests/ui/const-generics/generic_const_exprs/ice-predicates-of-no-entry-found-for-key-119275.rs
@@ -0,0 +1,18 @@
+// test for ICE #119275 "no entry found for key" in predicates_of.rs
+
+#![feature(generic_const_exprs)]
+#![allow(incomplete_features)]
+
+fn bug<const N: Nat>(&self)
+//~^ ERROR `self` parameter is only allowed in associated functions
+//~^^ ERROR cannot find type `Nat` in this scope
+where
+    for<const N: usize = 3, T = u32> [(); COT::BYTES]:,
+    //~^ ERROR only lifetime parameters can be used in this context
+    //~^^ ERROR defaults for generic parameters are not allowed in `for<...>` binders
+    //~^^^ ERROR defaults for generic parameters are not allowed in `for<...>` binders
+    //~^^^^ ERROR failed to resolve: use of undeclared type `COT`
+{
+}
+
+pub fn main() {}
diff --git a/tests/ui/const-generics/generic_const_exprs/ice-predicates-of-no-entry-found-for-key-119275.stderr b/tests/ui/const-generics/generic_const_exprs/ice-predicates-of-no-entry-found-for-key-119275.stderr
new file mode 100644
index 0000000000000..ee0ec38ab0631
--- /dev/null
+++ b/tests/ui/const-generics/generic_const_exprs/ice-predicates-of-no-entry-found-for-key-119275.stderr
@@ -0,0 +1,46 @@
+error: `self` parameter is only allowed in associated functions
+  --> $DIR/ice-predicates-of-no-entry-found-for-key-119275.rs:6:22
+   |
+LL | fn bug<const N: Nat>(&self)
+   |                      ^^^^^ not semantically valid as function parameter
+   |
+   = note: associated functions are those in `impl` or `trait` definitions
+
+error[E0412]: cannot find type `Nat` in this scope
+  --> $DIR/ice-predicates-of-no-entry-found-for-key-119275.rs:6:17
+   |
+LL | fn bug<const N: Nat>(&self)
+   |                 ^^^ not found in this scope
+
+error[E0658]: only lifetime parameters can be used in this context
+  --> $DIR/ice-predicates-of-no-entry-found-for-key-119275.rs:10:15
+   |
+LL |     for<const N: usize = 3, T = u32> [(); COT::BYTES]:,
+   |               ^             ^
+   |
+   = note: see issue #108185 <https://github.com/rust-lang/rust/issues/108185> for more information
+   = help: add `#![feature(non_lifetime_binders)]` to the crate attributes to enable
+   = note: this compiler was built on YYYY-MM-DD; consider upgrading it if it is out of date
+
+error: defaults for generic parameters are not allowed in `for<...>` binders
+  --> $DIR/ice-predicates-of-no-entry-found-for-key-119275.rs:10:9
+   |
+LL |     for<const N: usize = 3, T = u32> [(); COT::BYTES]:,
+   |         ^^^^^^^^^^^^^^^^^^
+
+error: defaults for generic parameters are not allowed in `for<...>` binders
+  --> $DIR/ice-predicates-of-no-entry-found-for-key-119275.rs:10:29
+   |
+LL |     for<const N: usize = 3, T = u32> [(); COT::BYTES]:,
+   |                             ^^^^^^^
+
+error[E0433]: failed to resolve: use of undeclared type `COT`
+  --> $DIR/ice-predicates-of-no-entry-found-for-key-119275.rs:10:43
+   |
+LL |     for<const N: usize = 3, T = u32> [(); COT::BYTES]:,
+   |                                           ^^^ use of undeclared type `COT`
+
+error: aborting due to 6 previous errors
+
+Some errors have detailed explanations: E0412, E0433, E0658.
+For more information about an error, try `rustc --explain E0412`.

From 91aae58568ffc2236662b14866deef7e63e4f8e9 Mon Sep 17 00:00:00 2001
From: Zalathar <Zalathar@users.noreply.github.com>
Date: Fri, 15 Mar 2024 22:27:30 +1100
Subject: [PATCH 21/22] coverage: Clean up marker statements that aren't needed
 later

Some of the marker statements used by coverage are added during MIR building
for use by the InstrumentCoverage pass (during analysis), and are not needed
afterwards.
---
 .../src/coverageinfo/mod.rs                   | 10 +---
 .../src/transform/validate.rs                 | 13 ++++-
 compiler/rustc_middle/src/mir/coverage.rs     |  5 +-
 compiler/rustc_middle/src/mir/syntax.rs       |  1 +
 .../src/cleanup_post_borrowck.rs              | 13 ++++-
 ...rage_cleanup.main.CleanupPostBorrowck.diff | 56 +++++++++++++++++++
 ...erage_cleanup.main.InstrumentCoverage.diff | 53 ++++++++++++++++++
 tests/mir-opt/instrument_coverage_cleanup.rs  | 22 ++++++++
 8 files changed, 159 insertions(+), 14 deletions(-)
 create mode 100644 tests/mir-opt/instrument_coverage_cleanup.main.CleanupPostBorrowck.diff
 create mode 100644 tests/mir-opt/instrument_coverage_cleanup.main.InstrumentCoverage.diff
 create mode 100644 tests/mir-opt/instrument_coverage_cleanup.rs

diff --git a/compiler/rustc_codegen_llvm/src/coverageinfo/mod.rs b/compiler/rustc_codegen_llvm/src/coverageinfo/mod.rs
index 133084b7c12ae..54f4bc0634021 100644
--- a/compiler/rustc_codegen_llvm/src/coverageinfo/mod.rs
+++ b/compiler/rustc_codegen_llvm/src/coverageinfo/mod.rs
@@ -85,14 +85,6 @@ impl<'tcx> CoverageInfoBuilderMethods<'tcx> for Builder<'_, '_, 'tcx> {
 
         let bx = self;
 
-        match coverage.kind {
-            // Marker statements have no effect during codegen,
-            // so return early and don't create `func_coverage`.
-            CoverageKind::SpanMarker | CoverageKind::BlockMarker { .. } => return,
-            // Match exhaustively to ensure that newly-added kinds are classified correctly.
-            CoverageKind::CounterIncrement { .. } | CoverageKind::ExpressionUsed { .. } => {}
-        }
-
         let Some(function_coverage_info) =
             bx.tcx.instance_mir(instance.def).function_coverage_info.as_deref()
         else {
@@ -109,7 +101,7 @@ impl<'tcx> CoverageInfoBuilderMethods<'tcx> for Builder<'_, '_, 'tcx> {
         let Coverage { kind } = coverage;
         match *kind {
             CoverageKind::SpanMarker | CoverageKind::BlockMarker { .. } => unreachable!(
-                "unexpected marker statement {kind:?} should have caused an early return"
+                "marker statement {kind:?} should have been removed by CleanupPostBorrowck"
             ),
             CoverageKind::CounterIncrement { id } => {
                 func_coverage.mark_counter_id_seen(id);
diff --git a/compiler/rustc_const_eval/src/transform/validate.rs b/compiler/rustc_const_eval/src/transform/validate.rs
index 68270dab28443..4bc49f906070d 100644
--- a/compiler/rustc_const_eval/src/transform/validate.rs
+++ b/compiler/rustc_const_eval/src/transform/validate.rs
@@ -4,6 +4,7 @@ use rustc_data_structures::fx::{FxHashMap, FxHashSet};
 use rustc_index::bit_set::BitSet;
 use rustc_index::IndexVec;
 use rustc_infer::traits::Reveal;
+use rustc_middle::mir::coverage::CoverageKind;
 use rustc_middle::mir::interpret::Scalar;
 use rustc_middle::mir::visit::{NonUseContext, PlaceContext, Visitor};
 use rustc_middle::mir::*;
@@ -345,11 +346,21 @@ impl<'a, 'tcx> Visitor<'tcx> for CfgChecker<'a, 'tcx> {
                     self.fail(location, format!("explicit `{kind:?}` is forbidden"));
                 }
             }
+            StatementKind::Coverage(coverage) => {
+                let kind = &coverage.kind;
+                if self.mir_phase >= MirPhase::Analysis(AnalysisPhase::PostCleanup)
+                    && let CoverageKind::BlockMarker { .. } | CoverageKind::SpanMarker { .. } = kind
+                {
+                    self.fail(
+                        location,
+                        format!("{kind:?} should have been removed after analysis"),
+                    );
+                }
+            }
             StatementKind::Assign(..)
             | StatementKind::StorageLive(_)
             | StatementKind::StorageDead(_)
             | StatementKind::Intrinsic(_)
-            | StatementKind::Coverage(_)
             | StatementKind::ConstEvalCounter
             | StatementKind::PlaceMention(..)
             | StatementKind::Nop => {}
diff --git a/compiler/rustc_middle/src/mir/coverage.rs b/compiler/rustc_middle/src/mir/coverage.rs
index 645a417c32250..588aa1f40d79c 100644
--- a/compiler/rustc_middle/src/mir/coverage.rs
+++ b/compiler/rustc_middle/src/mir/coverage.rs
@@ -88,14 +88,13 @@ pub enum CoverageKind {
     /// Marks a span that might otherwise not be represented in MIR, so that
     /// coverage instrumentation can associate it with its enclosing block/BCB.
     ///
-    /// Only used by the `InstrumentCoverage` pass, and has no effect during
-    /// codegen.
+    /// Should be erased before codegen (at some point after `InstrumentCoverage`).
     SpanMarker,
 
     /// Marks its enclosing basic block with an ID that can be referred to by
     /// side data in [`BranchInfo`].
     ///
-    /// Has no effect during codegen.
+    /// Should be erased before codegen (at some point after `InstrumentCoverage`).
     BlockMarker { id: BlockMarkerId },
 
     /// Marks the point in MIR control flow represented by a coverage counter.
diff --git a/compiler/rustc_middle/src/mir/syntax.rs b/compiler/rustc_middle/src/mir/syntax.rs
index 0ab797134c0af..752f5845afb2e 100644
--- a/compiler/rustc_middle/src/mir/syntax.rs
+++ b/compiler/rustc_middle/src/mir/syntax.rs
@@ -124,6 +124,7 @@ pub enum AnalysisPhase {
     /// * [`TerminatorKind::FalseEdge`]
     /// * [`StatementKind::FakeRead`]
     /// * [`StatementKind::AscribeUserType`]
+    /// * [`StatementKind::Coverage`] with [`CoverageKind::BlockMarker`] or [`CoverageKind::SpanMarker`]
     /// * [`Rvalue::Ref`] with `BorrowKind::Fake`
     ///
     /// Furthermore, `Deref` projections must be the first projection within any place (if they
diff --git a/compiler/rustc_mir_transform/src/cleanup_post_borrowck.rs b/compiler/rustc_mir_transform/src/cleanup_post_borrowck.rs
index 5b4bc4fa13424..aaf2035fc2103 100644
--- a/compiler/rustc_mir_transform/src/cleanup_post_borrowck.rs
+++ b/compiler/rustc_mir_transform/src/cleanup_post_borrowck.rs
@@ -5,15 +5,20 @@
 //!   - [`AscribeUserType`]
 //!   - [`FakeRead`]
 //!   - [`Assign`] statements with a [`Fake`] borrow
+//!   - [`Coverage`] statements of kind [`BlockMarker`] or [`SpanMarker`]
 //!
 //! [`AscribeUserType`]: rustc_middle::mir::StatementKind::AscribeUserType
 //! [`Assign`]: rustc_middle::mir::StatementKind::Assign
 //! [`FakeRead`]: rustc_middle::mir::StatementKind::FakeRead
 //! [`Nop`]: rustc_middle::mir::StatementKind::Nop
 //! [`Fake`]: rustc_middle::mir::BorrowKind::Fake
+//! [`Coverage`]: rustc_middle::mir::StatementKind::Coverage
+//! [`BlockMarker`]: rustc_middle::mir::coverage::CoverageKind::BlockMarker
+//! [`SpanMarker`]: rustc_middle::mir::coverage::CoverageKind::SpanMarker
 
 use crate::MirPass;
-use rustc_middle::mir::{Body, BorrowKind, Rvalue, StatementKind, TerminatorKind};
+use rustc_middle::mir::coverage::CoverageKind;
+use rustc_middle::mir::{Body, BorrowKind, Coverage, Rvalue, StatementKind, TerminatorKind};
 use rustc_middle::ty::TyCtxt;
 
 pub struct CleanupPostBorrowck;
@@ -25,6 +30,12 @@ impl<'tcx> MirPass<'tcx> for CleanupPostBorrowck {
                 match statement.kind {
                     StatementKind::AscribeUserType(..)
                     | StatementKind::Assign(box (_, Rvalue::Ref(_, BorrowKind::Fake, _)))
+                    | StatementKind::Coverage(box Coverage {
+                        // These kinds of coverage statements are markers inserted during
+                        // MIR building, and are not needed after InstrumentCoverage.
+                        kind: CoverageKind::BlockMarker { .. } | CoverageKind::SpanMarker { .. },
+                        ..
+                    })
                     | StatementKind::FakeRead(..) => statement.make_nop(),
                     _ => (),
                 }
diff --git a/tests/mir-opt/instrument_coverage_cleanup.main.CleanupPostBorrowck.diff b/tests/mir-opt/instrument_coverage_cleanup.main.CleanupPostBorrowck.diff
new file mode 100644
index 0000000000000..ff65ca7703928
--- /dev/null
+++ b/tests/mir-opt/instrument_coverage_cleanup.main.CleanupPostBorrowck.diff
@@ -0,0 +1,56 @@
+- // MIR for `main` before CleanupPostBorrowck
++ // MIR for `main` after CleanupPostBorrowck
+  
+  fn main() -> () {
+      let mut _0: ();
+      let mut _1: bool;
+  
+      coverage branch { true: BlockMarkerId(0), false: BlockMarkerId(1) } => /the/src/instrument_coverage_cleanup.rs:15:8: 15:36 (#0)
+  
+      coverage ExpressionId(0) => Expression { lhs: Counter(0), op: Subtract, rhs: Counter(1) };
+      coverage ExpressionId(1) => Expression { lhs: Counter(1), op: Add, rhs: Expression(0) };
+      coverage Code(Counter(0)) => /the/src/instrument_coverage_cleanup.rs:14:1 - 15:36;
+      coverage Code(Expression(0)) => /the/src/instrument_coverage_cleanup.rs:15:37 - 15:39;
+      coverage Code(Counter(1)) => /the/src/instrument_coverage_cleanup.rs:15:39 - 15:40;
+      coverage Code(Expression(1)) => /the/src/instrument_coverage_cleanup.rs:16:1 - 16:2;
+      coverage Branch { true_term: Expression(0), false_term: Counter(1) } => /the/src/instrument_coverage_cleanup.rs:15:8 - 15:36;
+  
+      bb0: {
+          Coverage::CounterIncrement(0);
+-         Coverage::SpanMarker;
++         nop;
+          StorageLive(_1);
+          _1 = std::hint::black_box::<bool>(const true) -> [return: bb1, unwind: bb5];
+      }
+  
+      bb1: {
+          switchInt(move _1) -> [0: bb3, otherwise: bb2];
+      }
+  
+      bb2: {
+          Coverage::CounterIncrement(1);
+-         Coverage::BlockMarker(1);
++         nop;
+          _0 = const ();
+          goto -> bb4;
+      }
+  
+      bb3: {
+          Coverage::ExpressionUsed(0);
+-         Coverage::BlockMarker(0);
++         nop;
+          _0 = const ();
+          goto -> bb4;
+      }
+  
+      bb4: {
+          Coverage::ExpressionUsed(1);
+          StorageDead(_1);
+          return;
+      }
+  
+      bb5 (cleanup): {
+          resume;
+      }
+  }
+  
diff --git a/tests/mir-opt/instrument_coverage_cleanup.main.InstrumentCoverage.diff b/tests/mir-opt/instrument_coverage_cleanup.main.InstrumentCoverage.diff
new file mode 100644
index 0000000000000..8757559149a43
--- /dev/null
+++ b/tests/mir-opt/instrument_coverage_cleanup.main.InstrumentCoverage.diff
@@ -0,0 +1,53 @@
+- // MIR for `main` before InstrumentCoverage
++ // MIR for `main` after InstrumentCoverage
+  
+  fn main() -> () {
+      let mut _0: ();
+      let mut _1: bool;
+  
+      coverage branch { true: BlockMarkerId(0), false: BlockMarkerId(1) } => /the/src/instrument_coverage_cleanup.rs:15:8: 15:36 (#0)
+  
++     coverage ExpressionId(0) => Expression { lhs: Counter(0), op: Subtract, rhs: Counter(1) };
++     coverage ExpressionId(1) => Expression { lhs: Counter(1), op: Add, rhs: Expression(0) };
++     coverage Code(Counter(0)) => /the/src/instrument_coverage_cleanup.rs:14:1 - 15:36;
++     coverage Code(Expression(0)) => /the/src/instrument_coverage_cleanup.rs:15:37 - 15:39;
++     coverage Code(Counter(1)) => /the/src/instrument_coverage_cleanup.rs:15:39 - 15:40;
++     coverage Code(Expression(1)) => /the/src/instrument_coverage_cleanup.rs:16:1 - 16:2;
++     coverage Branch { true_term: Expression(0), false_term: Counter(1) } => /the/src/instrument_coverage_cleanup.rs:15:8 - 15:36;
++ 
+      bb0: {
++         Coverage::CounterIncrement(0);
+          Coverage::SpanMarker;
+          StorageLive(_1);
+          _1 = std::hint::black_box::<bool>(const true) -> [return: bb1, unwind: bb5];
+      }
+  
+      bb1: {
+          switchInt(move _1) -> [0: bb3, otherwise: bb2];
+      }
+  
+      bb2: {
++         Coverage::CounterIncrement(1);
+          Coverage::BlockMarker(1);
+          _0 = const ();
+          goto -> bb4;
+      }
+  
+      bb3: {
++         Coverage::ExpressionUsed(0);
+          Coverage::BlockMarker(0);
+          _0 = const ();
+          goto -> bb4;
+      }
+  
+      bb4: {
++         Coverage::ExpressionUsed(1);
+          StorageDead(_1);
+          return;
+      }
+  
+      bb5 (cleanup): {
+          resume;
+      }
+  }
+  
diff --git a/tests/mir-opt/instrument_coverage_cleanup.rs b/tests/mir-opt/instrument_coverage_cleanup.rs
new file mode 100644
index 0000000000000..8a2fd67139bd9
--- /dev/null
+++ b/tests/mir-opt/instrument_coverage_cleanup.rs
@@ -0,0 +1,22 @@
+// Test that CleanupPostBorrowck cleans up the marker statements that are
+// inserted during MIR building (after InstrumentCoverage is done with them),
+// but leaves the statements that were added by InstrumentCoverage.
+//
+// Removed statement kinds: BlockMarker, SpanMarker
+// Retained statement kinds: CounterIncrement, ExpressionUsed
+
+//@ unit-test: InstrumentCoverage
+//@ compile-flags: -Cinstrument-coverage -Zcoverage-options=branch -Zno-profiler-runtime
+//@ compile-flags: --remap-path-prefix={{src-base}}=/the/src
+
+// EMIT_MIR instrument_coverage_cleanup.main.InstrumentCoverage.diff
+// EMIT_MIR instrument_coverage_cleanup.main.CleanupPostBorrowck.diff
+fn main() {
+    if !core::hint::black_box(true) {}
+}
+
+// CHECK-NOT: Coverage::BlockMarker
+// CHECK-NOT: Coverage::SpanMarker
+// CHECK:     Coverage::CounterIncrement
+// CHECK-NOT: Coverage::BlockMarker
+// CHECK-NOT: Coverage::SpanMarker

From e68cb00fb272fd9a45cc6c4ec4b2ed14e7ba0bad Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Matthias=20Kr=C3=BCger?= <matthias.krueger@famsik.de>
Date: Fri, 22 Mar 2024 11:35:31 +0100
Subject: [PATCH 22/22] address review comments

---
 ...nerics_of-no-entry-found-for-key-113017.rs | 15 +---
 ...cs_of-no-entry-found-for-key-113017.stderr | 87 ++-----------------
 ...e-failed-to-resolve-instance-for-110696.rs |  2 +-
 3 files changed, 12 insertions(+), 92 deletions(-)

diff --git a/tests/ui/const-generics/generic_const_exprs/ice-generics_of-no-entry-found-for-key-113017.rs b/tests/ui/const-generics/generic_const_exprs/ice-generics_of-no-entry-found-for-key-113017.rs
index 36e552ed88d1a..a2f8c876b5e4d 100644
--- a/tests/ui/const-generics/generic_const_exprs/ice-generics_of-no-entry-found-for-key-113017.rs
+++ b/tests/ui/const-generics/generic_const_exprs/ice-generics_of-no-entry-found-for-key-113017.rs
@@ -3,18 +3,11 @@
 #![feature(generic_const_exprs)]
 #![allow(incomplete_features)]
 
-pub fn String<V>(elem)
-//~^ ERROR expected one of `:`, `@`, or `|`, found `)`
+pub fn foo()
 where
-    V: 'a,
-    //~^ ERROR use of undeclared lifetime name `'a`
-    for<const N: usize = { || {}}> V: 'a,
-    //~^ ERROR use of undeclared lifetime name `'a`
-    //~^^ ERROR only lifetime parameters can be used in this context
-    //~^^^ ERROR defaults for generic parameters are not allowed in `for<...>` binders
-    for<C2: , R2, R3: > <&str as IntoIterator>::Item: 'static,
-    //~^ ERROR `&` without an explicit lifetime name cannot be used here
-    //~^^ ERROR only lifetime parameters can be used in this context
+    for<const N: usize = { || {}; 1 }> ():,
+    //~^ ERROR only lifetime parameters can be used in this context
+    //~^^  ERROR defaults for generic parameters are not allowed in `for<...>` binders
 {}
 
 pub fn main() {}
diff --git a/tests/ui/const-generics/generic_const_exprs/ice-generics_of-no-entry-found-for-key-113017.stderr b/tests/ui/const-generics/generic_const_exprs/ice-generics_of-no-entry-found-for-key-113017.stderr
index 54794022ebdb8..edf27f58efd56 100644
--- a/tests/ui/const-generics/generic_const_exprs/ice-generics_of-no-entry-found-for-key-113017.stderr
+++ b/tests/ui/const-generics/generic_const_exprs/ice-generics_of-no-entry-found-for-key-113017.stderr
@@ -1,92 +1,19 @@
-error: expected one of `:`, `@`, or `|`, found `)`
-  --> $DIR/ice-generics_of-no-entry-found-for-key-113017.rs:6:22
-   |
-LL | pub fn String<V>(elem)
-   |                      ^ expected one of `:`, `@`, or `|`
-   |
-   = note: anonymous parameters are removed in the 2018 edition (see RFC 1685)
-help: if this is a `self` type, give it a parameter name
-   |
-LL | pub fn String<V>(self: elem)
-   |                  +++++
-help: if this is a parameter name, give it a type
-   |
-LL | pub fn String<V>(elem: TypeName)
-   |                      ++++++++++
-help: if this is a type, explicitly ignore the parameter name
-   |
-LL | pub fn String<V>(_: elem)
-   |                  ++
-
-error[E0261]: use of undeclared lifetime name `'a`
-  --> $DIR/ice-generics_of-no-entry-found-for-key-113017.rs:9:8
-   |
-LL |     V: 'a,
-   |        ^^ undeclared lifetime
-   |
-   = note: for more information on higher-ranked polymorphism, visit https://doc.rust-lang.org/nomicon/hrtb.html
-help: consider making the bound lifetime-generic with a new `'a` lifetime
-   |
-LL |     for<'a> V: 'a,
-   |     +++++++
-help: consider introducing lifetime `'a` here
-   |
-LL | pub fn String<'a, V>(elem)
-   |               +++
-
-error[E0261]: use of undeclared lifetime name `'a`
-  --> $DIR/ice-generics_of-no-entry-found-for-key-113017.rs:11:39
-   |
-LL |     for<const N: usize = { || {}}> V: 'a,
-   |                                       ^^ undeclared lifetime
-   |
-help: consider making the bound lifetime-generic with a new `'a` lifetime
-   |
-LL |     for<'a, const N: usize = { || {}}> V: 'a,
-   |         +++
-help: consider introducing lifetime `'a` here
-   |
-LL | pub fn String<'a, V>(elem)
-   |               +++
-
-error[E0637]: `&` without an explicit lifetime name cannot be used here
-  --> $DIR/ice-generics_of-no-entry-found-for-key-113017.rs:15:26
-   |
-LL |     for<C2: , R2, R3: > <&str as IntoIterator>::Item: 'static,
-   |                          ^ explicit lifetime name needed here
-   |
-help: consider introducing a higher-ranked lifetime here
-   |
-LL |     for<'a> for<C2: , R2, R3: > <&'a str as IntoIterator>::Item: 'static,
-   |     +++++++                       ++
-
 error[E0658]: only lifetime parameters can be used in this context
-  --> $DIR/ice-generics_of-no-entry-found-for-key-113017.rs:11:15
+  --> $DIR/ice-generics_of-no-entry-found-for-key-113017.rs:8:15
    |
-LL |     for<const N: usize = { || {}}> V: 'a,
+LL |     for<const N: usize = { || {}; 1 }> ():,
    |               ^
    |
    = note: see issue #108185 <https://github.com/rust-lang/rust/issues/108185> for more information
    = help: add `#![feature(non_lifetime_binders)]` to the crate attributes to enable
    = note: this compiler was built on YYYY-MM-DD; consider upgrading it if it is out of date
 
-error[E0658]: only lifetime parameters can be used in this context
-  --> $DIR/ice-generics_of-no-entry-found-for-key-113017.rs:15:9
-   |
-LL |     for<C2: , R2, R3: > <&str as IntoIterator>::Item: 'static,
-   |         ^^    ^^  ^^
-   |
-   = note: see issue #108185 <https://github.com/rust-lang/rust/issues/108185> for more information
-   = help: add `#![feature(non_lifetime_binders)]` to the crate attributes to enable
-   = note: this compiler was built on YYYY-MM-DD; consider upgrading it if it is out of date
-
 error: defaults for generic parameters are not allowed in `for<...>` binders
-  --> $DIR/ice-generics_of-no-entry-found-for-key-113017.rs:11:9
+  --> $DIR/ice-generics_of-no-entry-found-for-key-113017.rs:8:9
    |
-LL |     for<const N: usize = { || {}}> V: 'a,
-   |         ^^^^^^^^^^^^^^^^^^^^^^^^^
+LL |     for<const N: usize = { || {}; 1 }> ():,
+   |         ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
 
-error: aborting due to 7 previous errors
+error: aborting due to 2 previous errors
 
-Some errors have detailed explanations: E0261, E0637, E0658.
-For more information about an error, try `rustc --explain E0261`.
+For more information about this error, try `rustc --explain E0658`.
diff --git a/tests/ui/type-alias-impl-trait/ice-failed-to-resolve-instance-for-110696.rs b/tests/ui/type-alias-impl-trait/ice-failed-to-resolve-instance-for-110696.rs
index 840be25dd2e02..fc71d0d61ff14 100644
--- a/tests/ui/type-alias-impl-trait/ice-failed-to-resolve-instance-for-110696.rs
+++ b/tests/ui/type-alias-impl-trait/ice-failed-to-resolve-instance-for-110696.rs
@@ -40,7 +40,7 @@ impl<T> MyFrom<Phantom2<T>> for Phantom1<T> {
 }
 
 impl<T: MyFrom<Phantom2<DummyT<U>>>, U> MyIndex<DummyT<T>> for Scope<U> {
-    //~^ ERROR the type parameter `T` is not constrained by the impl trait, self type, or predicates
+    //~^ ERROR the type parameter `T` is not constrained by the impl
     type O = T;
     fn my_index(self) -> Self::O {
         MyFrom::my_from(self.0).ok().unwrap()