Rollup of 6 pull requests

compiler/rustc_ast/src/lib.rs

@@ -10,7 +10,8 @@
 )]
 #![feature(box_syntax)]
 #![feature(box_patterns)]
-#![feature(const_fn)] // For the `transmute` in `P::new`
+#![cfg_attr(bootstrap, feature(const_fn))] // For the `transmute` in `P::new`
+#![cfg_attr(not(bootstrap), feature(const_fn_unsize))] // For the `transmute` in `P::new`
 #![feature(const_fn_transmute)]
 #![feature(const_panic)]
 #![feature(crate_visibility_modifier)]

compiler/rustc_ast_passes/src/ast_validation.rs

@@ -754,7 +754,7 @@ fn validate_generic_param_order(
             GenericParamKind::Type { default: _ } => (ParamKindOrd::Type, ident),
             GenericParamKind::Const { ref ty, kw_span: _, default: _ } => {
                 let ty = pprust::ty_to_string(ty);
-                let unordered = sess.features_untracked().const_generics;
+                let unordered = sess.features_untracked().unordered_const_ty_params();
                 (ParamKindOrd::Const { unordered }, Some(format!("const {}: {}", param.ident, ty)))
             }
         };

compiler/rustc_error_codes/src/error_codes.rs

@@ -416,7 +416,6 @@ E0716: include_str!("./error_codes/E0716.md"),
 E0718: include_str!("./error_codes/E0718.md"),
 E0719: include_str!("./error_codes/E0719.md"),
 E0720: include_str!("./error_codes/E0720.md"),
-E0723: include_str!("./error_codes/E0723.md"),
 E0724: include_str!("./error_codes/E0724.md"),
 E0725: include_str!("./error_codes/E0725.md"),
 E0727: include_str!("./error_codes/E0727.md"),
@@ -636,6 +635,7 @@ E0781: include_str!("./error_codes/E0781.md"),
     E0717, // rustc_promotable without stability attribute
 //  E0721, // `await` keyword
     E0722, // Malformed `#[optimize]` attribute
+//    E0723, unstable feature in `const` context
     E0726, // non-explicit (not `'_`) elided lifetime in unsupported position
 //  E0738, // Removed; errored on `#[track_caller] fn`s in `extern "Rust" { ... }`.
     E0757, // `#[ffi_const]` functions cannot be `#[ffi_pure]`

compiler/rustc_feature/src/active.rs

@@ -63,6 +63,10 @@ macro_rules! declare_features {
                     _ => panic!("`{}` was not listed in `declare_features`", feature),
                 }
             }
+
+            pub fn unordered_const_ty_params(&self) -> bool {
+                self.const_generics || self.const_generics_defaults
+            }
         }
     };
 }
@@ -633,6 +637,9 @@ declare_features! (
     /// Allows associated types in inherent impls.
     (active, inherent_associated_types, "1.52.0", Some(8995), None),
 
+    // Allows setting the threshold for the `large_assignments` lint.
+    (active, large_assignments, "1.52.0", Some(83518), None),
+
     /// Allows `extern "C-unwind" fn` to enable unwinding across ABI boundaries.
     (active, c_unwind, "1.52.0", Some(74990), None),
 
@@ -642,6 +649,12 @@ declare_features! (
     /// Allows `extern "wasm" fn`
     (active, wasm_abi, "1.53.0", Some(83788), None),
 
+    /// Allows trait bounds in `const fn`.
+    (active, const_fn_trait_bound, "1.53.0", Some(57563), None),
+
+    /// Allows unsizing coercions in `const fn`.
+    (active, const_fn_unsize, "1.53.0", Some(64992), None),
+
     // -------------------------------------------------------------------------
     // feature-group-end: actual feature gates
     // -------------------------------------------------------------------------

compiler/rustc_feature/src/builtin_attrs.rs

@@ -241,6 +241,10 @@ pub const BUILTIN_ATTRIBUTES: &[BuiltinAttribute] = &[
         const_eval_limit, CrateLevel, template!(NameValueStr: "N"), const_eval_limit,
         experimental!(const_eval_limit)
     ),
+    gated!(
+        move_size_limit, CrateLevel, template!(NameValueStr: "N"), large_assignments,
+        experimental!(move_size_limit)
+    ),
 
     // Entry point:
     ungated!(main, Normal, template!(Word)),

compiler/rustc_hir/src/hir.rs

@@ -296,7 +296,9 @@ impl GenericArg<'_> {
         match self {
             GenericArg::Lifetime(_) => ast::ParamKindOrd::Lifetime,
             GenericArg::Type(_) => ast::ParamKindOrd::Type,
-            GenericArg::Const(_) => ast::ParamKindOrd::Const { unordered: feats.const_generics },
+            GenericArg::Const(_) => {
+                ast::ParamKindOrd::Const { unordered: feats.unordered_const_ty_params() }
+            }
         }
     }
 }

compiler/rustc_hir/src/lib.rs

@@ -3,7 +3,6 @@
 //! [rustc dev guide]: https://rustc-dev-guide.rust-lang.org/hir.html
 
 #![feature(crate_visibility_modifier)]
-#![feature(const_fn)] // For the unsizing cast on `&[]`
 #![feature(const_panic)]
 #![feature(extended_key_value_attributes)]
 #![feature(in_band_lifetimes)]

compiler/rustc_index/src/lib.rs

@@ -1,5 +1,4 @@
 #![feature(allow_internal_unstable)]
-#![feature(const_fn)]
 #![feature(const_panic)]
 #![feature(extend_one)]
 #![feature(iter_zip)]

compiler/rustc_infer/src/lib.rs

@@ -16,7 +16,6 @@
 #![feature(bool_to_option)]
 #![feature(box_patterns)]
 #![feature(box_syntax)]
-#![feature(const_fn)]
 #![feature(const_panic)]
 #![feature(extend_one)]
 #![feature(iter_zip)]

compiler/rustc_lint_defs/src/builtin.rs

@@ -2877,6 +2877,39 @@ declare_lint! {
     };
 }
 
+declare_lint! {
+    /// The `large_assignments` lint detects when objects of large
+    /// types are being moved around.
+    ///
+    /// ### Example
+    ///
+    /// ```rust,ignore (can crash on some platforms)
+    /// let x = [0; 50000];
+    /// let y = x;
+    /// ```
+    ///
+    /// produces:
+    ///
+    /// ```text
+    /// warning: moving a large value
+    ///   --> $DIR/move-large.rs:1:3
+    ///   let y = x;
+    ///           - Copied large value here
+    /// ```
+    ///
+    /// ### Explanation
+    ///
+    /// When using a large type in a plain assignment or in a function
+    /// argument, idiomatic code can be inefficient.
+    /// Ideally appropriate optimizations would resolve this, but such
+    /// optimizations are only done in a best-effort manner.
+    /// This lint will trigger on all sites of large moves and thus allow the
+    /// user to resolve them in code.
+    pub LARGE_ASSIGNMENTS,
+    Warn,
+    "detects large moves or copies",
+}
+
 declare_lint_pass! {
     /// Does nothing as a lint pass, but registers some `Lint`s
     /// that are used by other parts of the compiler.
@@ -2962,6 +2995,7 @@ declare_lint_pass! {
         LEGACY_DERIVE_HELPERS,
         PROC_MACRO_BACK_COMPAT,
         OR_PATTERNS_BACK_COMPAT,
+        LARGE_ASSIGNMENTS,
     ]
 }
 

compiler/rustc_middle/src/lib.rs

@@ -29,7 +29,6 @@
 #![feature(bool_to_option)]
 #![feature(box_patterns)]
 #![feature(box_syntax)]
-#![feature(const_fn)]
 #![feature(const_panic)]
 #![feature(core_intrinsics)]
 #![feature(discriminant_kind)]

compiler/rustc_middle/src/middle/limits.rs

@@ -1,4 +1,8 @@
-//! Registering limits, recursion_limit, type_length_limit and const_eval_limit
+//! Registering limits:
+//! * recursion_limit,
+//! * move_size_limit,
+//! * type_length_limit, and
+//! * const_eval_limit
 //!
 //! There are various parts of the compiler that must impose arbitrary limits
 //! on how deeply they recurse to prevent stack overflow. Users can override
@@ -8,21 +12,22 @@
 use crate::bug;
 use rustc_ast as ast;
 use rustc_data_structures::sync::OnceCell;
-use rustc_session::{Limit, Session};
+use rustc_session::Session;
 use rustc_span::symbol::{sym, Symbol};
 
 use std::num::IntErrorKind;
 
 pub fn update_limits(sess: &Session, krate: &ast::Crate) {
     update_limit(sess, krate, &sess.recursion_limit, sym::recursion_limit, 128);
+    update_limit(sess, krate, &sess.move_size_limit, sym::move_size_limit, 0);
     update_limit(sess, krate, &sess.type_length_limit, sym::type_length_limit, 1048576);
     update_limit(sess, krate, &sess.const_eval_limit, sym::const_eval_limit, 1_000_000);
 }
 
 fn update_limit(
     sess: &Session,
     krate: &ast::Crate,
-    limit: &OnceCell<Limit>,
+    limit: &OnceCell<impl From<usize> + std::fmt::Debug>,
     name: Symbol,
     default: usize,
 ) {
@@ -34,7 +39,7 @@ fn update_limit(
         if let Some(s) = attr.value_str() {
             match s.as_str().parse() {
                 Ok(n) => {
-                    limit.set(Limit::new(n)).unwrap();
+                    limit.set(From::from(n)).unwrap();
                     return;
                 }
                 Err(e) => {
@@ -63,5 +68,5 @@ fn update_limit(
             }
         }
     }
-    limit.set(Limit::new(default)).unwrap();
+    limit.set(From::from(default)).unwrap();
 }

compiler/rustc_middle/src/mir/mod.rs

@@ -12,10 +12,10 @@ use crate::ty::print::{FmtPrinter, Printer};
 use crate::ty::subst::{Subst, SubstsRef};
 use crate::ty::{self, List, Ty, TyCtxt};
 use crate::ty::{AdtDef, InstanceDef, Region, ScalarInt, UserTypeAnnotationIndex};
-use rustc_hir as hir;
 use rustc_hir::def::{CtorKind, Namespace};
 use rustc_hir::def_id::{DefId, CRATE_DEF_INDEX};
 use rustc_hir::{self, GeneratorKind};
+use rustc_hir::{self as hir, HirId};
 use rustc_target::abi::{Size, VariantIdx};
 
 use polonius_engine::Atom;
@@ -1948,6 +1948,29 @@ rustc_index::newtype_index! {
     }
 }
 
+impl SourceScope {
+    /// Finds the original HirId this MIR item came from.
+    /// This is necessary after MIR optimizations, as otherwise we get a HirId
+    /// from the function that was inlined instead of the function call site.
+    pub fn lint_root(
+        self,
+        source_scopes: &IndexVec<SourceScope, SourceScopeData<'tcx>>,
+    ) -> Option<HirId> {
+        let mut data = &source_scopes[self];
+        // FIXME(oli-obk): we should be able to just walk the `inlined_parent_scope`, but it
+        // does not work as I thought it would. Needs more investigation and documentation.
+        while data.inlined.is_some() {
+            trace!(?data);
+            data = &source_scopes[data.parent_scope.unwrap()];
+        }
+        trace!(?data);
+        match &data.local_data {
+            ClearCrossCrate::Set(data) => Some(data.lint_root),
+            ClearCrossCrate::Clear => None,
+        }
+    }
+}
+
 #[derive(Clone, Debug, TyEncodable, TyDecodable, HashStable, TypeFoldable)]
 pub struct SourceScopeData<'tcx> {
     pub span: Span,

compiler/rustc_middle/src/ty/generics.rs

@@ -36,7 +36,7 @@ impl GenericParamDefKind {
             GenericParamDefKind::Lifetime => ast::ParamKindOrd::Lifetime,
             GenericParamDefKind::Type { .. } => ast::ParamKindOrd::Type,
             GenericParamDefKind::Const { .. } => {
-                ast::ParamKindOrd::Const { unordered: tcx.features().const_generics }
+                ast::ParamKindOrd::Const { unordered: tcx.features().unordered_const_ty_params() }
             }
         }
     }

compiler/rustc_mir/src/lib.rs

@@ -12,7 +12,6 @@ Rust MIR: a lowered representation of Rust.
 #![feature(bool_to_option)]
 #![feature(box_patterns)]
 #![feature(box_syntax)]
-#![feature(const_fn)]
 #![feature(const_panic)]
 #![feature(crate_visibility_modifier)]
 #![feature(decl_macro)]

compiler/rustc_mir/src/monomorphize/collector.rs

@@ -198,7 +198,9 @@ use rustc_middle::ty::subst::{GenericArgKind, InternalSubsts};
 use rustc_middle::ty::{self, GenericParamDefKind, Instance, Ty, TyCtxt, TypeFoldable};
 use rustc_middle::{middle::codegen_fn_attrs::CodegenFnAttrFlags, mir::visit::TyContext};
 use rustc_session::config::EntryFnType;
+use rustc_session::lint::builtin::LARGE_ASSIGNMENTS;
 use rustc_span::source_map::{dummy_spanned, respan, Span, Spanned, DUMMY_SP};
+use rustc_target::abi::Size;
 use smallvec::SmallVec;
 use std::iter;
 use std::ops::Range;
@@ -753,6 +755,46 @@ impl<'a, 'tcx> MirVisitor<'tcx> for MirNeighborCollector<'a, 'tcx> {
         self.super_terminator(terminator, location);
     }
 
+    fn visit_operand(&mut self, operand: &mir::Operand<'tcx>, location: Location) {
+        self.super_operand(operand, location);
+        let limit = self.tcx.sess.move_size_limit();
+        if limit == 0 {
+            return;
+        }
+        let limit = Size::from_bytes(limit);
+        let ty = operand.ty(self.body, self.tcx);
+        let ty = self.monomorphize(ty);
+        let layout = self.tcx.layout_of(ty::ParamEnv::reveal_all().and(ty));
+        if let Ok(layout) = layout {
+            if layout.size > limit {
+                debug!(?layout);
+                let source_info = self.body.source_info(location);
+                debug!(?source_info);
+                let lint_root = source_info.scope.lint_root(&self.body.source_scopes);
+                debug!(?lint_root);
+                let lint_root = match lint_root {
+                    Some(lint_root) => lint_root,
+                    // This happens when the issue is in a function from a foreign crate that
+                    // we monomorphized in the current crate. We can't get a `HirId` for things
+                    // in other crates.
+                    // FIXME: Find out where to report the lint on. Maybe simply crate-level lint root
+                    // but correct span? This would make the lint at least accept crate-level lint attributes.
+                    None => return,
+                };
+                self.tcx.struct_span_lint_hir(
+                    LARGE_ASSIGNMENTS,
+                    lint_root,
+                    source_info.span,
+                    |lint| {
+                        let mut err = lint.build(&format!("moving {} bytes", layout.size.bytes()));
+                        err.span_label(source_info.span, "value moved from here");
+                        err.emit()
+                    },
+                );
+            }
+        }
+    }
+
     fn visit_local(
         &mut self,
         _place_local: &Local,