Auto merge of #66449 - tmandry:rollup-3p1t0sb, r=tmandry

Rollup of 4 pull requests

Successful merges:

 - #66197 (Push `ast::{ItemKind, ImplItemKind}::OpaqueTy` hack down into lowering)
 - #66429 (Add a regression test for #62524)
 - #66435 (Correct `const_in_array_repeat_expressions` feature name)
 - #66443 (Port erased cleanup)

Failed merges:

r? @ghost

src/librustc/hir/lowering.rs

@@ -454,7 +454,6 @@ impl<'a> LoweringContext<'a> {
                     | ItemKind::Union(_, ref generics)
                     | ItemKind::Enum(_, ref generics)
                     | ItemKind::TyAlias(_, ref generics)
-                    | ItemKind::OpaqueTy(_, ref generics)
                     | ItemKind::Trait(_, _, ref generics, ..) => {
                         let def_id = self.lctx.resolver.definitions().local_def_id(item.id);
                         let count = generics

src/librustc/hir/lowering/item.rs

@@ -337,20 +337,22 @@ impl LoweringContext<'_> {
             ItemKind::Mod(ref m) => hir::ItemKind::Mod(self.lower_mod(m)),
             ItemKind::ForeignMod(ref nm) => hir::ItemKind::ForeignMod(self.lower_foreign_mod(nm)),
             ItemKind::GlobalAsm(ref ga) => hir::ItemKind::GlobalAsm(self.lower_global_asm(ga)),
-            ItemKind::TyAlias(ref t, ref generics) => hir::ItemKind::TyAlias(
-                self.lower_ty(t, ImplTraitContext::disallowed()),
-                self.lower_generics(generics, ImplTraitContext::disallowed()),
-            ),
-            ItemKind::OpaqueTy(ref b, ref generics) => hir::ItemKind::OpaqueTy(
-                hir::OpaqueTy {
-                    generics: self.lower_generics(generics,
-                        ImplTraitContext::OpaqueTy(None)),
-                    bounds: self.lower_param_bounds(b,
-                        ImplTraitContext::OpaqueTy(None)),
-                    impl_trait_fn: None,
-                    origin: hir::OpaqueTyOrigin::TypeAlias,
+            ItemKind::TyAlias(ref ty, ref generics) => match ty.kind.opaque_top_hack() {
+                None => {
+                    let ty = self.lower_ty(ty, ImplTraitContext::disallowed());
+                    let generics = self.lower_generics(generics, ImplTraitContext::disallowed());
+                    hir::ItemKind::TyAlias(ty, generics)
                 },
-            ),
+                Some(bounds) => {
+                    let ty = hir::OpaqueTy {
+                        generics: self.lower_generics(generics, ImplTraitContext::OpaqueTy(None)),
+                        bounds: self.lower_param_bounds(bounds, ImplTraitContext::OpaqueTy(None)),
+                        impl_trait_fn: None,
+                        origin: hir::OpaqueTyOrigin::TypeAlias,
+                    };
+                    hir::ItemKind::OpaqueTy(ty)
+                }
+            }
             ItemKind::Enum(ref enum_definition, ref generics) => {
                 hir::ItemKind::Enum(
                     hir::EnumDef {
@@ -916,16 +918,20 @@ impl LoweringContext<'_> {
 
                 (generics, hir::ImplItemKind::Method(sig, body_id))
             }
-            ImplItemKind::TyAlias(ref ty) => (
-                self.lower_generics(&i.generics, ImplTraitContext::disallowed()),
-                hir::ImplItemKind::TyAlias(self.lower_ty(ty, ImplTraitContext::disallowed())),
-            ),
-            ImplItemKind::OpaqueTy(ref bounds) => (
-                self.lower_generics(&i.generics, ImplTraitContext::disallowed()),
-                hir::ImplItemKind::OpaqueTy(
-                    self.lower_param_bounds(bounds, ImplTraitContext::disallowed()),
-                ),
-            ),
+            ImplItemKind::TyAlias(ref ty) => {
+                let generics = self.lower_generics(&i.generics, ImplTraitContext::disallowed());
+                let kind = match ty.kind.opaque_top_hack() {
+                    None => {
+                        let ty = self.lower_ty(ty, ImplTraitContext::disallowed());
+                        hir::ImplItemKind::TyAlias(ty)
+                    }
+                    Some(bs) => {
+                        let bounds = self.lower_param_bounds(bs, ImplTraitContext::disallowed());
+                        hir::ImplItemKind::OpaqueTy(bounds)
+                    }
+                };
+                (generics, kind)
+            },
             ImplItemKind::Macro(..) => bug!("`TyMac` should have been expanded by now"),
         };
 
@@ -950,11 +956,13 @@ impl LoweringContext<'_> {
             span: i.span,
             vis: self.lower_visibility(&i.vis, Some(i.id)),
             defaultness: self.lower_defaultness(i.defaultness, true /* [1] */),
-            kind: match i.kind {
+            kind: match &i.kind {
                 ImplItemKind::Const(..) => hir::AssocItemKind::Const,
-                ImplItemKind::TyAlias(..) => hir::AssocItemKind::Type,
-                ImplItemKind::OpaqueTy(..) => hir::AssocItemKind::OpaqueTy,
-                ImplItemKind::Method(ref sig, _) => hir::AssocItemKind::Method {
+                ImplItemKind::TyAlias(ty) => match ty.kind.opaque_top_hack() {
+                    None => hir::AssocItemKind::Type,
+                    Some(_) => hir::AssocItemKind::OpaqueTy,
+                },
+                ImplItemKind::Method(sig, _) => hir::AssocItemKind::Method {
                     has_self: sig.decl.has_self(),
                 },
                 ImplItemKind::Macro(..) => unimplemented!(),

src/librustc/hir/map/def_collector.rs

@@ -107,7 +107,7 @@ impl<'a> visit::Visitor<'a> for DefCollector<'a> {
             }
             ItemKind::Mod(..) | ItemKind::Trait(..) | ItemKind::TraitAlias(..) |
             ItemKind::Enum(..) | ItemKind::Struct(..) | ItemKind::Union(..) |
-            ItemKind::OpaqueTy(..) | ItemKind::ExternCrate(..) | ItemKind::ForeignMod(..) |
+            ItemKind::ExternCrate(..) | ItemKind::ForeignMod(..) |
             ItemKind::TyAlias(..) => DefPathData::TypeNs(i.ident.name),
             ItemKind::Fn(sig, generics, body) if sig.header.asyncness.node.is_async() => {
                 return self.visit_async_fn(
@@ -239,8 +239,7 @@ impl<'a> visit::Visitor<'a> for DefCollector<'a> {
             }
             ImplItemKind::Method(..) |
             ImplItemKind::Const(..) => DefPathData::ValueNs(ii.ident.name),
-            ImplItemKind::TyAlias(..) |
-            ImplItemKind::OpaqueTy(..) => DefPathData::TypeNs(ii.ident.name),
+            ImplItemKind::TyAlias(..) => DefPathData::TypeNs(ii.ident.name),
             ImplItemKind::Macro(..) => return self.visit_macro_invoc(ii.id),
         };
 

src/librustc/traits/error_reporting.rs

@@ -2176,15 +2176,15 @@ impl<'a, 'tcx> InferCtxt<'a, 'tcx> {
                 err.note(&format!("required by cast to type `{}`",
                                   self.ty_to_string(target)));
             }
-            ObligationCauseCode::RepeatVec(suggest_const_in_array_repeat_expression) => {
+            ObligationCauseCode::RepeatVec(suggest_const_in_array_repeat_expressions) => {
                 err.note("the `Copy` trait is required because the \
                           repeated element will be copied");
-                if suggest_const_in_array_repeat_expression {
+                if suggest_const_in_array_repeat_expressions {
                     err.note("this array initializer can be evaluated at compile-time, for more \
                               information, see issue \
                               https://github.com/rust-lang/rust/issues/49147");
                     if tcx.sess.opts.unstable_features.is_nightly_build() {
-                        err.help("add `#![feature(const_in_array_repeat_expression)]` to the \
+                        err.help("add `#![feature(const_in_array_repeat_expressions)]` to the \
                                   crate attributes to enable");
                     }
                 }

src/librustc/traits/mod.rs

@@ -206,7 +206,7 @@ pub enum ObligationCauseCode<'tcx> {
     SizedReturnType,
     /// Yield type must be Sized
     SizedYieldType,
-    /// [T,..n] --> T must be Copy. If `true`, suggest `const_in_array_repeat_expression` feature
+    /// [T,..n] --> T must be Copy. If `true`, suggest `const_in_array_repeat_expressions` feature
     /// flag.
     RepeatVec(bool),
 

src/librustc_error_codes/error_codes.rs

@@ -1,6 +1,11 @@
 // Error messages for EXXXX errors.  Each message should start and end with a
 // new line, and be wrapped to 80 characters.  In vim you can `:set tw=80` and
 // use `gq` to wrap paragraphs. Use `:set tw=0` to disable.
+//
+// /!\ IMPORTANT /!\
+//
+// Error messages' format must follow the RFC 1567 available here:
+// https://github.com/rust-lang/rfcs/pull/1567
 
 crate::register_diagnostics! {
 

src/librustc_error_codes/error_codes/E0023.md

@@ -1,6 +1,6 @@
-A pattern used to match against an enum variant must provide a sub-pattern for
-each field of the enum variant. This error indicates that a pattern attempted to
-extract an incorrect number of fields from a variant.
+A pattern attempted to extract an incorrect number of fields from a variant.
+
+Erroneous code example:
 
 ```
 enum Fruit {
@@ -9,6 +9,9 @@ enum Fruit {
 }
 ```
 
+A pattern used to match against an enum variant must provide a sub-pattern for
+each field of the enum variant.
+
 Here the `Apple` variant has two fields, and should be matched against like so:
 
 ```

src/librustc_error_codes/error_codes/E0025.md

@@ -1,5 +1,6 @@
-Each field of a struct can only be bound once in a pattern. Erroneous code
-example:
+Each field of a struct can only be bound once in a pattern.
+
+Erroneous code example:
 
 ```compile_fail,E0025
 struct Foo {

src/librustc_error_codes/error_codes/E0026.md

@@ -1,51 +1,34 @@
-This error indicates that a struct pattern attempted to extract a non-existent
-field from a struct. Struct fields are identified by the name used before the
-colon `:` so struct patterns should resemble the declaration of the struct type
-being matched.
+A struct pattern attempted to extract a non-existent field from a struct.
 
-```
-// Correct matching.
-struct Thing {
-    x: u32,
-    y: u32
-}
-
-let thing = Thing { x: 1, y: 2 };
-
-match thing {
-    Thing { x: xfield, y: yfield } => {}
-}
-```
-
-If you are using shorthand field patterns but want to refer to the struct field
-by a different name, you should rename it explicitly.
-
-Change this:
+Erroneous code example:
 
 ```compile_fail,E0026
 struct Thing {
     x: u32,
-    y: u32
+    y: u32,
 }
 
 let thing = Thing { x: 0, y: 0 };
 
 match thing {
-    Thing { x, z } => {}
+    Thing { x, z } => {} // error: `Thing::z` field doesn't exist
 }
 ```
 
-To this:
+If you are using shorthand field patterns but want to refer to the struct field
+by a different name, you should rename it explicitly. Struct fields are
+identified by the name used before the colon `:` so struct patterns should
+resemble the declaration of the struct type being matched.
 
 ```
 struct Thing {
     x: u32,
-    y: u32
+    y: u32,
 }
 
 let thing = Thing { x: 0, y: 0 };
 
 match thing {
-    Thing { x, y: z } => {}
+    Thing { x, y: z } => {} // we renamed `y` to `z`
 }
 ```

src/librustc_error_codes/error_codes/E0027.md

@@ -1,8 +1,7 @@
-This error indicates that a pattern for a struct fails to specify a sub-pattern
-for every one of the struct's fields. Ensure that each field from the struct's
-definition is mentioned in the pattern, or use `..` to ignore unwanted fields.
+A pattern for a struct fails to specify a sub-pattern for every one of the
+struct's fields.
 
-For example:
+Erroneous code example:
 
 ```compile_fail,E0027
 struct Dog {
@@ -18,7 +17,8 @@ match d {
 }
 ```
 
-This is correct (explicit):
+To fix this error, ensure that each field from the struct's definition is
+mentioned in the pattern, or use `..` to ignore unwanted fields. Example:
 
 ```
 struct Dog {

src/librustc_error_codes/error_codes/E0029.md

@@ -1,8 +1,6 @@
-In a match expression, only numbers and characters can be matched against a
-range. This is because the compiler checks that the range is non-empty at
-compile-time, and is unable to evaluate arbitrary comparison functions. If you
-want to capture values of an orderable type between two end-points, you can use
-a guard.
+Something other than numbers and characters has been used for a range.
+
+Erroneous code example:
 
 ```compile_fail,E0029
 let string = "salutations !";
@@ -20,3 +18,9 @@ match string {
     _ => {}
 }
 ```
+
+In a match expression, only numbers and characters can be matched against a
+range. This is because the compiler checks that the range is non-empty at
+compile-time, and is unable to evaluate arbitrary comparison functions. If you
+want to capture values of an orderable type between two end-points, you can use
+a guard.

src/librustc_error_codes/error_codes/E0033.md

@@ -1,8 +1,6 @@
-This error indicates that a pointer to a trait type cannot be implicitly
-dereferenced by a pattern. Every trait defines a type, but because the
-size of trait implementers isn't fixed, this type has no compile-time size.
-Therefore, all accesses to trait types must be through pointers. If you
-encounter this error you should try to avoid dereferencing the pointer.
+A trait type has been dereferenced.
+
+Erroneous code example:
 
 ```compile_fail,E0033
 # trait SomeTrait { fn method_one(&self){} fn method_two(&self){} }
@@ -17,7 +15,13 @@ trait_obj.method_one();
 trait_obj.method_two();
 ```
 
+A pointer to a trait type cannot be implicitly dereferenced by a pattern. Every
+trait defines a type, but because the size of trait implementers isn't fixed,
+this type has no compile-time size. Therefore, all accesses to trait types must
+be through pointers. If you encounter this error you should try to avoid
+dereferencing the pointer.
+
 You can read more about trait objects in the [Trait Objects] section of the
 Reference.
 
-[Trait Objects]: https://doc.rust-lang.org/reference/types.html#trait-objects
+[Trait Objects]: https://doc.rust-lang.org/reference/types.html#trait-objects

src/librustc_error_codes/error_codes/E0034.md

@@ -1,5 +1,7 @@
 The compiler doesn't know what method to call because more than one method
-has the same prototype. Erroneous code example:
+has the same prototype.
+
+Erroneous code example:
 
 ```compile_fail,E0034
 struct Test;

src/librustc_error_codes/error_codes/E0040.md

@@ -1,8 +1,6 @@
-It is not allowed to manually call destructors in Rust. It is also not
-necessary to do this since `drop` is called automatically whenever a value goes
-out of scope.
+It is not allowed to manually call destructors in Rust.
 
-Here's an example of this error:
+Erroneous code example:
 
 ```compile_fail,E0040
 struct Foo {
@@ -20,3 +18,22 @@ fn main() {
     x.drop(); // error: explicit use of destructor method
 }
 ```
+
+It is unnecessary to do this since `drop` is called automatically whenever a
+value goes out of scope. However, if you really need to drop a value by hand,
+you can use the `std::mem::drop` function:
+
+```
+struct Foo {
+    x: i32,
+}
+impl Drop for Foo {
+    fn drop(&mut self) {
+        println!("kaboom");
+    }
+}
+fn main() {
+    let mut x = Foo { x: -7 };
+    drop(x); // ok!
+}
+```

src/librustc_error_codes/error_codes/E0044.md

@@ -1,4 +1,5 @@
 You cannot use type or const parameters on foreign items.
+
 Example of erroneous code:
 
 ```compile_fail,E0044

src/librustc_error_codes/error_codes/E0045.md

@@ -1,18 +1,18 @@
-Rust only supports variadic parameters for interoperability with C code in its
-FFI. As such, variadic parameters can only be used with functions which are
-using the C ABI. Examples of erroneous code:
-
-```compile_fail
-#![feature(unboxed_closures)]
+Variadic parameters have been used on a non-C ABI function.
 
-extern "rust-call" { fn foo(x: u8, ...); }
+Erroneous code example:
 
-// or
+```compile_fail,E0045
+#![feature(unboxed_closures)]
 
-fn foo(x: u8, ...) {}
+extern "rust-call" {
+    fn foo(x: u8, ...); // error!
+}
 ```
 
-To fix such code, put them in an extern "C" block:
+Rust only supports variadic parameters for interoperability with C code in its
+FFI. As such, variadic parameters can only be used with functions which are
+using the C ABI. To fix such code, put them in an extern "C" block:
 
 ```
 extern "C" {