Retroactively feature gate ConstArgKind::Path

compiler/rustc_ast_lowering/src/asm.rs

@@ -221,7 +221,9 @@ impl<'a, 'hir> LoweringContext<'a, 'hir> {
                             let parent_def_id = self.current_def_id_parent;
                             let node_id = self.next_node_id();
                             // HACK(min_generic_const_args): see lower_anon_const
-                            if !expr.is_potential_trivial_const_arg() {
+                            if !self.tcx.features().const_arg_path
+                                || !expr.is_potential_trivial_const_arg()
+                            {
                                 self.create_def(
                                     parent_def_id,
                                     node_id,

compiler/rustc_ast_lowering/src/expr.rs

@@ -387,7 +387,7 @@ impl<'hir> LoweringContext<'_, 'hir> {
                 let node_id = self.next_node_id();
 
                 // HACK(min_generic_const_args): see lower_anon_const
-                if !arg.is_potential_trivial_const_arg() {
+                if !self.tcx.features().const_arg_path || !arg.is_potential_trivial_const_arg() {
                     // Add a definition for the in-band const def.
                     self.create_def(parent_def_id, node_id, kw::Empty, DefKind::AnonConst, f.span);
                 }

compiler/rustc_ast_lowering/src/lib.rs

@@ -2358,7 +2358,7 @@ impl<'a, 'hir> LoweringContext<'a, 'hir> {
         span: Span,
     ) -> &'hir hir::ConstArg<'hir> {
         let ct_kind = match res {
-            Res::Def(DefKind::ConstParam, _) => {
+            Res::Def(DefKind::ConstParam, _) if self.tcx.features().const_arg_path => {
                 let qpath = self.lower_qpath(
                     ty_id,
                     &None,
@@ -2433,7 +2433,8 @@ impl<'a, 'hir> LoweringContext<'a, 'hir> {
             self.resolver.get_partial_res(expr.id).and_then(|partial_res| partial_res.full_res());
         debug!("res={:?}", maybe_res);
         // FIXME(min_generic_const_args): for now we only lower params to ConstArgKind::Path
-        if let Some(res) = maybe_res
+        if self.tcx.features().const_arg_path
+            && let Some(res) = maybe_res
             && let Res::Def(DefKind::ConstParam, _) = res
             && let ExprKind::Path(qself, path) = &expr.kind
         {
@@ -2464,7 +2465,7 @@ impl<'a, 'hir> LoweringContext<'a, 'hir> {
     /// See [`hir::ConstArg`] for when to use this function vs
     /// [`Self::lower_anon_const_to_const_arg`].
     fn lower_anon_const_to_anon_const(&mut self, c: &AnonConst) -> &'hir hir::AnonConst {
-        if c.value.is_potential_trivial_const_arg() {
+        if self.tcx.features().const_arg_path && c.value.is_potential_trivial_const_arg() {
             // HACK(min_generic_const_args): see DefCollector::visit_anon_const
             // Over there, we guess if this is a bare param and only create a def if
             // we think it's not. However we may can guess wrong (see there for example)

compiler/rustc_feature/src/unstable.rs

@@ -193,6 +193,8 @@ declare_features! (
     (unstable, anonymous_lifetime_in_impl_trait, "1.63.0", None),
     /// Allows identifying the `compiler_builtins` crate.
     (internal, compiler_builtins, "1.13.0", None),
+    /// Gating for a new desugaring of const arguments of usages of const parameters
+    (internal, const_arg_path, "1.81.0", None),
     /// Allows writing custom MIR
     (internal, custom_mir, "1.65.0", None),
     /// Outputs useful `assert!` messages

compiler/rustc_middle/src/ty/consts.rs

@@ -240,7 +240,7 @@ impl<'tcx> Const<'tcx> {
 
         let ty = tcx.type_of(def).no_bound_vars().expect("const parameter types cannot be generic");
 
-        match Self::try_from_lit(tcx, ty, expr) {
+        match Self::try_from_lit_or_param(tcx, ty, expr) {
             Some(v) => v,
             None => ty::Const::new_unevaluated(
                 tcx,
@@ -281,7 +281,11 @@ impl<'tcx> Const<'tcx> {
     }
 
     #[instrument(skip(tcx), level = "debug")]
-    fn try_from_lit(tcx: TyCtxt<'tcx>, ty: Ty<'tcx>, expr: &'tcx hir::Expr<'tcx>) -> Option<Self> {
+    fn try_from_lit_or_param(
+        tcx: TyCtxt<'tcx>,
+        ty: Ty<'tcx>,
+        expr: &'tcx hir::Expr<'tcx>,
+    ) -> Option<Self> {
         // Unwrap a block, so that e.g. `{ P }` is recognised as a parameter. Const arguments
         // currently have to be wrapped in curly brackets, so it's necessary to special-case.
         let expr = match &expr.kind {
@@ -291,6 +295,22 @@ impl<'tcx> Const<'tcx> {
             _ => expr,
         };
 
+        if let hir::ExprKind::Path(
+            qpath @ hir::QPath::Resolved(
+                _,
+                &hir::Path { res: Res::Def(DefKind::ConstParam, _), .. },
+            ),
+        ) = expr.kind
+        {
+            if tcx.features().const_arg_path {
+                span_bug!(
+                    expr.span,
+                    "try_from_lit: received const param which shouldn't be possible"
+                );
+            }
+            return Some(Const::from_param(tcx, qpath, expr.hir_id));
+        };
+
         let lit_input = match expr.kind {
             hir::ExprKind::Lit(lit) => Some(LitToConstInput { lit: &lit.node, ty, neg: false }),
             hir::ExprKind::Unary(hir::UnOp::Neg, expr) => match expr.kind {
@@ -318,14 +338,6 @@ impl<'tcx> Const<'tcx> {
             }
         }
 
-        if let hir::ExprKind::Path(hir::QPath::Resolved(
-            _,
-            &hir::Path { res: Res::Def(DefKind::ConstParam, _), .. },
-        )) = expr.kind
-        {
-            span_bug!(expr.span, "try_from_lit: received const param which shouldn't be possible")
-        }
-
         None
     }
 

compiler/rustc_resolve/src/def_collector.rs

@@ -314,13 +314,15 @@ impl<'a, 'b, 'tcx> visit::Visitor<'a> for DefCollector<'a, 'b, 'tcx> {
     }
 
     fn visit_anon_const(&mut self, constant: &'a AnonConst) {
-        // HACK(min_generic_const_args): don't create defs for anon consts if we think they will
+        if self.resolver.tcx.features().const_arg_path
-        // later be turned into ConstArgKind::Path's. because this is before resolve is done, we
+            && constant.value.is_potential_trivial_const_arg()
-        // may accidentally identify a construction of a unit struct as a param and not create a
+        {
-        // def. we'll then create a def later in ast lowering in this case. the parent of nested
+            // HACK(min_generic_const_args): don't create defs for anon consts if we think they will
-        // items will be messed up, but that's ok because there can't be any if we're just looking
+            // later be turned into ConstArgKind::Path's. because this is before resolve is done, we
-        // for bare idents.
+            // may accidentally identify a construction of a unit struct as a param and not create a
-        if constant.value.is_potential_trivial_const_arg() {
+            // def. we'll then create a def later in ast lowering in this case. the parent of nested
+            // items will be messed up, but that's ok because there can't be any if we're just looking
+            // for bare idents.
             visit::walk_anon_const(self, constant)
         } else {
             let def =

compiler/rustc_span/src/symbol.rs

@@ -595,6 +595,7 @@ symbols! {
         conservative_impl_trait,
         console,
         const_allocate,
+        const_arg_path,
         const_async_blocks,
         const_closures,
         const_compare_raw_pointers,

tests/crashes/127972.rs

@@ -1,5 +1,5 @@
 //@ known-bug: #127962
-#![feature(generic_const_exprs)]
+#![feature(generic_const_exprs, const_arg_path)]
 
 fn zero_init<const usize: usize>() -> Substs1<{ (N) }> {
     Substs1([0; { (usize) }])

tests/crashes/128016.rs

@@ -1,10 +0,0 @@
-//@ known-bug: #128016
-macro_rules! len {
-    () => {
-        target
-    };
-}
-
-fn main() {
-    let val: [str; len!()] = [];
-}

tests/ui-fulldeps/stable-mir/check_instance.rs

@@ -17,12 +17,14 @@ extern crate rustc_driver;
 extern crate rustc_interface;
 extern crate stable_mir;
 
-use mir::{mono::Instance, TerminatorKind::*};
+use std::io::Write;
+use std::ops::ControlFlow;
+
+use mir::mono::Instance;
+use mir::TerminatorKind::*;
 use rustc_smir::rustc_internal;
 use stable_mir::ty::{RigidTy, TyKind};
 use stable_mir::*;
-use std::io::Write;
-use std::ops::ControlFlow;
 
 const CRATE_NAME: &str = "input";
 
@@ -33,7 +35,7 @@ fn test_stable_mir() -> ControlFlow<()> {
     // Get all items and split generic vs monomorphic items.
     let (generic, mono): (Vec<_>, Vec<_>) =
         items.into_iter().partition(|item| item.requires_monomorphization());
-    assert_eq!(mono.len(), 3, "Expected 3 mono functions");
+    assert_eq!(mono.len(), 4, "Expected 3 mono functions");
     assert_eq!(generic.len(), 2, "Expected 2 generic functions");
 
     // For all monomorphic items, get the correspondent instances.

tests/ui/coherence/negative-coherence/generic_const_type_mismatch.rs

@@ -5,7 +5,9 @@
 #![feature(with_negative_coherence)]
 trait Trait {}
 impl<const N: u8> Trait for [(); N] {}
+//~^ ERROR: mismatched types
 impl<const N: i8> Trait for [(); N] {}
 //~^ ERROR: conflicting implementations of trait `Trait`
+//~| ERROR: mismatched types
 
 fn main() {}

tests/ui/coherence/negative-coherence/generic_const_type_mismatch.stderr

@@ -1,11 +1,25 @@
 error[E0119]: conflicting implementations of trait `Trait` for type `[(); _]`
-  --> $DIR/generic_const_type_mismatch.rs:8:1
+  --> $DIR/generic_const_type_mismatch.rs:9:1
    |
 LL | impl<const N: u8> Trait for [(); N] {}
    | ----------------------------------- first implementation here
+LL |
 LL | impl<const N: i8> Trait for [(); N] {}
    | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ conflicting implementation for `[(); _]`
 
-error: aborting due to 1 previous error
+error[E0308]: mismatched types
+  --> $DIR/generic_const_type_mismatch.rs:7:34
+   |
+LL | impl<const N: u8> Trait for [(); N] {}
+   |                                  ^ expected `usize`, found `u8`
 
-For more information about this error, try `rustc --explain E0119`.
+error[E0308]: mismatched types
+  --> $DIR/generic_const_type_mismatch.rs:9:34
+   |
+LL | impl<const N: i8> Trait for [(); N] {}
+   |                                  ^ expected `usize`, found `i8`
+
+error: aborting due to 3 previous errors
+
+Some errors have detailed explanations: E0119, E0308.
+For more information about an error, try `rustc --explain E0119`.

tests/ui/const-generics/bad-subst-const-kind.rs

@@ -7,6 +7,7 @@ trait Q {
 
 impl<const N: u64> Q for [u8; N] {
     //~^ ERROR: the constant `N` is not of type `usize`
+    //~| ERROR: mismatched types
     const ASSOC: usize = 1;
 }
 

tests/ui/const-generics/bad-subst-const-kind.stderr

@@ -5,7 +5,7 @@ LL | impl<const N: u64> Q for [u8; N] {
    |                          ^^^^^^^ expected `usize`, found `u64`
 
 error: the constant `13` is not of type `u64`
-  --> $DIR/bad-subst-const-kind.rs:13:24
+  --> $DIR/bad-subst-const-kind.rs:14:24
    |
 LL | pub fn test() -> [u8; <[u8; 13] as Q>::ASSOC] {
    |                        ^^^^^^^^ expected `u64`, found `usize`
@@ -18,5 +18,12 @@ LL | impl<const N: u64> Q for [u8; N] {
    |      |
    |      unsatisfied trait bound introduced here
 
-error: aborting due to 2 previous errors
+error[E0308]: mismatched types
+  --> $DIR/bad-subst-const-kind.rs:8:31
+   |
+LL | impl<const N: u64> Q for [u8; N] {
+   |                               ^ expected `usize`, found `u64`
 
+error: aborting due to 3 previous errors
+
+For more information about this error, try `rustc --explain E0308`.

tests/ui/const-generics/early/trivial-const-arg-macro-nested.rs

@@ -0,0 +1,21 @@
+//@ check-pass
+
+// This is a regression test for #128016.
+
+macro_rules! len_inner {
+    () => {
+        BAR
+    };
+}
+
+macro_rules! len {
+    () => {
+        len_inner!()
+    };
+}
+
+const BAR: usize = 0;
+
+fn main() {
+    let val: [bool; len!()] = [];
+}

tests/ui/const-generics/early/trivial-const-arg-macro-param.rs

@@ -0,0 +1,13 @@
+//@ check-pass
+
+macro_rules! len {
+    ($x:ident) => {
+        $x
+    };
+}
+
+fn bar<const N: usize>() {
+    let val: [bool; len!(N)] = [true; N];
+}
+
+fn main() {}

tests/ui/const-generics/early/trivial-const-arg-macro-res-error.rs

@@ -0,0 +1,13 @@
+// This is a regression test for #128016.
+
+macro_rules! len {
+    () => {
+        target
+        //~^ ERROR cannot find value `target`
+    };
+}
+
+fn main() {
+    let val: [str; len!()] = [];
+    //~^ ERROR the size for values
+}

tests/ui/const-generics/early/trivial-const-arg-macro-res-error.stderr

@@ -0,0 +1,24 @@
+error[E0425]: cannot find value `target` in this scope
+  --> $DIR/trivial-const-arg-macro-res-error.rs:5:9
+   |
+LL |         target
+   |         ^^^^^^ not found in this scope
+...
+LL |     let val: [str; len!()] = [];
+   |                    ------ in this macro invocation
+   |
+   = note: this error originates in the macro `len` (in Nightly builds, run with -Z macro-backtrace for more info)
+
+error[E0277]: the size for values of type `str` cannot be known at compilation time
+  --> $DIR/trivial-const-arg-macro-res-error.rs:11:14
+   |
+LL |     let val: [str; len!()] = [];
+   |              ^^^^^^^^^^^^^ doesn't have a size known at compile-time
+   |
+   = help: the trait `Sized` is not implemented for `str`
+   = note: slice and array elements must have `Sized` type
+
+error: aborting due to 2 previous errors
+
+Some errors have detailed explanations: E0277, E0425.
+For more information about an error, try `rustc --explain E0277`.

tests/ui/const-generics/early/trivial-const-arg-macro.rs

@@ -0,0 +1,15 @@
+//@ check-pass
+
+// This is a regression test for #128016.
+
+macro_rules! len {
+    () => {
+        BAR
+    };
+}
+
+const BAR: usize = 0;
+
+fn main() {
+    let val: [bool; len!()] = [];
+}

tests/ui/const-generics/generic_const_exprs/type_mismatch.rs

@@ -8,6 +8,7 @@ trait Q {
 impl<const N: u64> Q for [u8; N] {}
 //~^ ERROR not all trait items implemented
 //~| ERROR the constant `N` is not of type `usize`
+//~| ERROR mismatched types
 
 pub fn q_user() -> [u8; <[u8; 13] as Q>::ASSOC] {}
 //~^ ERROR the constant `13` is not of type `u64`

tests/ui/const-generics/generic_const_exprs/type_mismatch.stderr

@@ -14,7 +14,7 @@ LL | impl<const N: u64> Q for [u8; N] {}
    | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ missing `ASSOC` in implementation
 
 error: the constant `13` is not of type `u64`
-  --> $DIR/type_mismatch.rs:12:26
+  --> $DIR/type_mismatch.rs:13:26
    |
 LL | pub fn q_user() -> [u8; <[u8; 13] as Q>::ASSOC] {}
    |                          ^^^^^^^^ expected `u64`, found `usize`
@@ -28,14 +28,20 @@ LL | impl<const N: u64> Q for [u8; N] {}
    |      unsatisfied trait bound introduced here
 
 error[E0308]: mismatched types
-  --> $DIR/type_mismatch.rs:12:20
+  --> $DIR/type_mismatch.rs:13:20
    |
 LL | pub fn q_user() -> [u8; <[u8; 13] as Q>::ASSOC] {}
    |        ------      ^^^^^^^^^^^^^^^^^^^^^^^^^^^^ expected `[u8; <[u8; 13] as Q>::ASSOC]`, found `()`
    |        |
    |        implicitly returns `()` as its body has no tail or `return` expression
 
-error: aborting due to 4 previous errors
+error[E0308]: mismatched types
+  --> $DIR/type_mismatch.rs:8:31
+   |
+LL | impl<const N: u64> Q for [u8; N] {}
+   |                               ^ expected `usize`, found `u64`
+
+error: aborting due to 5 previous errors
 
 Some errors have detailed explanations: E0046, E0308.
 For more information about an error, try `rustc --explain E0046`.

tests/ui/const-generics/generic_const_exprs/unevaluated-const-ice-119731.rs

@@ -14,8 +14,8 @@ mod v20 {
     //~^ ERROR cannot find value `v8` in this scope
     //~| ERROR cannot find function `v6` in this scope
     pub struct v17<const v10: usize, const v7: v11> {
-    //~^ WARN type `v17` should have an upper camel case name
+        //~^ WARN type `v17` should have an upper camel case name
-    //~| ERROR `[[usize; v4]; v4]` is forbidden as the type of a const generic parameter
+        //~| ERROR `[[usize; v4]; v4]` is forbidden as the type of a const generic parameter
         _p: (),
     }
 
@@ -25,10 +25,10 @@ mod v20 {
     }
 
     impl<const v10: usize> v17<v10, v2> {
-    //~^ ERROR maximum number of nodes exceeded in constant v20::v17::<v10, v2>::{constant#0}
+        //~^ ERROR maximum number of nodes exceeded in constant v20::v17::<v10, v2>::{constant#1}
-    //~| ERROR maximum number of nodes exceeded in constant v20::v17::<v10, v2>::{constant#0}
+        //~| ERROR maximum number of nodes exceeded in constant v20::v17::<v10, v2>::{constant#1}
         pub const fn v21() -> v18 {
-        //~^ ERROR cannot find type `v18` in this scope
+            //~^ ERROR cannot find type `v18` in this scope
             v18 { _p: () }
             //~^ ERROR cannot find struct, variant or union type `v18` in this scope
         }

tests/ui/const-generics/generic_const_exprs/unevaluated-const-ice-119731.stderr

@@ -72,13 +72,13 @@ help: add `#![feature(adt_const_params)]` to the crate attributes to enable more
 LL + #![feature(adt_const_params)]
    |
 
-error: maximum number of nodes exceeded in constant v20::v17::<v10, v2>::{constant#0}
+error: maximum number of nodes exceeded in constant v20::v17::<v10, v2>::{constant#1}
   --> $DIR/unevaluated-const-ice-119731.rs:27:37
    |
 LL |     impl<const v10: usize> v17<v10, v2> {
    |                                     ^^
 
-error: maximum number of nodes exceeded in constant v20::v17::<v10, v2>::{constant#0}
+error: maximum number of nodes exceeded in constant v20::v17::<v10, v2>::{constant#1}
   --> $DIR/unevaluated-const-ice-119731.rs:27:37
    |
 LL |     impl<const v10: usize> v17<v10, v2> {

tests/ui/const-generics/transmute-fail.rs

@@ -2,108 +2,108 @@
 #![feature(generic_const_exprs)]
 #![allow(incomplete_features)]
 
-fn foo<const W: usize, const H: usize>(v: [[u32;H+1]; W]) -> [[u32; W+1]; H] {
+fn foo<const W: usize, const H: usize>(v: [[u32; H + 1]; W]) -> [[u32; W + 1]; H] {
-  unsafe {
+    unsafe {
-    std::mem::transmute(v)
+        std::mem::transmute(v)
-    //~^ ERROR cannot transmute
+        //~^ ERROR cannot transmute
-  }
+    }
 }
 
 fn bar<const W: bool, const H: usize>(v: [[u32; H]; W]) -> [[u32; W]; H] {
-  //~^ ERROR the constant `W` is not of type `usize`
+    //~^ ERROR: the constant `W` is not of type `usize`
-  unsafe {
+    //~| ERROR: mismatched types
-    std::mem::transmute(v)
+    //~| ERROR: mismatched types
-    //~^ ERROR the constant `W` is not of type `usize`
+    unsafe {
-  }
+        std::mem::transmute(v)
+        //~^ ERROR: the constant `W` is not of type `usize`
+    }
 }
 
 fn baz<const W: usize, const H: usize>(v: [[u32; H]; W]) -> [u32; W * H * H] {
-  unsafe {
+    unsafe {
-    std::mem::transmute(v)
+        std::mem::transmute(v)
-    //~^ ERROR cannot transmute
+        //~^ ERROR cannot transmute
-  }
+    }
 }
 
 fn overflow(v: [[[u32; 8888888]; 9999999]; 777777777]) -> [[[u32; 9999999]; 777777777]; 8888888] {
-  unsafe {
+    unsafe {
-    std::mem::transmute(v)
+        std::mem::transmute(v)
-    //~^ ERROR cannot transmute
+        //~^ ERROR cannot transmute
-  }
+    }
 }
 
-fn transpose<const W: usize, const H: usize>(v: [[u32;H]; W]) -> [[u32; W]; H] {
+fn transpose<const W: usize, const H: usize>(v: [[u32; H]; W]) -> [[u32; W]; H] {
-  unsafe {
+    unsafe {
-    std::mem::transmute(v)
+        std::mem::transmute(v)
-    //~^ ERROR: cannot transmute between types of different sizes, or dependently-sized types
+        //~^ 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 {
+    unsafe { std::mem::transmute(v) }
-    std::mem::transmute(v)
-  }
 }
 
 fn flatten<const W: usize, const H: usize>(v: [[u32; H]; W]) -> [u32; W * H] {
-  unsafe {
+    unsafe {
-    std::mem::transmute(v)
+        std::mem::transmute(v)
-    //~^ ERROR: cannot transmute between types of different sizes, or dependently-sized types
+        //~^ 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] {
+fn coagulate<const W: usize, const H: usize>(v: [u32; H * W]) -> [[u32; W]; H] {
-  unsafe {
+    unsafe {
-    std::mem::transmute(v)
+        std::mem::transmute(v)
-    //~^ ERROR: cannot transmute between types of different sizes, or dependently-sized types
+        //~^ 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]
+    v: [[[u32; D]; H]; W],
 ) -> [u32; D * W * H] {
-  unsafe {
+    unsafe {
-    std::mem::transmute(v)
+        std::mem::transmute(v)
-    //~^ ERROR: cannot transmute between types of different sizes, or dependently-sized types
+        //~^ 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]
+    v: [[[u32; D]; H]; W],
 ) -> [[u32; D * W]; H] {
-  unsafe {
+    unsafe {
-    std::mem::transmute(v)
+        std::mem::transmute(v)
-    //~^ ERROR: cannot transmute between types of different sizes, or dependently-sized types
+        //~^ 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 {
+    unsafe {
-    std::mem::transmute(v)
+        std::mem::transmute(v)
-    //~^ ERROR: cannot transmute between types of different sizes, or dependently-sized types
+        //~^ 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 {
+    unsafe {
-    std::mem::transmute(v)
+        std::mem::transmute(v)
-    //~^ ERROR: cannot transmute between types of different sizes, or dependently-sized types
+        //~^ ERROR: cannot transmute between types of different sizes, or dependently-sized types
-  }
+    }
 }
 
-fn singleton_each<const L: usize>(v: [u8; L]) -> [[u8;1]; L] {
+fn singleton_each<const L: usize>(v: [u8; L]) -> [[u8; 1]; L] {
-  unsafe {
+    unsafe {
-    std::mem::transmute(v)
+        std::mem::transmute(v)
-    //~^ ERROR: cannot transmute between types of different sizes, or dependently-sized types
+        //~^ 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]
+    v: [[u32; 2 * H]; W + W],
 ) -> [[u32; W + W]; 2 * H] {
-  unsafe {
+    unsafe {
-    std::mem::transmute(v)
+        std::mem::transmute(v)
-    //~^ ERROR: cannot transmute between types of different sizes, or dependently-sized types
+        //~^ ERROR: cannot transmute between types of different sizes, or dependently-sized types
-  }
+    }
 }
 
 fn main() {}

tests/ui/const-generics/transmute-fail.stderr

@@ -5,119 +5,132 @@ LL | fn bar<const W: bool, const H: usize>(v: [[u32; H]; W]) -> [[u32; W]; H] {
    |                                          ^^^^^^^^^^^^^ expected `usize`, found `bool`
 
 error[E0512]: cannot transmute between types of different sizes, or dependently-sized types
-  --> $DIR/transmute-fail.rs:7:5
+  --> $DIR/transmute-fail.rs:7:9
    |
-LL |     std::mem::transmute(v)
+LL |         std::mem::transmute(v)
-   |     ^^^^^^^^^^^^^^^^^^^
+   |         ^^^^^^^^^^^^^^^^^^^
    |
-   = note: source type: `[[u32; H+1]; W]` (size can vary because of [u32; H+1])
+   = 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])
+   = note: target type: `[[u32; W + 1]; H]` (size can vary because of [u32; W + 1])
 
 error: the constant `W` is not of type `usize`
-  --> $DIR/transmute-fail.rs:15:5
+  --> $DIR/transmute-fail.rs:17:9
    |
-LL |     std::mem::transmute(v)
+LL |         std::mem::transmute(v)
-   |     ^^^^^^^^^^^^^^^^^^^ expected `usize`, found `bool`
+   |         ^^^^^^^^^^^^^^^^^^^ expected `usize`, found `bool`
 
 error[E0512]: cannot transmute between types of different sizes, or dependently-sized types
-  --> $DIR/transmute-fail.rs:22:5
+  --> $DIR/transmute-fail.rs:24:9
    |
-LL |     std::mem::transmute(v)
+LL |         std::mem::transmute(v)
-   |     ^^^^^^^^^^^^^^^^^^^
+   |         ^^^^^^^^^^^^^^^^^^^
    |
    = 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:29:5
+  --> $DIR/transmute-fail.rs:31:9
    |
-LL |     std::mem::transmute(v)
+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:36:5
+  --> $DIR/transmute-fail.rs:38:9
    |
-LL |     std::mem::transmute(v)
+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:49:5
+  --> $DIR/transmute-fail.rs:49:9
    |
-LL |     std::mem::transmute(v)
+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:56:5
+  --> $DIR/transmute-fail.rs:56:9
    |
-LL |     std::mem::transmute(v)
+LL |         std::mem::transmute(v)
-   |     ^^^^^^^^^^^^^^^^^^^
+   |         ^^^^^^^^^^^^^^^^^^^
    |
-   = note: source type: `[u32; H*W]` (this type does not have a fixed size)
+   = 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:65:5
+  --> $DIR/transmute-fail.rs:65:9
    |
-LL |     std::mem::transmute(v)
+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:74:5
+  --> $DIR/transmute-fail.rs:74:9
    |
-LL |     std::mem::transmute(v)
+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:81:5
+  --> $DIR/transmute-fail.rs:81:9
    |
-LL |     std::mem::transmute(v)
+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:88:5
+  --> $DIR/transmute-fail.rs:88:9
    |
-LL |     std::mem::transmute(v)
+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:95:5
+  --> $DIR/transmute-fail.rs:95:9
    |
-LL |     std::mem::transmute(v)
+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:104:5
+  --> $DIR/transmute-fail.rs:104:9
    |
-LL |     std::mem::transmute(v)
+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: aborting due to 14 previous errors
+error[E0308]: mismatched types
+  --> $DIR/transmute-fail.rs:12:53
+   |
+LL | fn bar<const W: bool, const H: usize>(v: [[u32; H]; W]) -> [[u32; W]; H] {
+   |                                                     ^ expected `usize`, found `bool`
 
-For more information about this error, try `rustc --explain E0512`.
+error[E0308]: mismatched types
+  --> $DIR/transmute-fail.rs:12:67
+   |
+LL | fn bar<const W: bool, const H: usize>(v: [[u32; H]; W]) -> [[u32; W]; H] {
+   |                                                                   ^ expected `usize`, found `bool`
+
+error: aborting due to 16 previous errors
+
+Some errors have detailed explanations: E0308, E0512.
+For more information about an error, try `rustc --explain E0308`.

tests/ui/const-generics/type_mismatch.rs

@@ -1,10 +1,12 @@
 fn foo<const N: usize>() -> [u8; N] {
     bar::<N>()
     //~^ ERROR the constant `N` is not of type `u8`
+    //~| ERROR: mismatched types
 }
 
 fn bar<const N: u8>() -> [u8; N] {}
 //~^ ERROR the constant `N` is not of type `usize`
+//~| ERROR: mismatched types
 //~| ERROR mismatched types
 
 fn main() {}

tests/ui/const-generics/type_mismatch.stderr

@@ -1,5 +1,5 @@
 error: the constant `N` is not of type `usize`
-  --> $DIR/type_mismatch.rs:6:26
+  --> $DIR/type_mismatch.rs:7:26
    |
 LL | fn bar<const N: u8>() -> [u8; N] {}
    |                          ^^^^^^^ expected `usize`, found `u8`
@@ -11,19 +11,31 @@ LL |     bar::<N>()
    |           ^ expected `u8`, found `usize`
    |
 note: required by a const generic parameter in `bar`
-  --> $DIR/type_mismatch.rs:6:8
+  --> $DIR/type_mismatch.rs:7:8
    |
 LL | fn bar<const N: u8>() -> [u8; N] {}
    |        ^^^^^^^^^^^ required by this const generic parameter in `bar`
 
 error[E0308]: mismatched types
-  --> $DIR/type_mismatch.rs:6:26
+  --> $DIR/type_mismatch.rs:7:26
    |
 LL | fn bar<const N: u8>() -> [u8; N] {}
    |    ---                   ^^^^^^^ expected `[u8; N]`, found `()`
    |    |
    |    implicitly returns `()` as its body has no tail or `return` expression
 
-error: aborting due to 3 previous errors
+error[E0308]: mismatched types
+  --> $DIR/type_mismatch.rs:2:11
+   |
+LL |     bar::<N>()
+   |           ^ expected `u8`, found `usize`
+
+error[E0308]: mismatched types
+  --> $DIR/type_mismatch.rs:7:31
+   |
+LL | fn bar<const N: u8>() -> [u8; N] {}
+   |                               ^ expected `usize`, found `u8`
+
+error: aborting due to 5 previous errors
 
 For more information about this error, try `rustc --explain E0308`.

tests/ui/consts/issue-36163.stderr

@@ -1,10 +1,10 @@
-error[E0391]: cycle detected when simplifying constant for the type system `Foo::{constant#0}`
+error[E0391]: cycle detected when simplifying constant for the type system `Foo::B::{constant#0}`
   --> $DIR/issue-36163.rs:4:9
    |
 LL |     B = A,
    |         ^
    |
-note: ...which requires const-evaluating + checking `Foo::{constant#0}`...
+note: ...which requires const-evaluating + checking `Foo::B::{constant#0}`...
   --> $DIR/issue-36163.rs:4:9
    |
 LL |     B = A,
@@ -19,7 +19,7 @@ note: ...which requires const-evaluating + checking `A`...
    |
 LL | const A: isize = Foo::B as isize;
    |                  ^^^^^^^^^^^^^^^
-   = note: ...which again requires simplifying constant for the type system `Foo::{constant#0}`, completing the cycle
+   = note: ...which again requires simplifying constant for the type system `Foo::B::{constant#0}`, completing the cycle
 note: cycle used when checking that `Foo` is well-formed
   --> $DIR/issue-36163.rs:3:1
    |

tests/ui/feature-gates/feature-gate-const-arg-path.rs

@@ -0,0 +1,5 @@
+//@ check-pass
+
+// this doesn't really have any user facing impact....
+
+fn main() {}

tests/ui/lifetimes/issue-95023.rs

@@ -2,12 +2,13 @@ struct ErrorKind;
 struct Error(ErrorKind);
 impl Fn(&isize) for Error {
     //~^ ERROR manual implementations of `Fn` are experimental [E0183]
-    //~^^ ERROR associated item constraints are not allowed here [E0229]
+    //~| ERROR associated item constraints are not allowed here [E0229]
     //~| ERROR not all trait items implemented
     //~| ERROR expected a `FnMut(&isize)` closure, found `Error`
     fn foo<const N: usize>(&self) -> Self::B<{ N }>;
     //~^ ERROR associated function in `impl` without body
-    //~^^ ERROR method `foo` is not a member of trait `Fn` [E0407]
+    //~| ERROR method `foo` is not a member of trait `Fn` [E0407]
-    //~^^^ ERROR associated type `B` not found for `Self` [E0220]
+    //~| ERROR associated type `B` not found for `Self` [E0220]
+    //~| ERROR: associated type `B` not found for `Self`
 }
 fn main() {}

tests/ui/lifetimes/issue-95023.stderr

@@ -56,7 +56,15 @@ error[E0220]: associated type `B` not found for `Self`
 LL |     fn foo<const N: usize>(&self) -> Self::B<{ N }>;
    |                                            ^ help: `Self` has the following associated type: `Output`
 
-error: aborting due to 7 previous errors
+error[E0220]: associated type `B` not found for `Self`
+  --> $DIR/issue-95023.rs:8:44
+   |
+LL |     fn foo<const N: usize>(&self) -> Self::B<{ N }>;
+   |                                            ^ help: `Self` has the following associated type: `Output`
+   |
+   = note: duplicate diagnostic emitted due to `-Z deduplicate-diagnostics=no`
+
+error: aborting due to 8 previous errors
 
 Some errors have detailed explanations: E0046, E0183, E0220, E0229, E0277, E0407.
 For more information about an error, try `rustc --explain E0046`.

tests/ui/specialization/default-proj-ty-as-type-of-const-issue-125757.rs

@@ -14,5 +14,6 @@ struct Wrapper<const C: <i32 as Trait>::Type> {}
 
 impl<const C: usize> Wrapper<C> {}
 //~^ ERROR the constant `C` is not of type `<i32 as Trait>::Type`
+//~| ERROR: mismatched types
 
 fn main() {}

tests/ui/specialization/default-proj-ty-as-type-of-const-issue-125757.stderr

@@ -20,5 +20,17 @@ note: required by a const generic parameter in `Wrapper`
 LL | struct Wrapper<const C: <i32 as Trait>::Type> {}
    |                ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ required by this const generic parameter in `Wrapper`
 
-error: aborting due to 2 previous errors
+error[E0308]: mismatched types
+  --> $DIR/default-proj-ty-as-type-of-const-issue-125757.rs:15:30
+   |
+LL | impl<const C: usize> Wrapper<C> {}
+   |                              ^ expected associated type, found `usize`
+   |
+   = note: expected associated type `<i32 as Trait>::Type`
+                         found type `usize`
+   = help: consider constraining the associated type `<i32 as Trait>::Type` to `usize`
+   = note: for more information, visit https://doc.rust-lang.org/book/ch19-03-advanced-traits.html
 
+error: aborting due to 3 previous errors
+
+For more information about this error, try `rustc --explain E0308`.

tests/ui/specialization/min_specialization/bad-const-wf-doesnt-specialize.rs

@@ -6,6 +6,7 @@
 struct S<const L: usize>;
 
 impl<const N: i32> Copy for S<N> {}
+//~^ ERROR: mismatched types
 impl<const M: usize> Copy for S<M> {}
 //~^ ERROR: conflicting implementations of trait `Copy` for type `S<_>`
 

tests/ui/specialization/min_specialization/bad-const-wf-doesnt-specialize.stderr

@@ -1,11 +1,19 @@
 error[E0119]: conflicting implementations of trait `Copy` for type `S<_>`
-  --> $DIR/bad-const-wf-doesnt-specialize.rs:9:1
+  --> $DIR/bad-const-wf-doesnt-specialize.rs:10:1
    |
 LL | impl<const N: i32> Copy for S<N> {}
    | -------------------------------- first implementation here
+LL |
 LL | impl<const M: usize> Copy for S<M> {}
    | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ conflicting implementation for `S<_>`
 
-error: aborting due to 1 previous error
+error[E0308]: mismatched types
+  --> $DIR/bad-const-wf-doesnt-specialize.rs:8:31
+   |
+LL | impl<const N: i32> Copy for S<N> {}
+   |                               ^ expected `usize`, found `i32`
 
-For more information about this error, try `rustc --explain E0119`.
+error: aborting due to 2 previous errors
+
+Some errors have detailed explanations: E0119, E0308.
+For more information about an error, try `rustc --explain E0119`.

tests/ui/transmutability/issue-101739-1.rs

@@ -6,7 +6,8 @@ mod assert {
     pub fn is_transmutable<Src, const ASSUME_ALIGNMENT: bool>()
     where
         Dst: BikeshedIntrinsicFrom<Src, ASSUME_ALIGNMENT>, //~ ERROR cannot find type `Dst` in this scope
-        //~^ the constant `ASSUME_ALIGNMENT` is not of type `Assume`
+                                                           //~| the constant `ASSUME_ALIGNMENT` is not of type `Assume`
+                                                           //~| ERROR: mismatched types
     {
     }
 }

tests/ui/transmutability/issue-101739-1.stderr

@@ -13,6 +13,13 @@ LL |         Dst: BikeshedIntrinsicFrom<Src, ASSUME_ALIGNMENT>,
 note: required by a const generic parameter in `BikeshedIntrinsicFrom`
   --> $SRC_DIR/core/src/mem/transmutability.rs:LL:COL
 
-error: aborting due to 2 previous errors
+error[E0308]: mismatched types
+  --> $DIR/issue-101739-1.rs:8:41
+   |
+LL |         Dst: BikeshedIntrinsicFrom<Src, ASSUME_ALIGNMENT>,
+   |                                         ^^^^^^^^^^^^^^^^ expected `Assume`, found `bool`
 
-For more information about this error, try `rustc --explain E0412`.
+error: aborting due to 3 previous errors
+
+Some errors have detailed explanations: E0308, E0412.
+For more information about an error, try `rustc --explain E0308`.

tests/ui/transmutability/issue-101739-2.rs

@@ -14,19 +14,23 @@ mod assert {
         const ASSUME_VISIBILITY: bool,
     >()
     where
-        Dst: BikeshedIntrinsicFrom< //~ ERROR trait takes at most 2 generic arguments but 5 generic arguments were supplied
+        Dst: BikeshedIntrinsicFrom<
-            Src,
+                //~^ ERROR trait takes at most 2 generic arguments but 5 generic arguments were supplied
-            ASSUME_ALIGNMENT,
+                Src,
-            ASSUME_LIFETIMES,
+                ASSUME_ALIGNMENT, //~ ERROR: mismatched types
-            ASSUME_VALIDITY,
+                ASSUME_LIFETIMES,
-            ASSUME_VISIBILITY,
+                ASSUME_VALIDITY,
-        >,
+                ASSUME_VISIBILITY,
-    {}
+            >,
+    {
+    }
 }
 
 fn via_const() {
-    #[repr(C)] struct Src;
+    #[repr(C)]
-    #[repr(C)] struct Dst;
+    struct Src;
+    #[repr(C)]
+    struct Dst;
 
     const FALSE: bool = false;
 

tests/ui/transmutability/issue-101739-2.stderr

@@ -3,14 +3,21 @@ error[E0107]: trait takes at most 2 generic arguments but 5 generic arguments we
    |
 LL |           Dst: BikeshedIntrinsicFrom<
    |                ^^^^^^^^^^^^^^^^^^^^^ expected at most 2 generic arguments
-LL |               Src,
+...
-LL |               ASSUME_ALIGNMENT,
+LL |                   ASSUME_ALIGNMENT,
-   |  _____________________________-
+   |  _________________________________-
-LL | |             ASSUME_LIFETIMES,
+LL | |                 ASSUME_LIFETIMES,
-LL | |             ASSUME_VALIDITY,
+LL | |                 ASSUME_VALIDITY,
-LL | |             ASSUME_VISIBILITY,
+LL | |                 ASSUME_VISIBILITY,
-   | |_____________________________- help: remove the unnecessary generic arguments
+   | |_________________________________- help: remove the unnecessary generic arguments
 
-error: aborting due to 1 previous error
+error[E0308]: mismatched types
+  --> $DIR/issue-101739-2.rs:20:17
+   |
+LL |                 ASSUME_ALIGNMENT,
+   |                 ^^^^^^^^^^^^^^^^ expected `Assume`, found `bool`
 
-For more information about this error, try `rustc --explain E0107`.
+error: aborting due to 2 previous errors
+
+Some errors have detailed explanations: E0107, E0308.
+For more information about an error, try `rustc --explain E0107`.

tests/ui/typeck/issue-114918/const-in-impl-fn-return-type.rs

@@ -3,16 +3,18 @@
 // of an impl fn produces a type mismatch error instead of triggering
 // a const eval cycle
 
-
 trait Trait {
-    fn func<const N: u32>() -> [ (); N ]; //~ ERROR the constant `N` is not of type `usize`
+    fn func<const N: u32>() -> [(); N];
+    //~^ ERROR: the constant `N` is not of type `usize`
+    //~| ERROR: mismatched types
 }
 
 struct S {}
 
 #[allow(unused_braces)]
 impl Trait for S {
-    fn func<const N: u32>() -> [ (); { () }] { //~ ERROR mismatched types
+    fn func<const N: u32>() -> [(); { () }] {
+        //~^ ERROR mismatched types
         N
     }
 }

tests/ui/typeck/issue-114918/const-in-impl-fn-return-type.stderr

@@ -1,15 +1,21 @@
 error[E0308]: mismatched types
-  --> $DIR/const-in-impl-fn-return-type.rs:15:40
+  --> $DIR/const-in-impl-fn-return-type.rs:16:39
    |
-LL |     fn func<const N: u32>() -> [ (); { () }] {
+LL |     fn func<const N: u32>() -> [(); { () }] {
-   |                                        ^^ expected `usize`, found `()`
+   |                                       ^^ expected `usize`, found `()`
 
 error: the constant `N` is not of type `usize`
-  --> $DIR/const-in-impl-fn-return-type.rs:8:32
+  --> $DIR/const-in-impl-fn-return-type.rs:7:32
    |
-LL |     fn func<const N: u32>() -> [ (); N ];
+LL |     fn func<const N: u32>() -> [(); N];
-   |                                ^^^^^^^^^ expected `usize`, found `u32`
+   |                                ^^^^^^^ expected `usize`, found `u32`
 
-error: aborting due to 2 previous errors
+error[E0308]: mismatched types
+  --> $DIR/const-in-impl-fn-return-type.rs:7:37
+   |
+LL |     fn func<const N: u32>() -> [(); N];
+   |                                     ^ expected `usize`, found `u32`
+
+error: aborting due to 3 previous errors
 
 For more information about this error, try `rustc --explain E0308`.