Use param's real type in try_eval_lit_or_param

compiler/rustc_middle/src/ty/consts.rs

@@ -135,6 +135,9 @@ impl<'tcx> Const<'tcx> {
                 _,
                 &hir::Path { res: Res::Def(DefKind::ConstParam, def_id), .. },
             )) => {
+                // Use the type from the param's definition, since we can resolve it,
+                // not the expected parameter type from WithOptConstParam.
+                let param_ty = tcx.type_of(def_id).subst_identity();
                 match tcx.named_bound_var(expr.hir_id) {
                     Some(rbv::ResolvedArg::EarlyBound(_)) => {
                         // Find the name and index of the const parameter by indexing the generics of
@@ -143,14 +146,14 @@ impl<'tcx> Const<'tcx> {
                         let generics = tcx.generics_of(item_def_id);
                         let index = generics.param_def_id_to_index[&def_id];
                         let name = tcx.item_name(def_id);
-                        Some(tcx.mk_const(ty::ParamConst::new(index, name), ty))
+                        Some(tcx.mk_const(ty::ParamConst::new(index, name), param_ty))
                     }
                     Some(rbv::ResolvedArg::LateBound(debruijn, index, _)) => Some(tcx.mk_const(
                         ty::ConstKind::Bound(debruijn, ty::BoundVar::from_u32(index)),
-                        ty,
+                        param_ty,
                     )),
                     Some(rbv::ResolvedArg::Error(guar)) => {
-                        Some(tcx.const_error_with_guaranteed(ty, guar))
+                        Some(tcx.const_error_with_guaranteed(param_ty, guar))
                     }
                     arg => bug!("unexpected bound var resolution for {:?}: {arg:?}", expr.hir_id),
                 }

compiler/rustc_trait_selection/src/traits/specialize/mod.rs

@@ -99,10 +99,10 @@ pub fn translate_substs<'tcx>(
             }
 
             fulfill_implication(infcx, param_env, source_trait_ref, target_impl).unwrap_or_else(
-                |_| {
+                |()| {
                     bug!(
-                        "When translating substitutions for specialization, the expected \
-                         specialization failed to hold"
+                        "When translating substitutions from {source_impl:?} to {target_impl:?}, \
+                        the expected specialization failed to hold"
                     )
                 },
             )

tests/ui/const-generics/type_mismatch.rs

@@ -1,5 +1,6 @@
 fn foo<const N: usize>() -> [u8; N] {
     bar::<N>() //~ ERROR mismatched types
+    //~^ ERROR the constant `N` is not of type `u8`
 }
 
 fn bar<const N: u8>() -> [u8; N] {}

tests/ui/const-generics/type_mismatch.stderr

@@ -1,23 +1,35 @@
+error: the constant `N` is not of type `u8`
+  --> $DIR/type_mismatch.rs:2:5
+   |
+LL |     bar::<N>()
+   |     ^^^^^^^^
+   |
+note: required by a bound in `bar`
+  --> $DIR/type_mismatch.rs:6:8
+   |
+LL | fn bar<const N: u8>() -> [u8; N] {}
+   |        ^^^^^^^^^^^ required by this bound in `bar`
+
 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:5:26
+  --> $DIR/type_mismatch.rs:6:26
    |
 LL | fn bar<const N: u8>() -> [u8; N] {}
    |    ---                   ^^^^^^^ expected `[u8; N]`, found `()`
    |    |
    |    implicitly returns `()` as its body has no tail or `return` expression
 
 error[E0308]: mismatched types
-  --> $DIR/type_mismatch.rs:5:31
+  --> $DIR/type_mismatch.rs:6:31
    |
 LL | fn bar<const N: u8>() -> [u8; N] {}
    |                               ^ expected `usize`, found `u8`
 
-error: aborting due to 3 previous errors
+error: aborting due to 4 previous errors
 
 For more information about this error, try `rustc --explain E0308`.

tests/ui/const-generics/type_not_in_scope.rs

@@ -6,6 +6,5 @@ impl X {
 }
 fn getn<const N: cfg_attr>() -> [u8; N] {}
 //~^ ERROR expected type, found built-in attribute `cfg_attr`
-//~| ERROR mismatched types
 
 fn main() {}

tests/ui/const-generics/type_not_in_scope.stderr

@@ -10,15 +10,7 @@ error[E0573]: expected type, found built-in attribute `cfg_attr`
 LL | fn getn<const N: cfg_attr>() -> [u8; N] {}
    |                  ^^^^^^^^ not a type
 
-error[E0308]: mismatched types
-  --> $DIR/type_not_in_scope.rs:7:33
-   |
-LL | fn getn<const N: cfg_attr>() -> [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: aborting due to 2 previous errors
 
-Some errors have detailed explanations: E0308, E0412, E0573.
-For more information about an error, try `rustc --explain E0308`.
+Some errors have detailed explanations: E0412, E0573.
+For more information about an error, try `rustc --explain E0412`.

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

@@ -0,0 +1,12 @@
+#![feature(min_specialization)]
+
+// An impl that has an erroneous const substitution should not specialize one
+// that is well-formed.
+
+struct S<const L: usize>;
+
+impl<const N: i32> Copy for S<N> {}
+impl<const M: usize> Copy for S<M> {}
+//~^ ERROR conflicting implementations of trait `Copy` for type `S<_>`
+
+fn main() {}

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

@@ -0,0 +1,11 @@
+error[E0119]: conflicting implementations of trait `Copy` for type `S<_>`
+  --> $DIR/bad-const-wf-doesnt-specialize.rs:9:1
+   |
+LL | impl<const N: i32> Copy for S<N> {}
+   | -------------------------------- first implementation here
+LL | impl<const M: usize> Copy for S<M> {}
+   | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ conflicting implementation for `S<_>`
+
+error: aborting due to previous error
+
+For more information about this error, try `rustc --explain E0119`.

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

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

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

@@ -4,13 +4,15 @@ error[E0412]: cannot find type `Dst` in this scope
 LL |         Dst: BikeshedIntrinsicFrom<Src, Context, ASSUME_ALIGNMENT>,
    |         ^^^ not found in this scope
 
-error[E0308]: mismatched types
-  --> $DIR/issue-101739-1.rs:8:50
+error: the constant `ASSUME_ALIGNMENT` is not of type `Assume`
+  --> $DIR/issue-101739-1.rs:8:14
    |
 LL |         Dst: BikeshedIntrinsicFrom<Src, Context, ASSUME_ALIGNMENT>,
-   |                                                  ^^^^^^^^^^^^^^^^ expected `Assume`, found `bool`
+   |              ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+   |
+note: required by a bound in `BikeshedIntrinsicFrom`
+  --> $SRC_DIR/core/src/mem/transmutability.rs:LL:COL
 
 error: aborting due to 2 previous errors
 
-Some errors have detailed explanations: E0308, E0412.
-For more information about an error, try `rustc --explain E0308`.
+For more information about this error, try `rustc --explain E0412`.