Fail relating constants of different types

Author: oli-obk

compiler/rustc_infer/src/infer/relate/combine.rs

@@ -168,7 +168,7 @@ impl<'tcx> InferCtxt<'tcx> {
         // ourselves with a check to find bugs being required for code to compile because it made inference progress.
         self.probe(|_| {
             if a.ty() == b.ty() {
-                return;
+                return Ok(());
             }
 
             // We don't have access to trait solving machinery in `rustc_infer` so the logic for determining if the
@@ -178,18 +178,15 @@ impl<'tcx> InferCtxt<'tcx> {
                 relation.param_env().and((a.ty(), b.ty())),
                 &mut OriginalQueryValues::default(),
             );
-            self.tcx.check_tys_might_be_eq(canonical).unwrap_or_else(|_| {
+            self.tcx.check_tys_might_be_eq(canonical).map_err(|_| {
                 // The error will only be reported later. If we emit an ErrorGuaranteed
                 // here, then we will never get to the code that actually emits the error.
                 self.tcx.dcx().delayed_bug(format!(
                     "cannot relate consts of different types (a={a:?}, b={b:?})",
                 ));
-                // We treat these constants as if they were of the same type, so that any
-                // such constants being used in impls make these impls match barring other mismatches.
-                // This helps with diagnostics down the road.
-            });
-        });
-
+                TypeError::Mismatch
+            })
+        })?;
         match (a.kind(), b.kind()) {
             (
                 ty::ConstKind::Infer(InferConst::Var(a_vid)),

tests/crashes/121585-1.rs

@@ -11,4 +11,4 @@ impl<const N: u64> Q for [u8; N] {
 }
 
 pub fn test() -> [u8; <[u8; 13] as Q>::ASSOC] { todo!() }
-//~^ ERROR: the constant `13` is not of type `u64`
+//~^ ERROR: `[u8; 13]: Q` is not satisfied

tests/crashes/121585-2.rs

@@ -1,16 +1,10 @@
-error: the constant `13` is not of type `u64`
+error[E0277]: the trait bound `[u8; 13]: Q` is not satisfied
   --> $DIR/bad-subst-const-kind.rs:13:24
    |
 LL | pub fn test() -> [u8; <[u8; 13] as Q>::ASSOC] { todo!() }
-   |                        ^^^^^^^^ expected `u64`, found `usize`
+   |                        ^^^^^^^^ the trait `Q` is not implemented for `[u8; 13]`
    |
-note: required for `[u8; 13]` to implement `Q`
-  --> $DIR/bad-subst-const-kind.rs:8:20
-   |
-LL | impl<const N: u64> Q for [u8; N] {
-   |      ------------  ^     ^^^^^^^
-   |      |
-   |      unsatisfied trait bound introduced here
+   = help: the trait `Q` is implemented for `[u8; N]`
 
 error[E0308]: mismatched types
   --> $DIR/bad-subst-const-kind.rs:8:31
@@ -20,4 +14,5 @@ LL | impl<const N: u64> Q for [u8; N] {
 
 error: aborting due to 2 previous errors
 
-For more information about this error, try `rustc --explain E0308`.
+Some errors have detailed explanations: E0277, E0308.
+For more information about an error, try `rustc --explain E0277`.

tests/crashes/121858-2.rs

@@ -10,7 +10,7 @@ impl<const N: u64> Q for [u8; N] {}
 //~| ERROR mismatched types
 
 pub fn q_user() -> [u8; <[u8; 13] as Q>::ASSOC] {}
-//~^ ERROR the constant `13` is not of type `u64`
+//~^ ERROR `[u8; 13]: Q` is not satisfied
 //~| ERROR mismatched types
 
 pub fn main() {}

tests/crashes/124151.rs

@@ -7,19 +7,13 @@ LL |     const ASSOC: usize;
 LL | impl<const N: u64> Q for [u8; N] {}
    | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ missing `ASSOC` in implementation
 
-error: the constant `13` is not of type `u64`
+error[E0277]: the trait bound `[u8; 13]: Q` is not satisfied
   --> $DIR/type_mismatch.rs:12:26
    |
 LL | pub fn q_user() -> [u8; <[u8; 13] as Q>::ASSOC] {}
-   |                          ^^^^^^^^ expected `u64`, found `usize`
+   |                          ^^^^^^^^ the trait `Q` is not implemented for `[u8; 13]`
    |
-note: required for `[u8; 13]` to implement `Q`
-  --> $DIR/type_mismatch.rs:8:20
-   |
-LL | impl<const N: u64> Q for [u8; N] {}
-   |      ------------  ^     ^^^^^^^
-   |      |
-   |      unsatisfied trait bound introduced here
+   = help: the trait `Q` is implemented for `[u8; N]`
 
 error[E0308]: mismatched types
   --> $DIR/type_mismatch.rs:12:20
@@ -37,5 +31,5 @@ LL | impl<const N: u64> Q for [u8; N] {}
 
 error: aborting due to 4 previous errors
 
-Some errors have detailed explanations: E0046, E0308.
+Some errors have detailed explanations: E0046, E0277, E0308.
 For more information about an error, try `rustc --explain E0046`.

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

@@ -1,14 +1,17 @@
-//@ known-bug: #121858
 #![feature(generic_const_exprs)]
+#![allow(incomplete_features)]
 
 struct Outer<const A: i64, const B: usize>();
 impl<const A: usize, const B: usize> Outer<A, B>
+//~^ ERROR: `A` is not of type `i64`
+//~| ERROR: mismatched types
 where
     [(); A + (B * 2)]:,
 {
-    fn o() -> Union {}
+    fn o() {}
 }
 
 fn main() {
     Outer::<1, 1>::o();
+    //~^ ERROR: no function or associated item named `o` found
 }