Register ConstArgHasType obligation when normalizing inherent projection consts

Author: lapla-cogito

compiler/rustc_next_trait_solver/src/solve/normalizes_to/inherent.rs

@@ -5,6 +5,7 @@
 //! 2. equate the self type, and
 //! 3. instantiate and register where clauses.
 
+use rustc_type_ir::inherent::*;
 use rustc_type_ir::{self as ty, Interner};
 
 use crate::delegate::SolverDelegate;
@@ -51,11 +52,20 @@ where
                 .map(|pred| goal.with(cx, pred)),
         );
 
-        let normalized = if inherent.kind(cx).is_type() {
+        let normalized: I::Term = if inherent.kind(cx).is_type() {
             cx.type_of(inherent.def_id).instantiate(cx, inherent_args).into()
         } else {
             cx.const_of_item(inherent.def_id).instantiate(cx, inherent_args).into()
         };
+
+        if let Some(ct) = normalized.as_const() {
+            let expected_ty = cx.type_of(inherent.def_id).instantiate(cx, inherent_args);
+            self.add_goal(
+                GoalSource::Misc,
+                goal.with(cx, ty::ClauseKind::ConstArgHasType(ct, expected_ty)),
+            );
+        }
+
         self.instantiate_normalizes_to_term(goal, normalized);
         self.evaluate_added_goals_and_make_canonical_response(Certainty::Yes)
     }

compiler/rustc_trait_selection/src/traits/project.rs

@@ -549,6 +549,17 @@ pub fn normalize_inherent_projection<'a, 'b, 'tcx>(
         tcx.const_of_item(alias_term.def_id).instantiate(tcx, args).into()
     };
 
+    if let Some(ct) = term.as_const() {
+        let expected_ty = tcx.type_of(alias_term.def_id).instantiate(tcx, args);
+        obligations.push(Obligation::with_depth(
+            tcx,
+            cause.clone(),
+            depth + 1,
+            param_env,
+            ty::ClauseKind::ConstArgHasType(ct, expected_ty),
+        ));
+    }
+
     let mut term = selcx.infcx.resolve_vars_if_possible(term);
     if term.has_aliases() {
         term =

tests/ui/const-generics/mgca/type-const-inherent-value-type-mismatch.current.stderr

@@ -0,0 +1,17 @@
+error: the constant `"this isn't a usize"` is not of type `usize`
+  --> $DIR/type-const-inherent-value-type-mismatch.rs:14:5
+   |
+LL |     type const N: usize = "this isn't a usize";
+   |     ^^^^^^^^^^^^^^^^^^^ expected `usize`, found `&'static str`
+
+error[E0308]: mismatched types
+  --> $DIR/type-const-inherent-value-type-mismatch.rs:18:11
+   |
+LL | fn f() -> [u8; const { Struct::N }] {}
+   |    -      ^^^^^^^^^^^^^^^^^^^^^^^^^ expected `[u8; const { Struct::N }]`, found `()`
+   |    |
+   |    implicitly returns `()` as its body has no tail or `return` expression
+
+error: aborting due to 2 previous errors
+
+For more information about this error, try `rustc --explain E0308`.

tests/ui/const-generics/mgca/type-const-inherent-value-type-mismatch.next.stderr

@@ -0,0 +1,24 @@
+error[E0284]: type annotations needed: cannot normalize `f::{constant#0}`
+  --> $DIR/type-const-inherent-value-type-mismatch.rs:18:11
+   |
+LL | fn f() -> [u8; const { Struct::N }] {}
+   |           ^^^^^^^^^^^^^^^^^^^^^^^^^ cannot normalize `f::{constant#0}`
+
+error: the constant `"this isn't a usize"` is not of type `usize`
+  --> $DIR/type-const-inherent-value-type-mismatch.rs:14:5
+   |
+LL |     type const N: usize = "this isn't a usize";
+   |     ^^^^^^^^^^^^^^^^^^^ expected `usize`, found `&'static str`
+
+error[E0308]: mismatched types
+  --> $DIR/type-const-inherent-value-type-mismatch.rs:18:11
+   |
+LL | fn f() -> [u8; const { Struct::N }] {}
+   |    -      ^^^^^^^^^^^^^^^^^^^^^^^^^ expected `[u8; const { Struct::N }]`, found `()`
+   |    |
+   |    implicitly returns `()` as its body has no tail or `return` expression
+
+error: aborting due to 3 previous errors
+
+Some errors have detailed explanations: E0284, E0308.
+For more information about an error, try `rustc --explain E0284`.

tests/ui/const-generics/mgca/type-const-inherent-value-type-mismatch.rs

@@ -0,0 +1,22 @@
+// Regression test for https://github.com/rust-lang/rust/issues/152962
+
+//@ revisions: current next
+//@ ignore-compare-mode-next-solver (explicit revisions)
+//@[next] compile-flags: -Znext-solver
+//@ compile-flags: -Zvalidate-mir
+
+#![feature(min_generic_const_args)]
+#![expect(incomplete_features)]
+
+struct Struct;
+
+impl Struct {
+    type const N: usize = "this isn't a usize";
+    //~^ ERROR the constant `"this isn't a usize"` is not of type `usize`
+}
+
+fn f() -> [u8; const { Struct::N }] {}
+//~^ ERROR mismatched types [E0308]
+//[next]~| ERROR type annotations needed
+
+fn main() {}