mGCA: Add associated const type check

compiler/rustc_hir_analysis/src/check/wfcheck.rs

@@ -1569,11 +1569,40 @@ pub(super) fn check_where_clauses<'tcx>(wfcx: &WfCheckingCtxt<'_, 'tcx>, def_id:
 
     let predicates = predicates.instantiate_identity(tcx);
 
+    let assoc_const_obligations: Vec<_> = predicates
+        .predicates
+        .iter()
+        .copied()
+        .zip(predicates.spans.iter().copied())
+        .filter_map(|(clause, sp)| {
+            let proj = clause.as_projection_clause()?;
+            let pred_binder = proj
+                .map_bound(|pred| {
+                    pred.term.as_const().map(|ct| {
+                        let assoc_const_ty = tcx
+                            .type_of(pred.projection_term.def_id)
+                            .instantiate(tcx, pred.projection_term.args);
+                        ty::ClauseKind::ConstArgHasType(ct, assoc_const_ty)
+                    })
+                })
+                .transpose();
+            pred_binder.map(|pred_binder| {
+                let cause = traits::ObligationCause::new(
+                    sp,
+                    wfcx.body_def_id,
+                    ObligationCauseCode::WhereClause(def_id.to_def_id(), sp),
+                );
+                Obligation::new(tcx, cause, wfcx.param_env, pred_binder)
+            })
+        })
+        .collect();
+
     assert_eq!(predicates.predicates.len(), predicates.spans.len());
     let wf_obligations = predicates.into_iter().flat_map(|(p, sp)| {
         traits::wf::clause_obligations(infcx, wfcx.param_env, wfcx.body_def_id, p, sp)
     });
-    let obligations: Vec<_> = wf_obligations.chain(default_obligations).collect();
+    let obligations: Vec<_> =
+        wf_obligations.chain(default_obligations).chain(assoc_const_obligations).collect();
     wfcx.register_obligations(obligations);
 }
 

compiler/rustc_trait_selection/src/traits/wf.rs

@@ -951,6 +951,34 @@ impl<'a, 'tcx> TypeVisitor<TyCtxt<'tcx>> for WfPredicates<'a, 'tcx> {
                         ty::Binder::dummy(ty::PredicateKind::DynCompatible(principal)),
                     ));
                 }
+
+                if !t.has_escaping_bound_vars() {
+                    for projection in data.projection_bounds() {
+                        let pred_binder = projection
+                            .with_self_ty(tcx, t)
+                            .map_bound(|p| {
+                                p.term.as_const().map(|ct| {
+                                    let assoc_const_ty = tcx
+                                        .type_of(p.projection_term.def_id)
+                                        .instantiate(tcx, p.projection_term.args);
+                                    ty::PredicateKind::Clause(ty::ClauseKind::ConstArgHasType(
+                                        ct,
+                                        assoc_const_ty,
+                                    ))
+                                })
+                            })
+                            .transpose();
+                        if let Some(pred_binder) = pred_binder {
+                            self.out.push(traits::Obligation::with_depth(
+                                tcx,
+                                self.cause(ObligationCauseCode::WellFormed(None)),
+                                self.recursion_depth,
+                                self.param_env,
+                                pred_binder,
+                            ));
+                        }
+                    }
+                }
             }
 
             // Inference variables are the complicated case, since we don't

tests/ui/const-generics/associated-const-bindings/dyn-compat-const-projection-behind-trait-alias-mentions-self.rs

@@ -15,6 +15,7 @@ trait Trait {
 struct Hold<T: ?Sized>(T);
 
 trait Bound = Trait<Y = { Hold::<Self> }>;
+//~^ ERROR the constant `Hold::<Self>` is not of type `i32`
 
 fn main() {
     let _: dyn Bound; //~ ERROR associated constant binding in trait object type mentions `Self`

tests/ui/const-generics/associated-const-bindings/dyn-compat-const-projection-behind-trait-alias-mentions-self.stderr

@@ -1,11 +1,23 @@
+error: the constant `Hold::<Self>` is not of type `i32`
+  --> $DIR/dyn-compat-const-projection-behind-trait-alias-mentions-self.rs:17:21
+   |
+LL | trait Bound = Trait<Y = { Hold::<Self> }>;
+   |                     ^^^^^^^^^^^^^^^^^^^^ expected `i32`, found struct constructor
+   |
+note: required by a const generic parameter in `Bound`
+  --> $DIR/dyn-compat-const-projection-behind-trait-alias-mentions-self.rs:17:21
+   |
+LL | trait Bound = Trait<Y = { Hold::<Self> }>;
+   |                     ^^^^^^^^^^^^^^^^^^^^ required by this const generic parameter in `Bound`
+
 error: associated constant binding in trait object type mentions `Self`
-  --> $DIR/dyn-compat-const-projection-behind-trait-alias-mentions-self.rs:20:12
+  --> $DIR/dyn-compat-const-projection-behind-trait-alias-mentions-self.rs:21:12
    |
 LL | trait Bound = Trait<Y = { Hold::<Self> }>;
    |                     -------------------- this binding mentions `Self`
 ...
 LL |     let _: dyn Bound;
    |            ^^^^^^^^^ contains a mention of `Self`
 
-error: aborting due to 1 previous error
+error: aborting due to 2 previous errors
 

tests/ui/const-generics/associated-const-bindings/dyn-const-projection-escaping-bound-vars.rs

@@ -0,0 +1,11 @@
+//! Check associated const binding with escaping bound vars doesn't cause ICE
+//! (#151642)
+//@ check-pass
+
+#![feature(min_generic_const_args)]
+#![expect(incomplete_features)]
+
+trait Trait2<'a> { type const ASSOC: i32; }
+fn g(_: for<'a> fn(Box<dyn Trait2<'a, ASSOC = 10>>)) {}
+
+fn main() {}

tests/ui/const-generics/associated-const-bindings/wf-mismatch-1.rs

@@ -0,0 +1,11 @@
+//! Check that we correctly handle associated const bindings
+//! in `impl Trait` where the RHS is a const param (#151642).
+
+#![feature(min_generic_const_args)]
+#![expect(incomplete_features)]
+
+trait Trait { type const CT: bool; }
+
+fn f<const N: i32>(_: impl Trait<CT = { N }>) {}
+//~^ ERROR the constant `N` is not of type `bool`
+fn main() {}

tests/ui/const-generics/associated-const-bindings/wf-mismatch-1.stderr

@@ -0,0 +1,14 @@
+error: the constant `N` is not of type `bool`
+  --> $DIR/wf-mismatch-1.rs:9:34
+   |
+LL | fn f<const N: i32>(_: impl Trait<CT = { N }>) {}
+   |                                  ^^^^^^^^^^ expected `bool`, found `i32`
+   |
+note: required by a const generic parameter in `f`
+  --> $DIR/wf-mismatch-1.rs:9:34
+   |
+LL | fn f<const N: i32>(_: impl Trait<CT = { N }>) {}
+   |                                  ^^^^^^^^^^ required by this const generic parameter in `f`
+
+error: aborting due to 1 previous error
+

tests/ui/const-generics/associated-const-bindings/wf-mismatch-2.rs

@@ -0,0 +1,13 @@
+//! Check that we correctly handle associated const bindings
+//! in `dyn Trait` where the RHS is a const param (#151642).
+
+#![feature(min_generic_const_args)]
+#![expect(incomplete_features)]
+
+trait Trait { type const CT: bool; }
+
+fn f<const N: i32>() {
+    let _: dyn Trait<CT = { N }>;
+    //~^ ERROR the constant `N` is not of type `bool`
+}
+fn main() {}

tests/ui/const-generics/associated-const-bindings/wf-mismatch-2.stderr

@@ -0,0 +1,8 @@
+error: the constant `N` is not of type `bool`
+  --> $DIR/wf-mismatch-2.rs:10:12
+   |
+LL |     let _: dyn Trait<CT = { N }>;
+   |            ^^^^^^^^^^^^^^^^^^^^^ expected `bool`, found `i32`
+
+error: aborting due to 1 previous error
+

tests/ui/const-generics/associated-const-bindings/wf-mismatch-3.rs

@@ -0,0 +1,17 @@
+//! Check that we correctly handle associated const bindings
+//! where the RHS is a normalizable const projection (#151642).
+
+#![feature(min_generic_const_args)]
+#![expect(incomplete_features)]
+
+trait Trait { type const CT: bool; }
+
+trait Bound { type const N: u32; }
+impl Bound for () { type const N: u32 = 0; }
+
+fn f() { let _: dyn Trait<CT = { <() as Bound>::N }>; }
+//~^ ERROR the constant `0` is not of type `bool`
+fn g(_: impl Trait<CT = { <() as Bound>::N }>) {}
+//~^ ERROR the constant `0` is not of type `bool`
+
+fn main() {}

tests/ui/const-generics/associated-const-bindings/wf-mismatch-3.stderr

@@ -0,0 +1,20 @@
+error: the constant `0` is not of type `bool`
+  --> $DIR/wf-mismatch-3.rs:14:20
+   |
+LL | fn g(_: impl Trait<CT = { <() as Bound>::N }>) {}
+   |                    ^^^^^^^^^^^^^^^^^^^^^^^^^ expected `bool`, found `u32`
+   |
+note: required by a const generic parameter in `g`
+  --> $DIR/wf-mismatch-3.rs:14:20
+   |
+LL | fn g(_: impl Trait<CT = { <() as Bound>::N }>) {}
+   |                    ^^^^^^^^^^^^^^^^^^^^^^^^^ required by this const generic parameter in `g`
+
+error: the constant `0` is not of type `bool`
+  --> $DIR/wf-mismatch-3.rs:12:17
+   |
+LL | fn f() { let _: dyn Trait<CT = { <() as Bound>::N }>; }
+   |                 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ expected `bool`, found `u32`
+
+error: aborting due to 2 previous errors
+