Check projection arguments before substitution

Author: compiler-errors

compiler/rustc_trait_selection/src/solve/project_goals.rs

@@ -1,4 +1,4 @@
-use crate::traits::specialization_graph;
+use crate::traits::{check_args_compatible, specialization_graph};
 
 use super::assembly::{self, structural_traits};
 use super::EvalCtxt;
@@ -190,11 +190,8 @@ impl<'tcx> assembly::GoalKind<'tcx> for ProjectionPredicate<'tcx> {
                 return ecx.evaluate_added_goals_and_make_canonical_response(Certainty::AMBIGUOUS);
             };
 
-            if !assoc_def.item.defaultness(tcx).has_value() {
-                let guar = tcx.sess.delay_span_bug(
-                    tcx.def_span(assoc_def.item.def_id),
-                    "missing value for assoc item in impl",
-                );
+            let error_response = |ecx: &mut EvalCtxt<'_, 'tcx>, reason| {
+                let guar = tcx.sess.delay_span_bug(tcx.def_span(assoc_def.item.def_id), reason);
                 let error_term = match assoc_def.item.kind {
                     ty::AssocKind::Const => ty::Const::new_error(
                         tcx,
@@ -208,7 +205,11 @@ impl<'tcx> assembly::GoalKind<'tcx> for ProjectionPredicate<'tcx> {
                 };
                 ecx.eq(goal.param_env, goal.predicate.term, error_term)
                     .expect("expected goal term to be fully unconstrained");
-                return ecx.evaluate_added_goals_and_make_canonical_response(Certainty::Yes);
+                ecx.evaluate_added_goals_and_make_canonical_response(Certainty::Yes)
+            };
+
+            if !assoc_def.item.defaultness(tcx).has_value() {
+                return error_response(ecx, "missing value for assoc item in impl");
             }
 
             // Getting the right args here is complex, e.g. given:
@@ -233,6 +234,13 @@ impl<'tcx> assembly::GoalKind<'tcx> for ProjectionPredicate<'tcx> {
                 assoc_def.defining_node,
             );
 
+            if !check_args_compatible(tcx, assoc_def.item, args) {
+                return error_response(
+                    ecx,
+                    "associated item has mismatched generic item arguments",
+                );
+            }
+
             // Finally we construct the actual value of the associated type.
             let term = match assoc_def.item.kind {
                 ty::AssocKind::Type => tcx.type_of(assoc_def.item.def_id).map_bound(|ty| ty.into()),

tests/ui/generic-associated-types/issue-102114.stderr renamed to tests/ui/generic-associated-types/issue-102114.current.stderr

@@ -1,5 +1,5 @@
 error[E0049]: type `B` has 1 type parameter but its trait declaration has 0 type parameters
-  --> $DIR/issue-102114.rs:11:12
+  --> $DIR/issue-102114.rs:14:12
    |
 LL |     type B<'b>;
    |            -- expected 0 type parameters

tests/ui/generic-associated-types/issue-102114.next.stderr

@@ -0,0 +1,12 @@
+error[E0049]: type `B` has 1 type parameter but its trait declaration has 0 type parameters
+  --> $DIR/issue-102114.rs:14:12
+   |
+LL |     type B<'b>;
+   |            -- expected 0 type parameters
+...
+LL |     type B<T> = Wrapper<T>;
+   |            ^ found 1 type parameter
+
+error: aborting due to previous error
+
+For more information about this error, try `rustc --explain E0049`.

tests/ui/generic-associated-types/issue-102114.rs

@@ -1,3 +1,6 @@
+// revisions: current next
+//[next] compile-flags: -Ztrait-solver=next
+
 trait A {
     type B<'b>;
     fn a() -> Self::B<'static>;