fix: silence mismatches involving unresolved projections

crates/hir-ty/src/chalk_ext.rs

@@ -29,6 +29,7 @@ pub trait TyExt {
     fn contains_unknown(&self) -> bool;
     fn is_ty_var(&self) -> bool;
     fn is_union(&self) -> bool;
+    fn is_projection(&self) -> bool;
 
     fn as_adt(&self) -> Option<(hir_def::AdtId, &Substitution)>;
     fn as_builtin(&self) -> Option<BuiltinType>;
@@ -93,6 +94,11 @@ impl TyExt for Ty {
         self.data(Interner).flags.contains(TypeFlags::HAS_ERROR)
     }
 
+    fn is_projection(&self) -> bool {
+        matches!(self.kind(Interner), TyKind::Alias(AliasTy::Projection(_))) ||
+            matches!(self.kind(Interner), TyKind::AssociatedType(_, _))
+    }
+
     fn is_ty_var(&self) -> bool {
         matches!(self.kind(Interner), TyKind::InferenceVar(_, _))
     }

crates/hir/src/lib.rs

@@ -1679,6 +1679,12 @@ impl DefWithBody {
             acc.extend(AnyDiagnostic::inference_diagnostic(db, self.into(), d, &source_map));
         }
         for (pat_or_expr, mismatch) in infer.type_mismatches() {
+            // Silence mismatches involving unresolved projections
+            let is_unknown_proj = |ty: &Ty| ty.contains_unknown() && ty.is_projection();
+            if is_unknown_proj(&mismatch.expected) || is_unknown_proj(&mismatch.actual) {
+                continue;
+            }
+
             let expr_or_pat = match pat_or_expr {
                 ExprOrPatId::ExprId(expr) => source_map.expr_syntax(expr).map(Either::Left),
                 ExprOrPatId::PatId(pat) => source_map.pat_syntax(pat).map(Either::Right),