Merge pull request #84273 from hamishknight/the-whole-hole

[CS] Avoid forming DependentMemberType with hole base in `InferableTypeOpener`

Author: hamishknight

lib/Sema/TypeOfReference.cpp

@@ -279,6 +279,19 @@ class InferableTypeOpener final {
     return PlaceholderType::get(cs.getASTContext(), errTy);
   }
 
+  Type transformDependentMemberType(DependentMemberType *DMT) {
+    auto assocTy = DMT->getAssocType();
+    ASSERT(assocTy && "Should not have structural type here");
+
+    // If the new base is a hole, propagate it to cover the entire
+    // DependentMemberType.
+    auto newBase = transform(DMT->getBase());
+    if (newBase->isPlaceholder())
+      return PlaceholderType::get(cs.getASTContext(), DMT);
+
+    return DependentMemberType::get(newBase, assocTy);
+  }
+
   Type transform(Type type) {
     if (!type)
       return type;
@@ -308,6 +321,8 @@ class InferableTypeOpener final {
         return transformTypeAliasType(aliasTy);
       if (auto *errTy = dyn_cast<ErrorType>(tyPtr))
         return transformErrorType(errTy);
+      if (auto *DMT = dyn_cast<DependentMemberType>(tyPtr))
+        return transformDependentMemberType(DMT);
 
       return std::nullopt;
     });

validation-test/compiler_crashers_2_fixed/a8575b8261697c42.swift

@@ -0,0 +1,4 @@
+// {"kind":"typecheck","original":"9e6249db","signature":"(anonymous namespace)::ConstraintGenerator::visitApplyExpr(swift::ApplyExpr*)"}
+// RUN: not %target-swift-frontend -typecheck %s
+(a as Sequence).Element {
+}

validation-test/compiler_crashers_2_fixed/fddb1549773c253.swift

@@ -0,0 +1,7 @@
+// {"kind":"typecheck","original":"5e6f691d","signature":"(anonymous namespace)::ConstraintGenerator::visitApplyExpr(swift::ApplyExpr*)"}
+// RUN: not %target-swift-frontend -typecheck %s
+protocol a {
+  associatedtype b
+  struct c<d, a {
+e {
+  d.b {