Merge pull request #42121 from xedin/rdar-91110069

[ConstraintSystem] Fix a bug in existential Self erasure

Author: DougGregor

include/swift/Sema/ConstraintSystem.h

@@ -5694,7 +5694,6 @@ Expr *getArgumentLabelTargetExpr(Expr *fn);
 /// variable and anything that depends on it to their non-dependent bounds.
 Type typeEraseOpenedExistentialReference(Type type, Type existentialBaseType,
                                          TypeVariableType *openedTypeVar,
-                                         const DeclContext *useDC,
                                          TypePosition outermostPosition);
 
 /// Returns true if a reference to a member on a given base type will apply

lib/Sema/CSSimplify.cpp

@@ -1872,7 +1872,7 @@ static ConstraintSystem::TypeMatchResult matchCallArguments(
         for (const auto &opened : openedExistentials) {
           paramTy = typeEraseOpenedExistentialReference(
               paramTy, opened.second->getExistentialType(), opened.first,
-              /*FIXME*/cs.DC, TypePosition::Contravariant);
+              TypePosition::Contravariant);
         }
       }
 
@@ -11396,7 +11396,7 @@ ConstraintSystem::simplifyApplicableFnConstraint(
     if (result2->hasTypeVariable() && !openedExistentials.empty()) {
       for (const auto &opened : openedExistentials) {
         result2 = typeEraseOpenedExistentialReference(
-            result2, opened.second->getExistentialType(), opened.first, DC,
+            result2, opened.second->getExistentialType(), opened.first,
             TypePosition::Covariant);
       }
     }

lib/Sema/ConstraintSystem.cpp

@@ -1795,16 +1795,16 @@ static bool isMainDispatchQueueMember(ConstraintLocator *locator) {
 /// routine will recurse into the concrete type.
 static Type
 typeEraseExistentialSelfReferences(
-    Type refTy, Type baseTy, const DeclContext *useDC,
+    Type refTy, Type baseTy,
     TypePosition outermostPosition) {
   assert(baseTy->isExistentialType());
   if (!refTy->hasTypeParameter()) {
     return refTy;
   }
 
-  auto contextSig = useDC->getGenericSignatureOfContext();
   const auto existentialSig =
-      baseTy->getASTContext().getOpenedArchetypeSignature(baseTy, contextSig);
+      baseTy->getASTContext().getOpenedArchetypeSignature(baseTy,
+                                                          GenericSignature());
 
   unsigned metatypeDepth = 0;
 
@@ -1916,7 +1916,7 @@ typeEraseExistentialSelfReferences(
 
 Type constraints::typeEraseOpenedExistentialReference(
     Type type, Type existentialBaseType, TypeVariableType *openedTypeVar,
-    const DeclContext *useDC, TypePosition outermostPosition) {
+    TypePosition outermostPosition) {
   Type selfGP = GenericTypeParamType::get(false, 0, 0, type->getASTContext());
 
   // First, temporarily reconstitute the 'Self' generic parameter.
@@ -1933,8 +1933,8 @@ Type constraints::typeEraseOpenedExistentialReference(
   });
 
   // Then, type-erase occurrences of covariant 'Self'-rooted type parameters.
-  type = typeEraseExistentialSelfReferences(
-      type, existentialBaseType, useDC, outermostPosition);
+  type = typeEraseExistentialSelfReferences(type, existentialBaseType,
+                                            outermostPosition);
 
   // Finally, swap the 'Self'-corresponding type variable back in.
   return type.transformRec([&](TypeBase *t) -> Optional<Type> {
@@ -2279,9 +2279,8 @@ ConstraintSystem::getTypeOfMemberReference(
     const auto selfGP = cast<GenericTypeParamType>(
         outerDC->getSelfInterfaceType()->getCanonicalType());
     auto openedTypeVar = replacements.lookup(selfGP);
-    type =
-        typeEraseOpenedExistentialReference(type, baseObjTy, openedTypeVar, DC,
-                                            TypePosition::Covariant);
+    type = typeEraseOpenedExistentialReference(type, baseObjTy, openedTypeVar,
+                                               TypePosition::Covariant);
   }
 
   // Construct an idealized parameter type of the initializer associated

validation-test/Sema/type_checker_crashers_fixed/rdar91110069.swift

@@ -0,0 +1,31 @@
+// RUN: %target-typecheck-verify-swift
+
+protocol Schema: RawRepresentable {
+  var rawValue: String { get }
+}
+
+enum MySchema: String, Schema {
+  case hello = "hello"
+}
+
+struct Parser<S: Schema> :  Equatable {
+}
+
+protocol Entity {
+}
+
+protocol MyInitializable {
+  init() throws
+}
+
+typealias MyInitializableEntity = MyInitializable & Entity
+
+extension Parser where S == MySchema {
+  func test(kind: Entity.Type) throws {
+    guard let entityType = kind as? MyInitializableEntity.Type else {
+      return
+    }
+
+    let _ = try entityType.init() // Ok
+  }
+}