[Name shadowing] Extend Objective-C initializer shadowing to imported inits.

There are multiple ways in which the Clang importer can produce an
initializer, and we have existing name shadowing rules to decide on
the best. Extend those rules to cover the case where a
Clang-importer-synthesized initializer collides with a C function
imported as an initializer. There's technically no reason to do the
latter because the former already exists, but some frameworks
currently depend on this.

Prior to this, the constraint solver was preferring the synthesized
initializer already (which is the right thing to do), for the wrong
reasons.

Author: DougGregor

lib/AST/NameLookup.cpp

@@ -334,7 +334,7 @@ static void recordShadowedDeclsAfterSignatureMatch(
 /// Look through the given set of declarations (that all have the same name),
 /// recording those that are shadowed by another declaration in the
 /// \c shadowed set.
-static void recordShadowDeclsAfterObjCInitMatch(
+static void recordShadowedDeclsForImportedInits(
                                 ArrayRef<ConstructorDecl *> ctors,
                                 llvm::SmallPtrSetImpl<ValueDecl *> &shadowed) {
   assert(ctors.size() > 1 && "No collisions");
@@ -372,18 +372,21 @@ static void recordShadowedDecls(ArrayRef<ValueDecl *> decls,
   llvm::SmallDenseMap<CanType, llvm::TinyPtrVector<ValueDecl *>> collisions;
   llvm::SmallVector<CanType, 2> collisionTypes;
   llvm::SmallDenseMap<NominalTypeDecl *, llvm::TinyPtrVector<ConstructorDecl *>>
-    objCInitializerCollisions;
-  llvm::TinyPtrVector<NominalTypeDecl *> objCInitializerCollisionNominals;
+    importedInitializerCollisions;
+  llvm::TinyPtrVector<NominalTypeDecl *> importedInitializerCollectionTypes;
 
   for (auto decl : decls) {
-    // Specifically keep track of Objective-C initializers, which can come from
-    // either init methods or factory methods.
-    if (decl->hasClangNode()) {
+    // Specifically keep track of imported initializers, which can come from
+    // Objective-C init methods, Objective-C factory methods, renamed C
+    // functions, or be synthesized by the importer.
+    if (decl->hasClangNode() ||
+        (isa<NominalTypeDecl>(decl->getDeclContext()) &&
+         cast<NominalTypeDecl>(decl->getDeclContext())->hasClangNode())) {
       if (auto ctor = dyn_cast<ConstructorDecl>(decl)) {
         auto nominal = ctor->getDeclContext()->getSelfNominalTypeDecl();
-        auto &knownInits = objCInitializerCollisions[nominal];
+        auto &knownInits = importedInitializerCollisions[nominal];
         if (knownInits.size() == 1) {
-          objCInitializerCollisionNominals.push_back(nominal);
+          importedInitializerCollectionTypes.push_back(nominal);
         }
         knownInits.push_back(ctor);
       }
@@ -431,9 +434,9 @@ static void recordShadowedDecls(ArrayRef<ValueDecl *> decls,
                                            shadowed);
   }
 
-  // Check whether we have shadowing for Objective-C initializer collisions.
-  for (auto nominal : objCInitializerCollisionNominals) {
-    recordShadowDeclsAfterObjCInitMatch(objCInitializerCollisions[nominal],
+  // Check whether we have shadowing for imported initializer collisions.
+  for (auto nominal : importedInitializerCollectionTypes) {
+    recordShadowedDeclsForImportedInits(importedInitializerCollisions[nominal],
                                         shadowed);
   }
 }

test/ClangImporter/Inputs/custom-modules/ImportAsMember.h

@@ -14,6 +14,9 @@ extern struct IAMStruct1 IAMStruct1CreateSimple(double value)
 extern struct IAMStruct1 IAMStruct1CreateSpecialLabel(void)
     __attribute__((swift_name("Struct1.init(specialLabel:)")));
 
+extern struct IAMStruct1 IAMStruct1CreateFull(double x, double y, double z)
+    __attribute__((swift_name("Struct1.init(x:y:z:)")));
+
 extern struct IAMStruct1 IAMStruct1Invert(struct IAMStruct1 s)
     __attribute__((swift_name("Struct1.inverted(self:)")));
 

test/ClangImporter/import-as-member.swift

@@ -5,3 +5,7 @@ import ImportAsMemberSubmodules
 
 let _: IAMSOuter.Inner?
 let _: IAMMultipleNested.Inner? // expected-error {{ambiguous type name 'Inner' in 'IAMMultipleNested'}}
+
+func testCreateShadowing(d: Double) -> Struct1 {
+  return Struct1(x: d, y: d, z: d)
+}