Fix class extension visibility bug

New code introduced for objcImp class extension support failed to check whether a class extension would be visible to Swift before importing it. This caused Swift to import extensions declared in private headers that ought not to be visible. Add the needed visibility check to the loop.

Fixes rdar://123543707.

Author: beccadax

lib/ClangImporter/ClangImporter.cpp

@@ -6013,8 +6013,13 @@ ClangCategoryLookupRequest::evaluate(Evaluator &evaluator,
     llvm::TinyPtrVector<Decl *> results;
     results.push_back(const_cast<ClassDecl *>(CD));
 
+    auto importer =
+       static_cast<ClangImporter *>(CD->getASTContext().getClangModuleLoader());
+    ClangImporter::Implementation &impl = importer->Impl;
+
     for (auto clangExt : clangClass->known_extensions()) {
-      results.push_back(importCategory(clangExt));
+      if (impl.getClangSema().isVisible(clangExt))
+        results.push_back(importCategory(clangExt));
     }
 
     return results;

test/ClangImporter/Inputs/frameworks/Module.framework/Headers/Module.h

@@ -8,6 +8,8 @@ const char *getModuleVersion(void);
 +alloc;
 @end
 
+@protocol ModuleProto @end
+
 #define MODULE_H_MACRO 1
 #__private_macro MODULE_H_MACRO
 

test/ClangImporter/Inputs/frameworks/Module.framework/Modules/module.private.modulemap

@@ -0,0 +1,4 @@
+framework module Module_Private {
+  umbrella "PrivateHeaders"
+  explicit module * { export * }
+}

test/ClangImporter/Inputs/frameworks/Module.framework/PrivateHeaders/Sub3.h

@@ -0,0 +1,5 @@
+#import <Module/Module.h>
+
+@interface Module () <ModuleProto>
+@property (readwrite) int extensionProperty;
+@end

test/ClangImporter/Inputs/frameworks/Module.framework/PrivateHeaders/Sub4.h

@@ -0,0 +1 @@
+#import <Module/Module.h>

test/ClangImporter/diags_from_module.swift

@@ -37,7 +37,7 @@ import Module
 // CHECK-PRIMARY: diags_from_module.swift:[[@LINE-4]]:8: error: could not build Objective-C module 'Module'
 
 // CHECK-WARN: Sub2.h:7:2: warning: here is some warning about something
-// CHECK-WARN: Module.h:20:1: warning: umbrella header for module 'Module' does not include header 'NotInModule.h'
+// CHECK-WARN: Module.h:22:1: warning: umbrella header for module 'Module' does not include header 'NotInModule.h'
 // FIXME: show [-Wincomplete-umbrella]
 
 // CHECK-NO-WARN-NOT: warning about something

test/ClangImporter/rdar123543707.swift

@@ -0,0 +1,15 @@
+// RUN: %empty-directory(%t)
+// RUN: %target-typecheck-verify-swift -F %S/Inputs/frameworks -module-cache-path %t/mcp1
+
+// REQUIRES: objc_interop
+
+import Module
+import Module_Private.Sub4
+
+@_objcImplementation extension Module {
+  // expected-error@-1 {{'@_objcImplementation' cannot be used to implement root class 'Module'}}
+  // expected-warning@-2 {{extension for main class interface should provide implementation for class method 'version()'}}
+  // expected-warning@-3 {{extension for main class interface should provide implementation for class method 'alloc()'}}
+}
+
+extension Module: @retroactive ModuleProto {} // no-error