[SemaObjC] Fix a -Wbridge-cast false-positive

[erik.pilkington]

Summary

Clang used to emit a bad -Wbridge-cast diagnostic on the cast in the attached test. This was because, after 09abecef7, struct __CFString was not added to lookup, so the objc_bridge attribute wasn't getting duplicated onto the most recent declaration, causing us to fail to find it in getObjCBridgeAttr. This patch fixes this by instead walking through the redeclarations to find an appropriate bridge attribute.

rdar://72823399

[ahatanak]

I see a warning when I compile the following (contrived) example:

typedef const struct __attribute__((objc_bridge(NSError))) __CFString * CFStringRef;

extern "C" {
  typedef const struct __attribute__((objc_bridge(NSString))) __CFString * CFStringRef;
}

@interface NSString @end
@interface NSError @end

void CFStringGetLength(CFStringRef theString);

int main() {
  CFStringGetLength((__bridge CFStringRef)(NSString *)0);
}

Should we try to restore the behavior prior to https://reviews.llvm.org/rG09abecef7bbfda18d34f046954eaa4d491062839 as much as we can? Or that's not important?

[erik.pilkington]

In D99661#2662601, @ahatanak wrote:

Should we try to restore the behavior prior to https://reviews.llvm.org/rG09abecef7bbfda18d34f046954eaa4d491062839 as much as we can? Or that's not important?

Sure, the new patch starts iterating through the redeclarations starting at the most recent declaration, which should mimic the old behaviour. I'm not sure it matters, having multiple objc_bridge attributes has never actually worked (objc_bridge attributes appearing earlier get "shadowed" by the most recent one), i.e. in your testcase CFStringGetLength((__bridge CFStringRef)(NSError *)0); has always lead to a -Wbridge-cast diagnostic.

[ahatanak]

I agree with you. If it's not going to work, maybe there should have been a warning.

clang/lib/Sema/SemaExprObjC.cpp

 }
 
 template <typename T>
 static inline T *getObjCBridgeAttr(const TypedefType *TD) {
   TypedefNameDecl *TDNDecl = TD->getDecl();
   QualType QT = TDNDecl->getUnderlyingType();
   if (QT->isPointerType()) {
     QT = QT->getPointeeType();
-    if (const RecordType *RT = QT->getAs<RecordType>())
-      if (RecordDecl *RD = RT->getDecl()->getMostRecentDecl())
-        return RD->getAttr<T>();
+    if (const RecordType *RT = QT->getAs<RecordType>()) {
+      for (auto *Redecl : RT->getDecl()->getMostRecentDecl()->redecls()) {
+        if (auto *attr = Redecl->getAttr<T>())
+          return attr;
+      }
+    }
   }
   return nullptr;
 }
 
 static ObjCBridgeRelatedAttr *ObjCBridgeRelatedAttrFromType(QualType T,
                                                             TypedefNameDecl *&TDNDecl) {
   while (const TypedefType *TD = dyn_cast<TypedefType>(T.getTypePtr())) {
     TDNDecl = TD->getDecl();

clang/test/SemaObjCXX/bridge-cast-redecl.mm

+// RUN: %clang_cc1 -std=gnu++17 -verify %s
+
+// expected-no-diagnostics
+
+typedef const struct __CFString * CFStringRef;
+
+extern "C" {
+  typedef const struct __attribute__((objc_bridge(NSString))) __CFString * CFStringRef;
+  typedef struct __attribute__((objc_bridge_mutable(NSMutableString))) __CFString * CFMutableStringRef;
+}
+
+@interface NSString @end
+@interface NSMutableString : NSString @end
+
+void CFStringGetLength(CFStringRef theString);
+
+int main() {
+  CFStringGetLength((__bridge CFStringRef)(NSString *)0);
+}