[ObjC] Prevent infinite loops when iterating over redeclaration of a method that was declared in an invalid interface

[arphaman]

Summary

This patch fixes an infinite loop that occurs when clang tries to iterate over redeclaration of a method that was declared in an invalid @interface. The existing validity checks don't catch this as that @interface is a duplicate of a previously declared valid @interface declaration, so we have to verify that the found redeclaration is in a valid declaration context.

[mehdi_amini]

LGTM, thks.
(See one inline comment to fix though)

lib/AST/DeclObjC.cpp

841 ↗

(On Diff #77980)

Either you should use dyn_cast, or you should just cast but without a if

[arphaman]

lib/AST/DeclObjC.cpp

841 ↗

(On Diff #77980)

Thanks! Yeah, this is supposed to be dyn_cast.

[erik.pilkington]

lib/AST/DeclObjC.cpp

841 ↗

(On Diff #77980)

Why dyn_cast? Can't we bank on a DeclContext being a Decl?

888 ↗

(On Diff #77980)

Do you think it would be cleaner to just do the check once here, if Redecl is non-null?

[arphaman]

lib/AST/DeclObjC.cpp

841 ↗

(On Diff #77980)

I think you're right, I just need a cast without an if since DeclContext subclasses are all Decls.

888 ↗

(On Diff #77980)

Yes, that would be neater. Thanks for the suggestion!

[arphaman]

I managed to get rid of the extra function and simplify the check thanks to suggestions from Erik.

cfe/trunk/lib/AST/DeclObjC.cpp

if (!CtxD->isInvalidDecl()) {
     } else if (ObjCCategoryImplDecl *CImplD =
                  dyn_cast<ObjCCategoryImplDecl>(CtxD)) {
       if (ObjCCategoryDecl *CatD = CImplD->getCategoryDecl())
         if (!CatD->isInvalidDecl())
           Redecl = CatD->getMethod(getSelector(), isInstanceMethod());
     }
   }
 
+  // Ensure that the discovered method redeclaration has a valid declaration
+  // context. Used to prevent infinite loops when iterating redeclarations in
+  // a partially invalid AST.
+  if (Redecl && cast<Decl>(Redecl->getDeclContext())->isInvalidDecl())
+    Redecl = nullptr;
+
   if (!Redecl && isRedeclaration()) {
     // This is the last redeclaration, go back to the first method.
     return cast<ObjCContainerDecl>(CtxD)->getMethod(getSelector(),
                                                     isInstanceMethod());
   }
 
   return Redecl ? Redecl : this;
 }

cfe/trunk/test/SemaObjC/method-redecls-invalid-interface.m

+// RUN: %clang_cc1 -fsyntax-only -verify -Wdocumentation -Wno-objc-root-class %s
+// rdar://29220965
+
+@interface InvalidInterface { // expected-note {{previous definition is here}}
+  int *_property;
+}
+
+@end
+
+/*!
+ */
+
+@interface InvalidInterface // expected-error {{duplicate interface definition for class 'InvalidInterface'}}
+@property int *property;
+
+-(void) method;
+@end
+
+@implementation InvalidInterface
+-(void) method { }
+@end