[PATCH] D49462: [ObjC] Error out when using forward-declared protocol in a @protocol expression

[John McCall via Phabricator via cfe-commits]

rjmccall added a comment.

Hmm.  I think this is a reasonable change to make to the language.  Have you investigated to see if this causes source-compatibility problems?



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Comment at: include/clang/Basic/DiagnosticSemaKinds.td:849
+def err_atprotocol_protocol : Error<
+  "@protocol is using a forward protocol declaration of %0">;
 def warn_readonly_property : Warning<
----------------
I think that's the only warning in `-Wat-protocol`; we can at least anonymize it and leave a comment saying it's now empty.


================
Comment at: lib/Sema/SemaExprObjC.cpp:1235
+  } else
     PDecl = PDecl->getDefinition();
 
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Please brace the second clause here.  I think even the people who don't generally use braces still advise being consistent within a single if-else chain.


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Comment at: test/CodeGenObjC/forward-declare-protocol-gnu.m:6
 
-Protocol *getProtocol(void)
-{
-	        return @protocol(P);
-}
+ at interface I <P>
+ at end
----------------
Does this really not require a definition of `P`?  Ugh.  I wonder if that's reasonable to fix, too.


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Comment at: test/Parser/objc-cxx-keyword-identifiers.mm:22
+ at protocol P2;
+ at protocol delete // expected-error {{expected identifier; 'delete' is a keyword in Objective-C++}}
+ at end
----------------
Why did this test need to change?


Repository:
  rC Clang

https://reviews.llvm.org/D49462