[cfe-commits] [PATCH] Warn on non-compatible returns from extern "C" functions

[Aaron Ballman]

On Mon, Feb 6, 2012 at 4:33 PM, Eli Friedman <eli.friedman at gmail.com> wrote:
> On Sun, Feb 5, 2012 at 9:31 AM, Aaron Ballman <aaron at aaronballman.com> wrote:
>> MSVC will warn the user when a declared return type of an extern "C"
>> function is not C-compatible
>> (http://msdn.microsoft.com/en-us/library/1e02627y(v=vs.100).aspx).
>> This patch adds the same style of warning to clang, under the
>> -Wreturn-type group, with test cases.
>>
>> Is there a better way for me to check whether a type is "C compatible?"
>
> CXXRecordDecl::isCLike was added recently... not sure if it's what you want.

Thanks, I'll check it out.

> "UDT" is not a term we use anywhere in clang; please don't use it here.

Suggestions on alternative wording?

> That said, I really don't understand the point of this warning.

class A {
public:
  A(const A&);
};

extern "C" A NotGoingToWork( void );

If the intention is to flag the function for export via C linkage, how
would that work when the return value is a class type?  It seems to me
that this is a sensible place for a warning since the resulting code
doesn't match the user's expectations.

Btw, this is in response to Bug 6143 (http://llvm.org/bugs/show_bug.cgi?id=6143)

~Aaron