[cfe-commits] r148324 - in /cfe/trunk: include/clang/Sema/Sema.h lib/Sema/SemaChecking.cpp lib/Sema/SemaExprObjC.cpp test/SemaObjC/format-strings-objc.m

[Nico Weber]

On Mon, Jan 30, 2012 at 9:37 AM, Nico Weber <thakis at chromium.org> wrote:
> On Mon, Jan 30, 2012 at 9:32 AM, Jean-Daniel Dupas
> <devlists at shadowlab.org> wrote:
>>
>> Le 30 janv. 2012 à 17:37, Nico Weber a écrit :
>>
>>> Cool!
>>>
>>> One thing that this warned on in the chromium source was:
>>>
>>> ../../webkit/plugins/npapi/plugin_web_event_converter_mac.mm:213:37:
>>> error: format specifies type 'wchar_t *' (aka 'wchar_t *') but the
>>> argument has type 'const WebUChar *' (aka 'const unsigned short *')
>>> [-Werror,-Wformat]
>>>       [NSString stringWithFormat:@"%S", key_event.text]);
>>>                                    ~^   ~~~~~~~~~~~~~~
>>>
>>> It looks like the current %S warning checks if the parameter type is
>>> wchar_t. http://developer.apple.com/library/mac/#documentation/Cocoa/Conceptual/Strings/Articles/formatSpecifiers.html#//apple_ref/doc/uid/TP40004265
>>> says that %S is always utf16 (or ucs16, it doesn't say). `man 3
>>> printf` says %S is for wchar_t, but I guess it refers to the wchar_t
>>> type that was effective when libc / AppKit was built. On my OS X 10.6
>>> box, it looks like printf expects a four byte wchar_t, while AppKit
>>> expects a two byte wchar_t. Since that code snippet above is about
>>> AppKit, the code is right and the warning is wrong (chromium isn't
>>> compiled with -fshort-wchar, but AppKit was, and the warning really
>>> needs to check against the wchar_t type that was used to build the
>>> library it's talking to).
>>>
>>> Since %S can expect utf32 (lib) or utf16 (AppKit), the %S warning is
>>> currently fairly useless. %S seems to be an Apple extension, so should
>>> we just hardcode %S to look for a 32bit type in c strings and for a
>>> 16bit type in @"" strings?
>>> Should we disable the warning for %S
>>> altogether?
>>
>>
>> I think we should just extends the printf checker to handle %S differently when the format spec is 'NSString' (it already has special handling for %@).
>
> The current %S warning implementation is wrong for just printf() as
> well: It compares the argument to wchar_t, but if you build your
> program with -fshort-wchar, clang won't warn (since your program uses
> wchar_t) yet printf won't work (because libc was built without
> -fshort-wchar). If you store your characters in an uint32* and pass
> that to printf() and build your program with -fshort-wchar, clang will
> warn (because uint32* doesn't match wchar_t* with -fshort-whar) yet
> the program will work correctly.

How about: We support it for format spec NSString and expect the type
to be some 16bit type, and we always warn on %S else? (It can't be
portable elsewhere, and as Hans said, the Ubuntu manpage even says "Do
not use.")

Nico