[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 9:32 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.