[Mesa-dev] [PATCH] glsl: empty declarations should be valid

Ian Romanick idr at freedesktop.org
Fri Aug 5 13:35:32 PDT 2011

Hash: SHA1

On 08/05/2011 12:41 AM, Chia-I Wu wrote:
> On Fri, Aug 5, 2011 at 1:48 PM, Chad Versace <chad at chad-versace.us> wrote:
>> On 08/04/2011 06:18 PM, Chad Versace wrote:
>>> On 08/04/2011 01:29 PM, Eric Anholt wrote:
>>>> On Thu,  4 Aug 2011 12:59:35 +0900, Chia-I Wu <olvaffe at gmail.com> wrote:
>>>>> From: Chia-I Wu <olv at lunarg.com>
>>>>> Unlike C++, empty declarations such as
>>>>>   float;
>>>>> should be valid.  The spec is not explicit about this actually.
>>>>> Some apps that generate their shader sources may rely on this.  This was
>>>>> noted when porting one of them to Linux from Windows.
>>>> Ew.  Looking the GLSL 1.20 spec, I see:
>>>> statement:
>>>>         declaration_statement
>>>> declaration_statement:
>>>>         declaration
>>>> declaration:
>>>>         init_declarator_list SEMICOLON
>>>> init_declarator_list:
>>>>         single_declaration
>>>> single_declaration:
>>>>         fully_specified_type
>>>>         fully_specified_type IDENTIFIER
>>>> so it looks like that is actually valid code.  That's awful.
>>> I first suspected that this was a spec grammar bug. But it is still present in
>>> the GLSL 4.10 spec, so it's unlikely to be a bug.
>>> Surprisingly, C also allows empty declarations. Compiling this
>>>     float;
>>>     int main() { return 0; }
>>> with `gcc --std=c99` succeeds and emits this warning:
>>>      warning: useless type name in empty declaration [enabled by default]
>>> I hate to say this, but I believe the spec grammar intentionally allows empty
>>> declarations. C allows it, and GLSL tries to mimic C.
>>> Even though I don't like empty declarations, this patch is
>>> Reviewed-by: Chad Versace <chad at chad-versace.us>
>> Also, please update the commit message to say that `gcc --std=c99` allows empty
>> declrations and include the appropriate quotation from the GLSL 1.20 spec's
>> grammar. Without that extra info, someone may stumble onto this commit and say WTF.
> Oops.  I've already committed it...

You have to give a little more time for review.  I would like to have
had an opportunity to weigh in, but it's a bit late now.
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