[Mesa-dev] A few fixes for the preprocessor for GLSL 1.30

[Carl Worth]

Eric recentl mentioned to me that when setting the following
environment variables with current master mesa:

	MESA_GL_VERSION_OVERRIDE=3.0
	MESA_GLSL_VERSION_OVERRIDE=130

that 8 piglit preprocessor tests start to fail.

I've investigated all of these failures and am here attaching a patch
series for review that fixes 5 of them. In the testing I've done, I
don't see any changes from this patch series other than the desired
piglit fixes. But, of course, I'd be happy for any review.

For the remaining three failures, I believe the tests themselves are
broken and should be fixed. These fall into two case:

1. feature-macros/gl_gragment_precision_high.{frag,vert}

   In these tests, the actual preprocessor functionality being tested,
   (that a directive of #version 130 causes the
   GL_FRAGMENT_PRECISION_HIGH macro to be pre-defined), is working fine.

   The tests are failing due to the following code:

	float f() { return 0; }

   Our implementation does not currently do implicit promotion here,
   so compilation fails with a type error:

	error: `return' with wrong type int, in function `f' returning
	float

   The GLSL specification is not explicit on whether this promotion
   should be happening, but other implementations appear to do it. So
   perhaps the promotion should be added to our implementation.

   Meanwhile, the test could legitimately be fixed to remove the type
   error which is a side issue from what the test is actually trying
   to do.

2. if/if-arg-must-be-defined-02.frag

   This test is trying to elicit an "undefined macro" error with
   something like the following code:

	#if 1
	...
	#elif UNDEFINED_MACRO
	...
	#endif

   I propose changing the test to use "#if 0" instead, in which case
   the current implementation would pass. It's not actually desirable
   to generate an error in the above case. Consider a use of a
   possibly undefined macro:

	#if PERHAPS_UNDEFINED < 5
	...
	#endif

   In order to protect this use, the user might add something like the
   following (or similar with #ifndef):

	#if ! defined PERHAPS_UNDEFINED
	... deal with it ...
	#elif PERHAPS_UNDEFINED
	...
	#endif

   In this case, the user's expectation is to get no error with this
   code. Yet this is precisly the formulation the current test case
   uses to elicit the error.

I'll be glad to push changes to piglit to fix these cases unless
someone can argue aginst that.

Thanks,

-Carl
-- 
carl.d.worth at intel.com