[Mesa-dev] mesa: Clean up enums used to keep track of shader types.

[Paul Berry]

In my early preparations for working on compute shaders, I've run into
some stumbling blocks due to the way the GLSL compiler keeps track of
which pipeline stage a given shader is being compiled for.

In some places, it uses a GLenum to store values like
GL_VERTEX_SHADER, GL_GEOMETRY_SHADER, or GL_COMPUTE_SHADER.  In a
small minority of places, it uses a GLenum to store values like
GL_VERTEX_PROGRAM_ARB, GL_FRAGMENT_PROGRAM_ARB, or
GL_GEOMETRY_PROGRAM_NV.  In other places, it uses the enum
gl_shader_type, which uses the values 0, 1, and 2 to represent vertex
shaders, geometry shaders, and fragment shaders, respectively.

To make matters worse, the functions for converting between these
representations are inconsistenly named, so when it's necessary to
convert from one to another, it's difficult to know which function to
call.

This patch series attempts to clean all that up by adopting a more
consistent nomenclature, and preferring to use the gl_shader_type enum
inside the shader compiler.  There are three advantages of preferring
gl_shader_type over the GLenums: 1. When switching on the shader type,
the compiler will warn if one of the enum values is unhandled.  2. It
can be used to index into an array of shader stages.  3. It avoids
uncertainty between the use of GL_*_SHADER enums and GL_*_PROGRAM
enums.

The series also renames gl_shader_type to gl_shader_stage to emphasize
that this enum represents shader stages in the order in which they
appear in the pipeline (a fact which the linker takes advantage of).
An additional advantage of this name change is that it makes it easier
to make the nomenclature consistent, because the term "stage" isn't
used very much in other parts of Mesa.

[PATCH 1/7] mesa: Clean up nomenclature for pipeline stages.
[PATCH 2/7] mesa: Store gl_shader_stage enum in gl_shader objects.
[PATCH 3/7] glsl: Change _mesa_glsl_parse_state ctor to use gl_shader_stage enum.
[PATCH 4/7] glsl: Make more use of gl_shader_stage enum in link_varyings.cpp.
[PATCH 5/7] glsl: Make more use of gl_shader_stage enum in lower_clip_distance.cpp.
[PATCH 6/7] glsl: Make more use of gl_shader_stage enum in ir_set_program_inouts.cpp.
[PATCH 7/7] mesa: Remove _mesa_progshader_enum_to_string(), which is no longer used.