Always emit precision in shader variable declarations.

Always emit precision in shader variable declarations.

After the shader compile (and before code output), the precision scopes are already lost.  In order to correctly output precisions, we need to emit precision in each variable declaration, therefore, each variable should have its precision set.  This CL fixes the bugs that the precisions are lost for variables using default precsions and struct fields.  Also, this CL fixes a bug in the grammar: constructors are not type_specifier and they shouldn't have precisions.

BUG=168
TEST=webgl conformance tests, gles2 conformance tests.
Committed: http://code.google.com/p/angleproject/source/detail?r=695

[Zhenyao Mo, 2011-06-15 21:57:19]

After further testing, it turns out that function parameters and return value
don't require precisions (at least for Angle).  Therefore, instead of checking
type precision in type_specifier, we do it in init_declarator_list and
struct_declaration.

This CL is tested with WebGL conformance tests, GLES2 conformance tests, a few
webgl demos, including webgl aquarium and worlds of webgl.

Please review.

[kbr1, 2011-06-16 00:29:36]

I'm concerned about relying on ANGLE's interpretation of the GLES2 spec for
correctness of this code. If we skip the precision checks for function arguments
and return values, then if a GLES2 implementation relies on them being there, it
is possible that the translator will generate a shader that won't compile. Of
course, this would only happen if the source shader was actually incorrect --
for example, leaving out the default precision qualifier in the fragment shader,
and explicitly specifying it for all variables, etc., but not function arguments
and return values. Is that correct? Or can correctly written shaders be
translated incorrectly with this change?

I think that this code should be written to spec, meaning that the precision
checks in type_specifier need to be made conditional depending on whether we're
parsing the signatures for builtins.

[Zhenyao Mo, 2011-06-17 00:21:44]

The new CL is tested on Win/Mac with WebGL conformance test suites, GLES2
conformance test suite (on Win only), and a few webgl demos, including Aquarium,
and Worlds of WebGL.

Please review again.

[kbr1, 2011-06-17 00:38:00]

LGTM. Thanks for moving this in the right direction. One minor comment.

http://codereview.appspot.com/4617041/diff/8001/src/compiler/Compiler.cpp
File src/compiler/Compiler.cpp (right):

http://codereview.appspot.com/4617041/diff/8001/src/compiler/Compiler.cpp#new...
src/compiler/Compiler.cpp:21: TParseContext parseContext(symbolTable,
extBehavior, intermediate, type, spec, 0, false, NULL, infoSink);
A comment would be really helpful here indicating that the builtins deliberately
don't specify precisions for the function arguments, and for that reason we
don't try to check them.