Carl Worth
f583f214d5
Here, "skipping" refers to the lexer not emitting any tokens for portions of
the file within an #if condition (or similar) that evaluates to false.
Previously, the lexer had a special <SKIP> start condition used to control
this skipping. This start condition was not handled like a normal start
condition. Instead, there was a particularly ugly block of code set to be
included at the top of the generated lexing loop that would change from
<INITIAL> to <SKIP> or from <SKIP> to <INITIAL> depending on various pieces of
parser state, (such as parser->skip_state and parser->lexing_directive).
Not only was that an ugly approach, but the <SKIP> start condition was
complicating several glcpp bug fixes I attempted recently that want to use
start conditions for other purposes, (such as a new <HASH> start condition).
The recently added RETURN_TOKEN macro gives us a convenient way to implement
skipping without using a lexer start condition. Now, at the top of the
generated lexer, we examine all the necessary parser state and set a new
parser->skipping bit. Then, in RETURN_TOKEN, we examine parser->skipping to
determine whether to actually emit the token or not.
Besides this, there are only a couple of other places where we need to examine
the skipping bit (other than when returning a token):
* To avoid emitting an error for #error if skipped.
* To avoid entering the <DEFINE> start condition for a #define that is
skipped.
With all of this in place in the present commit, there are hopefully no
behavioral changes with this patch, ("make check" still passes all of the
glcpp tests at least).
Reviewed-by: Jordan Justen <jordan.l.justen@intel.com>
glcpp -- GLSL "C" preprocessor This is a simple preprocessor designed to provide the preprocessing needs of the GLSL language. The requirements for this preprocessor are specified in the GLSL 1.30 specification availble from: http://www.opengl.org/registry/doc/GLSLangSpec.Full.1.30.10.pdf This specification is not precise on some semantics, (for example, #define and #if), defining these merely "as is standard for C++ preprocessors". To fill in these details, I've been using a draft of the C99 standard as available from: http://www.open-std.org/jtc1/sc22/wg14/www/docs/n1256.pdf Any downstream compiler accepting output from glcpp should be prepared to encounter and deal with the following preprocessor macros: #line #pragma #extension All other macros will be handled according to the GLSL specification and will not appear in the output. Known limitations ----------------- A file that ends with a function-like macro name as the last non-whitespace token will result in a parse error, (where it should be passed through as is).