[Mesa-dev] [PATCH 1/2] glcpp: Allow integer expression for #line directive.

[Carl Worth]

Carl Worth <cworth at cworth.org> writes:
> Matt Turner <mattst88 at gmail.com> writes:
>>
>> LINE_EXPANDED expression expression NEWLINE
>
> Yes. Thanks for the catch. I'll expand the testing and follow up with a
> new set of patches.

Except that that's totally bogus. We can't parse two adjacent
expressions with no intervening separator (assuming whitespace is valid
within each <expression>).

This looks to me like a bug in the GLSL specification. Real
preprocessors for languages like C do not accept expressions for #line,
(they do perform macro substitution, but the final result must be an
integer constant, not an expression). And that's what is in the C
specifications.

A deviation to accept an expression here, (together with the replacement
of a source-file string, with a source-file number), gives us something
unparseable, (or at least under-specified).

It feels like something specified without an implementation in hand,
(which can lead to problems like this).

Ian, I asked in the bug[*] already, but I'll ask again here. Where did
this bug report come from? And can we fix the problem by pushing to have
the specification updated?

If not, (that is, if there are real-world users with non-integer-literal
#line directives), then it would be nice to see what those actually are
so we could, at the very least, resolve the grammar ambiguity in a
direction that will solve the real-world cases.

[*] https://bugs.freedesktop.org/show_bug.cgi?id=72273

-- 
carl.d.worth at intel.com
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