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Re: [PATCH] Improve compatibility between M4 and CPP.
From: |
Raphael 'Kena' Poss |
Subject: |
Re: [PATCH] Improve compatibility between M4 and CPP. |
Date: |
Wed, 8 Jul 2009 13:52:46 +0100 |
Hi Eric,
Op 8 jul 2009, om 13:35 heeft Eric Blake het volgende geschreven:
If our synclines are not suitable with the c99 preprocessor already,
then
we are not compliant with POSIX. But naming a new option --
synclines-cpp
makes it sound like synclines are not c99-ready unless you use this
new
option. That is, until I read your documentation of the option:
The intended meaning of the name "synclines-cpp" was "synclines as
generated BY cpp", not "for cpp".
So in effect, what it looks like you are
trying to introduce is an option to make m4 line directives NOT
affect C99
preprocessing (ie. they will be silently ignored by the c99
preprocessor,
without affecting the c99 magic macros __LINE__ and __FILE__), but
still
be recognizable enough for a human reading the file to still
correlate the
lines back to previously preprocessed source code.
Either my attempt at documenting this option is poor, or I didn't
explain myself properly the first time (or both), but you did not
catch the intent behind this.
The purpose of these changes is to allow running M4 _between_ the C
preprocessor and _compiler_, i.e. between "cpp" and "cc1":
(C code) -> CPP -> (preprocessed code) -> M4 -> CC1
From that point, unfortunately one has to consider that the syncline
format accepted by "cc1", when it is separated from the preprocessor,
is not "#line N"; instead cc1's syncline information should be
provided by the (archaic, K&R style) different "# N" format. See
`do_linemarker' in GCC's libcpp/directives.c, compare with `do_line'.
So in order for CC1 to report messages/errors/warnings at the correct
locations in the original source, M4 should output synclines using
this format one way or another. Hence the new option.
And if we do add that as an option, we should break this into multiple
patches - one that adds an optional argument to __line__/__file__, and
another patch that introduces the new option, rather than doing it
all in
one patch.
My opinion is that they are related, i.e. provide the minimal set of
features that allows to fit M4 between CPP and CC1. Now you are the
maintainer and you probably now better, including how to apply these
two changes on your branch separately from each other.
Regards,
--
k