Re: New Flymake rewrite in emacs-26

[João Távora]

Eli Zaretskii <address@hidden> writes:

>> From: address@hidden (João Távora)
>> Cc: Eli Zaretskii <address@hidden>,  Mark Oteiza <address@hidden>,  Lele 
>> Gaifax <address@hidden>,  Leo Liu <address@hidden>,  Stefan Monnier 
>> <address@hidden>,  Emacs developers <address@hidden>
>> Date: Wed, 11 Oct 2017 01:07:19 +0100
>> 
>> Thanks for the idea. Certainly not nonsense, but also not a silver
>> bullet, since Makefiles can invoke gcc in arbitrary ways that fool a
>> guesser. Still, it’s probably decent in a fair amount of cases, and I’m
>> giving it a go to see if it works with Emacs sources and perhaps some
>> other GNU projects. I attach my flag-guessing function at the end.
>> 
>> First, my idea is to cache the result of these flags contingent on the
>> Makefile’s location and mtime. This, I think, is doable. Then I use a
>> regexp to extract the gcc invocation from the output.
>> 
>> The regexp is very poor but does the job. For the src/fringe.c file the
>> regexp is
>> 
>>    "gcc[[:space:]]+\\(\\(?:-.*\\)*\\)/path/to/fringe.c"
>> 
>> This indeed matches Make’s output and gets me something like this for
>> the match group 1
>> 
>>    -c -Demacs -I. -I. -I../lib -I../lib -isystem /usr/include/freetype2
>>     -isystem /usr/include/alsa -pthread -isystem /usr/include/librsvg-2.0
>>     -isystem /usr/include/gdk-pixbuf-2.0 -isystem /usr/include/libpng16
>>     -isystem /usr/include/cairo -isystem /usr/include/glib-2.0 -isystem
>>     /usr/lib/x86_64-linux-gnu/glib-2.0/include -isystem
>>     /usr/include/pixman-1 -isystem /usr/include/freetype2 -isystem
>>     /usr/include/libpng16 -isystem /usr/include/libpng16 -isystem
>>     /usr/include/libxml2 -isystem /usr/include/dbus-1.0 -isystem
>>     /usr/lib/x86_64-linux-gnu/dbus-1.0/include -pthread -isystem
>>     /usr/include/glib-2.0 -isystem
>>     /usr/lib/x86_64-linux-gnu/glib-2.0/include -isystem
>>     /usr/include/glib-2.0 -isystem
>>     /usr/lib/x86_64-linux-gnu/glib-2.0/include -isystem
>>     /usr/include/freetype2 -isystem /usr/include/freetype2 -isystem
>>     /usr/include/freetype2 -MMD -MF
>>     deps//home/capitaomorte/Source/Emacs/emacs-26/src/fringe.d -MP -isystem
>>     /usr/include/p11-kit-1 -fno-common -W -Wabi -Waddress
>>     [... elided many many -W flags]
>>     -Wno-type-limits -Wno-unused-parameter -Wno-format-nonliteral -g3 -O2
>> 
>> Unfortunately, not all flags make sense for flymake, like the -M family
>> of flags. Ideally, i’d need a way to parse this big string of flags back
>> into, say, an alist, and cherry pick the -I, -D, and -W flags from that
>> set. But I’m afraid split-string will insufficiently deal with escaped
>> spaces in the output.
>> 
>> Any ideas?
>
> We are talking about a solution specific to Emacs, right?

No, I was aiming for something more generic that includes at least Emacs
and perhaps otherGNU projects.

But I have no problem in making it work just for Emacs first.

> If so, and assuming that Flymake is already capable of parsing a
> Makefile,

It is not. The only thing it currently knows about Makefiles is what it
has known for many versions, which is to invoke their "check-syntax"
target with a special environment variable set to to a specific
temporary file which contains the buffer's contents. This invocation is
expected to compile files with the correct flags and produce errors and
warnings in the standard output.

> we could simply have somewhere the list of *FLAGS variables from the
> Emacs Makefile that Flymake needs to use.  That list will not include
> DEPFLAGS, for example,, which you say make no sense for Flymake.  Then
> Flymake could pick up the expanded value of each of these variables,
> and concatenate them.

If we are going to make it specific to Emacs, this sounds more
complicated than adding a "check-syntax" target to the Makefile, which
would bring the (minor) benefit that people using emacs < 26.1 could
also use older Flymake to edit Emacs sources.

João