Couldn't depcomp use SUNPRO_DEPENDENCIES for GCC 2.x?

[Jamie Lokier]

Dear Automake maintains,

Automake includes a script called "depcomp" which is used to compile
programs and simultaneously maintain automatic makefile dependencies.

In the script are these comments, for GCC 2.x:

    gcc)
    ## There are various ways to get dependency output from gcc.  Here's
    ## why we pick this rather obscure method:
    ## - Don't want to use -MD because we'd like the dependencies to end
    ##   up in a subdir.  Having to rename by hand is ugly.
    ##   (We might end up doing this anyway to support other compilers.)
    ## - The DEPENDENCIES_OUTPUT environment variable makes gcc act like
    ##   -MM, not -M (despite what the docs say).
    ## - Using -M directly means running the compiler twice (even worse
    ##   than renaming).

It then proceeds to do something very complicated involving a lot of
assumptions about the format of paths.

In my own makefiles, I have used the SUNPRO_DEPENDENCIES environment
variable to maintain dependencies with GCC 2.x, with no need for
complex post-processing.

Probably the author of "depcomp" didn't use SUNPRO_DEPENDENCIES
because until recently it wasn't documented.  However, it's been in
GCC since very long ago - I was using it as far back as 1995, and it
hasn't changed meaning in that time.

SUNPRO_DEPENDENCIES is like DEPENDENCIES_OUTPUT, except it is more
like -M than -MM.  Therefore it might be exactly the right thing for
"depcomp", allowing the "rather obscure method" to be discarded and
using much simpler code, just like the GCC 3.x case a few lines
above.

Regards,
-- Jamie