Re: [PATCH] Support for GNU make dependency generation

Hello,

I wasn't aware that there is another patch for the same feature, to begin
with.

On Tue, Oct 26, 2010 at 3:41 PM, David M. Warme <[email protected]> wrote:

>
> This implementation appears to suffer from the various problems that
> my proposed implementation fixes:
>
> 1. What does m4 put on the left-hand-side of the generated make
>   dependency rule when m4 is sending its output to stdout?  There
>   is no general way for m4 to know what the target is in this
>   case.  (Consider, e.g., when stdout is the write end of a pipe.)
>   My submitted patch avoids this problem by having the user
>   specify the generated rule's target explicitly on the command
>   line (always).
>

Well, now I'm a bit lost.  Is this a question about the implementation or
the description of a problem affecting the implementation?

The dependency on stdout is already contained in the makefile:

target : prereq1 prereq2 ...
        m4 $^ > $@

what the -X,--depend option does is to generate a dependency file for all
entries in $^: prereq1 prereq2 ...
Of course duplicate entries are ignored.  One problem can be triggered if m4
is used like:

target : prereq1
        do_something $< | m4 >$@

in this case the user should tell m4 which file originates its stdin and
this feature is actually missing in my patch, but it's quite trivial to add
it - won't be a problem.


> 2. By creating both the dependency file and the actual m4 target
>   file in one step, you wind up being in danger of "circular
>   dependencies"


Regardless of other considerations, this is the standard practice with GCC
and I would just want M4 to work with the same legacy.
You can always alias "m4" to "m4 > /dev/null" to produce only dependencies
and suppress stdout.

Best Regards,
Lorenzo

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