Re: [PATCH] Support for GNU make dependency generation

[David M. Warme]

Automake handles only simple cases.
Consider automatically generated include files, or an m4 script
that sinclude's the generated dependency file.  I am reluctant
to design features that handle only simple cases.

The execution time of m4 scripts has never been a serious factor
in my experience.

This still leaves problem #1 wide open.

On Tue, 2010-10-26 at 07:56 -0600, Eric Blake wrote:
> On 10/26/2010 07:41 AM, David M. Warme wrote:
> > 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" -- running make twice in a row causes stuff to
> >     be remade the second time.  In certain cases, even an endless
> >     succession of "make" invocations causes stuff to get remade
> >     every time.  Single commands that update two or more targets
> >     at once are the usual cause of this behavior.  The fix is to
> >     have two separate rules in your Makefile:
> 
> I'm reluctant to have to require to run m4 twice per file.  Dependencies 
> as a side effect of compilation is the most efficient way to generate 
> dependencies, and running twice defeats this.  There's a reason that 
> automake prefers to generate dependencies during compilation, and if 
> automake can write portable makefiles with gcc dependencies generated 
> during compilation, then I see no reason why m4 can't be hooked up to do 
> the same.
>