Re: RFC: doc for `Handling Tools that Produce Many Outputs'

[Tim Van Holder]

> >    What we need is a rule that forces a rebuild when data.h 
> is missing.
> > 
> >      data.c: data.foo
> >              foo data.foo
> >      data.h: data.c
> >              @if test -f $@; then :; else \
> >                rm -f data.c; \
> >                $(MAKE) $(AM_MAKEFLAGS) data.c; \
> >              fi
> > 
> 
> I believe this fails on the following corner case.  Suppose the
> date ordering is like this (with data.h being the oldest):
>       data.h   data.foo   data.c
> 
> data.h is out of date with respect to data.foo, so one wants to
> rebuild it, but I don't think that will happen:
>   - data.c is up to date with respect to data.foo, so the first
>     rule doesn't fire
>   - data.h is out of date with respect to data.c, so the second
>     rule does fire, but its action doesn't do anything because
>     data.h already exists

Wouldn't this help somewhat for a case like this:

     data.h: data.c
             @if test -f $@; then \
               touch $@; \
             else \
               rm -f data.c; \
               $(MAKE) $(AM_MAKEFLAGS) data.c; \
             fi

It wouldn't do anything about the contents of the file (but, like
Robert said, the user made a boo-boo by editing/touching data.c
in the first place), but it would prevent rerunning this rule's
commands on every subsequent make invocation.