Re: dependencies in other folders

[Philip Guenther]

On Fri, Aug 29, 2008 at 2:59 PM, Eduardo Suárez <address@hidden> wrote:
> mkdir test_make test_make/a test_make/b test_make/a/aa test_make/a/ab
> touch test_make/a/ab/foo.c test_make/b/bar.c
...
> %.c: ../ab/%.c
>        cp $< $@
...
> So that, bar.c gets copied to the Makefile directory, while foo.c does not.

Right.  Let's look at the error message:
  make: stat: ../ab/../ab/../ab/../ab/../<elided>/ab/../ab/../ab/foo.c:
File name too long

You told make to build foo.c; the pattern rule that matched said it
had "../ab/foo.c" as a prerequisite.  So make now checks to see if it
can build "../ab/foo.c" and finds a matching pattern rule: that same
rule!  It matches with the '%' being "../ab/foo", so the matching
prerequisite is "../ab/../ab/foo.c" and it continues to loop.

So, the problem is that the pattern rules results in a prerequisite
that matches the same rule again *and* refers to the same file.  The
other pattern rule doesn't have that problem with 'bar.c' because the
prerequisite is at a different directory level, so when the rule tries
to match again it fails because the prereq doesn't exist.


The first consideration in solving this is whether you can remove
these rules and instead just use the VPATH variable or the vpath
directive.  You should read chapter 4.5 "Searching Directories for
Prerequisites" in the info pages for the details.  That's probably the
simplest and cleanest way to solve this.

If there's some insurmountable blocker to using VPATH or vpath, then I
would consider changing the pattern rules to have two colons.  This
makes them 'terminal' rules, so that make will only apply them if the
prerequisite file exists and make won't try to build that prerequisite
file from something else.  If the source files (../ab/foo.c and
../../b/bar.c) need to themselves be built as part of the run, then
this won't work.


Philip Guenther