[bug #27497] Later double-colon rules don't fire if earlier ones think target is up to date

[anonymous]

URL:
  <http://savannah.gnu.org/bugs/?27497>

                 Summary: Later double-colon rules don't fire if earlier ones
think target is up to date
                 Project: make
            Submitted by: None
            Submitted on: Tue 22 Sep 2009 15:08:01 UTC
                Severity: 3 - Normal
              Item Group: Bug
                  Status: None
                 Privacy: Public
             Assigned to: None
             Open/Closed: Open
         Discussion Lock: Any
       Component Version: 3.81
        Operating System: POSIX-Based
           Fixed Release: None
           Triage Status: None

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Details:

I have a collection of files, %.a and %.b, and I want to generate %.c from
them. If %.b exists, I want %.c to depend on %.a and %.b, and otherwise I want
%.c to depend on only %.a. I do this:

all : foo.c

%.c :: %.a %.b
        echo %.a %.b > $@
        touch $@

%.c :: %.a
        echo %.a > $@

This works fine (except that if %.b is deleted, %.c isn't rebuilt):

$ touch foo.a
$ make
echo %.a > foo.c
$ touch foo.b
$ make
echo %.a %.b > foo.c
$

However, if I reverse the order of the rules:

all : foo.c

%.c :: %.a
        echo %.a > $@

%.c :: %.a %.b
        echo %.a %.b > $@
        touch $@

Then it no longer works:

$ touch foo.a
$ make
echo %.a > foo.c
$ touch foo.b
$ make
make: Nothing to be done for `all'.
$

Now, the first rule hasn't fired and updated foo.c, and the second rule says
foo.c is not up-to-date, so the second rule's actions should be run, but they
aren't.


$ make --version
GNU Make 3.81
Copyright (C) 2006  Free Software Foundation, Inc.
This is free software; see the source for copying conditions.
There is NO warranty; not even for MERCHANTABILITY or FITNESS FOR A
PARTICULAR PURPOSE.

This program built for x86_64-redhat-linux-gnu



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File Attachments:


-------------------------------------------------------
Date: Tue 22 Sep 2009 15:08:02 UTC  Name: WorkingMakefile  Size: 74B   By:
None
Example makefiles showing the problem
<http://savannah.gnu.org/bugs/download.php?file_id=18754>
-------------------------------------------------------
Date: Tue 22 Sep 2009 15:08:01 UTC  Name: BrokenMakefile  Size: 74B   By:
None
Example makefiles showing the problem
<http://savannah.gnu.org/bugs/download.php?file_id=18753>

    _______________________________________________________

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