[bug #61328] elide the distinction between "dir" and "dir/"

[David Boyce]

URL:
  <https://savannah.gnu.org/bugs/?61328>

                 Summary: elide the distinction between "dir" and "dir/"
                 Project: make
            Submitted by: boyski
            Submitted on: Sun 10 Oct 2021 11:01:25 PM UTC
                Severity: 3 - Normal
              Item Group: Enhancement
                  Status: None
                 Privacy: Public
             Assigned to: None
             Open/Closed: Open
         Discussion Lock: Any
       Component Version: SCM
        Operating System: None
           Fixed Release: None
           Triage Status: None

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Details:

It's documented that make implements a special case to treat pathnames
"foobar" and "./foobar" as identical even though comparisons are usually
lexical, but it does not do something similar with trailing slashes on
directory names. For instance in the test case below the target depends on its
parent directory $(@D) which comes out as "foo". We've supplied a rule for
making it but due to the behavior of the $(dir ...) function the target comes
out as "foo/" which doesn't match. This can be "fixed" with the patsubst
function but life would be more convenient and less mysterious if make
recognized them as the same.

The obvious concern is that we don't know a priori whether a target is a
directory or file. However, since "foo/" is illegal for anything but a
directory it seems harmless to assume directory. This special case could also
be made to apply exclusively to order-only prerequisites which is where
directory dependencies should be anyway.

Test case:

$ cat Makefile
.SECONDEXPANSION:

target := foo/bar

$(target): $$(@D)
        touch $@

$(dir $(target)):
        mkdir -p $@

$ make
make: *** No rule to make target 'foo', needed by 'foo/bar'.  Stop.

If $(dir $(target)) is wrapped as $(patsubst %/,%,$(dir $(target))) everything
works as anticipated.




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