[bug #66974] Irregular target introduction of unmatched wildcard include

URL:
  <https://savannah.gnu.org/bugs/?66974>

                 Summary: Irregular target introduction of unmatched wildcard
include
                   Group: make
               Submitter: None
               Submitted: Tue 01 Apr 2025 08:15:07 PM UTC
                Severity: 3 - Normal
              Item Group: Documentation
                  Status: None
                 Privacy: Public
             Assigned to: None
             Open/Closed: Open
         Discussion Lock: Any
       Component Version: 4.4.1
        Operating System: POSIX-Based
           Fixed Release: None
           Triage Status: None


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Follow-up Comments:


-------------------------------------------------------
Date: Tue 01 Apr 2025 08:15:07 PM UTC By: Anonymous
I have found a confusing behavior of including a file wildcard pattern that 
matches no files which then the pattern itself becomes a target to be built.

```sh
laptop$ cat Makefile 
include *.d

%.d: %.c
        echo target $@
        echo dependencies $^

nothing:

laptop$ ls
Makefile abc.c

laptop$ gmake nothing
echo target *.d
target *.d
echo dependencies abc.c
dependencies abc.c
gmake: Nothing to be done for 'nothing'.
```

The current GNU Make documentation explains that when an include directive 
can't find a file, Make will attempt to remake it. However, the behavior with

wildcards isn't sufficiently clear, particularly when no files match a
wildcard 
pattern (*.mk) and the pattern itself becomes a target to be built.

Add a brief note to the "Including Other Makefiles" section:

Wildcards in Include Directives

When using wildcards in include directives, if no files match the pattern, GNU

Make will attempt to build the literal wildcard pattern itself as a target. If

a pattern rule exists that could build such a target, Make will execute that 
rule with the wildcard pattern as the target name. This can lead to unexpected

behavior in complex Makefiles.

A safer alternative is to use the wildcard function to only include files that

actually exist:

    include $(wildcard *.mk)

This ensures that Make will only include existing files matching the pattern 
and won't attempt to build the pattern itself as a target.







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