[bug #58556] Make is confused by a target named ".o" and neither emptying .SUFFIXES nor MAKEFLAGS=r can prevent this

[Rossen Mikhov]

URL:
  <https://savannah.gnu.org/bugs/?58556>

                 Summary: Make is confused by a target named ".o" and neither
emptying .SUFFIXES nor MAKEFLAGS=r can prevent this
                 Project: make
            Submitted by: log65536
            Submitted on: Sun 14 Jun 2020 01:39:34 AM JST
                Severity: 3 - Normal
              Item Group: None
                  Status: None
                 Privacy: Public
             Assigned to: None
             Open/Closed: Open
         Discussion Lock: Any
       Component Version: None
        Operating System: None
           Fixed Release: None
           Triage Status: None

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Details:

In an empty directory:

$ make .o
cc      -o .o
cc: fatal error: no input files
compilation terminated.
make: *** [<builtin>: .o] Error 1

This was unexpected, because no prerequisites exist in the directory.
Looking into the relevant parts from "make -dp .o":

Considering target file '.o'.
 File '.o' does not exist.
 Finished prerequisites of target file '.o'.
Must remake target '.o'.
...
.o:
        $(LINK.o) $^ $(LOADLIBS) -o $@

It doesn't mention trying implicit rules, so it seems to be matching the
builtin as an explicit rule. Is this intentional?

Even if this is by design, there should be a way to turn it off from the
makefile. I tried:

$ printf 'MAKEFLAGS=r \n .SUFFIXES:' | make - .o
cc      -o .o
cc: fatal error: no input files
compilation terminated.
make: *** [<builtin>: .o] Error 1

This is strange, because now "make -p" doesn't mention any rules involving
".o" at all, yet it still manages to call the linker.

I should note that "make -r" from the command line does work properly, and
"MAKEFLAGS=r" does disable the bulitins for targets not named like a default
suffix.

I also note that I found this while trying to fix a buggy makefile. Being able
to actually work with a target named ".o" is not important here, it is just
that a more correct error message might have helped while debugging the
makefile.





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