[bug #40657] Suffix rules and prerequisites

[John Marshall]

URL:
  <http://savannah.gnu.org/bugs/?40657>

                 Summary: Suffix rules and prerequisites
                 Project: make
            Submitted by: jmarshall
            Submitted on: Thu 21 Nov 2013 14:08:34 GMT
                Severity: 3 - Normal
              Item Group: Documentation
                  Status: None
                 Privacy: Public
             Assigned to: None
             Open/Closed: Open
         Discussion Lock: Any
       Component Version: 3.81
        Operating System: Any
           Fixed Release: None
           Triage Status: None

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Details:

The "Suffix Rules" info node states

"Suffix rules cannot have any prerequisites of their own.  If they have any,
they are treated as normal files with funny names, not as suffix rules."

However this appears to be incorrect.  Here is the example following that
text, with -DHELLO added so we can see it for certain:

$ cat badsuffix.mk 
.c.o: foo.h
        $(CC) -DHELLO -c $(CFLAGS) $(CPPFLAGS) -o $@ $<
$ touch hello.c

$ make -f badsuffix.mk -n hello.o .c.o
cc -DHELLO -c   -o hello.o hello.c
make: *** No rule to make target `foo.h', needed by `.c.o'. Stop.

$ make -f badsuffix.mk -p | grep -B4 -A1 'badsuffix.mk.*line 2'
[snip]
%.o: %.c
# commands to execute (from `badsuffix.mk', line 2):
        $(CC) -DHELLO -c $(CFLAGS) $(CPPFLAGS) -o $@ $<
--
.c.o: foo.h
# Implicit rule search has not been done.
# Modification time never checked.
# File has not been updated.
# commands to execute (from `badsuffix.mk', line 2):
        $(CC) -DHELLO -c $(CFLAGS) $(CPPFLAGS) -o $@ $<

So both a suffix rule and a rule for a funnily-named file have been made, and
only one got the prerequisite.  Perusal of the NEWS file suggests that this
may have changed in 3.58 ("Suffix rules may have dependencies (which are
ignored)"), but it seems that the documentation has not caught up.




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