[bug #30794] Interpreting backslash in pattern rules is weird

[Krzysztof Malinowski]

URL:
  <http://savannah.gnu.org/bugs/?30794>

                 Summary: Interpreting backslash in pattern rules is weird
                 Project: make
            Submitted by: raspy
            Submitted on: Tue 17 Aug 2010 10:32:55 AM GMT
                Severity: 3 - Normal
              Item Group: Bug
                  Status: None
                 Privacy: Public
             Assigned to: None
             Open/Closed: Open
         Discussion Lock: Any
       Component Version: 3.82
        Operating System: MS Windows
           Fixed Release: None
           Triage Status: None

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Details:

Suppose the following test2.mk makefile:

backslash := $(subst /,\,/)

obj$(backslash)%.obj: src$(backslash)%.c
        xcopy $< $@

Invoking make with target like obj\foo.obj fails to find a rule. Note also
that in generated dump left backslash is eaten, while the right one is not:

$> make -f test2.mk obj\foo.obj -dpr
# GNU Make 3.82
# Built for Windows32
[...]
Reading makefiles...
Reading makefile `test2.mk'...
Updating makefiles....
[...]
Updating goal targets....
Considering target file `obj\foo.o'.
 File `obj\foo.o' does not exist.
 Looking for an implicit rule for `obj\foo.o'.
 No implicit rule found for `obj\foo.o'.
 Finished prerequisites of target file `obj\foo.o'.
Must remake target `obj\foo.o'.
make: *** No rule to make target `obj\foo.o'.  Stop.

# Make data base, printed on Tue Aug 17 12:22:29 2010

# Variables
[...]
# makefile (from `test2.mk', line 1)
backslash := \
[...]
# Implicit Rules

# No implicit rules.

# Files

# Not a target:
.SUFFIXES:
#  Implicit rule search has not been done.
#  Modification time never checked.
#  File has not been updated.

obj%.obj: src\%.c
#  Implicit rule search has not been done.
#  Modification time never checked.
#  File has not been updated.
#  recipe to execute (from `test2.mk', line 4):
        xcopy $< $@

# Not a target:
obj\foo.o:
#  Command line target.
#  Implicit rule search has been done.
#  File does not exist.
#  File has not been updated.
[...]




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