[PATCH v3 0/5] Makefile: "make tags" fixes & cleanup

The big win here is that none of the tags targets depend on "FORCE" anymore, so we'll only re-generate them if our sources change.

For v2, see https://lore.kernel.org/git/cover-0.5-0000000000-20210629T110837Z-avarab@gmail.com/

This fixes the series per feedback from Jeff King and Ramsay Jones, i.e:

 * In v2 the 3/5 broke things in a way that 4/5 fixed, that's now
   re-arranged and fixed.

 * I now use $(FOUND_SOURCE_FILES) instead of $(FIND_SOURCE_FILES)
   consistently. I was redundantly re-running the "find" command.

Ævar Arnfjörð Bjarmason (5):
  Makefile: move ".PHONY: cscope" near its target
  Makefile: add QUIET_GEN to "cscope" target
  Makefile: don't use "FORCE" for tags targets
  Makefile: the "cscope" target always creates a "cscope.out"
  Makefile: normalize clobbering & xargs for tags targets

 .gitignore |  2 +-
 Makefile   | 34 ++++++++++++++++++++--------------
 2 files changed, 21 insertions(+), 15 deletions(-)

Range-diff against v2:
1:  dd6cfd6022c = 1:  6b4ddc126d9 Makefile: move ".PHONY: cscope" near its target
2:  56daa09738f = 2:  d3d5d332e92 Makefile: add QUIET_GEN to "cscope" target
4:  b924cc3f566 ! 3:  9dd69d68178 Makefile: don't use "FORCE" for tags targets
    @@ Metadata
      ## Commit message ##
         Makefile: don't use "FORCE" for tags targets
     
    -    Remove the "FORCE" dependency from the "tags", "TAGS" and "cscope.out"
    +    Remove the "FORCE" dependency from the "tags", "TAGS" and "cscope"
         targets, instead make them depend on whether or not the relevant
         source files have changed.
     
    +    For the cscope target we need to change it to depend on the actual
    +    generated file while we generate while we're at it, as the next commit
    +    will discuss we always generate a cscope.out file.
    +
         Signed-off-by: Ævar Arnfjörð Bjarmason <avarab@gmail.com>
     
      ## Makefile ##
    @@ Makefile: FIND_SOURCE_FILES = ( \
     +
     +$(ETAGS_TARGET): $(FOUND_SOURCE_FILES)
      	$(QUIET_GEN)$(RM) "$(ETAGS_TARGET)+" && \
    - 	$(FIND_SOURCE_FILES) | xargs etags -a -o "$(ETAGS_TARGET)+" && \
    +-	$(FIND_SOURCE_FILES) | xargs etags -a -o "$(ETAGS_TARGET)+" && \
    ++	echo $(FOUND_SOURCE_FILES) | xargs etags -a -o "$(ETAGS_TARGET)+" && \
      	mv "$(ETAGS_TARGET)+" "$(ETAGS_TARGET)"
      
     -tags: FORCE
     +tags: $(FOUND_SOURCE_FILES)
      	$(QUIET_GEN)$(RM) tags+ && \
    - 	$(FIND_SOURCE_FILES) | xargs ctags -a -o tags+ && \
    +-	$(FIND_SOURCE_FILES) | xargs ctags -a -o tags+ && \
    ++	echo $(FOUND_SOURCE_FILES) | xargs ctags -a -o tags+ && \
      	mv tags+ tags
      
    --cscope.out:
    +-.PHONY: cscope
    +-cscope:
     +cscope.out: $(FOUND_SOURCE_FILES)
    - 	$(QUIET_GEN)$(RM) cscope.out && \
    --	$(FIND_SOURCE_FILES) | xargs cscope -f$@ -b
    -+	echo $(FOUND_SOURCE_FILES) | xargs cscope -f$@ -b
    + 	$(QUIET_GEN)$(RM) cscope* && \
    +-	$(FIND_SOURCE_FILES) | xargs cscope -b
    ++	echo $(FOUND_SOURCE_FILES) | xargs cscope -b
    ++
    ++.PHONY: cscope
    ++cscope: cscope.out
      
    - .PHONY: cscope
    - cscope: cscope.out
    + ### Detect prefix changes
    + TRACK_PREFIX = $(bindir_SQ):$(gitexecdir_SQ):$(template_dir_SQ):$(prefix_SQ):\
     @@ Makefile: check: config-list.h command-list.h
      		exit 1; \
      	fi
3:  35c8b839048 ! 4:  f8d151f1f6a Makefile: fix "cscope" target to refer to cscope.out
    @@ Metadata
     Author: Ævar Arnfjörð Bjarmason <avarab@gmail.com>
     
      ## Commit message ##
    -    Makefile: fix "cscope" target to refer to cscope.out
    +    Makefile: the "cscope" target always creates a "cscope.out"
     
    -    The cscope target added in a2a9150bf06 (makefile: Add a cscope target,
    -    2007-10-06) has for some reason been referring to cscope* instead of
    +    In the preceding commit the "cscope" target was changed to be a phony
    +    alias for the "cscope.out" target.
    +
    +    The cscope target was added in a2a9150bf06 (makefile: Add a cscope
    +    target, 2007-10-06), and has always referred to cscope* instead of to
         cscope.out.
     
    -    Let's generate the cscope.out file directly so we don't need to
    -    speculate. The "-fcscope.out" (note, no whitespace) argument is
    -    enabled by default on my system's cscope 15.9, but let's provide it
    -    explicitly for good measure.
    +    As far as I can tell this ambiguity was never needed. The
    +    "-fcscope.out" (note, no whitespace) argument is enabled by default,
    +    but let's provide it explicitly for good measure.
     
         Signed-off-by: Ævar Arnfjörð Bjarmason <avarab@gmail.com>
     
    @@ .gitignore
      *.obj
     
      ## Makefile ##
    -@@ Makefile: tags: FORCE
    - 	$(FIND_SOURCE_FILES) | xargs ctags -a -o tags+ && \
    +@@ Makefile: tags: $(FOUND_SOURCE_FILES)
      	mv tags+ tags
      
    -+cscope.out:
    -+	$(QUIET_GEN)$(RM) cscope.out && \
    -+	$(FIND_SOURCE_FILES) | xargs cscope -f$@ -b
    -+
    - .PHONY: cscope
    --cscope:
    + cscope.out: $(FOUND_SOURCE_FILES)
     -	$(QUIET_GEN)$(RM) cscope* && \
    --	$(FIND_SOURCE_FILES) | xargs cscope -b
    -+cscope: cscope.out
    +-	echo $(FOUND_SOURCE_FILES) | xargs cscope -b
    ++	$(QUIET_GEN)$(RM) cscope.out && \
    ++	echo $(FOUND_SOURCE_FILES) | xargs cscope -f$@ -b
      
    - ### Detect prefix changes
    - TRACK_PREFIX = $(bindir_SQ):$(gitexecdir_SQ):$(template_dir_SQ):$(prefix_SQ):\
    + .PHONY: cscope
    + cscope: cscope.out
     @@ Makefile: clean: profile-clean coverage-clean cocciclean
      	$(RM) $(HCC)
      	$(RM) -r bin-wrappers $(dep_dirs) $(compdb_dir) compile_commands.json
5:  5195d99e25c ! 5:  f3ff76d0e98 Makefile: normalize clobbering & xargs for tags targets
    @@ Metadata
      ## Commit message ##
         Makefile: normalize clobbering & xargs for tags targets
     
    -    Since the "tags", "TAGS" and "cscope.out" targets rely on ping into
    +    Since the "tags", "TAGS" and "cscope.out" targets rely on piping into
         xargs with an "echo <list> | xargs" pattern, we need to make sure
         we're in an append mode.
     
    -    Unlike recent changes of mine to make use of ".DELETE_ON_ERROR" we
    -    really do need the "rm $@+" at the beginning (note, not "rm $@").
    +    Unlike my recent change to make use of ".DELETE_ON_ERROR" in
    +    7b76d6bf221 (Makefile: add and use the ".DELETE_ON_ERROR" flag,
    +    2021-06-29), we really do need the "rm $@+" at the beginning (note,
    +    not "rm $@").
     
    -    This is because the xargs command may decide on multiple invocations
    -    of the program. We need to make sure we've got a union of its results
    +    This is because the xargs command may decide to invoke the program
    +    multiple times. We need to make sure we've got a union of its results
         at the end.
     
         For "ctags" and "etags" we used the "-a" flag for this, for cscope
    @@ Makefile: FIND_SOURCE_FILES = ( \
      
      $(ETAGS_TARGET): $(FOUND_SOURCE_FILES)
     -	$(QUIET_GEN)$(RM) "$(ETAGS_TARGET)+" && \
    --	$(FIND_SOURCE_FILES) | xargs etags -a -o "$(ETAGS_TARGET)+" && \
    +-	echo $(FOUND_SOURCE_FILES) | xargs etags -a -o "$(ETAGS_TARGET)+" && \
     -	mv "$(ETAGS_TARGET)+" "$(ETAGS_TARGET)"
     +	$(QUIET_GEN)$(RM) $@+ && \
     +	echo $(FOUND_SOURCE_FILES) | xargs etags -a -o $@+ && \
    @@ Makefile: FIND_SOURCE_FILES = ( \
      
      tags: $(FOUND_SOURCE_FILES)
     -	$(QUIET_GEN)$(RM) tags+ && \
    --	$(FIND_SOURCE_FILES) | xargs ctags -a -o tags+ && \
    +-	echo $(FOUND_SOURCE_FILES) | xargs ctags -a -o tags+ && \
     -	mv tags+ tags
     +	$(QUIET_GEN)$(RM) $@+ && \
     +	echo $(FOUND_SOURCE_FILES) | xargs ctags -a -o $@+ && \