[PATCH v2 0/5] Makefile: "make tags" fixes & cleanup

A v2 of my fixes to the tags targets. This no longer depends on my .DELETE_ON_ERROR change, and goes directly on top of "master". See [2] for the just-submitted v2 of that other series.

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.

I missed the interaction of the "-a" flag and xargs splitting the arguments into am implicit -n, so in v1 of this we could end up with incomplete tag files. In this v2 we more incrementally reach similar ends, but in the end result retain our rm/gen/mv dance, since it's needed in this case.

1. http://lore.kernel.org/git/cover-0.3-00000000000-20210622T141844Z-avarab@gmail.com
2. https://lore.kernel.org/git/patch-1.1-2557117855-20210629T084356Z-avarab@gmail.com/

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

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

Range-diff against v1:
1:  383a90c8ac = 1:  dd6cfd6022 Makefile: move ".PHONY: cscope" near its target
-:  ---------- > 2:  56daa09738 Makefile: add QUIET_GEN to "cscope" target
2:  ea39f1f5cd ! 3:  35c8b83904 Makefile: fix "cscope" target to refer to cscope.out
    @@ Commit message
     
         The cscope target added in a2a9150bf06 (makefile: Add a cscope target,
         2007-10-06) has for some reason been referring to cscope* instead of
    -    cscope.out. Let's generate the cscope.out file directly so we don't
    -    need to speculate.
    +    cscope.out.
     
    -    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.
    +    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.
     
         Signed-off-by: Ævar Arnfjörð Bjarmason <avarab@gmail.com>
     
    @@ Makefile: tags: FORCE
      	mv tags+ tags
      
     +cscope.out:
    ++	$(QUIET_GEN)$(RM) cscope.out && \
     +	$(FIND_SOURCE_FILES) | xargs cscope -f$@ -b
     +
      .PHONY: cscope
     -cscope:
    --	$(RM) cscope*
    +-	$(QUIET_GEN)$(RM) cscope* && \
     -	$(FIND_SOURCE_FILES) | xargs cscope -b
     +cscope: cscope.out
      
3:  67fc87665d ! 4:  b924cc3f56 Makefile: don't use "FORCE" for tags targets
    @@ Commit message
         targets, instead make them depend on whether or not the relevant
         source files have changed.
     
    -    I'm also removing the "-o" option from them, that seems to have been
    -    cargo-culted when they were initially added in f81e7c626f3 (Makefile:
    -    Add TAGS and tags targets, 2006-03-18). It would make sense to use
    -    that option if we had been appending to tag files, it doesn't make any
    -    sense that it was used after we'd just removed the files file being
    -    appended to.
    -
    -    This will potentially cause a partial file to be left behind if the
    -    command dies, but my in-flight series to use the ".DELETE_ON_ERROR"
    -    flag in the Makefile[1] will make that problem go away. I think even
    -    without that it's not problem we need to worry about in these cases.
    -
    -    1. https://lore.kernel.org/git/patch-1.1-9420448e74f-20210622T141100Z-avarab@gmail.com/
    -
         Signed-off-by: Ævar Arnfjörð Bjarmason <avarab@gmail.com>
     
      ## Makefile ##
    @@ Makefile: FIND_SOURCE_FILES = ( \
      	)
      
     -$(ETAGS_TARGET): FORCE
    --	$(QUIET_GEN)$(RM) "$(ETAGS_TARGET)+" && \
    --	$(FIND_SOURCE_FILES) | xargs etags -a -o "$(ETAGS_TARGET)+" && \
    --	mv "$(ETAGS_TARGET)+" "$(ETAGS_TARGET)"
     +FOUND_SOURCE_FILES = $(shell $(FIND_SOURCE_FILES))
    ++
    ++$(ETAGS_TARGET): $(FOUND_SOURCE_FILES)
    + 	$(QUIET_GEN)$(RM) "$(ETAGS_TARGET)+" && \
    + 	$(FIND_SOURCE_FILES) | xargs etags -a -o "$(ETAGS_TARGET)+" && \
    + 	mv "$(ETAGS_TARGET)+" "$(ETAGS_TARGET)"
      
     -tags: FORCE
    --	$(QUIET_GEN)$(RM) tags+ && \
    --	$(FIND_SOURCE_FILES) | xargs ctags -a -o tags+ && \
    --	mv tags+ tags
    -+$(ETAGS_TARGET): $(FOUND_SOURCE_FILES)
    -+	$(QUIET_GEN)echo $(FOUND_SOURCE_FILES) | \
    -+	xargs etags -o $@
    -+
     +tags: $(FOUND_SOURCE_FILES)
    -+	$(QUIET_GEN)echo $(FOUND_SOURCE_FILES) | \
    -+	xargs ctags -o $@
    + 	$(QUIET_GEN)$(RM) tags+ && \
    + 	$(FIND_SOURCE_FILES) | xargs ctags -a -o tags+ && \
    + 	mv tags+ tags
      
    - cscope.out:
    +-cscope.out:
    ++cscope.out: $(FOUND_SOURCE_FILES)
    + 	$(QUIET_GEN)$(RM) cscope.out && \
     -	$(FIND_SOURCE_FILES) | xargs cscope -f$@ -b
    -+	$(QUIET_GEN)echo $(FOUND_SOURCE_FILES) | \
    -+	xargs cscope -f$@ -b
    ++	echo $(FOUND_SOURCE_FILES) | xargs cscope -f$@ -b
      
      .PHONY: cscope
      cscope: cscope.out
-:  ---------- > 5:  5195d99e25 Makefile: normalize clobbering & xargs for tags targets