Re: [PATCH v2 7/9] sparse: Fix errors due to missing target-specific variables

Ramsay Jones [off-list ref] writes:

I decided not to mark the $(SP_OBJ) as .PHONY targets; after some
testing, it seems that it is not necessary, even if users do
something like:
    make git.sp 2>git.sp
Do you know of any advantages to doing so that I have missed?

The info documentation on GNU make states two reasons to use .PHONY.

One is to avoid existing file (e.g. git.sp in the above) to interfere
(especially when the target itself does not have a listed dependency), and
the other is that .PHONY tells make that it does not have to spend cycles
to consider implicit rules.

-help.o: common-cmds.h
+help.sp help.o: common-cmds.h

I am not sure if you even want any dependency listed for any %.sp target
to begin with. If sparse _were_ a normal build target, it would be sensible
to change the rule for sparse to create/update %.sp files, perhaps even
like this:

+%.sp: %.c GIT-CFLAGS FORCE

	rm -f $@+ $@

+	$(QUIET_SP)cgcc -no-compile $(ALL_CFLAGS) $(EXTRA_CPPFLAGS) \
+		$(SPARSE_FLAGS) $< 2>&1 >$@+

	mv $@+ $@

so that once you run sparse on help.c, unless you touch help.c or do
something to cause common-cmds.h to be updated, you do not have to
run the same thing again whose outcome you have already seen.

BUT. That is obviously not what we want.

In the case of sparse, you *do* want it to be run every time the user says
"make sparse", even when you already know you would get exactly the same
result from the previous run.

The situation is exactly the same as "make clean"; it runs even when it is
run immediately after another "make clean".

So why list any dependency?  If it is sensible to treat "sparse" target
just like "clean" target, it would make sense not to give it any
dependencies and mark it as .PHONY, no?

Junio C Hamano wrote:

Ramsay Jones [off-list ref] writes:

quoted

I decided not to mark the $(SP_OBJ) as .PHONY targets; after some
testing, it seems that it is not necessary, even if users do
something like:
    make git.sp 2>git.sp

[...]

quoted

-help.o: common-cmds.h
+help.sp help.o: common-cmds.h

I am not sure if you even want any dependency listed for any %.sp target
to begin with. 

without these common-cmds.h dependencies, I get something like:

    $ make clean
        ...
    $ make help.sp
    GIT_VERSION = 1.7.5.rc2.10.g4d94
        * new build flags or prefix
        SP help.c
    help.c:6:10: error: unable to open 'common-cmds.h'
    make: *** [help.sp] Error 1

whereas, with them:

    $ make clean
        ...
    $ make help.sp
    GIT_VERSION = 1.7.5.rc2.10.g937d2
        * new build flags or prefix
        GEN common-cmds.h
        SP help.c

[...]

So why list any dependency?  If it is sensible to treat "sparse" target
just like "clean" target, it would make sense not to give it any
dependencies and mark it as .PHONY, no?

After some experiments, looking through the output of "make -d ...", I think
I have a solution which (hopefully) addresses your concerns ...

Version 3 of the patch coming up ...

ATB,
Ramsay Jones