[PATCH v2 3/5] Makefile: don't needlessly "rm $@ $@+" before "mv $@+ $@"

From: Ævar Arnfjörð Bjarmason <avarab@gmail.com>
Date: Mar 29, 2021, 16:20 UTC
Message-ID: <patch-3.6-96e2338ed8e-20210329T161723Z-avarab@gmail.com>
In-Reply-To: <cover-0.6-00000000000-20210329T161723Z-avarab@gmail.com>

Now that preceding commits have moved the generation of objects and scripts in the Makefile to use the "[...] -o $@+ && mv $@+ $@" pattern we can stop removing "$@" and "$@+" before the rule is run.

I suppose that we could leave this at removing "$@" before we start out, per the "age old convention" comment in[1]. I.e. instead of:

    rm -f thing thing+
    prepare contents for thing >thing+
    mv thing+ thing

Do:

    rm -f thing
    prepare contents for thing >thing+
    mv thing+ thing

Since the removal of "thing+" is redundant as we're about to clobber it anyway, but we might be so paranoid as to be guarding against mv(1) leaving behind a corrupt "thing".

But I think guarding against "mv" failing is a step too far in paranoia, let's just rely on the "[...] -o $@+ && mv $@+ $@" pattern working instead.

Especially as we'll see in a follow-up commit, we're just about to use the GNU make ".DELETE_ON_ERROR" feature, which will reliably do this for us.

1. http://lore.kernel.org/git/xmqqpn097e9o.fsf@gitster.c.googlers.com

Signed-off-by: Ævar Arnfjörð Bjarmason <avarab@gmail.com>
---
 Makefile | 16 +++++-----------
 1 file changed, 5 insertions(+), 11 deletions(-)

diff --git a/Makefile b/Makefile
index ef2d4a9973b..f08635067b3 100644
--- a/Makefile
+++ b/Makefile
@@ -2210,7 +2210,6 @@ SCRIPT_DEFINES = $(SHELL_PATH_SQ):$(DIFF_SQ):$(GIT_VERSION):\
 	$(gitwebdir_SQ):$(PERL_PATH_SQ):$(SANE_TEXT_GREP):$(PAGER_ENV):\
 	$(perllibdir_SQ)
 define cmd_munge_script
-$(RM) $@ $@+ && \
 sed -e '1s|#!.*/sh|#!$(SHELL_PATH_SQ)|' \
     -e 's|@SHELL_PATH@|$(SHELL_PATH_SQ)|' \
     -e 's|@@DIFF@@|$(DIFF_SQ)|' \
@@ -2278,8 +2277,7 @@ endif
 PERL_DEFINES += $(gitexecdir) $(perllibdir) $(localedir)
 
 $(SCRIPT_PERL_GEN): % : %.perl GIT-PERL-DEFINES GIT-PERL-HEADER GIT-VERSION-FILE
-	$(QUIET_GEN)$(RM) $@ $@+ && \
-	sed -e '1{' \
+	$(QUIET_GEN)sed -e '1{' \
 	    -e '	s|#!.*perl|#!$(PERL_PATH_SQ)|' \
 	    -e '	r GIT-PERL-HEADER' \
 	    -e '	G' \
@@ -2299,8 +2297,7 @@ GIT-PERL-DEFINES: FORCE
 	    fi
 
 GIT-PERL-HEADER: $(PERL_HEADER_TEMPLATE) GIT-PERL-DEFINES Makefile
-	$(QUIET_GEN)$(RM) $@ && \
-	INSTLIBDIR='$(perllibdir_SQ)' && \
+	$(QUIET_GEN)INSTLIBDIR='$(perllibdir_SQ)' && \
 	INSTLIBDIR_EXTRA='$(PERLLIB_EXTRA_SQ)' && \
 	INSTLIBDIR="$$INSTLIBDIR$${INSTLIBDIR_EXTRA:+:$$INSTLIBDIR_EXTRA}" && \
 	sed -e 's=@@PATHSEP@@=$(pathsep)=g' \
@@ -2325,8 +2322,7 @@ git-instaweb: git-instaweb.sh GIT-SCRIPT-DEFINES
 	mv $@+ $@
 else # NO_PERL
 $(SCRIPT_PERL_GEN) git-instaweb: % : unimplemented.sh
-	$(QUIET_GEN)$(RM) $@ $@+ && \
-	sed -e '1s|#!.*/sh|#!$(SHELL_PATH_SQ)|' \
+	$(QUIET_GEN)sed -e '1s|#!.*/sh|#!$(SHELL_PATH_SQ)|' \
 	    -e 's|@@REASON@@|NO_PERL=$(NO_PERL)|g' \
 	    unimplemented.sh >$@+ && \
 	chmod +x $@+ && \
@@ -2339,15 +2335,13 @@ $(SCRIPT_PYTHON_GEN): GIT-BUILD-OPTIONS
 ifndef NO_PYTHON
 $(SCRIPT_PYTHON_GEN): GIT-CFLAGS GIT-PREFIX GIT-PYTHON-VARS
 $(SCRIPT_PYTHON_GEN): % : %.py
-	$(QUIET_GEN)$(RM) $@ $@+ && \
-	sed -e '1s|#!.*python|#!$(PYTHON_PATH_SQ)|' \
+	$(QUIET_GEN)sed -e '1s|#!.*python|#!$(PYTHON_PATH_SQ)|' \
 	    $< >$@+ && \
 	chmod +x $@+ && \
 	mv $@+ $@
 else # NO_PYTHON
 $(SCRIPT_PYTHON_GEN): % : unimplemented.sh
-	$(QUIET_GEN)$(RM) $@ $@+ && \
-	sed -e '1s|#!.*/sh|#!$(SHELL_PATH_SQ)|' \
+	$(QUIET_GEN)sed -e '1s|#!.*/sh|#!$(SHELL_PATH_SQ)|' \
 	    -e 's|@@REASON@@|NO_PYTHON=$(NO_PYTHON)|g' \
 	    unimplemented.sh >$@+ && \
 	chmod +x $@+ && \

-- 
2.31.1.461.gd47399f6574