[PATCH] Makefile: add and use the ".DELETE_ON_ERROR" flag

["Ævar Arnfjörð Bjarmason" <avarab@gmail.com>]

Use the GNU make ".DELETE_ON_ERROR" flag in our main Makefile, as we
already do in the Documentation/Makefile since db10fc6c09f (doc:
simplify Makefile using .DELETE_ON_ERROR, 2021-05-21).

Now if a command to make X fails X will be removed, the default
behavior of GNU make is to only do so if "make" itself is interrupted
with a signal.

E.g. if we now intentionally break one of the rules with:

    -       mv $@+ $@
    +       mv $@+ $@ && \
    +       false

We'll get output like:

    $ make git
        CC git.o
        LINK git
    make: *** [Makefile:2179: git] Error 1
    make: *** Deleting file 'git'
    $ file git
    git: cannot open `git' (No such file or directory)

Before this change we'd leave the file in place in under this
scenario.

As in db10fc6c09f this allows us to remove patterns of removing
leftover $@ files at the start of rules, since previous failing runs
of the Makefile won't have left those littered around anymore.

I'm not as confident that we should be replacing the "mv $@+ $@"
pattern entirely, since that means that external programs or one of
our other Makefiles might race and get partial content.

Signed-off-by: Ævar Arnfjörð Bjarmason <avarab@gmail.com>
---

Extracted from an earlier series of mine[1] which was tangled up with
wider use of the "stuff >$@+ && mv $@+ $@" pattern, which caused that
series not to go forward.

1. https://lore.kernel.org/git/cover-0.6-00000000000-20210329T161723Z-avarab@gmail.com/

 Makefile | 25 ++++++++++++++++---------
 1 file changed, 16 insertions(+), 9 deletions(-)

diff --git a/Makefile b/Makefile
index c3565fc0f8f..20a0fe6e88e 100644
--- a/Makefile
+++ b/Makefile
@@ -2160,6 +2160,16 @@ shell_compatibility_test: please_set_SHELL_PATH_to_a_more_modern_shell
 strip: $(PROGRAMS) git$X
 	$(STRIP) $(STRIP_OPTS) $^
 
+### Flags affecting all rules
+
+# A GNU make extension since gmake 3.72 (released in late 1994) to
+# remove the target of rules if commands in those rules fail. The
+# default is to only do that if make itself receives a signal. Affects
+# all targets, see:
+#
+#    info make --index-search=.DELETE_ON_ERROR
+.DELETE_ON_ERROR:
+
 ### Target-specific flags and dependencies
 
 # The generic compilation pattern rule and automatically
@@ -2243,7 +2253,6 @@ 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)|' \
@@ -2313,7 +2322,7 @@ endif
 PERL_DEFINES += $(gitexecdir) $(perllibdir) $(localedir)
 
 $(SCRIPT_PERL_GEN): % : %.perl GIT-PERL-DEFINES GIT-PERL-HEADER GIT-VERSION-FILE
-	$(QUIET_GEN)$(RM) $@ $@+ && \
+	$(QUIET_GEN) \
 	sed -e '1{' \
 	    -e '	s|#!.*perl|#!$(PERL_PATH_SQ)|' \
 	    -e '	r GIT-PERL-HEADER' \
@@ -2333,7 +2342,7 @@ GIT-PERL-DEFINES: FORCE
 	    fi
 
 GIT-PERL-HEADER: $(PERL_HEADER_TEMPLATE) GIT-PERL-DEFINES Makefile
-	$(QUIET_GEN)$(RM) $@ && \
+	$(QUIET_GEN) \
 	INSTLIBDIR='$(perllibdir_SQ)' && \
 	INSTLIBDIR_EXTRA='$(PERLLIB_EXTRA_SQ)' && \
 	INSTLIBDIR="$$INSTLIBDIR$${INSTLIBDIR_EXTRA:+:$$INSTLIBDIR_EXTRA}" && \
@@ -2359,7 +2368,7 @@ git-instaweb: git-instaweb.sh GIT-SCRIPT-DEFINES
 	mv $@+ $@
 else # NO_PERL
 $(SCRIPT_PERL_GEN) git-instaweb: % : unimplemented.sh
-	$(QUIET_GEN)$(RM) $@ $@+ && \
+	$(QUIET_GEN) \
 	sed -e '1s|#!.*/sh|#!$(SHELL_PATH_SQ)|' \
 	    -e 's|@@REASON@@|NO_PERL=$(NO_PERL)|g' \
 	    unimplemented.sh >$@+ && \
@@ -2373,14 +2382,14 @@ $(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) $@ $@+ && \
+	$(QUIET_GEN) \
 	sed -e '1s|#!.*python|#!$(PYTHON_PATH_SQ)|' \
 	    $< >$@+ && \
 	chmod +x $@+ && \
 	mv $@+ $@
 else # NO_PYTHON
 $(SCRIPT_PYTHON_GEN): % : unimplemented.sh
-	$(QUIET_GEN)$(RM) $@ $@+ && \
+	$(QUIET_GEN) \
 	sed -e '1s|#!.*/sh|#!$(SHELL_PATH_SQ)|' \
 	    -e 's|@@REASON@@|NO_PYTHON=$(NO_PYTHON)|g' \
 	    unimplemented.sh >$@+ && \
@@ -2388,8 +2397,7 @@ $(SCRIPT_PYTHON_GEN): % : unimplemented.sh
 	mv $@+ $@
 endif # NO_PYTHON
 
-CONFIGURE_RECIPE = $(RM) configure configure.ac+ && \
-		   sed -e 's/@@GIT_VERSION@@/$(GIT_VERSION)/g' \
+CONFIGURE_RECIPE = sed -e 's/@@GIT_VERSION@@/$(GIT_VERSION)/g' \
 			configure.ac >configure.ac+ && \
 		   autoconf -o configure configure.ac+ && \
 		   $(RM) configure.ac+
@@ -2514,7 +2522,6 @@ endif
 ifeq ($(GENERATE_COMPILATION_DATABASE),yes)
 all:: compile_commands.json
 compile_commands.json:
-	@$(RM) $@
 	$(QUIET_GEN)sed -e '1s/^/[/' -e '$$s/,$$/]/' $(compdb_dir)/*.o.json > $@+
 	@if test -s $@+; then mv $@+ $@; else $(RM) $@+; fi
 endif
-- 
2.32.0.599.g3967b4fa4ac