[PATCH] Documentation/Makefile: fix "make info" regression in dad9cd7d518

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

Fix a regression in my dad9cd7d518 (Makefile: move ".SUFFIXES" rule to
shared.mak, 2022-03-03). As explained in the GNU make documentation
for the $* variable, available at:

	info make --index-search='$*'

This rule relied on ".texi" being in the default list of suffixes, as
seen at:

	make -f/dev/null -p | grep -v -e ^# -e ^$|grep -F .SUFFIXES

The documentation explains what was going on here:

	In an explicit rule, there is no stem; so '$*' cannot be determined
	in that way.  Instead, if the target name ends with a recognized
	suffix (*note Old-Fashioned Suffix Rules: Suffix Rules.), '$*' is
	set to the target name minus the suffix.  For example, if the
	target name is 'foo.c', then '$*' is set to 'foo', since '.c' is a
	suffix.  GNU 'make' does this bizarre thing only for compatibility
	with other implementations of 'make'.  You should generally avoid
	using '$*' except in implicit rules or static pattern rules.

	If the target name in an explicit rule does not end with a
	recognized suffix, '$*' is set to the empty string for that rule.

I.e. this rule added back in 5cefc33bffd (Documentation: add
gitman.info target, 2007-12-10) was resolving gitman.texi from
gitman.info. We can instead just use the more obvious $< variable
referring to the prerequisite.

This was the only use of $* in our Makefiles in an explicit rule, the
three remaining ones are all implicit rules, and therefore didn't
depend on the ".SUFFIXES" list.

Reported-by: Adam Dinwoodie <adam@dinwoodie.org>
Signed-off-by: Ævar Arnfjörð Bjarmason <avarab@gmail.com>
---

On Tue, Apr 05 2022, Adam Dinwoodie wrote:

> With this commit, I get the same noisy warnings, but I also get the
> error "could not open .texi: No such file or directory".

Sorry about the regression. This fixes it, and as noted above I'm
pretty sure this was the only fallout of the change.

(I didn't have building the full extended documentation as part of my
local build, but I'll be adding it now).

 Documentation/Makefile | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/Documentation/Makefile b/Documentation/Makefile
index 1eb9192dae8..44c080e3e5b 100644
--- a/Documentation/Makefile
+++ b/Documentation/Makefile
@@ -390,7 +390,7 @@ gitman.texi: $(MAN_XML) cat-texi.perl texi.xsl
 	$(RM) $@+
 
 gitman.info: gitman.texi
-	$(QUIET_MAKEINFO)$(MAKEINFO) --no-split --no-validate $*.texi
+	$(QUIET_MAKEINFO)$(MAKEINFO) --no-split --no-validate $<
 
 $(patsubst %.txt,%.texi,$(MAN_TXT)): %.texi : %.xml
 	$(QUIET_DB2TEXI)$(DOCBOOK2X_TEXI) --to-stdout $*.xml >$@
-- 
2.35.1.1604.g35dc6517170