gdb/doc: don't have .pod targets separate to man page targets

While preparing the new release it was discovered that commit:

  commit 824083f34c222aa7419e2ea58e82d6f230d5f531
  Date:   Fri Apr 12 17:47:20 2024 +0100

      gdb/doc: use silent-rules.mk in the Makefile

was causing problems.  Given a release tar file, an attempt to build
and install GDB would give an error like this:

  [...]
    TEXI2POD gdb.pod
  cannot find GDBvn.texi at ../../../gdb-15.0.50.20240508/gdb/doc/../../etc/texi2pod.pl line 251, <GEN0> line 16.
  make[5]: *** [Makefile:663: gdb.pod] Error 2

The problem here is how the man pages are built, and how they are
distributed within a release.

Within the development (git) tree, the man page files are not part of
the source tree, these files are built as needed.  Within a release
tar file though, the man pages are included.  The idea being that a
user can build and install GDB, including getting the man pages,
without having to install the tools needed to generate the man pages.

The man pages are generated in a two step process.  First the .texi
file is processed with texi2pod to create a .pod file, then this .pod
file is processed to create the .1 or .5 man file.

Prior to the above commit these two steps were combined into a single
recipe, this meant that when a user performed a build/install from a
release tree all of the dependencies, as well as the final result,
were all present in the source tree, and so nothing needed to be
rebuilt.

However, the above commit split the two steps apart.  Now we had a
separate rule for building the .pod files, and the .1/.5 man page
files depended on the relevant .pod file.

As the .pod files are not shipped in a GDB release, this meant that
one of the dependencies of the man page files was now missing.  As a
result if a user tried to install from a release tree a rebuild of the
.pod files would be attempted, and if that succeeded then building the
man pages would follow that.

Unfortunately, building the .pod files would fail as the GDBvn.texi
file, though present in the source tree, was not present in the build
tree, which is where it is needed for the .pod file generation to
work.

To fix this, I propose merging the .pod creation and the .1/.5 man
page creation back into a single recipe.  Having these two steps split
is probably the "cleaner" solution, but makes it harder for us to
achieve our goal of shipping the prebuilt man page files.  I've added
a comment explaining what's going on (such a comment would have
prevented this mistake having been made in the first place).

One possibly weird thing here is that I have left both an
ECHO_TEXI2POD and a ECHO_TEXI2MAN in the rule $(MAN1S) and $(MAN5S)
recipes.  This is 100% not going to break anything, these just print
two different progress messages while executing the recipes, but I'm
not sure if this is considered poor style or not.  Maybe we're only
supposed to have a single ECHO_* per recipe?

Anyway, even if this is poor style, I figure it really is just a style
thing.  We can tweak this later as needed.  Otherwise, this commit
should fix the current issue blocking the next GDB release.

Approved-By: Tom Tromey <tom@tromey.com>

1 files changed, 19 insertions, 6 deletions

diff --git a/gdb/doc/Makefile.in b/gdb/doc/Makefile.in
index 3f3fe7b..6a112b9 100644
--- a/gdb/doc/Makefile.in
+++ b/gdb/doc/Makefile.in
@@ -658,17 +658,30 @@ annotate/index.html: $(ANNOTATE_DOC_FILES)
 		-I $(srcdir) \
 		$(srcdir)/annotate.texinfo
 
-# Man pages
-%.pod : gdb.texinfo $(GDB_DOC_FILES)
-	$(ECHO_TEXI2POD) $(TEXI2POD) $(MANCONF) -D$* < $(srcdir)/gdb.texinfo > $@
-
-$(MAN1S) : %.1 : %.pod $(GDB_DOC_FILES)
+# Man pages.  The TEXI2POD and TEXI2MAN steps are performed within a
+# single recipe to support how we distribute GDB releases.  A release
+# includes the .1 and .5 man pages in the source tree, but not the
+# .pod files.
+#
+# When building and installing a release of GDB it should not be
+# necessary to rebuild the .1 or .5 man page files, nor should it be
+# necessary to rebuild the .pod files.
+#
+# If we split the .pod creation from the creation of the .1 and .5
+# pages, then the .pod files must become a dependency, this will
+# trigger an attempt to rebuild these files while building and
+# installing a release of GDB, which is something we don't want.
+$(MAN1S) : %.1 : $(GDB_DOC_FILES)
+	$(ECHO_TEXI2POD) $(TEXI2POD) $(MANCONF) -D$* < $(srcdir)/gdb.texinfo > $*.pod
 	$(ECHO_TEXI2MAN) ($(POD2MAN1) $*.pod | sed -e '/^.if n .na/d' > $@.T$$$$ && \
 		mv -f $@.T$$$$ $@) || (rm -f $@.T$$$$ && exit 1)
+	$(SILENCE) rm -f $*.pod
 
-$(MAN5S) : %.5 : %.pod $(GDB_DOC_FILES)
+$(MAN5S) : %.5 : $(GDB_DOC_FILES)
+	$(ECHO_TEXI2POD) $(TEXI2POD) $(MANCONF) -D$* < $(srcdir)/gdb.texinfo > $*.pod
 	$(ECHO_TEXI2MAN) ($(POD2MAN1) $*.pod | sed -e '/^.if n .na/d' > $@.T$$$$ && \
 		mv -f $@.T$$$$ $@) || (rm -f $@.T$$$$ && exit 1)
+	$(SILENCE) rm -f $*.pod
 
 force: