[PATCHv3 3/6] gdb/doc: allow for version.subst in the source tree

[Andrew Burgess <aburgess@redhat.com>]

In a git checkout of the source code we don't have a version.subst
file in the gdb/doc directory.  When building the GDB docs the
version.subst file is generated on demand (we have a recipe for that).

However, in a release tar file we do include a copy of the
version.subst file in the source tree, as a result the version.subst
recipe will not be run.

If, in a release build, we force the running of any recipe that
depends on version.subst then we run into a problem.  For example,
slightly confusingly, if we 'touch gdb/doc/version.subst' within the
unpacked source tree of a release, then 'make -C gdb/doc GDBvn.texi'
in the build tree, we'll see:

  make: Entering directory '/tmp/build/build/gdb/doc'
    GEN    GDBvn.texi
  sed: can't read version.subst: No such file or directory
  make: Leaving directory '/tmp/build/build/gdb/doc'

The problem is that every reference to version.subst in GDB's Makefile
assumes that the version.subst file will always be in the build
directory.

Handily version.subst is always the first dependency in every recipe
that uses that file.  As such we can replace references to
version.subst with $<, make will expand this to the location where the
dependency was found.

In the case of the man page generation, the reference to version.subst
is hidden inside POD2MAN.  It seemed a little confusing adding a use
of  $< within POD2MAN, so I've moved the use into the recipe, which I
think is clearer.

I've also added comments for the two rules that I've modified to
explain our use of $<.

After this change it is possible to rebuild the man pages even when
version.subst is located in the source tree.
---
 gdb/doc/Makefile.in | 18 ++++++++++++++----
 1 file changed, 14 insertions(+), 4 deletions(-)

diff --git a/gdb/doc/Makefile.in b/gdb/doc/Makefile.in
index 70d65d58ed0..eb800bf3848 100644
--- a/gdb/doc/Makefile.in
+++ b/gdb/doc/Makefile.in
@@ -178,8 +178,8 @@ MANCONF = -Dman
 TEXI2POD = perl $(srcdir)/../../etc/texi2pod.pl \
 		$(MAKEINFOFLAGS) $(MAKEINFO_EXTRA_FLAGS)
 
-POD2MAN = pod2man --center="GNU Development Tools" \
-		--release="gdb-`sed q version.subst`"
+
+POD2MAN = pod2man --center="GNU Development Tools"
 
 # List of man pages generated from gdb.texi
 MAN1S = gdb.1 gdbserver.1 gcore.1 gdb-add-index.1
@@ -435,9 +435,14 @@ refcard.pdf : refcard.tex $(REFEDITS)
 	$(SILENCE) rm -f sedref.log sedref.tex tmp.sed
 
 # File to record current GDB version number.
+#
+# It is important that version.subst be the first dependency so that
+# $< can be used in the recipe, this allows us to find version.subst
+# in either the source tree or the build tree as this file is
+# included, pre-built, as part of a relase.
 GDBvn.texi : version.subst
 	$(ECHO_GEN)
-	$(SILENCE) echo "@set GDBVN `sed q version.subst`" > ./GDBvn.new
+	$(SILENCE) echo "@set GDBVN `sed q $<`" > ./GDBvn.new
 	$(SILENCE) if [ -n "$(PKGVERSION)" ]; then \
 	  echo "@set VERSION_PACKAGE $(PKGVERSION)" >> ./GDBvn.new; \
 	fi
@@ -652,11 +657,16 @@ annotate/index.html: $(ANNOTATE_DOC_FILES)
 # 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.
+#
+# It is important that version.subst be the first dependency so that
+# $< can be used in the recipe, this allows us to find version.subst
+# in either the source tree or the build tree as this file is
+# included, pre-built, as part of a relase.
 $(MAN1S) $(MAN5S) : version.subst $(GDB_DOC_FILES)
 	$(ECHO_TEXI2POD) $(TEXI2POD) $(MANCONF) -D$(basename $@) \
 		< $(srcdir)/gdb.texinfo > $(basename $@).pod
 	$(ECHO_TEXI2MAN) ($(POD2MAN) --section=$(subst .,,$(suffix $@)) \
-			$(basename $@).pod | \
+			--release="gdb-`sed q $<`" $(basename $@).pod | \
 		sed -e '/^.if n .na/d' > $@.T$$$$ && \
 		mv -f $@.T$$$$ $@) || (rm -f $@.T$$$$ && exit 1)
 	$(SILENCE) rm -f $(basename $@).pod
-- 
2.25.4