Makefile: generate doc versions via GIT-VERSION-GEN

The documentation we generate embeds information for the exact Git
version used as well as the date of the commit. This information is
injected by injecting attributes into the build process via command line
argument.

Refactor the logic so that we write the information into "asciidoc.conf"
and "asciidoctor-extensions.rb" via `GIT-VERSION-GEN` for AsciiDoc and
AsciiDoctor, respectively.

Signed-off-by: Patrick Steinhardt <ps@pks.im>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
diff --git a/Documentation/.gitignore b/Documentation/.gitignore
index a48448d..649df89 100644
--- a/Documentation/.gitignore
+++ b/Documentation/.gitignore
@@ -15,3 +15,5 @@
 GIT-ASCIIDOCFLAGS
 /.build/
 /GIT-EXCLUDED-PROGRAMS
+/asciidoc.conf
+/asciidoctor-extensions.rb
diff --git a/Documentation/Makefile b/Documentation/Makefile
index 0f55baa..9371f29 100644
--- a/Documentation/Makefile
+++ b/Documentation/Makefile
@@ -1,6 +1,8 @@
 # Import tree-wide shared Makefile behavior and libraries
 include ../shared.mak
 
+.PHONY: FORCE
+
 # Guard against environment variables
 MAN1_TXT =
 MAN5_TXT =
@@ -148,16 +150,12 @@
 man7dir = $(mandir)/man7
 # DESTDIR =
 
-GIT_DATE := $(shell git show --quiet --pretty='%as')
-
 ASCIIDOC = asciidoc
 ASCIIDOC_EXTRA =
 ASCIIDOC_HTML = xhtml11
 ASCIIDOC_DOCBOOK = docbook
 ASCIIDOC_CONF = -f asciidoc.conf
-ASCIIDOC_COMMON = $(ASCIIDOC) $(ASCIIDOC_EXTRA) $(ASCIIDOC_CONF) \
-		-amanmanual='Git Manual' -amansource='Git $(GIT_VERSION)' \
-		-arevdate='$(GIT_DATE)'
+ASCIIDOC_COMMON = $(ASCIIDOC) $(ASCIIDOC_EXTRA) $(ASCIIDOC_CONF)
 ASCIIDOC_DEPS = asciidoc.conf GIT-ASCIIDOCFLAGS
 TXT_TO_HTML = $(ASCIIDOC_COMMON) -b $(ASCIIDOC_HTML)
 TXT_TO_XML = $(ASCIIDOC_COMMON) -b $(ASCIIDOC_DOCBOOK)
@@ -210,6 +208,14 @@
 DBLATEX_COMMON =
 XMLTO_EXTRA += --skip-validation
 XMLTO_EXTRA += -x manpage.xsl
+
+asciidoctor-extensions.rb: asciidoctor-extensions.rb.in FORCE
+	$(QUIET_GEN)GIT_USER_AGENT="$(GIT_USER_AGENT)" $(SHELL_PATH) ../GIT-VERSION-GEN "$(shell pwd)/.." $< $@+
+	@if cmp $@+ $@ >/dev/null 2>&1; then $(RM) $@+; else mv $@+ $@; fi
+else
+asciidoc.conf: asciidoc.conf.in FORCE
+	$(QUIET_GEN)GIT_USER_AGENT="$(GIT_USER_AGENT)" $(SHELL_PATH) ../GIT-VERSION-GEN "$(shell pwd)/.." $< $@+
+	@if cmp $@+ $@ >/dev/null 2>&1; then $(RM) $@+; else mv $@+ $@; fi
 endif
 
 ASCIIDOC_DEPS += docinfo.html
@@ -341,6 +347,7 @@
 	$(RM) SubmittingPatches.txt
 	$(RM) $(cmds_txt) $(mergetools_txt) *.made
 	$(RM) GIT-ASCIIDOCFLAGS
+	$(RM) asciidoc.conf asciidoctor-extensions.rb
 
 docinfo.html: docinfo-html.in
 	$(QUIET_GEN)$(RM) $@ && cat $< >$@
@@ -364,7 +371,7 @@
 %.xml : %.txt $(ASCIIDOC_DEPS)
 	$(QUIET_ASCIIDOC)$(TXT_TO_XML) -d manpage -o $@ $<
 
-user-manual.xml: user-manual.txt user-manual.conf asciidoctor-extensions.rb GIT-ASCIIDOCFLAGS
+user-manual.xml: user-manual.txt user-manual.conf $(ASCIIDOC_DEPS)
 	$(QUIET_ASCIIDOC)$(TXT_TO_XML) -d book -o $@ $<
 
 technical/api-index.txt: technical/api-index-skel.txt \
@@ -373,7 +380,7 @@
 
 technical/%.html: ASCIIDOC_EXTRA += -a git-relative-html-prefix=../
 $(patsubst %,%.html,$(API_DOCS) technical/api-index $(TECH_DOCS)): %.html : %.txt \
-	asciidoc.conf GIT-ASCIIDOCFLAGS
+	$(ASCIIDOC_DEPS)
 	$(QUIET_ASCIIDOC)$(TXT_TO_HTML) $*.txt
 
 SubmittingPatches.txt: SubmittingPatches
@@ -416,13 +423,13 @@
 howto-index.txt: howto-index.sh $(HOWTO_TXT)
 	$(QUIET_GEN)'$(SHELL_PATH_SQ)' ./howto-index.sh $(sort $(HOWTO_TXT)) >$@
 
-$(patsubst %,%.html,$(ARTICLES)) : %.html : %.txt
+$(patsubst %,%.html,$(ARTICLES)) : %.html : %.txt $(ASCIIDOC_DEPS)
 	$(QUIET_ASCIIDOC)$(TXT_TO_HTML) $*.txt
 
 WEBDOC_DEST = /pub/software/scm/git/docs
 
 howto/%.html: ASCIIDOC_EXTRA += -a git-relative-html-prefix=../
-$(patsubst %.txt,%.html,$(HOWTO_TXT)): %.html : %.txt GIT-ASCIIDOCFLAGS
+$(patsubst %.txt,%.html,$(HOWTO_TXT)): %.html : %.txt $(ASCIIDOC_DEPS)
 	$(QUIET_ASCIIDOC) \
 	sed -e '1,/^$$/d' $< | \
 	$(TXT_TO_HTML) - >$@
diff --git a/Documentation/asciidoc.conf b/Documentation/asciidoc.conf.in
similarity index 96%
rename from Documentation/asciidoc.conf
rename to Documentation/asciidoc.conf.in
index f6da6d1..dbe36a5 100644
--- a/Documentation/asciidoc.conf
+++ b/Documentation/asciidoc.conf.in
@@ -21,6 +21,9 @@
 apostrophe=&#39;
 backtick=&#96;
 litdd=&#45;&#45;
+manmanual='Git Manual'
+mansource='Git @GIT_VERSION@'
+revdate='@GIT_DATE@'
 
 ifdef::backend-docbook[]
 [linkgit-inlinemacro]
diff --git a/Documentation/asciidoctor-extensions.rb b/Documentation/asciidoctor-extensions.rb.in
similarity index 92%
rename from Documentation/asciidoctor-extensions.rb
rename to Documentation/asciidoctor-extensions.rb.in
index cb24480..c4c200d 100644
--- a/Documentation/asciidoctor-extensions.rb
+++ b/Documentation/asciidoctor-extensions.rb.in
@@ -29,13 +29,9 @@
     class DocumentPostProcessor < Asciidoctor::Extensions::Postprocessor
       def process document, output
         if document.basebackend? 'docbook'
-          mansource = document.attributes['mansource']
-          manversion = document.attributes['manversion']
-          manmanual = document.attributes['manmanual']
           new_tags = "" \
-            "<refmiscinfo class=\"source\">#{mansource}</refmiscinfo>\n" \
-            "<refmiscinfo class=\"version\">#{manversion}</refmiscinfo>\n" \
-            "<refmiscinfo class=\"manual\">#{manmanual}</refmiscinfo>\n"
+            "<refmiscinfo class=\"source\">@GIT_VERSION@</refmiscinfo>\n" \
+            "<refmiscinfo class=\"manual\">Git Manual</refmiscinfo>\n"
           output = output.sub(/<\/refmeta>/, new_tags + "</refmeta>")
         end
         output
diff --git a/GIT-VERSION-GEN b/GIT-VERSION-GEN
index a1c8146..b468778 100755
--- a/GIT-VERSION-GEN
+++ b/GIT-VERSION-GEN
@@ -53,6 +53,7 @@
 
 GIT_VERSION=$(expr "$VN" : v*'\(.*\)')
 GIT_BUILT_FROM_COMMIT=$(git -C "$SOURCE_DIR" rev-parse -q --verify HEAD 2>/dev/null)
+GIT_DATE=$(git -C "$SOURCE_DIR" show --quiet --format='%as' 2>/dev/null)
 if test -z "$GIT_USER_AGENT"
 then
 	GIT_USER_AGENT="git/$GIT_VERSION"
@@ -72,6 +73,7 @@
 	-e "s|@GIT_PATCH_LEVEL@|$GIT_PATCH_LEVEL|" \
 	-e "s|@GIT_BUILT_FROM_COMMIT@|$GIT_BUILT_FROM_COMMIT|" \
 	-e "s|@GIT_USER_AGENT@|$GIT_USER_AGENT|" \
+	-e "s|@GIT_DATE@|$GIT_DATE|" \
 	"$INPUT" >"$OUTPUT"+
 
 if ! test -f "$OUTPUT" || ! cmp "$OUTPUT"+ "$OUTPUT" >/dev/null