btrfs-progs: build: add support for asciidoctor doc generator

We've been using asciidoc that's written in python2, which is going to
be phased out and deprecated next year. There's a replacement,
asciidoctor. Add a configure-time detection which tool is available,
update Documentation/Makefile.in.

The original asciidoc tool is still preferred as it produces slightly
better output. The file asciidoc.conf does not have a direct equivalten
in asciidoct and would need to be replaced by extension written in ruby.

The differences:

- the <literal> are not automatically underlined and are less visible in
  the generated manual page, but it's still acceptable
- the inline CSS for the html output looks subjectively worse, is less
  compact and colourful

Issue: kdave#89
Signed-off-by: David Sterba <dsterba@suse.com>

Author: kdave

Documentation/Makefile.in

@@ -46,8 +46,21 @@ man3dir = $(mandir)/man3
 man5dir = $(mandir)/man5
 man8dir = $(mandir)/man8
 
+ifeq (@ASCIIDOC_TOOL@,asciidoc)
 ASCIIDOC = @ASCIIDOC@
-ASCIIDOC_EXTRA =
+ASCIIDOC_ARGS = -abtrfs_version=$(BTRFS_VERSION) -f asciidoc.conf
+ASCIIDOC_HTML = html
+ASCIIDOC_DOCBOOK = docbook
+ASCIIDOC_DEPS = asciidoc.conf
+endif
+ifeq (@ASCIIDOC_TOOL@,asciidoctor)
+ASCIIDOC = @ASCIIDOCTOR@
+ASCIIDOC_ARGS = -abtrfs_version=$(BTRFS_VERSION)
+ASCIIDOC_HTML = xhtml5
+ASCIIDOC_DOCBOOK = docbook45
+ASCIIDOC_DEPS = 
+endif
+
 MANPAGE_XSL = manpage-normal.xsl
 XMLTO = @XMLTO@
 XMLTO_EXTRA =
@@ -121,16 +134,12 @@ clean:
 	$(QUIET_XMLTO)$(RM) -f $@ && \
 	$(XMLTO) -m $(MANPAGE_XSL) $(XMLTO_EXTRA) man $<
 
-%.xml : %.asciidoc asciidoc.conf
+%.xml : %.asciidoc $(ASCIIDOC_DEPS)
 	$(QUIET_ASCIIDOC)$(RM) -f $@+ $@ && \
-	$(ASCIIDOC) -b docbook -d manpage -f asciidoc.conf \
-		$(ASCIIDOC_EXTRA) -abtrfs_version=$(BTRFS_VERSION) \
-		-o $@+ $< && \
+	$(ASCIIDOC) $(ASCIIDOC_ARGS) -b $(ASCIIDOC_DOCBOOK) -d manpage -o $@+ $< && \
 	$(MV) $@+ $@
 
-%.html : %.asciidoc asciidoc.conf
+%.html : %.asciidoc $(ASCIIDOC_DEPS)
 	$(QUIET_ASCIIDOC)$(RM) -f $@+ $@ && \
-	$(ASCIIDOC) -b html -d article -f asciidoc.conf \
-		$(ASCIIDOC_EXTRA) -abtrfs_version=$(BTRFS_VERSION) \
-		-o $@+ $< && \
+	$(ASCIIDOC) $(ASCIIDOC_ARGS) -b $(ASCIIDOC_HTML) -d article -o $@+ $< && \
 	$(MV) $@+ $@

configure.ac

@@ -39,6 +39,7 @@ AC_CHECK_TOOL([AR], [ar])
 AC_PATH_PROG([RM], [rm], [rm])
 AC_PATH_PROG([RMDIR], [rmdir], [rmdir])
 
+
 AC_CHECK_FUNCS([openat], [],
 	[AC_MSG_ERROR([cannot find openat() function])])
 
@@ -88,13 +89,27 @@ AS_IF([test "x$enable_documentation" = xyes], [DISABLE_DOCUMENTATION=0], [DISABL
 AC_SUBST([DISABLE_DOCUMENTATION])
 
 dnl detect tools to build documentation
+ASCIIDOC_TOOL="none"
 if test "x$enable_documentation" = xyes; then
-	AC_PATH_PROG([ASCIIDOC], [asciidoc], [asciidoc])
 	AC_PATH_PROG([XMLTO], [xmlto], [xmlto])
 	AC_PATH_PROG([GZIP], [gzip], [gzip])
 	AC_PATH_PROG([MV], [mv], [mv])
 	AC_PROG_SED
+	AC_PATH_PROG([ASCIIDOC], [asciidoc])
+	AC_PATH_PROG([ASCIIDOCTOR], [asciidoctor])
+
+	dnl asciidoc is preferred
+	if test -n "$ASCIIDOC"; then
+		ASCIIDOC_TOOL="asciidoc"
+	else
+		if test -n "$ASCIIDOCTOR"; then
+			ASCIIDOC_TOOL="asciidoctor"
+		else
+			AC_MSG_ERROR([cannot find asciidoc or asciidoctor, cannot build documentation])
+		fi
+	fi
 fi
+AC_SUBST([ASCIIDOC_TOOL])
 
 AC_ARG_ENABLE([convert],
 	      AS_HELP_STRING([--disable-convert], [do not build btrfs-convert]),
@@ -246,6 +261,7 @@ AC_MSG_RESULT([
 	ldflags:            ${LDFLAGS}
 
 	documentation:      ${enable_documentation}
+	doc generator:      ${ASCIIDOC_TOOL}
 	backtrace support:  ${enable_backtrace}
 	btrfs-convert:      ${enable_convert} ${convertfs:+($convertfs)}
 	btrfs-restore zstd: ${enable_zstd}