configure: Detect pandoc for building documentation

Makefile.am

@@ -13,6 +13,8 @@ EXTRA_DIST = \
 	COPYING.LGPL \
 	COPYING.MIT \
 	ChangeLog \
+	README \
+	README.md \
 	update-version.sh \
 	run-test-valgrind.supp \
 	$(conf_DATA)
@@ -21,6 +23,9 @@ noinst_DATA = dovecot-config
 
 nodist_pkginclude_HEADERS = config.h
 
+README: README.md
+	$(PANDOC) -f markdown_github -t plain -o $@ $<
+
 ChangeLog:
 	git log --name-status --pretty="format:%ai %aN <%aE> (%h)%n%n%w(80,4,4)%s%n%n%b" 5d5c4f2bfb812c767084c0338dae692db476da10^.. > ChangeLog || rm -f ChangeLog
 

configure.ac

@@ -819,6 +819,17 @@ AC_SUBST(NOPLUGIN_LDFLAGS)
 
 DC_CC_WRAPPER
 
+AC_ARG_VAR(PANDOC, [Path to pandoc program])
+
+# Optional tool for making documentation
+AC_CHECK_PROGS(PANDOC, [pandoc], [true])
+
+if test "$PANDOC" = "true"; then
+ if test ! -e README; then
+   AC_MSG_ERROR([Cannot produce documentation without pandoc])
+ fi
+fi
+
 if test "$docdir" = ""; then
   dnl docdir supported only by autoconf v2.59c and later
   docdir='${datadir}/doc/${PACKAGE_TARNAME}'