--- a/ChangeLog	Thu Sep 20 11:09:53 2012 +0200
+++ b/ChangeLog	Fri Sep 21 14:11:18 2012 +0200
@@ -1,3 +1,13 @@
+2012-09-21  Akim Demaille  <akim@lrde.epita.fr>
+
+	maint.mk: factor the validation of RELEASE_TYPE
+	With help from Jim Meyering.
+	http://lists.gnu.org/archive/html/bug-gnulib/2012-09/msg00132.html
+	* top/maint.mk (_empty, _sp): Move their definition earlier.
+	(member-check, release-type): New.
+	Use the latter instead of $(RELEASE_TYPE).
+	Remove now useless local checks.
+
 2012-09-20  Akim Demaille  <akim@lrde.epita.fr>
 
 	maint.mk: silent rules

--- a/top/maint.mk	Thu Sep 20 11:09:53 2012 +0200
+++ b/top/maint.mk	Fri Sep 21 14:11:18 2012 +0200
@@ -28,6 +28,22 @@
 set $$(_build-aux) relative to $$(srcdir) instead of $$(build_aux)")
 endif
 
+# Helper variables.
+_empty =
+_sp = $(_empty) $(_empty)
+
+# member-check VARIABLE,VALID-VALUES
+# ----------------------------------
+# Check that $(VARIABLE) is in the space-separated list of VALID-VALUES, and
+# return it.  Die otherwise.
+member-check =                                                  \
+  $(if $($(1)),                                                 \
+    $(if $(findstring $(_sp),$($(1))),                          \
+        $(error invalid $(1): '$($(1))', expected $(2)),        \
+        $(or $(findstring $(_sp)$($(1))$(_sp),$(_sp)$(2)(_sp)), \
+          $(error invalid $(1): '$($(1))', expected $(2)))),    \
+    $(error $(1) undefined))
+
 # Do not save the original name or timestamp in the .tar.gz file.
 # Use --rsyncable if available.
 gzip_rsyncable := \
@@ -91,13 +107,17 @@
 # Old releases are stored here.
 release_archive_dir ?= ../release
 
+# Validate and return $(RELEASE_TYPE), or die.
+RELEASE_TYPES = alpha beta stable
+release-type = $(call member-check,RELEASE_TYPE,$(RELEASE_TYPES))
+
 # Override gnu_rel_host and url_dir_list in cfg.mk if these are not right.
 # Use alpha.gnu.org for alpha and beta releases.
 # Use ftp.gnu.org for stable releases.
 gnu_ftp_host-alpha = alpha.gnu.org
 gnu_ftp_host-beta = alpha.gnu.org
 gnu_ftp_host-stable = ftp.gnu.org
-gnu_rel_host ?= $(gnu_ftp_host-$(RELEASE_TYPE))
+gnu_rel_host ?= $(gnu_ftp_host-$(release-type))
 
 ifeq ($(gnu_rel_host),ftp.gnu.org)
 url_dir_list ?= http://ftpmirror.gnu.org/$(PACKAGE)
@@ -570,8 +590,6 @@
 	@h='c-ctype.h' re='\<c_($(ctype_re)) *\(' \
 	  $(_sc_header_without_use)
 
-_empty =
-_sp = $(_empty) $(_empty)
 # The following list was generated by running:
 # man signal.h|col -b|perl -ne '/bsd_signal.*;/.../sigwaitinfo.*;/ and print' \
 #   | perl -lne '/^\s+(?:int|void).*?(\w+).*/ and print $1' | fmt
@@ -1266,7 +1284,7 @@
 translation_project_ ?= coordinator@translationproject.org
 
 # Make info-gnu the default only for a stable release.
-ifeq ($(RELEASE_TYPE),stable)
+ifeq ($(release-type),stable)
   announcement_Cc_ ?= $(translation_project_), $(PACKAGE_BUGREPORT)
   announcement_mail_headers_ ?=						\
     To: info-gnu@gnu.org						\
@@ -1284,7 +1302,7 @@
 # annoucement message: it would start with " GEN announcement".
 	$(AM_V_at)$(srcdir)/$(_build-aux)/announce-gen			\
 	    --mail-headers='$(announcement_mail_headers_)'		\
-	    --release-type=$(RELEASE_TYPE)				\
+	    --release-type=$(release-type)				\
 	    --package=$(PACKAGE)					\
 	    --prev=$(PREV_VERSION)					\
 	    --curr=$(VERSION)						\
@@ -1386,9 +1404,7 @@
 gl_noteworthy_news_ = * Noteworthy changes in release ?.? (????-??-??) [?]
 .PHONY: release-prep
 release-prep:
-	$(AM_V_GEN)case $$RELEASE_TYPE in alpha|beta|stable) ;; \
-	  *) echo "invalid RELEASE_TYPE: $$RELEASE_TYPE" 1>&2; exit 1;; esac
-	$(AM_V_at)$(MAKE) --no-print-directory -s announcement \
+	$(AM_V_GEN)$(MAKE) --no-print-directory -s announcement \
 	  > ~/announce-$(my_distdir)
 	$(AM_V_at)if test -d $(release_archive_dir); then	\
 	  ln $(rel-files) $(release_archive_dir);		\