Makefile.am: Add check-po rule.

* Makefile.am (make-check-po-rule): New definition.
Add top-level 'eval' and calls to 'make-check-po-rule' to generate
'check-po.DOMAIN' rules.
(check-po): New rule.

Makefile.am

@@ -1003,14 +1003,49 @@ download-po.$(1):
 
 endef
 
+# Checking po files for issues.  This is useful to run after downloading new
+# po files.
+
+# make-check-po-rule DOMAIN DIRECTORY [FILE-NAME-PREFIX]
+define make-check-po-rule
+
+check-po.$(1):
+	if [ -f "$(top_srcdir)/$(2)/LINGUAS" ]; then				\
+	  LINGUAS="`grep -v '^[[:blank:]]*#' < $(top_srcdir)/$(2)/LINGUAS`" ;	\
+	else									\
+	  LINGUAS="`(cd $(top_srcdir)/$(2);					\
+	    for i in *.po; do echo $$$$i; done) | cut -d . -f 2`" ;		\
+	fi ;									\
+	for lang in $$$$LINGUAS; do						\
+	  if [ -f "$(top_srcdir)/$(2)/$(3)$$$$lang.po" ];			\
+	  then									\
+	    if ! msgfmt -c "$(top_srcdir)/$(2)/$(3)$$$$lang.po" ;		\
+		then								\
+		  exit 1 ;							\
+	    fi ;								\
+	  fi ;									\
+	done
+
+.PHONY: check-po.$(1)
+
+endef
+
 $(eval $(call make-download-po-rule,documentation-cookbook,po/doc,guix-cookbook.))
 $(eval $(call make-download-po-rule,documentation-manual,po/doc,guix-manual.))
 $(eval $(call make-download-po-rule,guix,po/guix))
 $(eval $(call make-download-po-rule,packages,po/packages))
 
+$(eval $(call make-check-po-rule,documentation-cookbook,po/doc,guix-cookbook.))
+$(eval $(call make-check-po-rule,documentation-manual,po/doc,guix-manual.))
+$(eval $(call make-check-po-rule,guix,po/guix))
+$(eval $(call make-check-po-rule,packages,po/packages))
+
 download-po: $(foreach domain,guix packages documentation-manual documentation-cookbook,download-po.$(domain))
 .PHONY: download-po
 
+check-po: $(foreach domain,guix packages documentation-manual documentation-cookbook,check-po.$(domain))
+.PHONY: check-po
+
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 ## Silent rules.  ##
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