maintainer-makefile vs vc-list-files/useless-if-before-free

[Simon Josefsson]

In a project that use maintainer-makefile, I get:

address@hidden:~/src/libidn master$ make syntax-check
avoid_if_before_free
/bin/sh: line 2: /build-aux/vc-list-files: No such file or directory
/bin/sh: line 2: /build-aux/useless-if-before-free: No such file or directory

The patch below makes the error messages better.  Ok to push?

I prefer that maintainer-makefile do not depend on vc-list-files and
useless-if-before-free modules: not every use of maint.mk requires
syntax-check to work, and not every use of syntax-check needs
useless-if-before-free tests.

/Simon

diff --git a/top/maint.mk b/top/maint.mk
index 9a683a7..cb73cc8 100644
--- a/top/maint.mk
+++ b/top/maint.mk
@@ -32,7 +32,8 @@ GIT = git
 VC = $(GIT)
 VC-tag = git tag -s -m '$(VERSION)' -u '$(gpg_key_ID)'
 
-VC_LIST = $(gnulib_dir)/build-aux/vc-list-files -C $(srcdir)
+VC_LIST_FILES ?= $(gnulib_dir)/build-aux/vc-list-files
+VC_LIST = $(VC_LIST_FILES) -C $(srcdir)
 
 VC_LIST_EXCEPT = \
   $(VC_LIST) | if test -f $(srcdir)/.x-$@; then grep -vEf $(srcdir)/.x-$@; 
else grep -v ChangeLog; fi
@@ -83,7 +84,13 @@ $(patsubst %, %.m, $(syntax-check-rules)):
 
 local-check := $(filter-out $(local-checks-to-skip), $(local-checks-available))
 
-syntax-check: $(local-check)
+check-vc-list-files:
+       test -x $(VC_LIST_FILES) || \
+       { echo '$(ME): need gnulib module vc-list-files' 1>&2; \
+       exit 1; } || :
+.PHONY: check-vc-list-files
+
+syntax-check: check-vc-list-files $(local-check)
 #      @grep -nE '#  *include <(limits|std(def|arg|bool))\.h>'         \
 #          $$(find -type f -name '*.[chly]') &&                        \
 #        { echo '$(ME): found conditional include' 1>&2;               \
@@ -111,6 +118,9 @@ define _prohibit_regexp
 endef
 
 sc_avoid_if_before_free:
+       test -x $(gnulib_dir)/build-aux/useless-if-before-free || \
+       { echo '$(ME): need gnulib module useless-if-before-free' 1>&2; \
+         exit 1; } || :
        @$(gnulib_dir)/build-aux/useless-if-before-free                 \
                $(useless_free_options)                                 \
            $$($(VC_LIST_EXCEPT)) &&                                    \