[PATCH] maint.mk: fix syntax checks without exclusions

[Eric Blake]

Commit 727075d0 skipped per-line exclusions if ${exclude} is left
undefined, but was immediately broken by commit 44de969c which
always initialized the variable to the empty string.

* top/maint.mk (_sc_search_regexp): Allow for empty variable.

Signed-off-by: Eric Blake <address@hidden>
---

Previously, I said

> cfg.mk is included _before_ maint.mk.  Therefore, $_sc_search_regexp) is
> expanded in cfg.mk prior to the place where maint.mk provides a default
> definition for $(exclude), so we are getting the wrong thing expanded,
> which breaks the syntax check rule in cfg.mk.

It turned out to be a lot simpler than that - a single character bug.

 ChangeLog    |    3 +++
 top/maint.mk |    2 +-
 2 files changed, 4 insertions(+), 1 deletions(-)

diff --git a/ChangeLog b/ChangeLog
index 376a5a2..6f82644 100644
--- a/ChangeLog
+++ b/ChangeLog
@@ -1,5 +1,8 @@
 2012-03-29  Eric Blake  <address@hidden>

+       maint.mk: fix syntax checks without exclusions
+       * top/maint.mk (_sc_search_regexp): Allow for empty variable.
+
        strerror_r: avoid compiler warning
        * lib/strerror_r.c (strerror_r): Hoist extern declaration to top
        level.
diff --git a/top/maint.mk b/top/maint.mk
index 951b358..2228a37 100644
--- a/top/maint.mk
+++ b/top/maint.mk
@@ -279,7 +279,7 @@ define _sc_search_regexp
    if test -n "$$files"; then                                          \
      if test -n "$$prohibit"; then                                     \
        grep $$with_grep_options $(_ignore_case) -nE "$$prohibit" $$files \
-         | grep -vE "$${exclude-^$$}"                                  \
+         | grep -vE "$${exclude:-^$$}"                                 \
          && { msg="$$halt" $(_sc_say_and_exit) } || :;                 \
      else                                                              \
        grep $$with_grep_options $(_ignore_case) -LE "$$require" $$files \
-- 
1.7.7.6