[patch] Avoid some of the sc_ rules to freeze

[jemarch]

Hi.

Just another little patch to avoid some of the sc_* rules to freeze if
the filtering of VC_LIST_EXCEPT gives an empty string (for example,
'make sc_error_exit_success' freezes if there are not source files in
${srcdir}/).

I found this problem due to the bazaar issue in vc-list-files.


2010-02-21  Jose E. Marchesi  <address@hidden>

        * top/maint.mk (sc_error_exit_success): Apply the rule only if the
        filtering of VC_LIST_EXCEPT is not empty.  Otherwise the main grep
        freezes waiting for data in the standard input.
        (sc_makefile_TAB_only_indentation): Likewise.
        (sc_makefile_path_separator_check): Likewise.
        (sc_m4_quote_check): Likewise.

diff --git a/top/maint.mk b/top/maint.mk
index 7d84b6c..11afe6b 100644
--- a/top/maint.mk
+++ b/top/maint.mk
@@ -217,9 +217,13 @@ sc_prohibit_magic_number_exit:
 # Using EXIT_SUCCESS as the first argument to error is misleading,
 # since when that parameter is 0, error does not exit.  Use `0' instead.
 sc_error_exit_success:
-       @grep -nE 'error \(EXIT_SUCCESS,'                               \
-           $$($(VC_LIST_EXCEPT) | grep -E '\.[chly]$$') &&             \
-         { echo '$(ME): found error (EXIT_SUCCESS' 1>&2; exit 1; } || :
+       @if $(VC_LIST_EXCEPT) | grep -E '\.[chly]$$' > /dev/null; then  \
+         grep -nE 'error \(EXIT_SUCCESS,'                              \
+               $$($(VC_LIST_EXCEPT) | grep -E '\.[chly]$$') &&         \
+         { echo '$(ME): found error (EXIT_SUCCESS'                     \
+               1>&2; exit 1; } || :;                                   \
+       else :;                                                         \
+       fi
 
 # `FATAL:' should be fully upper-cased in error messages
 # `WARNING:' should be fully upper-cased, or fully lower-cased
@@ -652,16 +656,22 @@ news-check: NEWS
        fi
 
 sc_makefile_TAB_only_indentation:
-       @grep -nE '^    [ ]{8}'                                         \
-           $$($(VC_LIST_EXCEPT) | grep -E 'akefile|\.mk$$')            \
-         && { echo '$(ME): found TAB-8-space indentation' 1>&2;        \
-              exit 1; } || :
+       @if $(VC_LIST_EXCEPT) | grep -E 'akefile|\.mk$$' > /dev/null; then      
\
+       grep -nE '^     [ ]{8}'                                                 
\
+               $$($(VC_LIST_EXCEPT) | grep -E 'akefile|\.mk$$')                
\
+           && { echo '$(ME): found TAB-8-space indentation' 1>&2;              
\
+               exit 1; } || :;                                                 
\
+       else :;                                                                 
\
+       fi
 
 sc_m4_quote_check:
-       @grep -nE '(AC_DEFINE(_UNQUOTED)?|AC_DEFUN)\([^[]'              \
-           $$($(VC_LIST_EXCEPT) | grep -E '(^configure\.ac|\.m4)$$')   \
-         && { echo '$(ME): quote the first arg to AC_DEF*' 1>&2;       \
-              exit 1; } || :
+       @if $(VC_LIST_EXCEPT) | grep -E '(^configure\.ac|\.m4)$$' > /dev/null; 
then     \
+         grep -nE '(AC_DEFINE(_UNQUOTED)?|AC_DEFUN)\([^[]'                     
        \
+               $$($(VC_LIST_EXCEPT) | grep -E '(^configure\.ac|\.m4)$$')       
        \
+           && { echo '$(ME): quote the first arg to AC_DEF*' 1>&2;             
        \
+               exit 1; } || :;                                                 
        \
+       else :;                                                                 
        \
+       fi
 
 fix_po_file_diag = \
 'you have changed the set of files with translatable diagnostics;\n\
@@ -700,9 +710,12 @@ sc_po_check:
 # path separator of `:', but rather the automake-provided `$(PATH_SEPARATOR)'.
 msg = '$(ME): Do not use `:'\'' above; use $$(PATH_SEPARATOR) instead'
 sc_makefile_path_separator_check:
-       @grep -nE 'PATH[=].*:'                                          \
-           $$($(VC_LIST_EXCEPT) | grep -E 'akefile|\.mk$$')            \
-         && { echo $(msg) 1>&2; exit 1; } || :
+       @if $(VC_LIST_EXCEPT) | grep -E 'akefile|\.mk$$' > /dev/null; then      
\
+         grep -nE 'PATH[=].*:'                                                 
\
+               $$($(VC_LIST_EXCEPT) | grep -E 'akefile|\.mk$$')                
\
+            && { echo $(msg) 1>&2; exit 1; } || :;                             
\
+       else :;                                                                 
\
+       fi
 
 # Check that `make alpha' will not fail at the end of the process.
 writable-files: