maint: teach "make syntax-check" the space-only indentation rule

* cfg.mk (sc_prohibit_tab_based_indentation): New rule.
* .x-sc_prohibit_tab_based_indentation: New file.
* Makefile.am (syntax_check_exceptions): Add file,
.x-sc_prohibit_tab_based_indentation.

1 files changed, 6 insertions, 0 deletions

diff --git a/cfg.mk b/cfg.mk
index 05dbb39b9..b63e76b7e 100644
--- a/cfg.mk
+++ b/cfg.mk
@@ -206,4 +206,10 @@ sc_strftime_check:
 	  rm -f $@-src $@-info;						\
 	fi
 
+# Indent only with spaces.
+sc_prohibit_tab_based_indentation:
+	@re='^ *	'						\
+	msg='TAB in indentation; use only spaces'			\
+	  $(_prohibit_regexp)
+
 include $(srcdir)/dist-check.mk