+# Check that we don't use $< in non-implicit Makefile rules.
+#
+# To find the Makefiles, trace AC_CONFIG_FILES. Using VC_LIST would
+# miss the Makefiles that are not under VC control (e.g., symlinks
+# installed for gettext). "Parsing" (recursive) uses of SUBDIRS seems
+# too delicate.
+#
+# Use GNU Make's --print-data-base to normalize the rules into some
+# easy to parse format: they are separated by two \n. Look for the
+# "section" about non-pattern rules (marked with "# Files") inside
+# which there are still the POSIX Make like implicit rules (".c.o").
+sc_prohibit_gnu_make_extensions_awk_ = \
+ BEGIN { \
+ RS = "\n\n"; \
+ in_rules = 0; \
+ } \
+ /^\# Files/ { \
+ in_rules = 1; \
+ } \
+ /\$$</ && in_rules && $$0 !~ /^(.*\n)*\.\w+(\.\w+)?:/ { \
+ print "Error: " file ": $$< in a non implicit rule\n" $$0; \
+ status = 1; \
+ } \
+ END { \
+ exit status; \
+ }
+sc_prohibit_gnu_make_extensions:
+ @if $(AWK) --version | grep GNU >/dev/null 2>&1; then \
+ (cd $(srcdir) && autoconf --trace AC_CONFIG_FILES:'$$1') | \
+ tr ' ' '\n' | \
+ $(SED) -ne '/Makefile/{s/\.in$$//;p;}' | \
+ while read m; do \
+ $(MAKE) -qp -f $$m .DUMMY-TARGET 2>/dev/null | \
+ $(AWK) -v file=$$m -e '$($@_awk_)' || exit 1; \
+ done; \
+ fi
+