mk/subst.mk: allow identity substitutions with escaped dots

This fixes the build of converters/help2man in SUBST_NOOP_OK=no mode.

1 files changed, 24 insertions, 1 deletions

diff --git a/regress/infra-unittests/subst.sh b/regress/infra-unittests/subst.sh
index ee404ee1508..5a06aadacf2 100644
--- a/regress/infra-unittests/subst.sh
+++ b/regress/infra-unittests/subst.sh
@@ -1,5 +1,5 @@
 #! /bin/sh
-# $NetBSD: subst.sh,v 1.31 2020/05/02 06:48:59 rillig Exp $
+# $NetBSD: subst.sh,v 1.32 2020/05/06 06:14:56 rillig Exp $
 #
 # Tests for mk/subst.mk.
 #
@@ -1189,6 +1189,29 @@ if test_case_begin "identity substitution implementation"; then
 	specials='!"%'\''()+,-/:;<=>@_`{|}~'
 	assert_identity "yes"	-e "sX${specials}X${specials}X"
 
+	# Regular expression meta-characters may be escaped using a
+	# backslash or be enclosed in square brackets.
+	assert_identity 'yes'	-e 's,library\.so,library.so,g'
+	assert_identity 'yes'	-e 's,library[.]so,library.so,g'
+	assert_identity 'yes'	-e 's,[*],*,'
+	assert_identity 'yes'	-e 's,[$],$,'
+
+	# When this happens, it is probably a mistake.
+	assert_identity	'no'	-e 's,,,'
+
+	# Backslashes are not considered identity substitutions since
+	# there might be tricky corner cases.
+	assert_identity	'no'	-e 's,\\,\\,'
+
+	# Back-references are not considered identity substitutions.
+	assert_identity 'no'	-e 's,\1,\1,'
+
+	# The & is interpreted specially in the replacement string.
+	assert_identity 'no'	-e 's,&&&,&&&,'
+	assert_identity 'no'	-e 's,\&,&,'
+	assert_identity 'no'	-e 's,[&],&,'
+	assert_identity 'no'	-e 's,&,\&,' # this would be an identity
+
 	test_case_end
 fi