From c31cf3ba8abba64cf8201ba7c4dd49534de33f74 Mon Sep 17 00:00:00 2001
From: rillig <rillig@pkgsrc.org>
Date: Tue, 2 Jan 2018 21:18:48 +0000
Subject: Allow package developers to easily see and check the SUBST changes.

---
 mk/subst.mk | 9 ++++++++-
 1 file changed, 8 insertions(+), 1 deletion(-)

(limited to 'mk/subst.mk')

diff --git a/mk/subst.mk b/mk/subst.mk
index 7309a38be3b..ba55964e44d 100644
--- a/mk/subst.mk
+++ b/mk/subst.mk
@@ -1,4 +1,4 @@
-# $NetBSD: subst.mk,v 1.55 2016/01/31 17:27:41 rillig Exp $
+# $NetBSD: subst.mk,v 1.56 2018/01/02 21:18:48 rillig Exp $
 #
 # This Makefile fragment implements a general text replacement facility.
 # Package makefiles define a ``class'', for each of which a particular
@@ -45,6 +45,10 @@
 #	before any substitutions are done to it. Since that test is not
 #	perfect, it can be disabled by setting this variable to "yes".
 #
+# SUBST_SHOW_DIFF.<class>
+#	During development of a package, this can be set to "yes" to see
+#	the actual changes as a unified diff.
+#
 # See also:
 #	PLIST_SUBST
 #
@@ -80,6 +84,9 @@ SUBST_MESSAGE.${_class_}?=	Substituting "${_class_}" in ${SUBST_FILES.${_class_}
 .  for v in ${SUBST_VARS.${_class_}}
 SUBST_FILTER_CMD.${_class_} +=	-e s,@${v}@,${${v}:S|\\|\\\\|gW:S|,|\\,|gW:S|&|\\\&|gW:Q},g
 .  endfor
+.  if !empty(SUBST_SHOW_DIFF.${_class_}:Uno:M[Yy][Ee][Ss])
+_SUBST_KEEP.${_class_}?=	${DIFF} -u "$$file" "$$tmpfile" || true
+.  endif
 _SUBST_KEEP.${_class_}?=	${DO_NADA}
 SUBST_SKIP_TEXT_CHECK.${_class_}?=	no
 
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