From 28af22c256a385db7d65a42ff6de0b8573131236 Mon Sep 17 00:00:00 2001
From: Ron Yorston <rmy@pobox.com>
Date: Sun, 30 Oct 2022 14:24:42 +0000
Subject: make: different treatment for escaped NL in macro in command

Austin Group defect report 1549 has been accepted.  It requires
that an escaped newline inside a macro expansion in a command is
replaced by a space.  Other escaped newlines in commands are
left in place, as before.
---
 miscutils/make.c     | 30 ++++++++++++++++++++++++------
 testsuite/make.tests | 13 +++++++++++++
 2 files changed, 37 insertions(+), 6 deletions(-)

diff --git a/miscutils/make.c b/miscutils/make.c
index df46256bb..111ab2914 100644
--- a/miscutils/make.c
+++ b/miscutils/make.c
@@ -1401,17 +1401,35 @@ static char *
 process_command(char *s)
 {
 	char *t, *u;
+	int len = strlen(s) + 1;
+	char *outside = xzalloc(len);
 
-	// Remove tab following escaped newline.  Stop processing at a
-	// non-escaped newline.
-	for (t = u = s; *u && *u != '\n'; u++) {
-		*t++ = *u;
+	for (t = skip_macro(s); *t; t = skip_macro(t + 1)) {
+		outside[t - s] = 1;
+	}
+
+	// Process escaped newlines.  Stop at first non-escaped newline.
+	for (t = u = s; *u && *u != '\n'; ) {
 		if (u[0] == '\\' && u[1] == '\n') {
-			*t++ = '\n';
-			u += (u[2] == '\t') ? 2 : 1;
+			if (posix || outside[u - s]) {
+				// Outside macro: remove tab following escaped newline.
+				*t++ = *u++;
+				*t++ = *u++;
+				u += (*u == '\t');
+			} else {
+				// Inside macro: replace escaped newline and any leading
+				// whitespace on the following line with a single space.
+				u += 2;
+				while (isspace(*u))
+					++u;
+				*t++ = ' ';
+			}
+		} else {
+			*t++ = *u++;
 		}
 	}
 	*t = '\0';
+	free(outside);
 	return s;
 }
 
diff --git a/testsuite/make.tests b/testsuite/make.tests
index 35d3b7149..8b46faf3c 100755
--- a/testsuite/make.tests
+++ b/testsuite/make.tests
@@ -307,6 +307,19 @@ target: file1 .WAIT file2
 '
 cd .. || exit 1; rm -rf make.tempdir 2>/dev/null
 
+# Escaped newlines inside macro expansions in commands get different
+# treatment than those outside.  In POSIX 2017 the output is 'a b ab'.
+testing "make replace escaped NL in macro in command with space" \
+	"make -f -" \
+	"a b a b\n" "" '
+M=word
+N=${M:word=a\
+b}
+target:
+	@echo ${N} ${M:word=a\
+b}
+'
+
 testing "make double-colon rule" \
 	"make -f -" "target1\ntarget2\n" "" '
 target::
-- 
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