From 1eee84b800408e53e659ff303eaa08ee09d67c3b Mon Sep 17 00:00:00 2001
From: Ron Yorston <rmy@pobox.com>
Date: Mon, 11 Mar 2024 09:12:47 +0000
Subject: make: allow '#' to be escaped with a backslash

POSIX doesn't allow the '#' comment marker to be escaped, though
some implementations do.

As a non-POSIX extension allow '#' to be escaped with a preceding
backslash.

It isn't necessary to escape '#' in macro expansions or command
lines:  these cases are covered by an existing extension.  Commit
0aceca867 (make: comments in macro expansions and command lines)

Adds 16-32 bytes.

(pdpmake GitHub issue 38)
---
 miscutils/make.c     | 14 +++++++++++---
 testsuite/make.tests |  9 +++++++++
 2 files changed, 20 insertions(+), 3 deletions(-)

diff --git a/miscutils/make.c b/miscutils/make.c
index 841daa93e..87f17aad7 100644
--- a/miscutils/make.c
+++ b/miscutils/make.c
@@ -1373,9 +1373,17 @@ process_line(char *s)
 
 	// Strip comment
 	// don't treat '#' in macro expansion as a comment
-	if (!posix)
-		t = find_char(s, '#');
-	else
+	// nor '#' outside macro expansion preceded by backslash
+	if (!posix) {
+		char *u = s;
+		while ((t = find_char(u, '#')) && t > u && t[-1] == '\\') {
+			for (u = t; *u; ++u) {
+				u[-1] = u[0];
+			}
+			*u = '\0';
+			u = t;
+		}
+	} else
 		t = strchr(s, '#');
 	if (t)
 		*t = '\0';
diff --git a/testsuite/make.tests b/testsuite/make.tests
index 745a840f3..1fc95a8d2 100755
--- a/testsuite/make.tests
+++ b/testsuite/make.tests
@@ -459,6 +459,15 @@ target:
 	: hash $(hash) hash
 '
 
+# A '#' character can be escaped with a backslash
+testing "make backslash-escaped hash isn't a comment" \
+	"make -f -" \
+	": hash # hash\n" "" '
+hash = \#
+target:
+	: hash $(hash) hash
+'
+
 # A '#' character in a command line doesn't start a comment
 testing "make hash in command line isn't a comment" \
 	"make -f -" \
-- 
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