2.36 format-patch regression fix

e900d494dc (diff: add an API for deferred freeing, 2021-02-11) added a
way to allow reusing diffopts: the no_free bit.  244c27242f (diff.[ch]:
have diff_free() call clear_pathspec(opts.pathspec), 2022-02-16) made
that mechanism mandatory.

git format-patch only sets no_free when --output is given, causing it to
forget pathspecs after the first commit.  Set no_free unconditionally
instead.

The existing test was unable to detect this breakage because it checks
stderr for the absence of a certain string, but format-patch writes to
stdout.  Also the test was not checking the case of one commit modifying
multiple files and a pathspec limiting the diff.  Replace it with a more
thorough one.

Signed-off-by: René Scharfe <l.s.r@web.de>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

builtin/log.c

@@ -1883,6 +1883,7 @@ int cmd_format_patch(int argc, const char **argv, const char *prefix)
 	rev.diff = 1;
 	rev.max_parents = 1;
 	rev.diffopt.flags.recursive = 1;
+	rev.diffopt.no_free = 1;
 	rev.subject_prefix = fmt_patch_subject_prefix;
 	memset(&s_r_opt, 0, sizeof(s_r_opt));
 	s_r_opt.def = "HEAD";
@@ -2008,13 +2009,7 @@ int cmd_format_patch(int argc, const char **argv, const char *prefix)
 
 	if (use_stdout) {
 		setup_pager();
-	} else if (rev.diffopt.close_file) {
-		/*
-		 * The diff code parsed --output; it has already opened the
-		 * file, but we must instruct it not to close after each diff.
-		 */
-		rev.diffopt.no_free = 1;
-	} else {
+	} else if (!rev.diffopt.close_file) {
 		int saved;
 
 		if (!output_directory)

t/t4014-format-patch.sh

@@ -926,11 +926,40 @@ test_expect_success 'format-patch --numstat should produce a patch' '
 '
 
 test_expect_success 'format-patch -- <path>' '
-	git format-patch main..side -- file 2>error &&
-	! grep "Use .--" error
+	rm -f *.patch &&
+	git checkout -b pathspec main &&
+
+	echo file_a 1 >file_a &&
+	echo file_b 1 >file_b &&
+	git add file_a file_b &&
+	git commit -m pathspec_initial &&
+
+	echo file_a 2 >>file_a &&
+	git add file_a &&
+	git commit -m pathspec_a &&
+
+	echo file_b 2 >>file_b &&
+	git add file_b &&
+	git commit -m pathspec_b &&
+
+	echo file_a 3 >>file_a &&
+	echo file_b 3 >>file_b &&
+	git add file_a file_b &&
+	git commit -m pathspec_ab &&
+
+	cat >expect <<-\EOF &&
+	0001-pathspec_initial.patch
+	0002-pathspec_a.patch
+	0003-pathspec_ab.patch
+	EOF
+
+	git format-patch main..pathspec -- file_a >output &&
+	test_cmp expect output &&
+	! grep file_b *.patch
 '
 
 test_expect_success 'format-patch --ignore-if-in-upstream HEAD' '
+	git checkout side &&
 	git format-patch --ignore-if-in-upstream HEAD
 '