stripspace: allow -s/-c outside git repository

v2.11.0-rc3~3^2~1 (stripspace: respect repository config, 2016-11-21)
improved stripspace --strip-comments / --comentlines by teaching them
to read repository config, but it went a little too far: when running
stripspace outside any repository, the result is

	$ git stripspace --strip-comments <test-input
	fatal: not a git repository (or any parent up to mount point /tmp)

That makes experimenting with the stripspace command unnecessarily
fussy.  Fix it by discovering the git directory gently, as intended
all along.

Reported-by: Han-Wen Nienhuys <hanwen@google.com>
Signed-off-by: Jonathan Nieder <jrnieder@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

builtin/stripspace.c

@@ -30,6 +30,7 @@ int cmd_stripspace(int argc, const char **argv, const char *prefix)
 {
 	struct strbuf buf = STRBUF_INIT;
 	enum stripspace_mode mode = STRIP_DEFAULT;
+	int nongit;
 
 	const struct option options[] = {
 		OPT_CMDMODE('s', "strip-comments", &mode,
@@ -46,7 +47,7 @@ int cmd_stripspace(int argc, const char **argv, const char *prefix)
 		usage_with_options(stripspace_usage, options);
 
 	if (mode == STRIP_COMMENTS || mode == COMMENT_LINES) {
-		setup_git_directory_gently(NULL);
+		setup_git_directory_gently(&nongit);
 		git_config(git_default_config, NULL);
 	}
 

t/t0030-stripspace.sh

@@ -430,9 +430,15 @@ test_expect_success '-c with changed comment char' '
 test_expect_success '-c with comment char defined in .git/config' '
 	test_config core.commentchar = &&
 	printf "= foo\n" >expect &&
-	printf "foo" | (
-		mkdir sub && cd sub && git stripspace -c
-	) >actual &&
+	rm -fr sub &&
+	mkdir sub &&
+	printf "foo" | git -C sub stripspace -c >actual &&
+	test_cmp expect actual
+'
+
+test_expect_success '-c outside git repository' '
+	printf "# foo\n" >expect &&
+	printf "foo" | nongit git stripspace -c >actual &&
 	test_cmp expect actual
 '