merge-file: correctly find files when called in subdir

Since b541248 (merge.conflictstyle: choose between "merge" and "diff3
-m" styles, 2008-08-29), git-merge-file uses setup_directory_gently(),
thus cd'ing around to find any possible config files to use.

This broke merge-file when it is called from within a subdirectory of
a repository, and the arguments are all relative paths.

Fix by prepending the prefix, as passed down from the main git
setup code, if there is any.

Signed-off-by: Thomas Rast <trast@student.ethz.ch>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

builtin/merge-file.c

@@ -28,6 +28,7 @@ int cmd_merge_file(int argc, const char **argv, const char *prefix)
 	xmparam_t xmp = {{0}};
 	int ret = 0, i = 0, to_stdout = 0;
 	int quiet = 0;
+	int prefixlen = 0;
 	struct option options[] = {
 		OPT_BOOLEAN('p', "stdout", &to_stdout, "send results to standard output"),
 		OPT_SET_INT(0, "diff3", &xmp.style, "use a diff3 based merge", XDL_MERGE_DIFF3),
@@ -65,10 +66,14 @@ int cmd_merge_file(int argc, const char **argv, const char *prefix)
 				     "%s\n", strerror(errno));
 	}
 
+	if (prefix)
+		prefixlen = strlen(prefix);
+
 	for (i = 0; i < 3; i++) {
+		const char *fname = prefix_filename(prefix, prefixlen, argv[i]);
 		if (!names[i])
 			names[i] = argv[i];
-		if (read_mmfile(mmfs + i, argv[i]))
+		if (read_mmfile(mmfs + i, fname))
 			return -1;
 		if (buffer_is_binary(mmfs[i].ptr, mmfs[i].size))
 			return error("Cannot merge binary files: %s\n",

t/t6023-merge-file.sh

@@ -64,6 +64,14 @@ cp new1.txt test.txt
 test_expect_success "merge without conflict" \
 	"git merge-file test.txt orig.txt new2.txt"
 
+test_expect_success 'works in subdirectory' '
+	mkdir dir &&
+	cp new1.txt dir/a.txt &&
+	cp orig.txt dir/o.txt &&
+	cp new2.txt dir/b.txt &&
+	( cd dir && git merge-file a.txt o.txt b.txt )
+'
+
 cp new1.txt test.txt
 test_expect_success "merge without conflict (--quiet)" \
 	"git merge-file --quiet test.txt orig.txt new2.txt"