diff: run arguments through precompose_argv

When running diff commands, a pathspec containing decomposed
unicode code points is not converted to precomposed unicode form
under Mac OS X, but we normalize the paths in the index and the
history to precomposed form on that platform.  As a result, the
pathspec would not match and no diff is shown.

Unlike many builtin commands, the "diff" family of commands do
not use parse_options(), which is how other builtin commands
indirectly call precompose_argv() to normalize argv[] into
precomposed form on Mac OSX.  Teach these commands to call
precompose_argv() themselves.

Note that precomopose_argv() normalizes not just paths but all
command line arguments, so things like "git diff -G $string"
when $string has the decomposed form would first be normalized
into the precomposed form and would stop hitting the same string
in the decomposed form in the diff output with this change.

It is not a problem per-se, as "log" family of commands already use
parse_options() and call precompose_argv()--we can think of this
change as making the "diff" family of commands behave in a similar
way as the commands in the "log" family.

Signed-off-by: Alexander Rinass <alex@fournova.com>
Helped-by: Torsten Bögershausen <tboegi@web.de>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

builtin/diff-files.c

@@ -24,6 +24,7 @@ int cmd_diff_files(int argc, const char **argv, const char *prefix)
 	gitmodules_config();
 	git_config(git_diff_basic_config, NULL); /* no "diff" UI options */
 	rev.abbrev = 0;
+	precompose_argv(argc, argv);
 
 	argc = setup_revisions(argc, argv, &rev, NULL);
 	while (1 < argc && argv[1][0] == '-') {

builtin/diff-index.c

@@ -21,6 +21,7 @@ int cmd_diff_index(int argc, const char **argv, const char *prefix)
 	gitmodules_config();
 	git_config(git_diff_basic_config, NULL); /* no "diff" UI options */
 	rev.abbrev = 0;
+	precompose_argv(argc, argv);
 
 	argc = setup_revisions(argc, argv, &rev, NULL);
 	for (i = 1; i < argc; i++) {

builtin/diff-tree.c

@@ -114,6 +114,8 @@ int cmd_diff_tree(int argc, const char **argv, const char *prefix)
 	opt->disable_stdin = 1;
 	memset(&s_r_opt, 0, sizeof(s_r_opt));
 	s_r_opt.tweak = diff_tree_tweak_rev;
+
+	precompose_argv(argc, argv);
 	argc = setup_revisions(argc, argv, opt, &s_r_opt);
 
 	while (--argc > 0) {

builtin/diff.c

@@ -319,6 +319,7 @@ int cmd_diff(int argc, const char **argv, const char *prefix)
 	if (!no_index)
 		gitmodules_config();
 	git_config(git_diff_ui_config, NULL);
+	precompose_argv(argc, argv);
 
 	init_revisions(&rev, prefix);
 

t/t3910-mac-os-precompose.sh

@@ -49,12 +49,54 @@ test_expect_success "setup" '
 test_expect_success "setup case mac" '
 	git checkout -b mac_os
 '
+# This will test nfd2nfc in git diff
+test_expect_success "git diff f.Adiar" '
+	touch f.$Adiarnfc &&
+	git add f.$Adiarnfc &&
+	echo f.Adiarnfc >f.$Adiarnfc &&
+	git diff f.$Adiarnfd >expect &&
+	git diff f.$Adiarnfc >actual &&
+	test_cmp expect actual &&
+	git reset HEAD f.Adiarnfc &&
+	rm f.$Adiarnfc expect actual
+'
+# This will test nfd2nfc in git diff-files
+test_expect_success "git diff-files f.Adiar" '
+	touch f.$Adiarnfc &&
+	git add f.$Adiarnfc &&
+	echo f.Adiarnfc >f.$Adiarnfc &&
+	git diff-files f.$Adiarnfd >expect &&
+	git diff-files f.$Adiarnfc >actual &&
+	test_cmp expect actual &&
+	git reset HEAD f.Adiarnfc &&
+	rm f.$Adiarnfc expect actual
+'
+# This will test nfd2nfc in git diff-index
+test_expect_success "git diff-index f.Adiar" '
+	touch f.$Adiarnfc &&
+	git add f.$Adiarnfc &&
+	echo f.Adiarnfc >f.$Adiarnfc &&
+	git diff-index HEAD f.$Adiarnfd >expect &&
+	git diff-index HEAD f.$Adiarnfc >actual &&
+	test_cmp expect actual &&
+	git reset HEAD f.Adiarnfc &&
+	rm f.$Adiarnfc expect actual
+'
 # This will test nfd2nfc in readdir()
 test_expect_success "add file Adiarnfc" '
 	echo f.Adiarnfc >f.$Adiarnfc &&
 	git add f.$Adiarnfc &&
 	git commit -m "add f.$Adiarnfc"
 '
+# This will test nfd2nfc in git diff-tree
+test_expect_success "git diff-tree f.Adiar" '
+	echo f.Adiarnfc >>f.$Adiarnfc &&
+	git diff-tree HEAD f.$Adiarnfd >expect &&
+	git diff-tree HEAD f.$Adiarnfc >actual &&
+	test_cmp expect actual &&
+	git checkout f.$Adiarnfc &&
+	rm expect actual
+'
 # This will test nfd2nfc in git stage()
 test_expect_success "stage file d.Adiarnfd/f.Adiarnfd" '
 	mkdir d.$Adiarnfd &&