attr: enable attr pathspec magic for git-add and git-stash

Allow users to limit or exclude files based on file attributes
during git-add and git-stash.

For example, the chromium project would like to use

    $ git add . ':(exclude,attr:submodule)'

as submodules are managed by an external tool, forbidding end users
to record changes with "git add".  Allowing "git add" to often
records changes that users do not want in their commits.

This commit does not change any attr magic implementation. It is
only adding attr as an allowed pathspec in git-add and git-stash,
which was previously blocked by GUARD_PATHSPEC and a pathspec mask
in parse_pathspec()).

However, we fix a bug in prefix_magic() where attr values were
unintentionally removed.  This was triggerable when parse_pathspec()
is called with PATHSPEC_PREFIX_ORIGIN as a flag, which was the case
for git-stash (Bug originally filed here [*])

Furthermore, while other commands hit this code path it did not
result in unexpected behavior because this bug only impacts the
pathspec->items->original field which is NOT used to filter
paths. However, git-stash does use pathspec->items->original when
building args used to call other git commands.  (See add_pathspecs()
usage and implementation in stash.c)

It is possible that when the attr pathspec feature was first added
in b0db704652 (pathspec: allow querying for attributes, 2017-03-13),
"PATHSPEC_ATTR" was just unintentionally left out of a few
GUARD_PATHSPEC() invocations.

Later, to get a more user-friendly error message when attr was used
with git-add, PATHSPEC_ATTR was added as a mask to git-add's
invocation of parse_pathspec() 84d938b732 (add: do not accept
pathspec magic 'attr', 2018-09-18).  However, this user-friendly
error message was never added for git-stash.

[Reference]
 * https://lore.kernel.org/git/CAMmZTi-0QKtj7Q=sbC5qhipGsQxJFOY-Qkk1jfkRYwfF5FcUVg@mail.gmail.com/)

Signed-off-by: Joanna Wang <jojwang@google.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

builtin/add.c

@@ -424,7 +424,7 @@ int cmd_add(int argc, const char **argv, const char *prefix)
 	 * Check the "pathspec '%s' did not match any files" block
 	 * below before enabling new magic.
 	 */
-	parse_pathspec(&pathspec, PATHSPEC_ATTR,
+	parse_pathspec(&pathspec, 0,
 		       PATHSPEC_PREFER_FULL |
 		       PATHSPEC_SYMLINK_LEADING_PATH,
 		       prefix, argv);
@@ -433,7 +433,7 @@ int cmd_add(int argc, const char **argv, const char *prefix)
 		if (pathspec.nr)
 			die(_("'%s' and pathspec arguments cannot be used together"), "--pathspec-from-file");
 
-		parse_pathspec_file(&pathspec, PATHSPEC_ATTR,
+		parse_pathspec_file(&pathspec, 0,
 				    PATHSPEC_PREFER_FULL |
 				    PATHSPEC_SYMLINK_LEADING_PATH,
 				    prefix, pathspec_from_file, pathspec_file_nul);
@@ -504,7 +504,8 @@ int cmd_add(int argc, const char **argv, const char *prefix)
 			       PATHSPEC_LITERAL |
 			       PATHSPEC_GLOB |
 			       PATHSPEC_ICASE |
-			       PATHSPEC_EXCLUDE);
+			       PATHSPEC_EXCLUDE |
+			       PATHSPEC_ATTR);
 
 		for (i = 0; i < pathspec.nr; i++) {
 			const char *path = pathspec.items[i].match;

dir.c

@@ -2179,7 +2179,8 @@ static int exclude_matches_pathspec(const char *path, int pathlen,
 		       PATHSPEC_LITERAL |
 		       PATHSPEC_GLOB |
 		       PATHSPEC_ICASE |
-		       PATHSPEC_EXCLUDE);
+		       PATHSPEC_EXCLUDE |
+		       PATHSPEC_ATTR);
 
 	for (i = 0; i < pathspec->nr; i++) {
 		const struct pathspec_item *item = &pathspec->items[i];

pathspec.c

@@ -109,16 +109,37 @@ static struct pathspec_magic {
 	{ PATHSPEC_ATTR,    '\0', "attr" },
 };
 
-static void prefix_magic(struct strbuf *sb, int prefixlen, unsigned magic)
+static void prefix_magic(struct strbuf *sb, int prefixlen,
+			 unsigned magic, const char *element)
 {
-	int i;
+	/* No magic was found in element, just add prefix magic */
+	if (!magic) {
+		strbuf_addf(sb, ":(prefix:%d)", prefixlen);
+		return;
+	}
+
+	/*
+	 * At this point, we know that parse_element_magic() was able
+	 * to extract some pathspec magic from element. So we know
+	 * element is correctly formatted in either shorthand or
+	 * longhand form
+	 */
+	if (element[1] != '(') {
+		/* Process an element in shorthand form (e.g. ":!/<match>") */
 		strbuf_addstr(sb, ":(");
-	for (i = 0; i < ARRAY_SIZE(pathspec_magic); i++)
-		if (magic & pathspec_magic[i].bit) {
+		for (int i = 0; i < ARRAY_SIZE(pathspec_magic); i++) {
+			if ((magic & pathspec_magic[i].bit) &&
+			    pathspec_magic[i].mnemonic) {
 				if (sb->buf[sb->len - 1] != '(')
 					strbuf_addch(sb, ',');
 				strbuf_addstr(sb, pathspec_magic[i].name);
 			}
+		}
+	} else {
+		/* For the longhand form, we copy everything up to the final ')' */
+		size_t len = strchr(element, ')') - element;
+		strbuf_add(sb, element, len);
+	}
 	strbuf_addf(sb, ",prefix:%d)", prefixlen);
 }
 
@@ -493,7 +514,7 @@ static void init_pathspec_item(struct pathspec_item *item, unsigned flags,
 		struct strbuf sb = STRBUF_INIT;
 
 		/* Preserve the actual prefix length of each pattern */
-		prefix_magic(&sb, prefixlen, element_magic);
+		prefix_magic(&sb, prefixlen, element_magic, elt);
 
 		strbuf_addstr(&sb, match);
 		item->original = strbuf_detach(&sb, NULL);

t/t6135-pathspec-with-attrs.sh

@@ -64,12 +64,24 @@ test_expect_success 'setup .gitattributes' '
 	fileSetLabel label
 	fileValue label=foo
 	fileWrongLabel label☺
+	newFileA* labelA
+	newFileB* labelB
 	EOF
 	echo fileSetLabel label1 >sub/.gitattributes &&
 	git add .gitattributes sub/.gitattributes &&
 	git commit -m "add attributes"
 '
 
+test_expect_success 'setup .gitignore' '
+	cat <<-\EOF >.gitignore &&
+	actual
+	expect
+	pathspec_file
+	EOF
+	git add .gitignore &&
+	git commit -m "add gitignore"
+'
+
 test_expect_success 'check specific set attr' '
 	cat <<-\EOF >expect &&
 	fileSetLabel
@@ -150,6 +162,7 @@ test_expect_success 'check specific value attr (2)' '
 test_expect_success 'check unspecified attr' '
 	cat <<-\EOF >expect &&
 	.gitattributes
+	.gitignore
 	fileA
 	fileAB
 	fileAC
@@ -175,6 +188,7 @@ test_expect_success 'check unspecified attr' '
 test_expect_success 'check unspecified attr (2)' '
 	cat <<-\EOF >expect &&
 	HEAD:.gitattributes
+	HEAD:.gitignore
 	HEAD:fileA
 	HEAD:fileAB
 	HEAD:fileAC
@@ -200,6 +214,7 @@ test_expect_success 'check unspecified attr (2)' '
 test_expect_success 'check multiple unspecified attr' '
 	cat <<-\EOF >expect &&
 	.gitattributes
+	.gitignore
 	fileC
 	fileNoLabel
 	fileWrongLabel
@@ -239,16 +254,99 @@ test_expect_success 'fail on multiple attr specifiers in one pathspec item' '
 	test_i18ngrep "Only one" actual
 '
 
-test_expect_success 'fail if attr magic is used places not implemented' '
+test_expect_success 'fail if attr magic is used in places not implemented' '
 	# The main purpose of this test is to check that we actually fail
 	# when you attempt to use attr magic in commands that do not implement
-	# attr magic. This test does not advocate git-add to stay that way,
-	# though, but git-add is convenient as it has its own internal pathspec
-	# parsing.
-	test_must_fail git add ":(attr:labelB)" 2>actual &&
+	# attr magic. This test does not advocate check-ignore to stay that way.
+	# When you teach the command to grok the pathspec, you need to find
+	# another command to replace it for the test.
+	test_must_fail git check-ignore ":(attr:labelB)" 2>actual &&
 	test_i18ngrep "magic not supported" actual
 '
 
+test_expect_success 'check that attr magic works for git stash push' '
+	cat <<-\EOF >expect &&
+	A	sub/newFileA-foo
+	EOF
+	>sub/newFileA-foo &&
+	>sub/newFileB-foo &&
+	git stash push --include-untracked -- ":(exclude,attr:labelB)" &&
+	git stash show --include-untracked --name-status >actual &&
+	test_cmp expect actual
+'
+
+test_expect_success 'check that attr magic works for git add --all' '
+	cat <<-\EOF >expect &&
+	sub/newFileA-foo
+	EOF
+	>sub/newFileA-foo &&
+	>sub/newFileB-foo &&
+	git add --all ":(exclude,attr:labelB)" &&
+	git diff --name-only --cached >actual &&
+	git restore -W -S . &&
+	test_cmp expect actual
+'
+
+test_expect_success 'check that attr magic works for git add -u' '
+	cat <<-\EOF >expect &&
+	sub/fileA
+	EOF
+	>sub/newFileA-foo &&
+	>sub/newFileB-foo &&
+	>sub/fileA &&
+	>sub/fileB &&
+	git add -u ":(exclude,attr:labelB)" &&
+	git diff --name-only --cached  >actual &&
+	git restore -S -W . && rm sub/new* &&
+	test_cmp expect actual
+'
+
+test_expect_success 'check that attr magic works for git add <path>' '
+	cat <<-\EOF >expect &&
+	fileA
+	fileB
+	sub/fileA
+	EOF
+	>fileA &&
+	>fileB &&
+	>sub/fileA &&
+	>sub/fileB &&
+	git add ":(exclude,attr:labelB)sub/*" &&
+	git diff --name-only --cached >actual &&
+	git restore -S -W . &&
+	test_cmp expect actual
+'
+
+test_expect_success 'check that attr magic works for git -add .' '
+	cat <<-\EOF >expect &&
+	sub/fileA
+	EOF
+	>fileA &&
+	>fileB &&
+	>sub/fileA &&
+	>sub/fileB &&
+	cd sub &&
+	git add . ":(exclude,attr:labelB)" &&
+	cd .. &&
+	git diff --name-only --cached >actual &&
+	git restore -S -W . &&
+	test_cmp expect actual
+'
+
+test_expect_success 'check that attr magic works for git add --pathspec-from-file' '
+	cat <<-\EOF >pathspec_file &&
+	:(exclude,attr:labelB)
+	EOF
+	cat <<-\EOF >expect &&
+	sub/newFileA-foo
+	EOF
+	>sub/newFileA-foo &&
+	>sub/newFileB-foo &&
+	git add --all --pathspec-from-file=pathspec_file &&
+	git diff --name-only --cached >actual &&
+	test_cmp expect actual
+'
+
 test_expect_success 'abort on giving invalid label on the command line' '
 	test_must_fail git ls-files . ":(attr:☺)"
 '