attr: add builtin objectmode values support

Gives all paths builtin objectmode values based on the paths' modes
(one of 100644, 100755, 120000, 040000, 160000). Users may use
this feature to filter by file types. For example a pathspec such as
':(attr:builtin_objectmode=160000)' could filter for submodules without
needing to have `builtin_objectmode=160000` to be set in .gitattributes
for every submodule path.

These values are also reflected in `git check-attr` results.
If the git_attr_direction is set to GIT_ATTR_INDEX or GIT_ATTR_CHECKIN
and a path is not found in the index, the value will be unspecified.

This patch also reserves the builtin_* attribute namespace for objectmode
and any future builtin attributes. Any user defined attributes using this
reserved namespace will result in a warning. This is a breaking change for
any existing builtin_* attributes.
Pathspecs with some builtin_* attribute name (excluding builtin_objectmode)
will behave like any attribute where there are no user specified values.

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

Documentation/gitattributes.txt

@@ -100,6 +100,21 @@ for a path to `Unspecified` state.  This can be done by listing
 the name of the attribute prefixed with an exclamation point `!`.
 
 
+RESERVED BUILTIN_* ATTRIBUTES
+-----------------------------
+
+builtin_* is a reserved namespace for builtin attribute values. Any
+user defined attributes under this namespace will be ignored and
+trigger a warning.
+
+`builtin_objectmode`
+~~~~~~~~~~~~~~~~~~~~
+This attribute is for filtering files by their file bit modes (40000,
+120000, 160000, 100755, 100644). e.g. ':(attr:builtin_objectmode=160000)'.
+You may also check these values with `git check-attr builtin_objectmode -- <file>`.
+If the object is not in the index `git check-attr --cached` will return unspecified.
+
+
 EFFECTS
 -------
 

attr.c

@@ -17,6 +17,7 @@
 #include "utf8.h"
 #include "quote.h"
 #include "read-cache-ll.h"
+#include "refs.h"
 #include "revision.h"
 #include "object-store-ll.h"
 #include "setup.h"
@@ -183,6 +184,15 @@ static void all_attrs_init(struct attr_hashmap *map, struct attr_check *check)
 	}
 }
 
+/*
+ * Atribute name cannot begin with "builtin_" which
+ * is a reserved namespace for built in attributes values.
+ */
+static int attr_name_reserved(const char *name)
+{
+	return starts_with(name, "builtin_");
+}
+
 static int attr_name_valid(const char *name, size_t namelen)
 {
 	/*
@@ -315,7 +325,7 @@ static const char *parse_attr(const char *src, int lineno, const char *cp,
 			cp++;
 			len--;
 		}
-		if (!attr_name_valid(cp, len)) {
+		if (!attr_name_valid(cp, len) || attr_name_reserved(cp)) {
 			report_invalid_attr(cp, len, src, lineno);
 			return NULL;
 		}
@@ -379,7 +389,7 @@ static struct match_attr *parse_attr_line(const char *line, const char *src,
 		name += strlen(ATTRIBUTE_MACRO_PREFIX);
 		name += strspn(name, blank);
 		namelen = strcspn(name, blank);
-		if (!attr_name_valid(name, namelen)) {
+		if (!attr_name_valid(name, namelen) || attr_name_reserved(name)) {
 			report_invalid_attr(name, namelen, src, lineno);
 			goto fail_return;
 		}
@@ -1240,6 +1250,85 @@ static struct object_id *default_attr_source(void)
 	return &attr_source;
 }
 
+static const char *interned_mode_string(unsigned int mode)
+{
+	static struct {
+		unsigned int val;
+		char str[7];
+	} mode_string[] = {
+		{ .val = 0040000 },
+		{ .val = 0100644 },
+		{ .val = 0100755 },
+		{ .val = 0120000 },
+		{ .val = 0160000 },
+	};
+	int i;
+
+	for (i = 0; i < ARRAY_SIZE(mode_string); i++) {
+		if (mode_string[i].val != mode)
+			continue;
+		if (!*mode_string[i].str)
+			snprintf(mode_string[i].str, sizeof(mode_string[i].str),
+				 "%06o", mode);
+		return mode_string[i].str;
+	}
+	BUG("Unsupported mode 0%o", mode);
+}
+
+static const char *builtin_object_mode_attr(struct index_state *istate, const char *path)
+{
+	unsigned int mode;
+
+	if (direction == GIT_ATTR_CHECKIN) {
+		struct object_id oid;
+		struct stat st;
+		if (lstat(path, &st))
+			die_errno(_("unable to stat '%s'"), path);
+		mode = canon_mode(st.st_mode);
+		if (S_ISDIR(mode)) {
+			/*
+			 *`path` is either a directory or it is a submodule,
+			 * in which case it is already indexed as submodule
+			 * or it does not exist in the index yet and we need to
+			 * check if we can resolve to a ref.
+			*/
+			int pos = index_name_pos(istate, path, strlen(path));
+			if (pos >= 0) {
+				 if (S_ISGITLINK(istate->cache[pos]->ce_mode))
+					 mode = istate->cache[pos]->ce_mode;
+			} else if (resolve_gitlink_ref(path, "HEAD", &oid) == 0) {
+				mode = S_IFGITLINK;
+			}
+		}
+	} else {
+		/*
+		 * For GIT_ATTR_CHECKOUT and GIT_ATTR_INDEX we only check
+		 * for mode in the index.
+		 */
+		int pos = index_name_pos(istate, path, strlen(path));
+		if (pos >= 0)
+			mode = istate->cache[pos]->ce_mode;
+		else
+			return ATTR__UNSET;
+	}
+
+	return interned_mode_string(mode);
+}
+
+
+static const char *compute_builtin_attr(struct index_state *istate,
+					  const char *path,
+					  const struct git_attr *attr) {
+	static const struct git_attr *object_mode_attr;
+
+	if (!object_mode_attr)
+		object_mode_attr = git_attr("builtin_objectmode");
+
+	if (attr == object_mode_attr)
+		return builtin_object_mode_attr(istate, path);
+	return ATTR__UNSET;
+}
+
 void git_check_attr(struct index_state *istate,
 		    const char *path,
 		    struct attr_check *check)
@@ -1253,7 +1342,7 @@ void git_check_attr(struct index_state *istate,
 		unsigned int n = check->items[i].attr->attr_nr;
 		const char *value = check->all_attrs[n].value;
 		if (value == ATTR__UNKNOWN)
-			value = ATTR__UNSET;
+			value = compute_builtin_attr(istate, path, check->all_attrs[n].attr);
 		check->items[i].value = value;
 	}
 }

t/t0003-attributes.sh

@@ -19,6 +19,20 @@ attr_check () {
 	test_must_be_empty err
 }
 
+attr_check_object_mode_basic () {
+	path="$1" &&
+	expect="$2" &&
+	check_opts="$3" &&
+	git check-attr $check_opts builtin_objectmode -- "$path" >actual 2>err &&
+	echo "$path: builtin_objectmode: $expect" >expect &&
+	test_cmp expect actual
+}
+
+attr_check_object_mode () {
+	attr_check_object_mode_basic "$@" &&
+	test_must_be_empty err
+}
+
 attr_check_quote () {
 	path="$1" quoted_path="$2" expect="$3" &&
 
@@ -558,4 +572,66 @@ test_expect_success EXPENSIVE 'large attributes file ignored in index' '
 	test_cmp expect err
 '
 
+test_expect_success 'builtin object mode attributes work (dir and regular paths)' '
+	>normal &&
+	attr_check_object_mode normal 100644 &&
+	mkdir dir &&
+	attr_check_object_mode dir 040000
+'
+
+test_expect_success POSIXPERM 'builtin object mode attributes work (executable)' '
+	>exec &&
+	chmod +x exec &&
+	attr_check_object_mode exec 100755
+'
+
+test_expect_success SYMLINKS 'builtin object mode attributes work (symlinks)' '
+	ln -s to_sym sym &&
+	attr_check_object_mode sym 120000
+'
+
+test_expect_success 'native object mode attributes work with --cached' '
+	>normal &&
+	git add normal &&
+	empty_blob=$(git rev-parse :normal) &&
+	git update-index --index-info <<-EOF &&
+	100755 $empty_blob 0	exec
+	120000 $empty_blob 0	symlink
+	EOF
+	attr_check_object_mode normal 100644 --cached &&
+	attr_check_object_mode exec 100755 --cached &&
+	attr_check_object_mode symlink 120000 --cached
+'
+
+test_expect_success 'check object mode attributes work for submodules' '
+	mkdir sub &&
+	(
+		cd sub &&
+		git init &&
+		mv .git .real &&
+		echo "gitdir: .real" >.git &&
+		test_commit first
+	) &&
+	attr_check_object_mode sub 160000 &&
+	attr_check_object_mode sub unspecified --cached &&
+	git add sub &&
+	attr_check_object_mode sub 160000 --cached
+'
+
+test_expect_success 'we do not allow user defined builtin_* attributes' '
+	echo "foo* builtin_foo" >.gitattributes &&
+	git add .gitattributes 2>actual &&
+	echo "builtin_foo is not a valid attribute name: .gitattributes:1" >expect &&
+	test_cmp expect actual
+'
+
+test_expect_success 'user defined builtin_objectmode values are ignored' '
+	echo "foo* builtin_objectmode=12345" >.gitattributes &&
+	git add .gitattributes &&
+	>foo_1 &&
+	attr_check_object_mode_basic foo_1 100644 &&
+	echo "builtin_objectmode is not a valid attribute name: .gitattributes:1" >expect &&
+	test_cmp expect err
+'
+
 test_done

t/t6135-pathspec-with-attrs.sh

@@ -295,4 +295,31 @@ test_expect_success 'reading from .gitattributes in a subdirectory (3)' '
 	test_cmp expect actual
 '
 
+test_expect_success POSIXPERM 'pathspec with builtin_objectmode attr can be used' '
+	>mode_exec_file_1 &&
+
+	git status -s ":(attr:builtin_objectmode=100644)mode_exec_*" >actual &&
+	echo ?? mode_exec_file_1 >expect &&
+	test_cmp expect actual &&
+
+	git add mode_exec_file_1 &&
+	chmod +x mode_exec_file_1 &&
+	git status -s ":(attr:builtin_objectmode=100755)mode_exec_*" >actual &&
+	echo AM mode_exec_file_1 >expect &&
+	test_cmp expect actual
+'
+
+test_expect_success POSIXPERM 'builtin_objectmode attr can be excluded' '
+	>mode_1_regular &&
+	>mode_1_exec  &&
+	chmod +x mode_1_exec &&
+	git status -s ":(exclude,attr:builtin_objectmode=100644)" "mode_1_*" >actual &&
+	echo ?? mode_1_exec >expect &&
+	test_cmp expect actual &&
+
+	git status -s ":(exclude,attr:builtin_objectmode=100755)" "mode_1_*" >actual &&
+	echo ?? mode_1_regular >expect &&
+	test_cmp expect actual
+'
+
 test_done