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>

1 files changed, 92 insertions, 3 deletions

diff --git a/attr.c b/attr.c
index e62876dfd3..679e42258c 100644
--- a/attr.c
+++ b/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;
 	}
 }