Add basic infrastructure to assign attributes to paths

This adds the basic infrastructure to assign attributes to
paths, in a way similar to what the exclusion mechanism does
based on $GIT_DIR/info/exclude and .gitignore files.

An attribute is just a simple string that does not contain any
whitespace.  They can be specified in $GIT_DIR/info/attributes
file, and .gitattributes file in each directory.

Each line in these files defines a pattern matching rule.
Similar to the exclusion mechanism, a later match overrides an
earlier match in the same file, and entries from .gitattributes
file in the same directory takes precedence over the ones from
parent directories.  Lines in $GIT_DIR/info/attributes file are
used as the lowest precedence default rules.

A line is either a comment (an empty line, or a line that begins
with a '#'), or a rule, which is a whitespace separated list of
tokens.  The first token on the line is a shell glob pattern.
The rest are names of attributes, each of which can optionally
be prefixed with '!'.  Such a line means "if a path matches this
glob, this attribute is set (or unset -- if the attribute name
is prefixed with '!').  For glob matching, the same "if the
pattern does not have a slash in it, the basename of the path is
matched with fnmatch(3) against the pattern, otherwise, the path
is matched with the pattern with FNM_PATHNAME" rule as the
exclusion mechanism is used.

This does not define what an attribute means.  Tying an
attribute to various effects it has on git operation for paths
that have it will be specified separately.

Signed-off-by: Junio C Hamano <junkio@cox.net>

1 files changed, 380 insertions, 0 deletions

diff --git a/attr.c b/attr.c
new file mode 100644
index 000000000..7435d927a
--- /dev/null
+++ b/attr.c
@@ -0,0 +1,380 @@
+#include "cache.h"
+#include "attr.h"
+
+/*
+ * The basic design decision here is that we are not going to have
+ * insanely large number of attributes.
+ *
+ * This is a randomly chosen prime.
+ */
+#define HASHSIZE 257
+
+#ifndef DEBUG_ATTR
+#define DEBUG_ATTR 0
+#endif
+
+struct git_attr {
+	struct git_attr *next;
+	unsigned h;
+	char name[FLEX_ARRAY];
+};
+
+static struct git_attr *(git_attr_hash[HASHSIZE]);
+
+static unsigned hash_name(const char *name, int namelen)
+{
+	unsigned val = 0;
+	unsigned char c;
+
+	while (namelen--) {
+		c = *name++;
+		val = ((val << 7) | (val >> 22)) ^ c;
+	}
+	return val;
+}
+
+struct git_attr *git_attr(const char *name, int len)
+{
+	unsigned hval = hash_name(name, len);
+	unsigned pos = hval % HASHSIZE;
+	struct git_attr *a;
+
+	for (a = git_attr_hash[pos]; a; a = a->next) {
+		if (a->h == hval &&
+		    !memcmp(a->name, name, len) && !a->name[len])
+			return a;
+	}
+
+	a = xmalloc(sizeof(*a) + len + 1);
+	memcpy(a->name, name, len);
+	a->name[len] = 0;
+	a->h = hval;
+	a->next = git_attr_hash[pos];
+	git_attr_hash[pos] = a;
+	return a;
+}
+
+/*
+ * .gitattributes file is one line per record, each of which is
+ *
+ * (1) glob pattern.
+ * (2) whitespace
+ * (3) whitespace separated list of attribute names, each of which
+ *     could be prefixed with '!' to mean "not set".
+ */
+
+struct attr_state {
+	int unset;
+	struct git_attr *attr;
+};
+
+struct match_attr {
+	char *pattern;
+	unsigned num_attr;
+	struct attr_state state[FLEX_ARRAY];
+};
+
+static const char blank[] = " \t\r\n";
+
+static struct match_attr *parse_attr_line(const char *line)
+{
+	int namelen;
+	int num_attr;
+	const char *cp, *name;
+	struct match_attr *res = res;
+	int pass;
+
+	cp = line + strspn(line, blank);
+	if (!*cp || *cp == '#')
+		return NULL;
+	name = cp;
+	namelen = strcspn(name, blank);
+
+	for (pass = 0; pass < 2; pass++) {
+		/* pass 0 counts and allocates, pass 1 fills */
+		num_attr = 0;
+		cp = name + namelen;
+		cp = cp + strspn(cp, blank);
+		while (*cp) {
+			const char *ep;
+			ep = cp + strcspn(cp, blank);
+			if (pass) {
+				struct attr_state *e;
+
+				e = &(res->state[num_attr]);
+				if (*cp == '!') {
+					e->unset = 1;
+					cp++;
+				}
+				e->attr = git_attr(cp, ep - cp);
+			}
+			num_attr++;
+			cp = ep + strspn(ep, blank);
+		}
+		if (pass)
+			break;
+		res = xcalloc(1,
+			      sizeof(*res) +
+			      sizeof(struct attr_state) * num_attr +
+			      namelen + 1);
+		res->pattern = (char*)&(res->state[num_attr]);
+		memcpy(res->pattern, name, namelen);
+		res->pattern[namelen] = 0;
+		res->num_attr = num_attr;
+	}
+	return res;
+}
+
+/*
+ * Like info/exclude and .gitignore, the attribute information can
+ * come from many places.
+ *
+ * (1) .gitattribute file of the same directory;
+ * (2) .gitattribute file of the parent directory if (1) does not have any match;
+ *     this goes recursively upwards, just like .gitignore
+ * (3) perhaps $GIT_DIR/info/attributes, as the final fallback.
+ *
+ * In the same file, later entries override the earlier match, so in the
+ * global list, we would have entries from info/attributes the earliest
+ * (reading the file from top to bottom), .gitattribute of the root
+ * directory (again, reading the file from top to bottom) down to the
+ * current directory, and then scan the list backwards to find the first match.
+ * This is exactly the same as what excluded() does in dir.c to deal with
+ * .gitignore
+ */
+
+static struct attr_stack {
+	struct attr_stack *prev;
+	char *origin;
+	unsigned num_matches;
+	struct match_attr **attrs;
+} *attr_stack;
+
+static void free_attr_elem(struct attr_stack *e)
+{
+	int i;
+	free(e->origin);
+	for (i = 0; i < e->num_matches; i++)
+		free(e->attrs[i]);
+	free(e);
+}
+
+static const char *builtin_attr[] = {
+	NULL,
+};
+
+static struct attr_stack *read_attr_from_array(const char **list)
+{
+	struct attr_stack *res;
+	const char *line;
+
+	res = xcalloc(1, sizeof(*res));
+	while ((line = *(list++)) != NULL) {
+		struct match_attr *a = parse_attr_line(line);
+		if (!a)
+			continue;
+		res->attrs = xrealloc(res->attrs, res->num_matches + 1);
+		res->attrs[res->num_matches++] = a;
+	}
+	return res;
+}
+
+static struct attr_stack *read_attr_from_file(const char *path)
+{
+	FILE *fp;
+	struct attr_stack *res;
+	char buf[2048];
+
+	res = xcalloc(1, sizeof(*res));
+	fp = fopen(path, "r");
+	if (!fp)
+		return res;
+
+	while (fgets(buf, sizeof(buf), fp)) {
+		struct match_attr *a = parse_attr_line(buf);
+		if (!a)
+			continue;
+		res->attrs = xrealloc(res->attrs, res->num_matches + 1);
+		res->attrs[res->num_matches++] = a;
+	}
+	fclose(fp);
+	return res;
+}
+
+#if DEBUG_ATTR
+static void debug_info(const char *what, struct attr_stack *elem)
+{
+	fprintf(stderr, "%s: %s\n", what, elem->origin ? elem->origin : "()");
+}
+#define debug_push(a) debug_info("push", (a))
+#define debug_pop(a) debug_info("pop", (a))
+#else
+#define debug_push(a) do { ; } while (0)
+#define debug_pop(a) do { ; } while (0)
+#endif
+
+static void prepare_attr_stack(const char *path, int dirlen)
+{
+	struct attr_stack *elem, *info;
+	int len;
+	char pathbuf[PATH_MAX];
+
+	/*
+	 * At the bottom of the attribute stack is the built-in
+	 * set of attribute definitions.  Then, contents from
+	 * .gitattribute files from directories closer to the
+	 * root to the ones in deeper directories are pushed
+	 * to the stack.  Finally, at the very top of the stack
+	 * we always keep the contents of $GIT_DIR/info/attributes.
+	 *
+	 * When checking, we use entries from near the top of the
+	 * stack, preferring $GIT_DIR/info/attributes, then
+	 * .gitattributes in deeper directories to shallower ones,
+	 * and finally use the built-in set as the default.
+	 */
+	if (!attr_stack) {
+		elem = read_attr_from_array(builtin_attr);
+		elem->origin = NULL;
+		elem->prev = attr_stack;
+		attr_stack = elem;
+
+		elem = read_attr_from_file(GITATTRIBUTES_FILE);
+		elem->origin = strdup("");
+		elem->prev = attr_stack;
+		attr_stack = elem;
+		debug_push(elem);
+
+		elem = read_attr_from_file(git_path(INFOATTRIBUTES_FILE));
+		elem->origin = NULL;
+		elem->prev = attr_stack;
+		attr_stack = elem;
+	}
+
+	/*
+	 * Pop the "info" one that is always at the top of the stack.
+	 */
+	info = attr_stack;
+	attr_stack = info->prev;
+
+	/*
+	 * Pop the ones from directories that are not the prefix of
+	 * the path we are checking.
+	 */
+	while (attr_stack && attr_stack->origin) {
+		int namelen = strlen(attr_stack->origin);
+
+		elem = attr_stack;
+		if (namelen <= dirlen &&
+		    !strncmp(elem->origin, path, namelen))
+			break;
+
+		debug_pop(elem);
+		attr_stack = elem->prev;
+		free_attr_elem(elem);
+	}
+
+	/*
+	 * Read from parent directories and push them down
+	 */
+	while (1) {
+		char *cp;
+
+		len = strlen(attr_stack->origin);
+		if (dirlen <= len)
+			break;
+		memcpy(pathbuf, path, dirlen);
+		memcpy(pathbuf + dirlen, "/", 2);
+		cp = strchr(pathbuf + len + 1, '/');
+		strcpy(cp + 1, GITATTRIBUTES_FILE);
+		elem = read_attr_from_file(pathbuf);
+		*cp = '\0';
+		elem->origin = strdup(pathbuf);
+		elem->prev = attr_stack;
+		attr_stack = elem;
+		debug_push(elem);
+	}
+
+	/*
+	 * Finally push the "info" one at the top of the stack.
+	 */
+	info->prev = attr_stack;
+	attr_stack = info;
+}
+
+static int path_matches(const char *pathname, int pathlen,
+			const char *pattern,
+			const char *base, int baselen)
+{
+	if (!strchr(pattern, '/')) {
+		/* match basename */
+		const char *basename = strrchr(pathname, '/');
+		basename = basename ? basename + 1 : pathname;
+		return (fnmatch(pattern, basename, 0) == 0);
+	}
+	/*
+	 * match with FNM_PATHNAME; the pattern has base implicitly
+	 * in front of it.
+	 */
+	if (*pattern == '/')
+		pattern++;
+	if (pathlen < baselen ||
+	    (baselen && pathname[baselen - 1] != '/') ||
+	    strncmp(pathname, base, baselen))
+		return 0;
+	return fnmatch(pattern, pathname + baselen, FNM_PATHNAME) == 0;
+}
+
+/*
+ * I do not like this at all.  Only because we allow individual
+ * attribute to be set or unset incrementally by individual
+ * lines in .gitattribute files, we need to do this triple
+ * loop which looks quite wasteful.
+ */
+static int fill(const char *path, int pathlen,
+		struct attr_stack *stk, struct git_attr_check *check,
+		int num, int rem)
+{
+	int i, j, k;
+	const char *base = stk->origin ? stk->origin : "";
+
+	for (i = stk->num_matches - 1; 0 < rem && 0 <= i; i--) {
+		struct match_attr *a = stk->attrs[i];
+		if (path_matches(path, pathlen,
+				 a->pattern, base, strlen(base))) {
+			for (j = 0; j < a->num_attr; j++) {
+				struct git_attr *attr = a->state[j].attr;
+				int set = !a->state[j].unset;
+				for (k = 0; k < num; k++) {
+					if (0 <= check[k].isset ||
+					    check[k].attr != attr)
+						continue;
+					check[k].isset = set;
+					rem--;
+				}
+			}
+		}
+	}
+	return rem;
+}
+
+int git_checkattr(const char *path, int num, struct git_attr_check *check)
+{
+	struct attr_stack *stk;
+	const char *cp;
+	int dirlen, pathlen, i, rem;
+
+	for (i = 0; i < num; i++)
+		check[i].isset = -1;
+
+	pathlen = strlen(path);
+	cp = strrchr(path, '/');
+	if (!cp)
+		dirlen = 0;
+	else
+		dirlen = cp - path;
+	prepare_attr_stack(path, dirlen);
+	rem = num;
+	for (stk = attr_stack; 0 < rem && stk; stk = stk->prev)
+		rem = fill(path, pathlen, stk, check, num, rem);
+	return 0;
+}