1 files changed, 872 insertions, 88 deletions

diff --git a/sha1_name.c b/sha1_name.c
index d67de18ba5..ff5992acc9 100644
--- a/sha1_name.c
+++ b/sha1_name.c
@@ -3,6 +3,11 @@
 #include "commit.h"
 #include "tree.h"
 #include "blob.h"
+#include "tree-walk.h"
+#include "refs.h"
+#include "remote.h"
+
+static int get_sha1_oneline(const char *, unsigned char *, struct commit_list *);
 
 static int find_short_object_filename(int len, const char *name, unsigned char *sha1)
 {
@@ -69,20 +74,23 @@ static int match_sha(unsigned len, const unsigned char *a, const unsigned char *
 static int find_short_packed_object(int len, const unsigned char *match, unsigned char *sha1)
 {
 	struct packed_git *p;
-	unsigned char found_sha1[20];
+	const unsigned char *found_sha1 = NULL;
 	int found = 0;
 
 	prepare_packed_git();
 	for (p = packed_git; p && found < 2; p = p->next) {
-		unsigned num = num_packed_objects(p);
-		unsigned first = 0, last = num;
+		uint32_t num, last;
+		uint32_t first = 0;
+		open_pack_index(p);
+		num = p->num_objects;
+		last = num;
 		while (first < last) {
-			unsigned mid = (first + last) / 2;
-			unsigned char now[20];
+			uint32_t mid = (first + last) / 2;
+			const unsigned char *now;
 			int cmp;
 
-			nth_packed_object_sha1(p, mid, now);
-			cmp = memcmp(match, now, 20);
+			now = nth_packed_object_sha1(p, mid);
+			cmp = hashcmp(match, now);
 			if (!cmp) {
 				first = mid;
 				break;
@@ -94,17 +102,17 @@ static int find_short_packed_object(int len, const unsigned char *match, unsigne
 			last = mid;
 		}
 		if (first < num) {
-			unsigned char now[20], next[20];
-			nth_packed_object_sha1(p, first, now);
+			const unsigned char *now, *next;
+		       now = nth_packed_object_sha1(p, first);
 			if (match_sha(len, match, now)) {
-				if (nth_packed_object_sha1(p, first+1, next) ||
-				    !match_sha(len, match, next)) {
+				next = nth_packed_object_sha1(p, first+1);
+			       if (!next|| !match_sha(len, match, next)) {
 					/* unique within this pack */
 					if (!found) {
-						memcpy(found_sha1, now, 20);
+						found_sha1 = now;
 						found++;
 					}
-					else if (memcmp(found_sha1, now, 20)) {
+					else if (hashcmp(found_sha1, now)) {
 						found = 2;
 						break;
 					}
@@ -118,7 +126,7 @@ static int find_short_packed_object(int len, const unsigned char *match, unsigne
 		}
 	}
 	if (found == 1)
-		memcpy(sha1, found_sha1, 20);
+		hashcpy(sha1, found_sha1);
 	return found;
 }
 
@@ -131,6 +139,7 @@ static int find_unique_short_object(int len, char *canonical,
 	int has_unpacked, has_packed;
 	unsigned char unpacked_sha1[20], packed_sha1[20];
 
+	prepare_alt_odb();
 	has_unpacked = find_short_object_filename(len, canonical, unpacked_sha1);
 	has_packed = find_short_packed_object(len, res, packed_sha1);
 	if (!has_unpacked && !has_packed)
@@ -138,13 +147,13 @@ static int find_unique_short_object(int len, char *canonical,
 	if (1 < has_unpacked || 1 < has_packed)
 		return SHORT_NAME_AMBIGUOUS;
 	if (has_unpacked != has_packed) {
-		memcpy(sha1, (has_packed ? packed_sha1 : unpacked_sha1), 20);
+		hashcpy(sha1, (has_packed ? packed_sha1 : unpacked_sha1));
 		return 0;
 	}
 	/* Both have unique ones -- do they match? */
-	if (memcmp(packed_sha1, unpacked_sha1, 20))
+	if (hashcmp(packed_sha1, unpacked_sha1))
 		return SHORT_NAME_AMBIGUOUS;
-	memcpy(sha1, packed_sha1, 20);
+	hashcpy(sha1, packed_sha1);
 	return 0;
 }
 
@@ -155,9 +164,9 @@ static int get_short_sha1(const char *name, int len, unsigned char *sha1,
 	char canonical[40];
 	unsigned char res[20];
 
-	if (len < MINIMUM_ABBREV)
+	if (len < MINIMUM_ABBREV || len > 40)
 		return -1;
-	memset(res, 0, 20);
+	hashclr(res);
 	memset(canonical, 'x', 40);
 	for (i = 0; i < len ;i++) {
 		unsigned char c = name[i];
@@ -186,26 +195,25 @@ static int get_short_sha1(const char *name, int len, unsigned char *sha1,
 
 const char *find_unique_abbrev(const unsigned char *sha1, int len)
 {
-	int status, is_null;
+	int status, exists;
 	static char hex[41];
 
-	is_null = !memcmp(sha1, null_sha1, 20);
+	exists = has_sha1_file(sha1);
 	memcpy(hex, sha1_to_hex(sha1), 40);
-	if (len == 40)
+	if (len == 40 || !len)
 		return hex;
 	while (len < 40) {
 		unsigned char sha1_ret[20];
 		status = get_short_sha1(hex, len, sha1_ret, 1);
-		if (!status ||
-		    (is_null && status != SHORT_NAME_AMBIGUOUS)) {
+		if (exists
+		    ? !status
+		    : status == SHORT_NAME_NOT_FOUND) {
 			hex[len] = 0;
 			return hex;
 		}
-		if (status != SHORT_NAME_AMBIGUOUS)
-			return NULL;
 		len++;
 	}
-	return NULL;
+	return hex;
 }
 
 static int ambiguous_path(const char *path, int len)
@@ -233,33 +241,207 @@ static int ambiguous_path(const char *path, int len)
 	return slash;
 }
 
-static int get_sha1_basic(const char *str, int len, unsigned char *sha1)
+/*
+ * *string and *len will only be substituted, and *string returned (for
+ * later free()ing) if the string passed in is a magic short-hand form
+ * to name a branch.
+ */
+static char *substitute_branch_name(const char **string, int *len)
+{
+	struct strbuf buf = STRBUF_INIT;
+	int ret = interpret_branch_name(*string, &buf);
+
+	if (ret == *len) {
+		size_t size;
+		*string = strbuf_detach(&buf, &size);
+		*len = size;
+		return (char *)*string;
+	}
+
+	return NULL;
+}
+
+int dwim_ref(const char *str, int len, unsigned char *sha1, char **ref)
+{
+	char *last_branch = substitute_branch_name(&str, &len);
+	const char **p, *r;
+	int refs_found = 0;
+
+	*ref = NULL;
+	for (p = ref_rev_parse_rules; *p; p++) {
+		char fullref[PATH_MAX];
+		unsigned char sha1_from_ref[20];
+		unsigned char *this_result;
+		int flag;
+
+		this_result = refs_found ? sha1_from_ref : sha1;
+		mksnpath(fullref, sizeof(fullref), *p, len, str);
+		r = resolve_ref(fullref, this_result, 1, &flag);
+		if (r) {
+			if (!refs_found++)
+				*ref = xstrdup(r);
+			if (!warn_ambiguous_refs)
+				break;
+		} else if ((flag & REF_ISSYMREF) && strcmp(fullref, "HEAD"))
+			warning("ignoring dangling symref %s.", fullref);
+	}
+	free(last_branch);
+	return refs_found;
+}
+
+int dwim_log(const char *str, int len, unsigned char *sha1, char **log)
 {
-	static const char *prefix[] = {
-		"",
-		"refs",
-		"refs/tags",
-		"refs/heads",
-		NULL
-	};
+	char *last_branch = substitute_branch_name(&str, &len);
 	const char **p;
+	int logs_found = 0;
+
+	*log = NULL;
+	for (p = ref_rev_parse_rules; *p; p++) {
+		struct stat st;
+		unsigned char hash[20];
+		char path[PATH_MAX];
+		const char *ref, *it;
+
+		mksnpath(path, sizeof(path), *p, len, str);
+		ref = resolve_ref(path, hash, 1, NULL);
+		if (!ref)
+			continue;
+		if (!stat(git_path("logs/%s", path), &st) &&
+		    S_ISREG(st.st_mode))
+			it = path;
+		else if (strcmp(ref, path) &&
+			 !stat(git_path("logs/%s", ref), &st) &&
+			 S_ISREG(st.st_mode))
+			it = ref;
+		else
+			continue;
+		if (!logs_found++) {
+			*log = xstrdup(it);
+			hashcpy(sha1, hash);
+		}
+		if (!warn_ambiguous_refs)
+			break;
+	}
+	free(last_branch);
+	return logs_found;
+}
+
+static inline int upstream_mark(const char *string, int len)
+{
+	const char *suffix[] = { "@{upstream}", "@{u}" };
+	int i;
+
+	for (i = 0; i < ARRAY_SIZE(suffix); i++) {
+		int suffix_len = strlen(suffix[i]);
+		if (suffix_len <= len
+		    && !memcmp(string, suffix[i], suffix_len))
+			return suffix_len;
+	}
+	return 0;
+}
+
+static int get_sha1_1(const char *name, int len, unsigned char *sha1);
+
+static int get_sha1_basic(const char *str, int len, unsigned char *sha1)
+{
+	static const char *warn_msg = "refname '%.*s' is ambiguous.";
+	char *real_ref = NULL;
+	int refs_found = 0;
+	int at, reflog_len;
 
 	if (len == 40 && !get_sha1_hex(str, sha1))
 		return 0;
 
+	/* basic@{time or number or -number} format to query ref-log */
+	reflog_len = at = 0;
+	if (len && str[len-1] == '}') {
+		for (at = len-2; at >= 0; at--) {
+			if (str[at] == '@' && str[at+1] == '{') {
+				if (!upstream_mark(str + at, len - at)) {
+					reflog_len = (len-1) - (at+2);
+					len = at;
+				}
+				break;
+			}
+		}
+	}
+
 	/* Accept only unambiguous ref paths. */
-	if (ambiguous_path(str, len))
+	if (len && ambiguous_path(str, len))
 		return -1;
 
-	for (p = prefix; *p; p++) {
-		char *pathname = git_path("%s/%.*s", *p, len, str);
-		if (!read_ref(pathname, sha1))
-			return 0;
+	if (!len && reflog_len) {
+		struct strbuf buf = STRBUF_INIT;
+		int ret;
+		/* try the @{-N} syntax for n-th checkout */
+		ret = interpret_branch_name(str+at, &buf);
+		if (ret > 0) {
+			/* substitute this branch name and restart */
+			return get_sha1_1(buf.buf, buf.len, sha1);
+		} else if (ret == 0) {
+			return -1;
+		}
+		/* allow "@{...}" to mean the current branch reflog */
+		refs_found = dwim_ref("HEAD", 4, sha1, &real_ref);
+	} else if (reflog_len)
+		refs_found = dwim_log(str, len, sha1, &real_ref);
+	else
+		refs_found = dwim_ref(str, len, sha1, &real_ref);
+
+	if (!refs_found)
+		return -1;
+
+	if (warn_ambiguous_refs && refs_found > 1)
+		warning(warn_msg, len, str);
+
+	if (reflog_len) {
+		int nth, i;
+		unsigned long at_time;
+		unsigned long co_time;
+		int co_tz, co_cnt;
+
+		/* a @{-N} placed anywhere except the start is an error */
+		if (str[at+2] == '-')
+			return -1;
+
+		/* Is it asking for N-th entry, or approxidate? */
+		for (i = nth = 0; 0 <= nth && i < reflog_len; i++) {
+			char ch = str[at+2+i];
+			if ('0' <= ch && ch <= '9')
+				nth = nth * 10 + ch - '0';
+			else
+				nth = -1;
+		}
+		if (100000000 <= nth) {
+			at_time = nth;
+			nth = -1;
+		} else if (0 <= nth)
+			at_time = 0;
+		else {
+			int errors = 0;
+			char *tmp = xstrndup(str + at + 2, reflog_len);
+			at_time = approxidate_careful(tmp, &errors);
+			free(tmp);
+			if (errors)
+				return -1;
+		}
+		if (read_ref_at(real_ref, at_time, nth, sha1, NULL,
+				&co_time, &co_tz, &co_cnt)) {
+			if (at_time)
+				warning("Log for '%.*s' only goes "
+					"back to %s.", len, str,
+					show_date(co_time, co_tz, DATE_RFC2822));
+			else {
+				free(real_ref);
+				die("Log for '%.*s' only has %d entries.",
+				    len, str, co_cnt);
+			}
+		}
 	}
-	return -1;
-}
 
-static int get_sha1_1(const char *name, int len, unsigned char *sha1);
+	free(real_ref);
+	return 0;
+}
 
 static int get_parent(const char *name, int len,
 		      unsigned char *result, int idx)
@@ -277,13 +459,13 @@ static int get_parent(const char *name, int len,
 	if (parse_commit(commit))
 		return -1;
 	if (!idx) {
-		memcpy(result, commit->object.sha1, 20);
+		hashcpy(result, commit->object.sha1);
 		return 0;
 	}
 	p = commit->parents;
 	while (p) {
 		if (!--idx) {
-			memcpy(result, p->item->object.sha1, 20);
+			hashcpy(result, p->item->object.sha1);
 			return 0;
 		}
 		p = p->next;
@@ -295,26 +477,61 @@ static int get_nth_ancestor(const char *name, int len,
 			    unsigned char *result, int generation)
 {
 	unsigned char sha1[20];
-	int ret = get_sha1_1(name, len, sha1);
+	struct commit *commit;
+	int ret;
+
+	ret = get_sha1_1(name, len, sha1);
 	if (ret)
 		return ret;
+	commit = lookup_commit_reference(sha1);
+	if (!commit)
+		return -1;
 
 	while (generation--) {
-		struct commit *commit = lookup_commit_reference(sha1);
-
-		if (!commit || parse_commit(commit) || !commit->parents)
+		if (parse_commit(commit) || !commit->parents)
 			return -1;
-		memcpy(sha1, commit->parents->item->object.sha1, 20);
+		commit = commit->parents->item;
 	}
-	memcpy(result, sha1, 20);
+	hashcpy(result, commit->object.sha1);
 	return 0;
 }
 
+struct object *peel_to_type(const char *name, int namelen,
+			    struct object *o, enum object_type expected_type)
+{
+	if (name && !namelen)
+		namelen = strlen(name);
+	if (!o) {
+		unsigned char sha1[20];
+		if (get_sha1_1(name, namelen, sha1))
+			return NULL;
+		o = parse_object(sha1);
+	}
+	while (1) {
+		if (!o || (!o->parsed && !parse_object(o->sha1)))
+			return NULL;
+		if (o->type == expected_type)
+			return o;
+		if (o->type == OBJ_TAG)
+			o = ((struct tag*) o)->tagged;
+		else if (o->type == OBJ_COMMIT)
+			o = &(((struct commit *) o)->tree->object);
+		else {
+			if (name)
+				error("%.*s: expected %s type, but the object "
+				      "dereferences to %s type",
+				      namelen, name, typename(expected_type),
+				      typename(o->type));
+			return NULL;
+		}
+	}
+}
+
 static int peel_onion(const char *name, int len, unsigned char *sha1)
 {
 	unsigned char outer[20];
 	const char *sp;
-	const char *type_string = NULL;
+	unsigned int expected_type = 0;
 	struct object *o;
 
 	/*
@@ -338,13 +555,15 @@ static int peel_onion(const char *name, int len, unsigned char *sha1)
 
 	sp++; /* beginning of type name, or closing brace for empty */
 	if (!strncmp(commit_type, sp, 6) && sp[6] == '}')
-		type_string = commit_type;
+		expected_type = OBJ_COMMIT;
 	else if (!strncmp(tree_type, sp, 4) && sp[4] == '}')
-		type_string = tree_type;
+		expected_type = OBJ_TREE;
 	else if (!strncmp(blob_type, sp, 4) && sp[4] == '}')
-		type_string = blob_type;
+		expected_type = OBJ_BLOB;
 	else if (sp[0] == '}')
-		type_string = NULL;
+		expected_type = OBJ_NONE;
+	else if (sp[0] == '/')
+		expected_type = OBJ_COMMIT;
 	else
 		return -1;
 
@@ -354,38 +573,64 @@ static int peel_onion(const char *name, int len, unsigned char *sha1)
 	o = parse_object(outer);
 	if (!o)
 		return -1;
-	if (!type_string) {
+	if (!expected_type) {
 		o = deref_tag(o, name, sp - name - 2);
 		if (!o || (!o->parsed && !parse_object(o->sha1)))
 			return -1;
-		memcpy(sha1, o->sha1, 20);
+		hashcpy(sha1, o->sha1);
+		return 0;
 	}
-	else {
-		/* At this point, the syntax look correct, so
-		 * if we do not get the needed object, we should
-		 * barf.
+
+	/*
+	 * At this point, the syntax look correct, so
+	 * if we do not get the needed object, we should
+	 * barf.
+	 */
+	o = peel_to_type(name, len, o, expected_type);
+	if (!o)
+		return -1;
+
+	hashcpy(sha1, o->sha1);
+	if (sp[0] == '/') {
+		/* "$commit^{/foo}" */
+		char *prefix;
+		int ret;
+		struct commit_list *list = NULL;
+
+		/*
+		 * $commit^{/}. Some regex implementation may reject.
+		 * We don't need regex anyway. '' pattern always matches.
 		 */
+		if (sp[1] == '}')
+			return 0;
 
-		while (1) {
-			if (!o || (!o->parsed && !parse_object(o->sha1)))
-				return -1;
-			if (o->type == type_string) {
-				memcpy(sha1, o->sha1, 20);
-				return 0;
+		prefix = xstrndup(sp + 1, name + len - 1 - (sp + 1));
+		commit_list_insert((struct commit *)o, &list);
+		ret = get_sha1_oneline(prefix, sha1, list);
+		free(prefix);
+		return ret;
+	}
+	return 0;
+}
+
+static int get_describe_name(const char *name, int len, unsigned char *sha1)
+{
+	const char *cp;
+
+	for (cp = name + len - 1; name + 2 <= cp; cp--) {
+		char ch = *cp;
+		if (hexval(ch) & ~0377) {
+			/* We must be looking at g in "SOMETHING-g"
+			 * for it to be describe output.
+			 */
+			if (ch == 'g' && cp[-1] == '-') {
+				cp++;
+				len -= cp - name;
+				return get_short_sha1(cp, len, sha1, 1);
 			}
-			if (o->type == tag_type)
-				o = ((struct tag*) o)->tagged;
-			else if (o->type == commit_type)
-				o = &(((struct commit *) o)->tree->object);
-			else
-				return error("%.*s: expected %s type, but the object dereferences to %s type",
-					     len, name, type_string,
-					     o->type);
-			if (!o->parsed)
-				parse_object(o->sha1);
 		}
 	}
-	return 0;
+	return -1;
 }
 
 static int get_sha1_1(const char *name, int len, unsigned char *sha1)
@@ -393,9 +638,8 @@ static int get_sha1_1(const char *name, int len, unsigned char *sha1)
 	int ret, has_suffix;
 	const char *cp;
 
-	/* "name~3" is "name^^^",
-	 * "name~" and "name~0" are name -- not "name^0"!
-	 * "name^" is not "name^0"; it is "name^1".
+	/*
+	 * "name~3" is "name^^^", "name~" is "name~1", and "name^" is "name^1".
 	 */
 	has_suffix = 0;
 	for (cp = name + len - 1; name <= cp; cp--) {
@@ -413,11 +657,10 @@ static int get_sha1_1(const char *name, int len, unsigned char *sha1)
 		cp++;
 		while (cp < name + len)
 			num = num * 10 + *cp++ - '0';
-		if (has_suffix == '^') {
-			if (!num && len1 == len - 1)
-				num = 1;
+		if (!num && len1 == len - 1)
+			num = 1;
+		if (has_suffix == '^')
 			return get_parent(name, len1, sha1, num);
-		}
 		/* else if (has_suffix == '~') -- goes without saying */
 		return get_nth_ancestor(name, len1, sha1, num);
 	}
@@ -429,15 +672,556 @@ static int get_sha1_1(const char *name, int len, unsigned char *sha1)
 	ret = get_sha1_basic(name, len, sha1);
 	if (!ret)
 		return 0;
+
+	/* It could be describe output that is "SOMETHING-gXXXX" */
+	ret = get_describe_name(name, len, sha1);
+	if (!ret)
+		return 0;
+
 	return get_short_sha1(name, len, sha1, 0);
 }
 
 /*
+ * This interprets names like ':/Initial revision of "git"' by searching
+ * through history and returning the first commit whose message starts
+ * the given regular expression.
+ *
+ * For future extension, ':/!' is reserved. If you want to match a message
+ * beginning with a '!', you have to repeat the exclamation mark.
+ */
+#define ONELINE_SEEN (1u<<20)
+
+static int handle_one_ref(const char *path,
+		const unsigned char *sha1, int flag, void *cb_data)
+{
+	struct commit_list **list = cb_data;
+	struct object *object = parse_object(sha1);
+	if (!object)
+		return 0;
+	if (object->type == OBJ_TAG) {
+		object = deref_tag(object, path, strlen(path));
+		if (!object)
+			return 0;
+	}
+	if (object->type != OBJ_COMMIT)
+		return 0;
+	commit_list_insert_by_date((struct commit *)object, list);
+	return 0;
+}
+
+static int get_sha1_oneline(const char *prefix, unsigned char *sha1,
+			    struct commit_list *list)
+{
+	struct commit_list *backup = NULL, *l;
+	int found = 0;
+	regex_t regex;
+
+	if (prefix[0] == '!') {
+		if (prefix[1] != '!')
+			die ("Invalid search pattern: %s", prefix);
+		prefix++;
+	}
+
+	if (regcomp(&regex, prefix, REG_EXTENDED))
+		die("Invalid search pattern: %s", prefix);
+
+	for (l = list; l; l = l->next) {
+		l->item->object.flags |= ONELINE_SEEN;
+		commit_list_insert(l->item, &backup);
+	}
+	while (list) {
+		char *p, *to_free = NULL;
+		struct commit *commit;
+		enum object_type type;
+		unsigned long size;
+		int matches;
+
+		commit = pop_most_recent_commit(&list, ONELINE_SEEN);
+		if (!parse_object(commit->object.sha1))
+			continue;
+		if (commit->buffer)
+			p = commit->buffer;
+		else {
+			p = read_sha1_file(commit->object.sha1, &type, &size);
+			if (!p)
+				continue;
+			to_free = p;
+		}
+
+		p = strstr(p, "\n\n");
+		matches = p && !regexec(&regex, p + 2, 0, NULL, 0);
+		free(to_free);
+
+		if (matches) {
+			hashcpy(sha1, commit->object.sha1);
+			found = 1;
+			break;
+		}
+	}
+	regfree(&regex);
+	free_commit_list(list);
+	for (l = backup; l; l = l->next)
+		clear_commit_marks(l->item, ONELINE_SEEN);
+	free_commit_list(backup);
+	return found ? 0 : -1;
+}
+
+struct grab_nth_branch_switch_cbdata {
+	long cnt, alloc;
+	struct strbuf *buf;
+};
+
+static int grab_nth_branch_switch(unsigned char *osha1, unsigned char *nsha1,
+				  const char *email, unsigned long timestamp, int tz,
+				  const char *message, void *cb_data)
+{
+	struct grab_nth_branch_switch_cbdata *cb = cb_data;
+	const char *match = NULL, *target = NULL;
+	size_t len;
+	int nth;
+
+	if (!prefixcmp(message, "checkout: moving from ")) {
+		match = message + strlen("checkout: moving from ");
+		target = strstr(match, " to ");
+	}
+
+	if (!match || !target)
+		return 0;
+
+	len = target - match;
+	nth = cb->cnt++ % cb->alloc;
+	strbuf_reset(&cb->buf[nth]);
+	strbuf_add(&cb->buf[nth], match, len);
+	return 0;
+}
+
+/*
+ * Parse @{-N} syntax, return the number of characters parsed
+ * if successful; otherwise signal an error with negative value.
+ */
+static int interpret_nth_prior_checkout(const char *name, struct strbuf *buf)
+{
+	long nth;
+	int i, retval;
+	struct grab_nth_branch_switch_cbdata cb;
+	const char *brace;
+	char *num_end;
+
+	if (name[0] != '@' || name[1] != '{' || name[2] != '-')
+		return -1;
+	brace = strchr(name, '}');
+	if (!brace)
+		return -1;
+	nth = strtol(name+3, &num_end, 10);
+	if (num_end != brace)
+		return -1;
+	if (nth <= 0)
+		return -1;
+	cb.alloc = nth;
+	cb.buf = xmalloc(nth * sizeof(struct strbuf));
+	for (i = 0; i < nth; i++)
+		strbuf_init(&cb.buf[i], 20);
+	cb.cnt = 0;
+	retval = 0;
+	for_each_recent_reflog_ent("HEAD", grab_nth_branch_switch, 40960, &cb);
+	if (cb.cnt < nth) {
+		cb.cnt = 0;
+		for_each_reflog_ent("HEAD", grab_nth_branch_switch, &cb);
+	}
+	if (cb.cnt < nth)
+		goto release_return;
+	i = cb.cnt % nth;
+	strbuf_reset(buf);
+	strbuf_add(buf, cb.buf[i].buf, cb.buf[i].len);
+	retval = brace-name+1;
+
+release_return:
+	for (i = 0; i < nth; i++)
+		strbuf_release(&cb.buf[i]);
+	free(cb.buf);
+
+	return retval;
+}
+
+int get_sha1_mb(const char *name, unsigned char *sha1)
+{
+	struct commit *one, *two;
+	struct commit_list *mbs;
+	unsigned char sha1_tmp[20];
+	const char *dots;
+	int st;
+
+	dots = strstr(name, "...");
+	if (!dots)
+		return get_sha1(name, sha1);
+	if (dots == name)
+		st = get_sha1("HEAD", sha1_tmp);
+	else {
+		struct strbuf sb;
+		strbuf_init(&sb, dots - name);
+		strbuf_add(&sb, name, dots - name);
+		st = get_sha1(sb.buf, sha1_tmp);
+		strbuf_release(&sb);
+	}
+	if (st)
+		return st;
+	one = lookup_commit_reference_gently(sha1_tmp, 0);
+	if (!one)
+		return -1;
+
+	if (get_sha1(dots[3] ? (dots + 3) : "HEAD", sha1_tmp))
+		return -1;
+	two = lookup_commit_reference_gently(sha1_tmp, 0);
+	if (!two)
+		return -1;
+	mbs = get_merge_bases(one, two, 1);
+	if (!mbs || mbs->next)
+		st = -1;
+	else {
+		st = 0;
+		hashcpy(sha1, mbs->item->object.sha1);
+	}
+	free_commit_list(mbs);
+	return st;
+}
+
+/*
+ * This reads short-hand syntax that not only evaluates to a commit
+ * object name, but also can act as if the end user spelled the name
+ * of the branch from the command line.
+ *
+ * - "@{-N}" finds the name of the Nth previous branch we were on, and
+ *   places the name of the branch in the given buf and returns the
+ *   number of characters parsed if successful.
+ *
+ * - "<branch>@{upstream}" finds the name of the other ref that
+ *   <branch> is configured to merge with (missing <branch> defaults
+ *   to the current branch), and places the name of the branch in the
+ *   given buf and returns the number of characters parsed if
+ *   successful.
+ *
+ * If the input is not of the accepted format, it returns a negative
+ * number to signal an error.
+ *
+ * If the input was ok but there are not N branch switches in the
+ * reflog, it returns 0.
+ */
+int interpret_branch_name(const char *name, struct strbuf *buf)
+{
+	char *cp;
+	struct branch *upstream;
+	int namelen = strlen(name);
+	int len = interpret_nth_prior_checkout(name, buf);
+	int tmp_len;
+
+	if (!len)
+		return len; /* syntax Ok, not enough switches */
+	if (0 < len && len == namelen)
+		return len; /* consumed all */
+	else if (0 < len) {
+		/* we have extra data, which might need further processing */
+		struct strbuf tmp = STRBUF_INIT;
+		int used = buf->len;
+		int ret;
+
+		strbuf_add(buf, name + len, namelen - len);
+		ret = interpret_branch_name(buf->buf, &tmp);
+		/* that data was not interpreted, remove our cruft */
+		if (ret < 0) {
+			strbuf_setlen(buf, used);
+			return len;
+		}
+		strbuf_reset(buf);
+		strbuf_addbuf(buf, &tmp);
+		strbuf_release(&tmp);
+		/* tweak for size of {-N} versus expanded ref name */
+		return ret - used + len;
+	}
+
+	cp = strchr(name, '@');
+	if (!cp)
+		return -1;
+	tmp_len = upstream_mark(cp, namelen - (cp - name));
+	if (!tmp_len)
+		return -1;
+	len = cp + tmp_len - name;
+	cp = xstrndup(name, cp - name);
+	upstream = branch_get(*cp ? cp : NULL);
+	if (!upstream
+	    || !upstream->merge
+	    || !upstream->merge[0]->dst)
+		return error("No upstream branch found for '%s'", cp);
+	free(cp);
+	cp = shorten_unambiguous_ref(upstream->merge[0]->dst, 0);
+	strbuf_reset(buf);
+	strbuf_addstr(buf, cp);
+	free(cp);
+	return len;
+}
+
+int strbuf_branchname(struct strbuf *sb, const char *name)
+{
+	int len = strlen(name);
+	if (interpret_branch_name(name, sb) == len)
+		return 0;
+	strbuf_add(sb, name, len);
+	return len;
+}
+
+int strbuf_check_branch_ref(struct strbuf *sb, const char *name)
+{
+	strbuf_branchname(sb, name);
+	if (name[0] == '-')
+		return CHECK_REF_FORMAT_ERROR;
+	strbuf_splice(sb, 0, 0, "refs/heads/", 11);
+	return check_ref_format(sb->buf);
+}
+
+/*
  * This is like "get_sha1_basic()", except it allows "sha1 expressions",
  * notably "xyz^" for "parent of xyz"
  */
 int get_sha1(const char *name, unsigned char *sha1)
 {
-	prepare_alt_odb();
-	return get_sha1_1(name, strlen(name), sha1);
+	struct object_context unused;
+	return get_sha1_with_context(name, sha1, &unused);
+}
+
+/* Must be called only when object_name:filename doesn't exist. */
+static void diagnose_invalid_sha1_path(const char *prefix,
+				       const char *filename,
+				       const unsigned char *tree_sha1,
+				       const char *object_name)
+{
+	struct stat st;
+	unsigned char sha1[20];
+	unsigned mode;
+
+	if (!prefix)
+		prefix = "";
+
+	if (!lstat(filename, &st))
+		die("Path '%s' exists on disk, but not in '%s'.",
+		    filename, object_name);
+	if (errno == ENOENT || errno == ENOTDIR) {
+		char *fullname = xmalloc(strlen(filename)
+					     + strlen(prefix) + 1);
+		strcpy(fullname, prefix);
+		strcat(fullname, filename);
+
+		if (!get_tree_entry(tree_sha1, fullname,
+				    sha1, &mode)) {
+			die("Path '%s' exists, but not '%s'.\n"
+			    "Did you mean '%s:%s' aka '%s:./%s'?",
+			    fullname,
+			    filename,
+			    object_name,
+			    fullname,
+			    object_name,
+			    filename);
+		}
+		die("Path '%s' does not exist in '%s'",
+		    filename, object_name);
+	}
+}
+
+/* Must be called only when :stage:filename doesn't exist. */
+static void diagnose_invalid_index_path(int stage,
+					const char *prefix,
+					const char *filename)
+{
+	struct stat st;
+	struct cache_entry *ce;
+	int pos;
+	unsigned namelen = strlen(filename);
+	unsigned fullnamelen;
+	char *fullname;
+
+	if (!prefix)
+		prefix = "";
+
+	/* Wrong stage number? */
+	pos = cache_name_pos(filename, namelen);
+	if (pos < 0)
+		pos = -pos - 1;
+	if (pos < active_nr) {
+		ce = active_cache[pos];
+		if (ce_namelen(ce) == namelen &&
+		    !memcmp(ce->name, filename, namelen))
+			die("Path '%s' is in the index, but not at stage %d.\n"
+			    "Did you mean ':%d:%s'?",
+			    filename, stage,
+			    ce_stage(ce), filename);
+	}
+
+	/* Confusion between relative and absolute filenames? */
+	fullnamelen = namelen + strlen(prefix);
+	fullname = xmalloc(fullnamelen + 1);
+	strcpy(fullname, prefix);
+	strcat(fullname, filename);
+	pos = cache_name_pos(fullname, fullnamelen);
+	if (pos < 0)
+		pos = -pos - 1;
+	if (pos < active_nr) {
+		ce = active_cache[pos];
+		if (ce_namelen(ce) == fullnamelen &&
+		    !memcmp(ce->name, fullname, fullnamelen))
+			die("Path '%s' is in the index, but not '%s'.\n"
+			    "Did you mean ':%d:%s' aka ':%d:./%s'?",
+			    fullname, filename,
+			    ce_stage(ce), fullname,
+			    ce_stage(ce), filename);
+	}
+
+	if (!lstat(filename, &st))
+		die("Path '%s' exists on disk, but not in the index.", filename);
+	if (errno == ENOENT || errno == ENOTDIR)
+		die("Path '%s' does not exist (neither on disk nor in the index).",
+		    filename);
+
+	free(fullname);
+}
+
+
+int get_sha1_with_mode_1(const char *name, unsigned char *sha1, unsigned *mode,
+			 int only_to_die, const char *prefix)
+{
+	struct object_context oc;
+	int ret;
+	ret = get_sha1_with_context_1(name, sha1, &oc, only_to_die, prefix);
+	*mode = oc.mode;
+	return ret;
+}
+
+static char *resolve_relative_path(const char *rel)
+{
+	if (prefixcmp(rel, "./") && prefixcmp(rel, "../"))
+		return NULL;
+
+	if (!startup_info)
+		die("BUG: startup_info struct is not initialized.");
+
+	if (!is_inside_work_tree())
+		die("relative path syntax can't be used outside working tree.");
+
+	/* die() inside prefix_path() if resolved path is outside worktree */
+	return prefix_path(startup_info->prefix,
+			   startup_info->prefix ? strlen(startup_info->prefix) : 0,
+			   rel);
+}
+
+int get_sha1_with_context_1(const char *name, unsigned char *sha1,
+			    struct object_context *oc,
+			    int only_to_die, const char *prefix)
+{
+	int ret, bracket_depth;
+	int namelen = strlen(name);
+	const char *cp;
+
+	memset(oc, 0, sizeof(*oc));
+	oc->mode = S_IFINVALID;
+	ret = get_sha1_1(name, namelen, sha1);
+	if (!ret)
+		return ret;
+	/* sha1:path --> object name of path in ent sha1
+	 * :path -> object name of absolute path in index
+	 * :./path -> object name of path relative to cwd in index
+	 * :[0-3]:path -> object name of path in index at stage
+	 * :/foo -> recent commit matching foo
+	 */
+	if (name[0] == ':') {
+		int stage = 0;
+		struct cache_entry *ce;
+		char *new_path = NULL;
+		int pos;
+		if (!only_to_die && namelen > 2 && name[1] == '/') {
+			struct commit_list *list = NULL;
+			for_each_ref(handle_one_ref, &list);
+			return get_sha1_oneline(name + 2, sha1, list);
+		}
+		if (namelen < 3 ||
+		    name[2] != ':' ||
+		    name[1] < '0' || '3' < name[1])
+			cp = name + 1;
+		else {
+			stage = name[1] - '0';
+			cp = name + 3;
+		}
+		new_path = resolve_relative_path(cp);
+		if (!new_path) {
+			namelen = namelen - (cp - name);
+		} else {
+			cp = new_path;
+			namelen = strlen(cp);
+		}
+
+		strncpy(oc->path, cp,
+			sizeof(oc->path));
+		oc->path[sizeof(oc->path)-1] = '\0';
+
+		if (!active_cache)
+			read_cache();
+		pos = cache_name_pos(cp, namelen);
+		if (pos < 0)
+			pos = -pos - 1;
+		while (pos < active_nr) {
+			ce = active_cache[pos];
+			if (ce_namelen(ce) != namelen ||
+			    memcmp(ce->name, cp, namelen))
+				break;
+			if (ce_stage(ce) == stage) {
+				hashcpy(sha1, ce->sha1);
+				oc->mode = ce->ce_mode;
+				free(new_path);
+				return 0;
+			}
+			pos++;
+		}
+		if (only_to_die && name[1] && name[1] != '/')
+			diagnose_invalid_index_path(stage, prefix, cp);
+		free(new_path);
+		return -1;
+	}
+	for (cp = name, bracket_depth = 0; *cp; cp++) {
+		if (*cp == '{')
+			bracket_depth++;
+		else if (bracket_depth && *cp == '}')
+			bracket_depth--;
+		else if (!bracket_depth && *cp == ':')
+			break;
+	}
+	if (*cp == ':') {
+		unsigned char tree_sha1[20];
+		char *object_name = NULL;
+		if (only_to_die) {
+			object_name = xmalloc(cp-name+1);
+			strncpy(object_name, name, cp-name);
+			object_name[cp-name] = '\0';
+		}
+		if (!get_sha1_1(name, cp-name, tree_sha1)) {
+			const char *filename = cp+1;
+			char *new_filename = NULL;
+
+			new_filename = resolve_relative_path(filename);
+			if (new_filename)
+				filename = new_filename;
+			ret = get_tree_entry(tree_sha1, filename, sha1, &oc->mode);
+			if (only_to_die) {
+				diagnose_invalid_sha1_path(prefix, filename,
+							   tree_sha1, object_name);
+				free(object_name);
+			}
+			hashcpy(oc->tree, tree_sha1);
+			strncpy(oc->path, filename,
+				sizeof(oc->path));
+			oc->path[sizeof(oc->path)-1] = '\0';
+
+			free(new_filename);
+			return ret;
+		} else {
+			if (only_to_die)
+				die("Invalid object name '%s'.", object_name);
+		}
+	}
+	return ret;
 }