1 files changed, 954 insertions, 528 deletions

diff --git a/sha1_name.c b/sha1_name.c
index 709ff2eee6..c7c5ab376c 100644
--- a/sha1_name.c
+++ b/sha1_name.c
@@ -1,4 +1,5 @@
 #include "cache.h"
+#include "config.h"
 #include "tag.h"
 #include "commit.h"
 #include "tree.h"
@@ -6,54 +7,129 @@
 #include "tree-walk.h"
 #include "refs.h"
 #include "remote.h"
+#include "dir.h"
+#include "sha1-array.h"
+#include "packfile.h"
+
+static int get_oid_oneline(const char *, struct object_id *, struct commit_list *);
+
+typedef int (*disambiguate_hint_fn)(const struct object_id *, void *);
+
+struct disambiguate_state {
+	int len; /* length of prefix in hex chars */
+	char hex_pfx[GIT_MAX_HEXSZ + 1];
+	struct object_id bin_pfx;
+
+	disambiguate_hint_fn fn;
+	void *cb_data;
+	struct object_id candidate;
+	unsigned candidate_exists:1;
+	unsigned candidate_checked:1;
+	unsigned candidate_ok:1;
+	unsigned disambiguate_fn_used:1;
+	unsigned ambiguous:1;
+	unsigned always_call_fn:1;
+};
+
+static void update_candidates(struct disambiguate_state *ds, const struct object_id *current)
+{
+	if (ds->always_call_fn) {
+		ds->ambiguous = ds->fn(current, ds->cb_data) ? 1 : 0;
+		return;
+	}
+	if (!ds->candidate_exists) {
+		/* this is the first candidate */
+		oidcpy(&ds->candidate, current);
+		ds->candidate_exists = 1;
+		return;
+	} else if (!oidcmp(&ds->candidate, current)) {
+		/* the same as what we already have seen */
+		return;
+	}
+
+	if (!ds->fn) {
+		/* cannot disambiguate between ds->candidate and current */
+		ds->ambiguous = 1;
+		return;
+	}
+
+	if (!ds->candidate_checked) {
+		ds->candidate_ok = ds->fn(&ds->candidate, ds->cb_data);
+		ds->disambiguate_fn_used = 1;
+		ds->candidate_checked = 1;
+	}
 
-static int get_sha1_oneline(const char *, unsigned char *, struct commit_list *);
+	if (!ds->candidate_ok) {
+		/* discard the candidate; we know it does not satisfy fn */
+		oidcpy(&ds->candidate, current);
+		ds->candidate_checked = 0;
+		return;
+	}
 
-static int find_short_object_filename(int len, const char *name, unsigned char *sha1)
+	/* if we reach this point, we know ds->candidate satisfies fn */
+	if (ds->fn(current, ds->cb_data)) {
+		/*
+		 * if both current and candidate satisfy fn, we cannot
+		 * disambiguate.
+		 */
+		ds->candidate_ok = 0;
+		ds->ambiguous = 1;
+	}
+
+	/* otherwise, current can be discarded and candidate is still good */
+}
+
+static int append_loose_object(const struct object_id *oid, const char *path,
+			       void *data)
 {
+	oid_array_append(data, oid);
+	return 0;
+}
+
+static int match_sha(unsigned, const unsigned char *, const unsigned char *);
+
+static void find_short_object_filename(struct disambiguate_state *ds)
+{
+	int subdir_nr = ds->bin_pfx.hash[0];
 	struct alternate_object_database *alt;
-	char hex[40];
-	int found = 0;
 	static struct alternate_object_database *fakeent;
 
 	if (!fakeent) {
-		const char *objdir = get_object_directory();
-		int objdir_len = strlen(objdir);
-		int entlen = objdir_len + 43;
-		fakeent = xmalloc(sizeof(*fakeent) + entlen);
-		memcpy(fakeent->base, objdir, objdir_len);
-		fakeent->name = fakeent->base + objdir_len + 1;
-		fakeent->name[-1] = '/';
+		/*
+		 * Create a "fake" alternate object database that
+		 * points to our own object database, to make it
+		 * easier to get a temporary working space in
+		 * alt->name/alt->base while iterating over the
+		 * object databases including our own.
+		 */
+		fakeent = alloc_alt_odb(get_object_directory());
 	}
 	fakeent->next = alt_odb_list;
 
-	sprintf(hex, "%.2s", name);
-	for (alt = fakeent; alt && found < 2; alt = alt->next) {
-		struct dirent *de;
-		DIR *dir;
-		sprintf(alt->name, "%.2s/", name);
-		dir = opendir(alt->base);
-		if (!dir)
-			continue;
-		while ((de = readdir(dir)) != NULL) {
-			if (strlen(de->d_name) != 38)
-				continue;
-			if (memcmp(de->d_name, name + 2, len - 2))
-				continue;
-			if (!found) {
-				memcpy(hex + 2, de->d_name, 38);
-				found++;
-			}
-			else if (memcmp(hex + 2, de->d_name, 38)) {
-				found = 2;
+	for (alt = fakeent; alt && !ds->ambiguous; alt = alt->next) {
+		int pos;
+
+		if (!alt->loose_objects_subdir_seen[subdir_nr]) {
+			struct strbuf *buf = alt_scratch_buf(alt);
+			for_each_file_in_obj_subdir(subdir_nr, buf,
+						    append_loose_object,
+						    NULL, NULL,
+						    &alt->loose_objects_cache);
+			alt->loose_objects_subdir_seen[subdir_nr] = 1;
+		}
+
+		pos = oid_array_lookup(&alt->loose_objects_cache, &ds->bin_pfx);
+		if (pos < 0)
+			pos = -1 - pos;
+		while (!ds->ambiguous && pos < alt->loose_objects_cache.nr) {
+			const struct object_id *oid;
+			oid = alt->loose_objects_cache.oid + pos;
+			if (!match_sha(ds->len, ds->bin_pfx.hash, oid->hash))
 				break;
-			}
+			update_candidates(ds, oid);
+			pos++;
 		}
-		closedir(dir);
 	}
-	if (found == 1)
-		return get_sha1_hex(hex, sha1) == 0;
-	return found;
 }
 
 static int match_sha(unsigned len, const unsigned char *a, const unsigned char *b)
@@ -71,103 +147,187 @@ static int match_sha(unsigned len, const unsigned char *a, const unsigned char *
 	return 1;
 }
 
-static int find_short_packed_object(int len, const unsigned char *match, unsigned char *sha1)
+static void unique_in_pack(struct packed_git *p,
+			   struct disambiguate_state *ds)
 {
-	struct packed_git *p;
-	const unsigned char *found_sha1 = NULL;
-	int found = 0;
-
-	prepare_packed_git();
-	for (p = packed_git; p && found < 2; p = p->next) {
-		uint32_t num, last;
-		uint32_t first = 0;
-		open_pack_index(p);
-		num = p->num_objects;
-		last = num;
-		while (first < last) {
-			uint32_t mid = (first + last) / 2;
-			const unsigned char *now;
-			int cmp;
-
-			now = nth_packed_object_sha1(p, mid);
-			cmp = hashcmp(match, now);
-			if (!cmp) {
-				first = mid;
-				break;
-			}
-			if (cmp > 0) {
-				first = mid+1;
-				continue;
-			}
-			last = mid;
+	uint32_t num, last, i, first = 0;
+	const struct object_id *current = NULL;
+
+	open_pack_index(p);
+	num = p->num_objects;
+	last = num;
+	while (first < last) {
+		uint32_t mid = first + (last - first) / 2;
+		const unsigned char *current;
+		int cmp;
+
+		current = nth_packed_object_sha1(p, mid);
+		cmp = hashcmp(ds->bin_pfx.hash, current);
+		if (!cmp) {
+			first = mid;
+			break;
 		}
-		if (first < num) {
-			const unsigned char *now, *next;
-		       now = nth_packed_object_sha1(p, first);
-			if (match_sha(len, match, now)) {
-				next = nth_packed_object_sha1(p, first+1);
-			       if (!next|| !match_sha(len, match, next)) {
-					/* unique within this pack */
-					if (!found) {
-						found_sha1 = now;
-						found++;
-					}
-					else if (hashcmp(found_sha1, now)) {
-						found = 2;
-						break;
-					}
-				}
-				else {
-					/* not even unique within this pack */
-					found = 2;
-					break;
-				}
-			}
+		if (cmp > 0) {
+			first = mid+1;
+			continue;
 		}
+		last = mid;
 	}
-	if (found == 1)
-		hashcpy(sha1, found_sha1);
-	return found;
+
+	/*
+	 * At this point, "first" is the location of the lowest object
+	 * with an object name that could match "bin_pfx".  See if we have
+	 * 0, 1 or more objects that actually match(es).
+	 */
+	for (i = first; i < num && !ds->ambiguous; i++) {
+		struct object_id oid;
+		current = nth_packed_object_oid(&oid, p, i);
+		if (!match_sha(ds->len, ds->bin_pfx.hash, current->hash))
+			break;
+		update_candidates(ds, current);
+	}
+}
+
+static void find_short_packed_object(struct disambiguate_state *ds)
+{
+	struct packed_git *p;
+
+	prepare_packed_git();
+	for (p = packed_git; p && !ds->ambiguous; p = p->next)
+		unique_in_pack(p, ds);
 }
 
 #define SHORT_NAME_NOT_FOUND (-1)
 #define SHORT_NAME_AMBIGUOUS (-2)
 
-static int find_unique_short_object(int len, char *canonical,
-				    unsigned char *res, unsigned char *sha1)
+static int finish_object_disambiguation(struct disambiguate_state *ds,
+					struct object_id *oid)
 {
-	int has_unpacked, has_packed;
-	unsigned char unpacked_sha1[20], packed_sha1[20];
+	if (ds->ambiguous)
+		return SHORT_NAME_AMBIGUOUS;
 
-	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)
+	if (!ds->candidate_exists)
 		return SHORT_NAME_NOT_FOUND;
-	if (1 < has_unpacked || 1 < has_packed)
+
+	if (!ds->candidate_checked)
+		/*
+		 * If this is the only candidate, there is no point
+		 * calling the disambiguation hint callback.
+		 *
+		 * On the other hand, if the current candidate
+		 * replaced an earlier candidate that did _not_ pass
+		 * the disambiguation hint callback, then we do have
+		 * more than one objects that match the short name
+		 * given, so we should make sure this one matches;
+		 * otherwise, if we discovered this one and the one
+		 * that we previously discarded in the reverse order,
+		 * we would end up showing different results in the
+		 * same repository!
+		 */
+		ds->candidate_ok = (!ds->disambiguate_fn_used ||
+				    ds->fn(&ds->candidate, ds->cb_data));
+
+	if (!ds->candidate_ok)
 		return SHORT_NAME_AMBIGUOUS;
-	if (has_unpacked != has_packed) {
-		hashcpy(sha1, (has_packed ? packed_sha1 : unpacked_sha1));
+
+	oidcpy(oid, &ds->candidate);
+	return 0;
+}
+
+static int disambiguate_commit_only(const struct object_id *oid, void *cb_data_unused)
+{
+	int kind = sha1_object_info(oid->hash, NULL);
+	return kind == OBJ_COMMIT;
+}
+
+static int disambiguate_committish_only(const struct object_id *oid, void *cb_data_unused)
+{
+	struct object *obj;
+	int kind;
+
+	kind = sha1_object_info(oid->hash, NULL);
+	if (kind == OBJ_COMMIT)
+		return 1;
+	if (kind != OBJ_TAG)
 		return 0;
-	}
-	/* Both have unique ones -- do they match? */
-	if (hashcmp(packed_sha1, unpacked_sha1))
-		return SHORT_NAME_AMBIGUOUS;
-	hashcpy(sha1, packed_sha1);
+
+	/* We need to do this the hard way... */
+	obj = deref_tag(parse_object(oid), NULL, 0);
+	if (obj && obj->type == OBJ_COMMIT)
+		return 1;
+	return 0;
+}
+
+static int disambiguate_tree_only(const struct object_id *oid, void *cb_data_unused)
+{
+	int kind = sha1_object_info(oid->hash, NULL);
+	return kind == OBJ_TREE;
+}
+
+static int disambiguate_treeish_only(const struct object_id *oid, void *cb_data_unused)
+{
+	struct object *obj;
+	int kind;
+
+	kind = sha1_object_info(oid->hash, NULL);
+	if (kind == OBJ_TREE || kind == OBJ_COMMIT)
+		return 1;
+	if (kind != OBJ_TAG)
+		return 0;
+
+	/* We need to do this the hard way... */
+	obj = deref_tag(parse_object(oid), NULL, 0);
+	if (obj && (obj->type == OBJ_TREE || obj->type == OBJ_COMMIT))
+		return 1;
 	return 0;
 }
 
-static int get_short_sha1(const char *name, int len, unsigned char *sha1,
-			  int quietly)
+static int disambiguate_blob_only(const struct object_id *oid, void *cb_data_unused)
 {
-	int i, status;
-	char canonical[40];
-	unsigned char res[20];
+	int kind = sha1_object_info(oid->hash, NULL);
+	return kind == OBJ_BLOB;
+}
+
+static disambiguate_hint_fn default_disambiguate_hint;
+
+int set_disambiguate_hint_config(const char *var, const char *value)
+{
+	static const struct {
+		const char *name;
+		disambiguate_hint_fn fn;
+	} hints[] = {
+		{ "none", NULL },
+		{ "commit", disambiguate_commit_only },
+		{ "committish", disambiguate_committish_only },
+		{ "tree", disambiguate_tree_only },
+		{ "treeish", disambiguate_treeish_only },
+		{ "blob", disambiguate_blob_only }
+	};
+	int i;
+
+	if (!value)
+		return config_error_nonbool(var);
 
-	if (len < MINIMUM_ABBREV || len > 40)
+	for (i = 0; i < ARRAY_SIZE(hints); i++) {
+		if (!strcasecmp(value, hints[i].name)) {
+			default_disambiguate_hint = hints[i].fn;
+			return 0;
+		}
+	}
+
+	return error("unknown hint type for '%s': %s", var, value);
+}
+
+static int init_object_disambiguation(const char *name, int len,
+				      struct disambiguate_state *ds)
+{
+	int i;
+
+	if (len < MINIMUM_ABBREV || len > GIT_SHA1_HEXSZ)
 		return -1;
-	hashclr(res);
-	memset(canonical, 'x', 40);
+
+	memset(ds, 0, sizeof(*ds));
+
 	for (i = 0; i < len ;i++) {
 		unsigned char c = name[i];
 		unsigned char val;
@@ -181,40 +341,190 @@ static int get_short_sha1(const char *name, int len, unsigned char *sha1,
 		}
 		else
 			return -1;
-		canonical[i] = c;
+		ds->hex_pfx[i] = c;
 		if (!(i & 1))
 			val <<= 4;
-		res[i >> 1] |= val;
+		ds->bin_pfx.hash[i >> 1] |= val;
+	}
+
+	ds->len = len;
+	ds->hex_pfx[len] = '\0';
+	prepare_alt_odb();
+	return 0;
+}
+
+static int show_ambiguous_object(const struct object_id *oid, void *data)
+{
+	const struct disambiguate_state *ds = data;
+	struct strbuf desc = STRBUF_INIT;
+	int type;
+
+
+	if (ds->fn && !ds->fn(oid, ds->cb_data))
+		return 0;
+
+	type = sha1_object_info(oid->hash, NULL);
+	if (type == OBJ_COMMIT) {
+		struct commit *commit = lookup_commit(oid);
+		if (commit) {
+			struct pretty_print_context pp = {0};
+			pp.date_mode.type = DATE_SHORT;
+			format_commit_message(commit, " %ad - %s", &desc, &pp);
+		}
+	} else if (type == OBJ_TAG) {
+		struct tag *tag = lookup_tag(oid);
+		if (!parse_tag(tag) && tag->tag)
+			strbuf_addf(&desc, " %s", tag->tag);
+	}
+
+	advise("  %s %s%s",
+	       find_unique_abbrev(oid->hash, DEFAULT_ABBREV),
+	       typename(type) ? typename(type) : "unknown type",
+	       desc.buf);
+
+	strbuf_release(&desc);
+	return 0;
+}
+
+static int get_short_oid(const char *name, int len, struct object_id *oid,
+			  unsigned flags)
+{
+	int status;
+	struct disambiguate_state ds;
+	int quietly = !!(flags & GET_OID_QUIETLY);
+
+	if (init_object_disambiguation(name, len, &ds) < 0)
+		return -1;
+
+	if (HAS_MULTI_BITS(flags & GET_OID_DISAMBIGUATORS))
+		die("BUG: multiple get_short_oid disambiguator flags");
+
+	if (flags & GET_OID_COMMIT)
+		ds.fn = disambiguate_commit_only;
+	else if (flags & GET_OID_COMMITTISH)
+		ds.fn = disambiguate_committish_only;
+	else if (flags & GET_OID_TREE)
+		ds.fn = disambiguate_tree_only;
+	else if (flags & GET_OID_TREEISH)
+		ds.fn = disambiguate_treeish_only;
+	else if (flags & GET_OID_BLOB)
+		ds.fn = disambiguate_blob_only;
+	else
+		ds.fn = default_disambiguate_hint;
+
+	find_short_object_filename(&ds);
+	find_short_packed_object(&ds);
+	status = finish_object_disambiguation(&ds, oid);
+
+	if (!quietly && (status == SHORT_NAME_AMBIGUOUS)) {
+		error(_("short SHA1 %s is ambiguous"), ds.hex_pfx);
+
+		/*
+		 * We may still have ambiguity if we simply saw a series of
+		 * candidates that did not satisfy our hint function. In
+		 * that case, we still want to show them, so disable the hint
+		 * function entirely.
+		 */
+		if (!ds.ambiguous)
+			ds.fn = NULL;
+
+		advise(_("The candidates are:"));
+		for_each_abbrev(ds.hex_pfx, show_ambiguous_object, &ds);
 	}
 
-	status = find_unique_short_object(i, canonical, res, sha1);
-	if (!quietly && (status == SHORT_NAME_AMBIGUOUS))
-		return error("short SHA1 %.*s is ambiguous.", len, canonical);
 	return status;
 }
 
-const char *find_unique_abbrev(const unsigned char *sha1, int len)
+static int collect_ambiguous(const struct object_id *oid, void *data)
+{
+	oid_array_append(data, oid);
+	return 0;
+}
+
+int for_each_abbrev(const char *prefix, each_abbrev_fn fn, void *cb_data)
+{
+	struct oid_array collect = OID_ARRAY_INIT;
+	struct disambiguate_state ds;
+	int ret;
+
+	if (init_object_disambiguation(prefix, strlen(prefix), &ds) < 0)
+		return -1;
+
+	ds.always_call_fn = 1;
+	ds.fn = collect_ambiguous;
+	ds.cb_data = &collect;
+	find_short_object_filename(&ds);
+	find_short_packed_object(&ds);
+
+	ret = oid_array_for_each_unique(&collect, fn, cb_data);
+	oid_array_clear(&collect);
+	return ret;
+}
+
+/*
+ * Return the slot of the most-significant bit set in "val". There are various
+ * ways to do this quickly with fls() or __builtin_clzl(), but speed is
+ * probably not a big deal here.
+ */
+static unsigned msb(unsigned long val)
+{
+	unsigned r = 0;
+	while (val >>= 1)
+		r++;
+	return r;
+}
+
+int find_unique_abbrev_r(char *hex, const unsigned char *sha1, int len)
 {
 	int status, exists;
-	static char hex[41];
 
+	if (len < 0) {
+		unsigned long count = approximate_object_count();
+		/*
+		 * Add one because the MSB only tells us the highest bit set,
+		 * not including the value of all the _other_ bits (so "15"
+		 * is only one off of 2^4, but the MSB is the 3rd bit.
+		 */
+		len = msb(count) + 1;
+		/*
+		 * We now know we have on the order of 2^len objects, which
+		 * expects a collision at 2^(len/2). But we also care about hex
+		 * chars, not bits, and there are 4 bits per hex. So all
+		 * together we need to divide by 2 and round up.
+		 */
+		len = DIV_ROUND_UP(len, 2);
+		/*
+		 * For very small repos, we stick with our regular fallback.
+		 */
+		if (len < FALLBACK_DEFAULT_ABBREV)
+			len = FALLBACK_DEFAULT_ABBREV;
+	}
+
+	sha1_to_hex_r(hex, sha1);
+	if (len == GIT_SHA1_HEXSZ || !len)
+		return GIT_SHA1_HEXSZ;
 	exists = has_sha1_file(sha1);
-	memcpy(hex, sha1_to_hex(sha1), 40);
-	if (len == 40 || !len)
-		return hex;
-	while (len < 40) {
-		unsigned char sha1_ret[20];
-		status = get_short_sha1(hex, len, sha1_ret, 1);
+	while (len < GIT_SHA1_HEXSZ) {
+		struct object_id oid_ret;
+		status = get_short_oid(hex, len, &oid_ret, GET_OID_QUIETLY);
 		if (exists
 		    ? !status
 		    : status == SHORT_NAME_NOT_FOUND) {
-			int cut_at = len + unique_abbrev_extra_length;
-			cut_at = (cut_at < 40) ? cut_at : 40;
-			hex[cut_at] = 0;
-			return hex;
+			hex[len] = 0;
+			return len;
 		}
 		len++;
 	}
+	return len;
+}
+
+const char *find_unique_abbrev(const unsigned char *sha1, int len)
+{
+	static int bufno;
+	static char hexbuffer[4][GIT_MAX_HEXSZ + 1];
+	char *hex = hexbuffer[bufno];
+	bufno = (bufno + 1) % ARRAY_SIZE(hexbuffer);
+	find_unique_abbrev_r(hex, sha1, len);
 	return hex;
 }
 
@@ -243,123 +553,81 @@ static int ambiguous_path(const char *path, int len)
 	return slash;
 }
 
-/*
- * *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)
+static inline int at_mark(const char *string, int len,
+			  const char **suffix, int nr)
 {
-	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 i;
 
-int dwim_log(const char *str, int len, unsigned char *sha1, char **log)
-{
-	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;
+	for (i = 0; i < nr; i++) {
+		int suffix_len = strlen(suffix[i]);
+		if (suffix_len <= len
+		    && !strncasecmp(string, suffix[i], suffix_len))
+			return suffix_len;
 	}
-	free(last_branch);
-	return logs_found;
+	return 0;
 }
 
 static inline int upstream_mark(const char *string, int len)
 {
 	const char *suffix[] = { "@{upstream}", "@{u}" };
-	int i;
+	return at_mark(string, len, suffix, ARRAY_SIZE(suffix));
+}
 
-	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 inline int push_mark(const char *string, int len)
+{
+	const char *suffix[] = { "@{push}" };
+	return at_mark(string, len, suffix, ARRAY_SIZE(suffix));
 }
 
-static int get_sha1_1(const char *name, int len, unsigned char *sha1);
+static int get_oid_1(const char *name, int len, struct object_id *oid, unsigned lookup_flags);
+static int interpret_nth_prior_checkout(const char *name, int namelen, struct strbuf *buf);
 
-static int get_sha1_basic(const char *str, int len, unsigned char *sha1)
+static int get_oid_basic(const char *str, int len, struct object_id *oid,
+			  unsigned int flags)
 {
 	static const char *warn_msg = "refname '%.*s' is ambiguous.";
+	static const char *object_name_msg = N_(
+	"Git normally never creates a ref that ends with 40 hex characters\n"
+	"because it will be ignored when you just specify 40-hex. These refs\n"
+	"may be created by mistake. For example,\n"
+	"\n"
+	"  git checkout -b $br $(git rev-parse ...)\n"
+	"\n"
+	"where \"$br\" is somehow empty and a 40-hex ref is created. Please\n"
+	"examine these refs and maybe delete them. Turn this message off by\n"
+	"running \"git config advice.objectNameWarning false\"");
+	struct object_id tmp_oid;
 	char *real_ref = NULL;
 	int refs_found = 0;
-	int at, reflog_len;
-
-	if (len == 40 && !get_sha1_hex(str, sha1))
+	int at, reflog_len, nth_prior = 0;
+
+	if (len == GIT_SHA1_HEXSZ && !get_oid_hex(str, oid)) {
+		if (warn_ambiguous_refs && warn_on_object_refname_ambiguity) {
+			refs_found = dwim_ref(str, len, tmp_oid.hash, &real_ref);
+			if (refs_found > 0) {
+				warning(warn_msg, len, str);
+				if (advice_object_name_warning)
+					fprintf(stderr, "%s\n", _(object_name_msg));
+			}
+			free(real_ref);
+		}
 		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--) {
+		for (at = len-4; at >= 0; at--) {
 			if (str[at] == '@' && str[at+1] == '{') {
-				if (!upstream_mark(str + at, len - at)) {
+				if (str[at+2] == '-') {
+					if (at != 0)
+						/* @{-N} not at start */
+						return -1;
+					nth_prior = 1;
+					continue;
+				}
+				if (!upstream_mark(str + at, len - at) &&
+				    !push_mark(str + at, len - at)) {
 					reflog_len = (len-1) - (at+2);
 					len = at;
 				}
@@ -372,40 +640,40 @@ static int get_sha1_basic(const char *str, int len, unsigned char *sha1)
 	if (len && ambiguous_path(str, len))
 		return -1;
 
-	if (!len && reflog_len) {
+	if (nth_prior) {
 		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;
+		int detached;
+
+		if (interpret_nth_prior_checkout(str, len, &buf) > 0) {
+			detached = (buf.len == GIT_SHA1_HEXSZ && !get_oid_hex(buf.buf, oid));
+			strbuf_release(&buf);
+			if (detached)
+				return 0;
 		}
+	}
+
+	if (!len && reflog_len)
 		/* 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);
+		refs_found = dwim_ref("HEAD", 4, oid->hash, &real_ref);
+	else if (reflog_len)
+		refs_found = dwim_log(str, len, oid->hash, &real_ref);
 	else
-		refs_found = dwim_ref(str, len, sha1, &real_ref);
+		refs_found = dwim_ref(str, len, oid->hash, &real_ref);
 
 	if (!refs_found)
 		return -1;
 
-	if (warn_ambiguous_refs && refs_found > 1)
+	if (warn_ambiguous_refs && !(flags & GET_OID_QUIETLY) &&
+	    (refs_found > 1 ||
+	     !get_short_oid(str, len, &tmp_oid, GET_OID_QUIETLY)))
 		warning(warn_msg, len, str);
 
 	if (reflog_len) {
 		int nth, i;
-		unsigned long at_time;
-		unsigned long co_time;
+		timestamp_t at_time;
+		timestamp_t 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];
@@ -424,17 +692,33 @@ static int get_sha1_basic(const char *str, int len, unsigned char *sha1)
 			char *tmp = xstrndup(str + at + 2, reflog_len);
 			at_time = approxidate_careful(tmp, &errors);
 			free(tmp);
-			if (errors)
+			if (errors) {
+				free(real_ref);
 				return -1;
+			}
 		}
-		if (read_ref_at(real_ref, at_time, nth, sha1, NULL,
+		if (read_ref_at(real_ref, flags, at_time, nth, oid->hash, 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);
+			if (!len) {
+				if (starts_with(real_ref, "refs/heads/")) {
+					str = real_ref + 11;
+					len = strlen(real_ref + 11);
+				} else {
+					/* detached HEAD */
+					str = "HEAD";
+					len = 4;
+				}
+			}
+			if (at_time) {
+				if (!(flags & GET_OID_QUIETLY)) {
+					warning("Log for '%.*s' only goes "
+						"back to %s.", len, str,
+						show_date(co_time, co_tz, DATE_MODE(RFC2822)));
+				}
+			} else {
+				if (flags & GET_OID_QUIETLY) {
+					exit(128);
+				}
 				die("Log for '%.*s' only has %d entries.",
 				    len, str, co_cnt);
 			}
@@ -446,28 +730,26 @@ static int get_sha1_basic(const char *str, int len, unsigned char *sha1)
 }
 
 static int get_parent(const char *name, int len,
-		      unsigned char *result, int idx)
+		      struct object_id *result, int idx)
 {
-	unsigned char sha1[20];
-	int ret = get_sha1_1(name, len, sha1);
+	struct object_id oid;
+	int ret = get_oid_1(name, len, &oid, GET_OID_COMMITTISH);
 	struct commit *commit;
 	struct commit_list *p;
 
 	if (ret)
 		return ret;
-	commit = lookup_commit_reference(sha1);
-	if (!commit)
-		return -1;
+	commit = lookup_commit_reference(&oid);
 	if (parse_commit(commit))
 		return -1;
 	if (!idx) {
-		hashcpy(result, commit->object.sha1);
+		oidcpy(result, &commit->object.oid);
 		return 0;
 	}
 	p = commit->parents;
 	while (p) {
 		if (!--idx) {
-			hashcpy(result, p->item->object.sha1);
+			oidcpy(result, &p->item->object.oid);
 			return 0;
 		}
 		p = p->next;
@@ -476,16 +758,16 @@ static int get_parent(const char *name, int len,
 }
 
 static int get_nth_ancestor(const char *name, int len,
-			    unsigned char *result, int generation)
+			    struct object_id *result, int generation)
 {
-	unsigned char sha1[20];
+	struct object_id oid;
 	struct commit *commit;
 	int ret;
 
-	ret = get_sha1_1(name, len, sha1);
+	ret = get_oid_1(name, len, &oid, GET_OID_COMMITTISH);
 	if (ret)
 		return ret;
-	commit = lookup_commit_reference(sha1);
+	commit = lookup_commit_reference(&oid);
 	if (!commit)
 		return -1;
 
@@ -494,7 +776,7 @@ static int get_nth_ancestor(const char *name, int len,
 			return -1;
 		commit = commit->parents->item;
 	}
-	hashcpy(result, commit->object.sha1);
+	oidcpy(result, &commit->object.oid);
 	return 0;
 }
 
@@ -503,16 +785,10 @@ struct object *peel_to_type(const char *name, int namelen,
 {
 	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)))
+		if (!o || (!o->parsed && !parse_object(&o->oid)))
 			return NULL;
-		if (o->type == expected_type)
+		if (expected_type == OBJ_ANY || o->type == expected_type)
 			return o;
 		if (o->type == OBJ_TAG)
 			o = ((struct tag*) o)->tagged;
@@ -529,9 +805,10 @@ struct object *peel_to_type(const char *name, int namelen,
 	}
 }
 
-static int peel_onion(const char *name, int len, unsigned char *sha1)
+static int peel_onion(const char *name, int len, struct object_id *oid,
+		      unsigned lookup_flags)
 {
-	unsigned char outer[20];
+	struct object_id outer;
 	const char *sp;
 	unsigned int expected_type = 0;
 	struct object *o;
@@ -556,12 +833,16 @@ static int peel_onion(const char *name, int len, unsigned char *sha1)
 		return -1;
 
 	sp++; /* beginning of type name, or closing brace for empty */
-	if (!strncmp(commit_type, sp, 6) && sp[6] == '}')
+	if (starts_with(sp, "commit}"))
 		expected_type = OBJ_COMMIT;
-	else if (!strncmp(tree_type, sp, 4) && sp[4] == '}')
+	else if (starts_with(sp, "tag}"))
+		expected_type = OBJ_TAG;
+	else if (starts_with(sp, "tree}"))
 		expected_type = OBJ_TREE;
-	else if (!strncmp(blob_type, sp, 4) && sp[4] == '}')
+	else if (starts_with(sp, "blob}"))
 		expected_type = OBJ_BLOB;
+	else if (starts_with(sp, "object}"))
+		expected_type = OBJ_ANY;
 	else if (sp[0] == '}')
 		expected_type = OBJ_NONE;
 	else if (sp[0] == '/')
@@ -569,17 +850,23 @@ static int peel_onion(const char *name, int len, unsigned char *sha1)
 	else
 		return -1;
 
-	if (get_sha1_1(name, sp - name - 2, outer))
+	lookup_flags &= ~GET_OID_DISAMBIGUATORS;
+	if (expected_type == OBJ_COMMIT)
+		lookup_flags |= GET_OID_COMMITTISH;
+	else if (expected_type == OBJ_TREE)
+		lookup_flags |= GET_OID_TREEISH;
+
+	if (get_oid_1(name, sp - name - 2, &outer, lookup_flags))
 		return -1;
 
-	o = parse_object(outer);
+	o = parse_object(&outer);
 	if (!o)
 		return -1;
 	if (!expected_type) {
 		o = deref_tag(o, name, sp - name - 2);
-		if (!o || (!o->parsed && !parse_object(o->sha1)))
+		if (!o || (!o->parsed && !parse_object(&o->oid)))
 			return -1;
-		hashcpy(sha1, o->sha1);
+		oidcpy(oid, &o->oid);
 		return 0;
 	}
 
@@ -592,7 +879,7 @@ static int peel_onion(const char *name, int len, unsigned char *sha1)
 	if (!o)
 		return -1;
 
-	hashcpy(sha1, o->sha1);
+	oidcpy(oid, &o->oid);
 	if (sp[0] == '/') {
 		/* "$commit^{/foo}" */
 		char *prefix;
@@ -608,34 +895,35 @@ static int peel_onion(const char *name, int len, unsigned char *sha1)
 
 		prefix = xstrndup(sp + 1, name + len - 1 - (sp + 1));
 		commit_list_insert((struct commit *)o, &list);
-		ret = get_sha1_oneline(prefix, sha1, list);
+		ret = get_oid_oneline(prefix, oid, list);
 		free(prefix);
 		return ret;
 	}
 	return 0;
 }
 
-static int get_describe_name(const char *name, int len, unsigned char *sha1)
+static int get_describe_name(const char *name, int len, struct object_id *oid)
 {
 	const char *cp;
+	unsigned flags = GET_OID_QUIETLY | GET_OID_COMMIT;
 
 	for (cp = name + len - 1; name + 2 <= cp; cp--) {
 		char ch = *cp;
-		if (hexval(ch) & ~0377) {
+		if (!isxdigit(ch)) {
 			/* 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);
+				return get_short_oid(cp, len, oid, flags);
 			}
 		}
 	}
 	return -1;
 }
 
-static int get_sha1_1(const char *name, int len, unsigned char *sha1)
+static int get_oid_1(const char *name, int len, struct object_id *oid, unsigned lookup_flags)
 {
 	int ret, has_suffix;
 	const char *cp;
@@ -662,25 +950,25 @@ static int get_sha1_1(const char *name, int len, unsigned char *sha1)
 		if (!num && len1 == len - 1)
 			num = 1;
 		if (has_suffix == '^')
-			return get_parent(name, len1, sha1, num);
+			return get_parent(name, len1, oid, num);
 		/* else if (has_suffix == '~') -- goes without saying */
-		return get_nth_ancestor(name, len1, sha1, num);
+		return get_nth_ancestor(name, len1, oid, num);
 	}
 
-	ret = peel_onion(name, len, sha1);
+	ret = peel_onion(name, len, oid, lookup_flags);
 	if (!ret)
 		return 0;
 
-	ret = get_sha1_basic(name, len, sha1);
+	ret = get_oid_basic(name, len, oid, lookup_flags);
 	if (!ret)
 		return 0;
 
 	/* It could be describe output that is "SOMETHING-gXXXX" */
-	ret = get_describe_name(name, len, sha1);
+	ret = get_describe_name(name, len, oid);
 	if (!ret)
 		return 0;
 
-	return get_short_sha1(name, len, sha1, 0);
+	return get_short_oid(name, len, oid, lookup_flags);
 }
 
 /*
@@ -688,16 +976,22 @@ static int get_sha1_1(const char *name, int len, unsigned char *sha1)
  * 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.
+ * For negative-matching, prefix the pattern-part with '!-', like: ':/!-WIP'.
+ *
+ * For a literal '!' character at the beginning of a pattern, you have to repeat
+ * that, like: ':/!!foo'
+ *
+ * For future extension, all other sequences beginning with ':/!' are reserved.
  */
+
+/* Remember to update object flag allocation in object.h */
 #define ONELINE_SEEN (1u<<20)
 
-static int handle_one_ref(const char *path,
-		const unsigned char *sha1, int flag, void *cb_data)
+static int handle_one_ref(const char *path, const struct object_id *oid,
+			  int flag, void *cb_data)
 {
 	struct commit_list **list = cb_data;
-	struct object *object = parse_object(sha1);
+	struct object *object = parse_object(oid);
 	if (!object)
 		return 0;
 	if (object->type == OBJ_TAG) {
@@ -707,55 +1001,51 @@ static int handle_one_ref(const char *path,
 	}
 	if (object->type != OBJ_COMMIT)
 		return 0;
-	commit_list_insert_by_date((struct commit *)object, list);
+	commit_list_insert((struct commit *)object, list);
 	return 0;
 }
 
-static int get_sha1_oneline(const char *prefix, unsigned char *sha1,
+static int get_oid_oneline(const char *prefix, struct object_id *oid,
 			    struct commit_list *list)
 {
 	struct commit_list *backup = NULL, *l;
 	int found = 0;
+	int negative = 0;
 	regex_t regex;
 
 	if (prefix[0] == '!') {
-		if (prefix[1] != '!')
-			die ("Invalid search pattern: %s", prefix);
 		prefix++;
+
+		if (prefix[0] == '-') {
+			prefix++;
+			negative = 1;
+		} else if (prefix[0] != '!') {
+			return -1;
+		}
 	}
 
 	if (regcomp(&regex, prefix, REG_EXTENDED))
-		die("Invalid search pattern: %s", prefix);
+		return -1;
 
 	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;
+		const char *p, *buf;
 		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))
+		if (!parse_object(&commit->object.oid))
 			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);
+		buf = get_commit_buffer(commit, NULL);
+		p = strstr(buf, "\n\n");
+		matches = negative ^ (p && !regexec(&regex, p + 2, 0, NULL, 0));
+		unuse_commit_buffer(commit, buf);
 
 		if (matches) {
-			hashcpy(sha1, commit->object.sha1);
+			oidcpy(oid, &commit->object.oid);
 			found = 1;
 			break;
 		}
@@ -769,31 +1059,29 @@ static int get_sha1_oneline(const char *prefix, unsigned char *sha1,
 }
 
 struct grab_nth_branch_switch_cbdata {
-	long cnt, alloc;
-	struct strbuf *buf;
+	int remaining;
+	struct strbuf buf;
 };
 
-static int grab_nth_branch_switch(unsigned char *osha1, unsigned char *nsha1,
-				  const char *email, unsigned long timestamp, int tz,
+static int grab_nth_branch_switch(struct object_id *ooid, struct object_id *noid,
+				  const char *email, timestamp_t 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 ");
+	if (skip_prefix(message, "checkout: moving from ", &match))
 		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);
+	if (--(cb->remaining) == 0) {
+		len = target - match;
+		strbuf_reset(&cb->buf);
+		strbuf_add(&cb->buf, match, len);
+		return 1; /* we are done */
+	}
 	return 0;
 }
 
@@ -801,227 +1089,343 @@ static int grab_nth_branch_switch(unsigned char *osha1, unsigned char *nsha1,
  * 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)
+static int interpret_nth_prior_checkout(const char *name, int namelen,
+					struct strbuf *buf)
 {
 	long nth;
-	int i, retval;
+	int retval;
 	struct grab_nth_branch_switch_cbdata cb;
 	const char *brace;
 	char *num_end;
 
+	if (namelen < 4)
+		return -1;
 	if (name[0] != '@' || name[1] != '{' || name[2] != '-')
 		return -1;
-	brace = strchr(name, '}');
+	brace = memchr(name, '}', namelen);
 	if (!brace)
 		return -1;
-	nth = strtol(name+3, &num_end, 10);
+	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;
+	cb.remaining = nth;
+	strbuf_init(&cb.buf, 20);
+
 	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 (0 < for_each_reflog_ent_reverse("HEAD", grab_nth_branch_switch, &cb)) {
+		strbuf_reset(buf);
+		strbuf_addbuf(buf, &cb.buf);
+		retval = brace - name + 1;
 	}
-	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);
 
+	strbuf_release(&cb.buf);
 	return retval;
 }
 
-int get_sha1_mb(const char *name, unsigned char *sha1)
+int get_oid_mb(const char *name, struct object_id *oid)
 {
 	struct commit *one, *two;
 	struct commit_list *mbs;
-	unsigned char sha1_tmp[20];
+	struct object_id oid_tmp;
 	const char *dots;
 	int st;
 
 	dots = strstr(name, "...");
 	if (!dots)
-		return get_sha1(name, sha1);
+		return get_oid(name, oid);
 	if (dots == name)
-		st = get_sha1("HEAD", sha1_tmp);
+		st = get_oid("HEAD", &oid_tmp);
 	else {
 		struct strbuf sb;
 		strbuf_init(&sb, dots - name);
 		strbuf_add(&sb, name, dots - name);
-		st = get_sha1(sb.buf, sha1_tmp);
+		st = get_oid_committish(sb.buf, &oid_tmp);
 		strbuf_release(&sb);
 	}
 	if (st)
 		return st;
-	one = lookup_commit_reference_gently(sha1_tmp, 0);
+	one = lookup_commit_reference_gently(&oid_tmp, 0);
 	if (!one)
 		return -1;
 
-	if (get_sha1(dots[3] ? (dots + 3) : "HEAD", sha1_tmp))
+	if (get_oid_committish(dots[3] ? (dots + 3) : "HEAD", &oid_tmp))
 		return -1;
-	two = lookup_commit_reference_gently(sha1_tmp, 0);
+	two = lookup_commit_reference_gently(&oid_tmp, 0);
 	if (!two)
 		return -1;
-	mbs = get_merge_bases(one, two, 1);
+	mbs = get_merge_bases(one, two);
 	if (!mbs || mbs->next)
 		st = -1;
 	else {
 		st = 0;
-		hashcpy(sha1, mbs->item->object.sha1);
+		oidcpy(oid, &mbs->item->object.oid);
 	}
 	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)
+/* parse @something syntax, when 'something' is not {.*} */
+static int interpret_empty_at(const char *name, int namelen, int len, struct strbuf *buf)
 {
-	char *cp;
-	struct branch *upstream;
-	int namelen = strlen(name);
-	int len = interpret_nth_prior_checkout(name, buf);
-	int tmp_len;
+	const char *next;
 
-	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;
+	if (len || name[1] == '{')
+		return -1;
 
-		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;
+	/* make sure it's a single @, or @@{.*}, not @foo */
+	next = memchr(name + len + 1, '@', namelen - len - 1);
+	if (next && next[1] != '{')
+		return -1;
+	if (!next)
+		next = name + namelen;
+	if (next != name + 1)
+		return -1;
+
+	strbuf_reset(buf);
+	strbuf_add(buf, "HEAD", 4);
+	return 1;
+}
+
+static int reinterpret(const char *name, int namelen, int len,
+		       struct strbuf *buf, unsigned allowed)
+{
+	/* 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, buf->len, &tmp, allowed);
+	/* 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;
+}
+
+static void set_shortened_ref(struct strbuf *buf, const char *ref)
+{
+	char *s = shorten_unambiguous_ref(ref, 0);
+	strbuf_reset(buf);
+	strbuf_addstr(buf, s);
+	free(s);
+}
+
+static int branch_interpret_allowed(const char *refname, unsigned allowed)
+{
+	if (!allowed)
+		return 1;
 
-	cp = strchr(name, '@');
-	if (!cp)
+	if ((allowed & INTERPRET_BRANCH_LOCAL) &&
+	    starts_with(refname, "refs/heads/"))
+		return 1;
+	if ((allowed & INTERPRET_BRANCH_REMOTE) &&
+	    starts_with(refname, "refs/remotes/"))
+		return 1;
+
+	return 0;
+}
+
+static int interpret_branch_mark(const char *name, int namelen,
+				 int at, struct strbuf *buf,
+				 int (*get_mark)(const char *, int),
+				 const char *(*get_data)(struct branch *,
+							 struct strbuf *),
+				 unsigned allowed)
+{
+	int len;
+	struct branch *branch;
+	struct strbuf err = STRBUF_INIT;
+	const char *value;
+
+	len = get_mark(name + at, namelen - at);
+	if (!len)
 		return -1;
-	tmp_len = upstream_mark(cp, namelen - (cp - name));
-	if (!tmp_len)
+
+	if (memchr(name, ':', at))
 		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;
+
+	if (at) {
+		char *name_str = xmemdupz(name, at);
+		branch = branch_get(name_str);
+		free(name_str);
+	} else
+		branch = branch_get(NULL);
+
+	value = get_data(branch, &err);
+	if (!value)
+		die("%s", err.buf);
+
+	if (!branch_interpret_allowed(value, allowed))
+		return -1;
+
+	set_shortened_ref(buf, value);
+	return len + at;
 }
 
-int strbuf_branchname(struct strbuf *sb, const char *name)
+int interpret_branch_name(const char *name, int namelen, struct strbuf *buf,
+			  unsigned allowed)
+{
+	char *at;
+	const char *start;
+	int len;
+
+	if (!namelen)
+		namelen = strlen(name);
+
+	if (!allowed || (allowed & INTERPRET_BRANCH_LOCAL)) {
+		len = interpret_nth_prior_checkout(name, namelen, buf);
+		if (!len) {
+			return len; /* syntax Ok, not enough switches */
+		} else if (len > 0) {
+			if (len == namelen)
+				return len; /* consumed all */
+			else
+				return reinterpret(name, namelen, len, buf, allowed);
+		}
+	}
+
+	for (start = name;
+	     (at = memchr(start, '@', namelen - (start - name)));
+	     start = at + 1) {
+
+		if (!allowed || (allowed & INTERPRET_BRANCH_HEAD)) {
+			len = interpret_empty_at(name, namelen, at - name, buf);
+			if (len > 0)
+				return reinterpret(name, namelen, len, buf,
+						   allowed);
+		}
+
+		len = interpret_branch_mark(name, namelen, at - name, buf,
+					    upstream_mark, branch_get_upstream,
+					    allowed);
+		if (len > 0)
+			return len;
+
+		len = interpret_branch_mark(name, namelen, at - name, buf,
+					    push_mark, branch_get_push,
+					    allowed);
+		if (len > 0)
+			return len;
+	}
+
+	return -1;
+}
+
+void strbuf_branchname(struct strbuf *sb, const char *name, unsigned allowed)
 {
 	int len = strlen(name);
-	if (interpret_branch_name(name, sb) == len)
-		return 0;
-	strbuf_add(sb, name, len);
-	return len;
+	int used = interpret_branch_name(name, len, sb, allowed);
+
+	if (used < 0)
+		used = 0;
+	strbuf_add(sb, name + used, len - used);
 }
 
 int strbuf_check_branch_ref(struct strbuf *sb, const char *name)
 {
-	strbuf_branchname(sb, name);
+	strbuf_branchname(sb, name, INTERPRET_BRANCH_LOCAL);
 	if (name[0] == '-')
-		return CHECK_REF_FORMAT_ERROR;
+		return -1;
 	strbuf_splice(sb, 0, 0, "refs/heads/", 11);
-	return check_ref_format(sb->buf);
+	return check_refname_format(sb->buf, 0);
 }
 
 /*
- * This is like "get_sha1_basic()", except it allows "sha1 expressions",
+ * This is like "get_oid_basic()", except it allows "object ID expressions",
  * notably "xyz^" for "parent of xyz"
  */
-int get_sha1(const char *name, unsigned char *sha1)
+int get_oid(const char *name, struct object_id *oid)
 {
 	struct object_context unused;
-	return get_sha1_with_context(name, sha1, &unused);
+	return get_oid_with_context(name, 0, oid, &unused);
+}
+
+
+/*
+ * Many callers know that the user meant to name a commit-ish by
+ * syntactical positions where the object name appears.  Calling this
+ * function allows the machinery to disambiguate shorter-than-unique
+ * abbreviated object names between commit-ish and others.
+ *
+ * Note that this does NOT error out when the named object is not a
+ * commit-ish. It is merely to give a hint to the disambiguation
+ * machinery.
+ */
+int get_oid_committish(const char *name, struct object_id *oid)
+{
+	struct object_context unused;
+	return get_oid_with_context(name, GET_OID_COMMITTISH,
+				    oid, &unused);
+}
+
+int get_oid_treeish(const char *name, struct object_id *oid)
+{
+	struct object_context unused;
+	return get_oid_with_context(name, GET_OID_TREEISH,
+				    oid, &unused);
+}
+
+int get_oid_commit(const char *name, struct object_id *oid)
+{
+	struct object_context unused;
+	return get_oid_with_context(name, GET_OID_COMMIT,
+				    oid, &unused);
+}
+
+int get_oid_tree(const char *name, struct object_id *oid)
+{
+	struct object_context unused;
+	return get_oid_with_context(name, GET_OID_TREE,
+				    oid, &unused);
+}
+
+int get_oid_blob(const char *name, struct object_id *oid)
+{
+	struct object_context unused;
+	return get_oid_with_context(name, GET_OID_BLOB,
+				    oid, &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)
+static void diagnose_invalid_oid_path(const char *prefix,
+				      const char *filename,
+				      const struct object_id *tree_oid,
+				      const char *object_name,
+				      int object_name_len)
 {
-	struct stat st;
-	unsigned char sha1[20];
+	struct object_id oid;
 	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)) {
+	if (file_exists(filename))
+		die("Path '%s' exists on disk, but not in '%.*s'.",
+		    filename, object_name_len, object_name);
+	if (is_missing_file_error(errno)) {
+		char *fullname = xstrfmt("%s%s", prefix, filename);
+
+		if (!get_tree_entry(tree_oid->hash, fullname,
+				    oid.hash, &mode)) {
 			die("Path '%s' exists, but not '%s'.\n"
-			    "Did you mean '%s:%s'?",
+			    "Did you mean '%.*s:%s' aka '%.*s:./%s'?",
 			    fullname,
 			    filename,
-			    object_name,
-			    fullname);
+			    object_name_len, object_name,
+			    fullname,
+			    object_name_len, object_name,
+			    filename);
 		}
-		die("Path '%s' does not exist in '%s'",
-		    filename, object_name);
+		die("Path '%s' does not exist in '%.*s'",
+		    filename, object_name_len, object_name);
 	}
 }
 
@@ -1030,12 +1434,10 @@ static void diagnose_invalid_index_path(int stage,
 					const char *prefix,
 					const char *filename)
 {
-	struct stat st;
-	struct cache_entry *ce;
+	const struct cache_entry *ce;
 	int pos;
 	unsigned namelen = strlen(filename);
-	unsigned fullnamelen;
-	char *fullname;
+	struct strbuf fullname = STRBUF_INIT;
 
 	if (!prefix)
 		prefix = "";
@@ -1055,50 +1457,37 @@ static void diagnose_invalid_index_path(int stage,
 	}
 
 	/* 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);
+	strbuf_addstr(&fullname, prefix);
+	strbuf_addstr(&fullname, filename);
+	pos = cache_name_pos(fullname.buf, fullname.len);
 	if (pos < 0)
 		pos = -pos - 1;
 	if (pos < active_nr) {
 		ce = active_cache[pos];
-		if (ce_namelen(ce) == fullnamelen &&
-		    !memcmp(ce->name, fullname, fullnamelen))
+		if (ce_namelen(ce) == fullname.len &&
+		    !memcmp(ce->name, fullname.buf, fullname.len))
 			die("Path '%s' is in the index, but not '%s'.\n"
-			    "Did you mean ':%d:%s'?",
-			    fullname, filename,
-			    ce_stage(ce), fullname);
+			    "Did you mean ':%d:%s' aka ':%d:./%s'?",
+			    fullname.buf, filename,
+			    ce_stage(ce), fullname.buf,
+			    ce_stage(ce), filename);
 	}
 
-	if (!lstat(filename, &st))
+	if (file_exists(filename))
 		die("Path '%s' exists on disk, but not in the index.", filename);
-	if (errno == ENOENT || errno == ENOTDIR)
+	if (is_missing_file_error(errno))
 		die("Path '%s' does not exist (neither on disk nor in the index).",
 		    filename);
 
-	free(fullname);
+	strbuf_release(&fullname);
 }
 
 
-int get_sha1_with_mode_1(const char *name, unsigned char *sha1, unsigned *mode, int gently, const char *prefix)
-{
-	struct object_context oc;
-	int ret;
-	ret = get_sha1_with_context_1(name, sha1, &oc, gently, prefix);
-	*mode = oc.mode;
-	return ret;
-}
-
 static char *resolve_relative_path(const char *rel)
 {
-	if (prefixcmp(rel, "./") && prefixcmp(rel, "../"))
+	if (!starts_with(rel, "./") && !starts_with(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.");
 
@@ -1108,20 +1497,28 @@ static char *resolve_relative_path(const char *rel)
 			   rel);
 }
 
-int get_sha1_with_context_1(const char *name, unsigned char *sha1,
-			    struct object_context *oc,
-			    int gently, const char *prefix)
+static int get_oid_with_context_1(const char *name,
+				  unsigned flags,
+				  const char *prefix,
+				  struct object_id *oid,
+				  struct object_context *oc)
 {
 	int ret, bracket_depth;
 	int namelen = strlen(name);
 	const char *cp;
+	int only_to_die = flags & GET_OID_ONLY_TO_DIE;
+
+	if (only_to_die)
+		flags |= GET_OID_QUIETLY;
 
 	memset(oc, 0, sizeof(*oc));
 	oc->mode = S_IFINVALID;
-	ret = get_sha1_1(name, namelen, sha1);
+	strbuf_init(&oc->symlink_path, 0);
+	ret = get_oid_1(name, namelen, oid, flags);
 	if (!ret)
 		return ret;
-	/* sha1:path --> object name of path in ent sha1
+	/*
+	 * 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
@@ -1129,13 +1526,15 @@ int get_sha1_with_context_1(const char *name, unsigned char *sha1,
 	 */
 	if (name[0] == ':') {
 		int stage = 0;
-		struct cache_entry *ce;
+		const struct cache_entry *ce;
 		char *new_path = NULL;
 		int pos;
-		if (namelen > 2 && name[1] == '/') {
+		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);
+			commit_list_sort_by_date(&list);
+			return get_oid_oneline(name + 2, oid, list);
 		}
 		if (namelen < 3 ||
 		    name[2] != ':' ||
@@ -1153,9 +1552,8 @@ int get_sha1_with_context_1(const char *name, unsigned char *sha1,
 			namelen = strlen(cp);
 		}
 
-		strncpy(oc->path, cp,
-			sizeof(oc->path));
-		oc->path[sizeof(oc->path)-1] = '\0';
+		if (flags & GET_OID_RECORD_PATH)
+			oc->path = xstrdup(cp);
 
 		if (!active_cache)
 			read_cache();
@@ -1168,14 +1566,14 @@ int get_sha1_with_context_1(const char *name, unsigned char *sha1,
 			    memcmp(ce->name, cp, namelen))
 				break;
 			if (ce_stage(ce) == stage) {
-				hashcpy(sha1, ce->sha1);
+				oidcpy(oid, &ce->oid);
 				oc->mode = ce->ce_mode;
 				free(new_path);
 				return 0;
 			}
 			pos++;
 		}
-		if (!gently)
+		if (only_to_die && name[1] && name[1] != '/')
 			diagnose_invalid_index_path(stage, prefix, cp);
 		free(new_path);
 		return -1;
@@ -1189,37 +1587,65 @@ int get_sha1_with_context_1(const char *name, unsigned char *sha1,
 			break;
 	}
 	if (*cp == ':') {
-		unsigned char tree_sha1[20];
-		char *object_name = NULL;
-		if (!gently) {
-			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)) {
+		struct object_id tree_oid;
+		int len = cp - name;
+		unsigned sub_flags = flags;
+
+		sub_flags &= ~GET_OID_DISAMBIGUATORS;
+		sub_flags |= GET_OID_TREEISH;
+
+		if (!get_oid_1(name, len, &tree_oid, sub_flags)) {
 			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 (!gently) {
-				diagnose_invalid_sha1_path(prefix, filename,
-							   tree_sha1, object_name);
-				free(object_name);
+			if (flags & GET_OID_FOLLOW_SYMLINKS) {
+				ret = get_tree_entry_follow_symlinks(tree_oid.hash,
+					filename, oid->hash, &oc->symlink_path,
+					&oc->mode);
+			} else {
+				ret = get_tree_entry(tree_oid.hash, filename,
+						     oid->hash, &oc->mode);
+				if (ret && only_to_die) {
+					diagnose_invalid_oid_path(prefix,
+								   filename,
+								   &tree_oid,
+								   name, len);
+				}
 			}
-			hashcpy(oc->tree, tree_sha1);
-			strncpy(oc->path, filename,
-				sizeof(oc->path));
-			oc->path[sizeof(oc->path)-1] = '\0';
+			hashcpy(oc->tree, tree_oid.hash);
+			if (flags & GET_OID_RECORD_PATH)
+				oc->path = xstrdup(filename);
 
 			free(new_filename);
 			return ret;
 		} else {
-			if (!gently)
-				die("Invalid object name '%s'.", object_name);
+			if (only_to_die)
+				die("Invalid object name '%.*s'.", len, name);
 		}
 	}
 	return ret;
 }
+
+/*
+ * Call this function when you know "name" given by the end user must
+ * name an object but it doesn't; the function _may_ die with a better
+ * diagnostic message than "no such object 'name'", e.g. "Path 'doc' does not
+ * exist in 'HEAD'" when given "HEAD:doc", or it may return in which case
+ * you have a chance to diagnose the error further.
+ */
+void maybe_die_on_misspelt_object_name(const char *name, const char *prefix)
+{
+	struct object_context oc;
+	struct object_id oid;
+	get_oid_with_context_1(name, GET_OID_ONLY_TO_DIE, prefix, &oid, &oc);
+}
+
+int get_oid_with_context(const char *str, unsigned flags, struct object_id *oid, struct object_context *oc)
+{
+	if (flags & GET_OID_FOLLOW_SYMLINKS && flags & GET_OID_ONLY_TO_DIE)
+		die("BUG: incompatible flags for get_sha1_with_context");
+	return get_oid_with_context_1(str, flags, NULL, oid, oc);
+}