1 files changed, 1065 insertions, 278 deletions

diff --git a/sha1_name.c b/sha1_name.c
index 0781477a71..da6874c15e 100644
--- a/sha1_name.c
+++ b/sha1_name.c
@@ -5,15 +5,87 @@
 #include "blob.h"
 #include "tree-walk.h"
 #include "refs.h"
+#include "remote.h"
+#include "dir.h"
 
-static int find_short_object_filename(int len, const char *name, unsigned char *sha1)
+static int get_sha1_oneline(const char *, unsigned char *, struct commit_list *);
+
+typedef int (*disambiguate_hint_fn)(const unsigned char *, void *);
+
+struct disambiguate_state {
+	disambiguate_hint_fn fn;
+	void *cb_data;
+	unsigned char candidate[20];
+	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 unsigned char *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 */
+		hashcpy(ds->candidate, current);
+		ds->candidate_exists = 1;
+		return;
+	} else if (!hashcmp(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;
+	}
+
+	if (!ds->candidate_ok) {
+		/* discard the candidate; we know it does not satisfy fn */
+		hashcpy(ds->candidate, current);
+		ds->candidate_checked = 0;
+		return;
+	}
+
+	/* 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 void find_short_object_filename(int len, const char *hex_pfx, struct disambiguate_state *ds)
 {
 	struct alternate_object_database *alt;
 	char hex[40];
-	int found = 0;
 	static struct alternate_object_database *fakeent;
 
 	if (!fakeent) {
+		/*
+		 * 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.
+		 */
 		const char *objdir = get_object_directory();
 		int objdir_len = strlen(objdir);
 		int entlen = objdir_len + 43;
@@ -24,33 +96,28 @@ static int find_short_object_filename(int len, const char *name, unsigned char *
 	}
 	fakeent->next = alt_odb_list;
 
-	sprintf(hex, "%.2s", name);
-	for (alt = fakeent; alt && found < 2; alt = alt->next) {
+	sprintf(hex, "%.2s", hex_pfx);
+	for (alt = fakeent; alt && !ds->ambiguous; alt = alt->next) {
 		struct dirent *de;
 		DIR *dir;
-		sprintf(alt->name, "%.2s/", name);
+		sprintf(alt->name, "%.2s/", hex_pfx);
 		dir = opendir(alt->base);
 		if (!dir)
 			continue;
-		while ((de = readdir(dir)) != NULL) {
+
+		while (!ds->ambiguous && (de = readdir(dir)) != NULL) {
+			unsigned char sha1[20];
+
 			if (strlen(de->d_name) != 38)
 				continue;
-			if (memcmp(de->d_name, name + 2, len - 2))
+			if (memcmp(de->d_name, hex_pfx + 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;
-				break;
-			}
+			memcpy(hex + 2, de->d_name, 38);
+			if (!get_sha1_hex(hex, sha1))
+				update_candidates(ds, sha1);
 		}
 		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)
@@ -68,99 +135,157 @@ 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(int len,
+			  const unsigned char *bin_pfx,
+			   struct packed_git *p,
+			   struct disambiguate_state *ds)
 {
-	struct packed_git *p;
-	unsigned char found_sha1[20];
-	int found = 0;
+	uint32_t num, last, i, first = 0;
+	const unsigned char *current = NULL;
 
-	prepare_packed_git();
-	for (p = packed_git; p && found < 2; p = p->next) {
-		unsigned num = num_packed_objects(p);
-		unsigned first = 0, last = num;
-		while (first < last) {
-			unsigned mid = (first + last) / 2;
-			unsigned char now[20];
-			int cmp;
-
-			nth_packed_object_sha1(p, mid, now);
-			cmp = hashcmp(match, now);
-			if (!cmp) {
-				first = mid;
-				break;
-			}
-			if (cmp > 0) {
-				first = mid+1;
-				continue;
-			}
-			last = mid;
+	open_pack_index(p);
+	num = p->num_objects;
+	last = num;
+	while (first < last) {
+		uint32_t mid = (first + last) / 2;
+		const unsigned char *current;
+		int cmp;
+
+		current = nth_packed_object_sha1(p, mid);
+		cmp = hashcmp(bin_pfx, current);
+		if (!cmp) {
+			first = mid;
+			break;
 		}
-		if (first < num) {
-			unsigned char now[20], next[20];
-			nth_packed_object_sha1(p, first, now);
-			if (match_sha(len, match, now)) {
-				if (nth_packed_object_sha1(p, first+1, next) ||
-				    !match_sha(len, match, next)) {
-					/* unique within this pack */
-					if (!found) {
-						hashcpy(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;
+	}
+
+	/*
+	 * 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++) {
+		current = nth_packed_object_sha1(p, i);
+		if (!match_sha(len, bin_pfx, current))
+			break;
+		update_candidates(ds, current);
 	}
-	if (found == 1)
-		hashcpy(sha1, found_sha1);
-	return found;
+}
+
+static void find_short_packed_object(int len, const unsigned char *bin_pfx,
+				     struct disambiguate_state *ds)
+{
+	struct packed_git *p;
+
+	prepare_packed_git();
+	for (p = packed_git; p && !ds->ambiguous; p = p->next)
+		unique_in_pack(len, bin_pfx, 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,
+					unsigned char *sha1)
 {
-	int has_unpacked, has_packed;
-	unsigned char unpacked_sha1[20], packed_sha1[20];
+	if (ds->ambiguous)
+		return SHORT_NAME_AMBIGUOUS;
 
-	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));
+
+	hashcpy(sha1, ds->candidate);
+	return 0;
+}
+
+static int disambiguate_commit_only(const unsigned char *sha1, void *cb_data_unused)
+{
+	int kind = sha1_object_info(sha1, NULL);
+	return kind == OBJ_COMMIT;
+}
+
+static int disambiguate_committish_only(const unsigned char *sha1, void *cb_data_unused)
+{
+	struct object *obj;
+	int kind;
+
+	kind = sha1_object_info(sha1, 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(sha1), NULL, 0);
+	if (obj && 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_tree_only(const unsigned char *sha1, void *cb_data_unused)
 {
-	int i, status;
-	char canonical[40];
-	unsigned char res[20];
+	int kind = sha1_object_info(sha1, NULL);
+	return kind == OBJ_TREE;
+}
 
-	if (len < MINIMUM_ABBREV || len > 40)
-		return -1;
-	hashclr(res);
-	memset(canonical, 'x', 40);
+static int disambiguate_treeish_only(const unsigned char *sha1, void *cb_data_unused)
+{
+	struct object *obj;
+	int kind;
+
+	kind = sha1_object_info(sha1, 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(lookup_object(sha1), NULL, 0);
+	if (obj && (obj->type == OBJ_TREE || obj->type == OBJ_COMMIT))
+		return 1;
+	return 0;
+}
+
+static int disambiguate_blob_only(const unsigned char *sha1, void *cb_data_unused)
+{
+	int kind = sha1_object_info(sha1, NULL);
+	return kind == OBJ_BLOB;
+}
+
+static int prepare_prefixes(const char *name, int len,
+			    unsigned char *bin_pfx,
+			    char *hex_pfx)
+{
+	int i;
+
+	hashclr(bin_pfx);
+	memset(hex_pfx, 'x', 40);
 	for (i = 0; i < len ;i++) {
 		unsigned char c = name[i];
 		unsigned char val;
@@ -174,40 +299,96 @@ static int get_short_sha1(const char *name, int len, unsigned char *sha1,
 		}
 		else
 			return -1;
-		canonical[i] = c;
+		hex_pfx[i] = c;
 		if (!(i & 1))
 			val <<= 4;
-		res[i >> 1] |= val;
+		bin_pfx[i >> 1] |= val;
 	}
+	return 0;
+}
+
+static int get_short_sha1(const char *name, int len, unsigned char *sha1,
+			  unsigned flags)
+{
+	int status;
+	char hex_pfx[40];
+	unsigned char bin_pfx[20];
+	struct disambiguate_state ds;
+	int quietly = !!(flags & GET_SHA1_QUIETLY);
+
+	if (len < MINIMUM_ABBREV || len > 40)
+		return -1;
+	if (prepare_prefixes(name, len, bin_pfx, hex_pfx) < 0)
+		return -1;
+
+	prepare_alt_odb();
+
+	memset(&ds, 0, sizeof(ds));
+	if (flags & GET_SHA1_COMMIT)
+		ds.fn = disambiguate_commit_only;
+	else if (flags & GET_SHA1_COMMITTISH)
+		ds.fn = disambiguate_committish_only;
+	else if (flags & GET_SHA1_TREE)
+		ds.fn = disambiguate_tree_only;
+	else if (flags & GET_SHA1_TREEISH)
+		ds.fn = disambiguate_treeish_only;
+	else if (flags & GET_SHA1_BLOB)
+		ds.fn = disambiguate_blob_only;
+
+	find_short_object_filename(len, hex_pfx, &ds);
+	find_short_packed_object(len, bin_pfx, &ds);
+	status = finish_object_disambiguation(&ds, sha1);
 
-	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 error("short SHA1 %.*s is ambiguous.", len, hex_pfx);
 	return status;
 }
 
+int for_each_abbrev(const char *prefix, each_abbrev_fn fn, void *cb_data)
+{
+	char hex_pfx[40];
+	unsigned char bin_pfx[20];
+	struct disambiguate_state ds;
+	int len = strlen(prefix);
+
+	if (len < MINIMUM_ABBREV || len > 40)
+		return -1;
+	if (prepare_prefixes(prefix, len, bin_pfx, hex_pfx) < 0)
+		return -1;
+
+	prepare_alt_odb();
+
+	memset(&ds, 0, sizeof(ds));
+	ds.always_call_fn = 1;
+	ds.cb_data = cb_data;
+	ds.fn = fn;
+
+	find_short_object_filename(len, hex_pfx, &ds);
+	find_short_packed_object(len, bin_pfx, &ds);
+	return ds.ambiguous;
+}
+
 const char *find_unique_abbrev(const unsigned char *sha1, int len)
 {
-	int status, is_null;
+	int status, exists;
 	static char hex[41];
 
-	is_null = is_null_sha1(sha1);
 	memcpy(hex, sha1_to_hex(sha1), 40);
 	if (len == 40 || !len)
 		return hex;
+	exists = has_sha1_file(sha1);
 	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)) {
+		status = get_short_sha1(hex, len, sha1_ret, GET_SHA1_QUIETLY);
+		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)
@@ -235,90 +416,84 @@ static int ambiguous_path(const char *path, int len)
 	return slash;
 }
 
-static const char *ref_fmt[] = {
-	"%.*s",
-	"refs/%.*s",
-	"refs/tags/%.*s",
-	"refs/heads/%.*s",
-	"refs/remotes/%.*s",
-	"refs/remotes/%.*s/HEAD",
-	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)
 {
-	const char **p, *r;
-	int refs_found = 0;
+	int i;
 
-	*ref = NULL;
-	for (p = ref_fmt; *p; p++) {
-		unsigned char sha1_from_ref[20];
-		unsigned char *this_result;
-
-		this_result = refs_found ? sha1_from_ref : sha1;
-		r = resolve_ref(mkpath(*p, len, str), this_result, 1, NULL);
-		if (r) {
-			if (!refs_found++)
-				*ref = xstrdup(r);
-			if (!warn_ambiguous_refs)
-				break;
-		}
+	for (i = 0; i < nr; i++) {
+		int suffix_len = strlen(suffix[i]);
+		if (suffix_len <= len
+		    && !memcmp(string, suffix[i], suffix_len))
+			return suffix_len;
 	}
-	return refs_found;
+	return 0;
 }
 
-int dwim_log(const char *str, int len, unsigned char *sha1, char **log)
+static inline int upstream_mark(const char *string, int len)
 {
-	const char **p;
-	int logs_found = 0;
-
-	*log = NULL;
-	for (p = ref_fmt; *p; p++) {
-		struct stat st;
-		unsigned char hash[20];
-		char path[PATH_MAX];
-		const char *ref, *it;
+	const char *suffix[] = { "@{upstream}", "@{u}" };
+	return at_mark(string, len, suffix, ARRAY_SIZE(suffix));
+}
 
-		strcpy(path, mkpath(*p, len, str));
-		ref = resolve_ref(path, hash, 0, 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;
-	}
-	return logs_found;
+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_basic(const char *str, int len, unsigned char *sha1)
+static int get_sha1_1(const char *name, int len, unsigned char *sha1, 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,
+			  unsigned int flags)
 {
-	static const char *warning = "warning: refname '%.*s' is ambiguous.\n";
+	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\"");
+	unsigned char tmp_sha1[20];
 	char *real_ref = NULL;
 	int refs_found = 0;
-	int at, reflog_len;
+	int at, reflog_len, nth_prior = 0;
 
-	if (len == 40 && !get_sha1_hex(str, sha1))
+	if (len == 40 && !get_sha1_hex(str, sha1)) {
+		if (warn_ambiguous_refs && warn_on_object_refname_ambiguity) {
+			refs_found = dwim_ref(str, len, tmp_sha1, &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} format to query ref-log */
+	/* basic@{time or number or -number} format to query ref-log */
 	reflog_len = at = 0;
-	if (str[len-1] == '}') {
-		for (at = 0; at < len - 1; at++) {
+	if (len && str[len-1] == '}') {
+		for (at = len-4; at >= 0; at--) {
 			if (str[at] == '@' && str[at+1] == '{') {
-				reflog_len = (len-1) - (at+2);
-				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;
+				}
 				break;
 			}
 		}
@@ -328,10 +503,22 @@ 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 detached;
+
+		if (interpret_nth_prior_checkout(str, len, &buf) > 0) {
+			detached = (buf.len == 40 && !get_sha1_hex(buf.buf, sha1));
+			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)
+	else if (reflog_len)
 		refs_found = dwim_log(str, len, sha1, &real_ref);
 	else
 		refs_found = dwim_ref(str, len, sha1, &real_ref);
@@ -339,8 +526,10 @@ static int get_sha1_basic(const char *str, int len, unsigned char *sha1)
 	if (!refs_found)
 		return -1;
 
-	if (warn_ambiguous_refs && refs_found > 1)
-		fprintf(stderr, warning, len, str);
+	if (warn_ambiguous_refs && !(flags & GET_SHA1_QUIETLY) &&
+	    (refs_found > 1 ||
+	     !get_short_sha1(str, len, tmp_sha1, GET_SHA1_QUIETLY)))
+		warning(warn_msg, len, str);
 
 	if (reflog_len) {
 		int nth, i;
@@ -356,21 +545,46 @@ static int get_sha1_basic(const char *str, int len, unsigned char *sha1)
 			else
 				nth = -1;
 		}
-		if (0 <= nth)
+		if (100000000 <= nth) {
+			at_time = nth;
+			nth = -1;
+		} else if (0 <= nth)
 			at_time = 0;
-		else
-			at_time = approxidate(str + at + 2);
-		if (read_ref_at(real_ref, at_time, nth, sha1, NULL,
+		else {
+			int errors = 0;
+			char *tmp = xstrndup(str + at + 2, reflog_len);
+			at_time = approxidate_careful(tmp, &errors);
+			free(tmp);
+			if (errors) {
+				free(real_ref);
+				return -1;
+			}
+		}
+		if (read_ref_at(real_ref, flags, at_time, nth, sha1, NULL,
 				&co_time, &co_tz, &co_cnt)) {
-			if (at_time)
-				fprintf(stderr,
-					"warning: Log for '%.*s' only goes "
-					"back to %s.\n", len, str,
-					show_rfc2822_date(co_time, co_tz));
-			else
-				fprintf(stderr,
-					"warning: Log for '%.*s' only has "
-					"%d entries.\n", len, str, co_cnt);
+			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_SHA1_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_SHA1_QUIETLY) {
+					exit(128);
+				}
+				die("Log for '%.*s' only has %d entries.",
+				    len, str, co_cnt);
+			}
 		}
 	}
 
@@ -378,21 +592,17 @@ static int get_sha1_basic(const char *str, int len, unsigned char *sha1)
 	return 0;
 }
 
-static int get_sha1_1(const char *name, int len, unsigned char *sha1);
-
 static int get_parent(const char *name, int len,
 		      unsigned char *result, int idx)
 {
 	unsigned char sha1[20];
-	int ret = get_sha1_1(name, len, sha1);
+	int ret = get_sha1_1(name, len, sha1, GET_SHA1_COMMITTISH);
 	struct commit *commit;
 	struct commit_list *p;
 
 	if (ret)
 		return ret;
 	commit = lookup_commit_reference(sha1);
-	if (!commit)
-		return -1;
 	if (parse_commit(commit))
 		return -1;
 	if (!idx) {
@@ -414,26 +624,56 @@ 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, GET_SHA1_COMMITTISH);
 	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;
-		hashcpy(sha1, commit->parents->item->object.sha1);
+		commit = commit->parents->item;
 	}
-	hashcpy(result, sha1);
+	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);
+	while (1) {
+		if (!o || (!o->parsed && !parse_object(o->sha1)))
+			return NULL;
+		if (expected_type == OBJ_ANY || 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;
 	unsigned int expected_type = 0;
+	unsigned lookup_flags = 0;
 	struct object *o;
 
 	/*
@@ -456,18 +696,29 @@ 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] == '/')
+		expected_type = OBJ_COMMIT;
 	else
 		return -1;
 
-	if (get_sha1_1(name, sp - name - 2, outer))
+	if (expected_type == OBJ_COMMIT)
+		lookup_flags = GET_SHA1_COMMITTISH;
+	else if (expected_type == OBJ_TREE)
+		lookup_flags = GET_SHA1_TREEISH;
+
+	if (get_sha1_1(name, sp - name - 2, outer, lookup_flags))
 		return -1;
 
 	o = parse_object(outer);
@@ -478,31 +729,37 @@ static int peel_onion(const char *name, int len, unsigned char *sha1)
 		if (!o || (!o->parsed && !parse_object(o->sha1)))
 			return -1;
 		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 == expected_type) {
-				hashcpy(sha1, o->sha1);
-				return 0;
-			}
-			if (o->type == OBJ_TAG)
-				o = ((struct tag*) o)->tagged;
-			else if (o->type == OBJ_COMMIT)
-				o = &(((struct commit *) o)->tree->object);
-			else
-				return error("%.*s: expected %s type, but the object dereferences to %s type",
-					     len, name, typename(expected_type),
-					     typename(o->type));
-			if (!o->parsed)
-				parse_object(o->sha1);
-		}
+		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;
 }
@@ -510,31 +767,31 @@ static int peel_onion(const char *name, int len, unsigned char *sha1)
 static int get_describe_name(const char *name, int len, unsigned char *sha1)
 {
 	const char *cp;
+	unsigned flags = GET_SHA1_QUIETLY | GET_SHA1_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_sha1(cp, len, sha1, flags);
 			}
 		}
 	}
 	return -1;
 }
 
-static int get_sha1_1(const char *name, int len, unsigned char *sha1)
+static int get_sha1_1(const char *name, int len, unsigned char *sha1, unsigned lookup_flags)
 {
 	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--) {
@@ -552,11 +809,10 @@ 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);
 	}
@@ -565,7 +821,7 @@ static int get_sha1_1(const char *name, int len, unsigned char *sha1)
 	if (!ret)
 		return 0;
 
-	ret = get_sha1_basic(name, len, sha1);
+	ret = get_sha1_basic(name, len, sha1, lookup_flags);
 	if (!ret)
 		return 0;
 
@@ -574,63 +830,359 @@ static int get_sha1_1(const char *name, int len, unsigned char *sha1)
 	if (!ret)
 		return 0;
 
-	return get_short_sha1(name, len, sha1, 0);
+	return get_short_sha1(name, len, sha1, lookup_flags);
 }
 
-static int handle_one_ref(const char *path,
-		const unsigned char *sha1, int flag, void *cb_data)
+/*
+ * 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.
+ */
+
+/* Remember to update object flag allocation in object.h */
+#define ONELINE_SEEN (1u<<20)
+
+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->hash);
 	if (!object)
 		return 0;
-	if (object->type == OBJ_TAG)
+	if (object->type == OBJ_TAG) {
 		object = deref_tag(object, path, strlen(path));
+		if (!object)
+			return 0;
+	}
 	if (object->type != OBJ_COMMIT)
 		return 0;
-	insert_by_date((struct commit *)object, list);
+	commit_list_insert((struct commit *)object, list);
 	return 0;
 }
 
-/*
- * This interprets names like ':/Initial revision of "git"' by searching
- * through history and returning the first commit whose message starts
- * with the given string.
- *
- * 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)
-int get_sha1_oneline(const char *prefix, unsigned char *sha1)
+static int get_sha1_oneline(const char *prefix, unsigned char *sha1,
+			    struct commit_list *list)
 {
-	struct commit_list *list = NULL, *backup = NULL, *l;
-	struct commit *commit;
+	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 (!save_commit_buffer)
-		return error("Could not expand oneline-name.");
-	for_each_ref(handle_one_ref, &list);
-	for (l = list; l; l = l->next)
+
+	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 ((commit = pop_most_recent_commit(&list, ONELINE_SEEN))) {
-		char *p;
-		parse_object(commit->object.sha1);
-		if (!commit->buffer || !(p = strstr(commit->buffer, "\n\n")))
+	}
+	while (list) {
+		const char *p, *buf;
+		struct commit *commit;
+		int matches;
+
+		commit = pop_most_recent_commit(&list, ONELINE_SEEN);
+		if (!parse_object(commit->object.sha1))
 			continue;
-		if (!prefixcmp(p + 2, prefix)) {
+		buf = get_commit_buffer(commit, NULL);
+		p = strstr(buf, "\n\n");
+		matches = p && !regexec(&regex, p + 2, 0, NULL, 0);
+		unuse_commit_buffer(commit, buf);
+
+		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);
-	return commit == NULL;
+	free_commit_list(backup);
+	return found ? 0 : -1;
+}
+
+struct grab_nth_branch_switch_cbdata {
+	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,
+				  const char *message, void *cb_data)
+{
+	struct grab_nth_branch_switch_cbdata *cb = cb_data;
+	const char *match = NULL, *target = NULL;
+	size_t len;
+
+	if (skip_prefix(message, "checkout: moving from ", &match))
+		target = strstr(match, " to ");
+
+	if (!match || !target)
+		return 0;
+	if (--(cb->remaining) == 0) {
+		len = target - match;
+		strbuf_reset(&cb->buf);
+		strbuf_add(&cb->buf, match, len);
+		return 1; /* we are done */
+	}
+	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, int namelen,
+					struct strbuf *buf)
+{
+	long nth;
+	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 = memchr(name, '}', namelen);
+	if (!brace)
+		return -1;
+	nth = strtol(name + 3, &num_end, 10);
+	if (num_end != brace)
+		return -1;
+	if (nth <= 0)
+		return -1;
+	cb.remaining = nth;
+	strbuf_init(&cb.buf, 20);
+
+	retval = 0;
+	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;
+	}
+
+	strbuf_release(&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_committish(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_committish(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);
+	if (!mbs || mbs->next)
+		st = -1;
+	else {
+		st = 0;
+		hashcpy(sha1, mbs->item->object.sha1);
+	}
+	free_commit_list(mbs);
+	return st;
+}
+
+/* parse @something syntax, when 'something' is not {.*} */
+static int interpret_empty_at(const char *name, int namelen, int len, struct strbuf *buf)
+{
+	const char *next;
+
+	if (len || name[1] == '{')
+		return -1;
+
+	/* 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)
+{
+	/* 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);
+	/* 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 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 *))
+{
+	int len;
+	struct branch *branch;
+	struct strbuf err = STRBUF_INIT;
+	const char *value;
+
+	len = get_mark(name + at, namelen - at);
+	if (!len)
+		return -1;
+
+	if (memchr(name, ':', at))
+		return -1;
+
+	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);
+
+	set_shortened_ref(buf, value);
+	return len + at;
+}
+
+/*
+ * 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, int namelen, struct strbuf *buf)
+{
+	char *at;
+	const char *start;
+	int len = interpret_nth_prior_checkout(name, namelen, buf);
+
+	if (!namelen)
+		namelen = strlen(name);
+
+	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);
+	}
+
+	for (start = name;
+	     (at = memchr(start, '@', namelen - (start - name)));
+	     start = at + 1) {
+
+		len = interpret_empty_at(name, namelen, at - name, buf);
+		if (len > 0)
+			return reinterpret(name, namelen, len, buf);
+
+		len = interpret_branch_mark(name, namelen, at - name, buf,
+					    upstream_mark, branch_get_upstream);
+		if (len > 0)
+			return len;
+
+		len = interpret_branch_mark(name, namelen, at - name, buf,
+					    push_mark, branch_get_push);
+		if (len > 0)
+			return len;
+	}
+
+	return -1;
+}
+
+int strbuf_branchname(struct strbuf *sb, const char *name)
+{
+	int len = strlen(name);
+	int used = interpret_branch_name(name, len, sb);
+
+	if (used == len)
+		return 0;
+	if (used < 0)
+		used = 0;
+	strbuf_add(sb, name + used, len - used);
+	return len;
+}
+
+int strbuf_check_branch_ref(struct strbuf *sb, const char *name)
+{
+	strbuf_branchname(sb, name);
+	if (name[0] == '-')
+		return -1;
+	strbuf_splice(sb, 0, 0, "refs/heads/", 11);
+	return check_refname_format(sb->buf, 0);
 }
 
 /*
@@ -639,25 +1191,199 @@ int get_sha1_oneline(const char *prefix, unsigned char *sha1)
  */
 int get_sha1(const char *name, unsigned char *sha1)
 {
+	struct object_context unused;
+	return get_sha1_with_context(name, 0, sha1, &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_sha1_committish(const char *name, unsigned char *sha1)
+{
+	struct object_context unused;
+	return get_sha1_with_context(name, GET_SHA1_COMMITTISH,
+				     sha1, &unused);
+}
+
+int get_sha1_treeish(const char *name, unsigned char *sha1)
+{
+	struct object_context unused;
+	return get_sha1_with_context(name, GET_SHA1_TREEISH,
+				     sha1, &unused);
+}
+
+int get_sha1_commit(const char *name, unsigned char *sha1)
+{
+	struct object_context unused;
+	return get_sha1_with_context(name, GET_SHA1_COMMIT,
+				     sha1, &unused);
+}
+
+int get_sha1_tree(const char *name, unsigned char *sha1)
+{
+	struct object_context unused;
+	return get_sha1_with_context(name, GET_SHA1_TREE,
+				     sha1, &unused);
+}
+
+int get_sha1_blob(const char *name, unsigned char *sha1)
+{
+	struct object_context unused;
+	return get_sha1_with_context(name, GET_SHA1_BLOB,
+				     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,
+				       int object_name_len)
+{
+	unsigned char sha1[20];
+	unsigned mode;
+
+	if (!prefix)
+		prefix = "";
+
+	if (file_exists(filename))
+		die("Path '%s' exists on disk, but not in '%.*s'.",
+		    filename, object_name_len, object_name);
+	if (errno == ENOENT || errno == ENOTDIR) {
+		char *fullname = xstrfmt("%s%s", prefix, 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_len, object_name,
+			    fullname,
+			    object_name_len, object_name,
+			    filename);
+		}
+		die("Path '%s' does not exist in '%.*s'",
+		    filename, object_name_len, 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)
+{
+	const 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 (file_exists(filename))
+		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);
+}
+
+
+static char *resolve_relative_path(const char *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.");
+
+	/* 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);
+}
+
+static int get_sha1_with_context_1(const char *name,
+				   unsigned flags,
+				   const char *prefix,
+				   unsigned char *sha1,
+				   struct object_context *oc)
+{
 	int ret, bracket_depth;
-	unsigned unused;
 	int namelen = strlen(name);
 	const char *cp;
+	int only_to_die = flags & GET_SHA1_ONLY_TO_DIE;
 
-	prepare_alt_odb();
-	ret = get_sha1_1(name, namelen, sha1);
+	memset(oc, 0, sizeof(*oc));
+	oc->mode = S_IFINVALID;
+	ret = get_sha1_1(name, namelen, sha1, flags);
 	if (!ret)
 		return ret;
-	/* sha1:path --> object name of path in ent sha1
-	 * :path -> object name of path in index
+	/*
+	 * 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;
+		const struct cache_entry *ce;
+		char *new_path = NULL;
 		int pos;
-		if (namelen > 2 && name[1] == '/')
-			return get_sha1_oneline(name + 2, sha1);
+		if (!only_to_die && namelen > 2 && name[1] == '/') {
+			struct commit_list *list = NULL;
+
+			for_each_ref(handle_one_ref, &list);
+			commit_list_sort_by_date(&list);
+			return get_sha1_oneline(name + 2, sha1, list);
+		}
 		if (namelen < 3 ||
 		    name[2] != ':' ||
 		    name[1] < '0' || '3' < name[1])
@@ -666,11 +1392,18 @@ int get_sha1(const char *name, unsigned char *sha1)
 			stage = name[1] - '0';
 			cp = name + 3;
 		}
-		namelen = namelen - (cp - name);
+		new_path = resolve_relative_path(cp);
+		if (!new_path) {
+			namelen = namelen - (cp - name);
+		} else {
+			cp = new_path;
+			namelen = strlen(cp);
+		}
+
+		strlcpy(oc->path, cp, sizeof(oc->path));
+
 		if (!active_cache)
 			read_cache();
-		if (active_nr < 0)
-			return -1;
 		pos = cache_name_pos(cp, namelen);
 		if (pos < 0)
 			pos = -pos - 1;
@@ -681,10 +1414,15 @@ int get_sha1(const char *name, unsigned char *sha1)
 				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++) {
@@ -697,9 +1435,58 @@ int get_sha1(const char *name, unsigned char *sha1)
 	}
 	if (*cp == ':') {
 		unsigned char tree_sha1[20];
-		if (!get_sha1_1(name, cp-name, tree_sha1))
-			return get_tree_entry(tree_sha1, cp+1, sha1,
-					      &unused);
+		int len = cp - name;
+		if (!get_sha1_1(name, len, tree_sha1, GET_SHA1_TREEISH)) {
+			const char *filename = cp+1;
+			char *new_filename = NULL;
+
+			new_filename = resolve_relative_path(filename);
+			if (new_filename)
+				filename = new_filename;
+			if (flags & GET_SHA1_FOLLOW_SYMLINKS) {
+				ret = get_tree_entry_follow_symlinks(tree_sha1,
+					filename, sha1, &oc->symlink_path,
+					&oc->mode);
+			} else {
+				ret = get_tree_entry(tree_sha1, filename,
+						     sha1, &oc->mode);
+				if (ret && only_to_die) {
+					diagnose_invalid_sha1_path(prefix,
+								   filename,
+								   tree_sha1,
+								   name, len);
+				}
+			}
+			hashcpy(oc->tree, tree_sha1);
+			strlcpy(oc->path, filename, sizeof(oc->path));
+
+			free(new_filename);
+			return ret;
+		} else {
+			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;
+	unsigned char sha1[20];
+	get_sha1_with_context_1(name, GET_SHA1_ONLY_TO_DIE, prefix, sha1, &oc);
+}
+
+int get_sha1_with_context(const char *str, unsigned flags, unsigned char *sha1, struct object_context *orc)
+{
+	if (flags & GET_SHA1_FOLLOW_SYMLINKS && flags & GET_SHA1_ONLY_TO_DIE)
+		die("BUG: incompatible flags for get_sha1_with_context");
+	return get_sha1_with_context_1(str, flags, NULL, sha1, orc);
+}