1 files changed, 512 insertions, 225 deletions

diff --git a/sha1_name.c b/sha1_name.c
index 03ffc2caaa..65ad066d9b 100644
--- a/sha1_name.c
+++ b/sha1_name.c
@@ -9,14 +9,82 @@
 
 static int get_sha1_oneline(const char *, unsigned char *, struct commit_list *);
 
-static int find_short_object_filename(int len, const char *name, unsigned char *sha1)
+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;
@@ -27,33 +95,28 @@ 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)
@@ -71,103 +134,157 @@ 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;
-	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 unsigned char *current = NULL;
+
+	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) {
-			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;
+	}
+
+	/*
+	 * 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;
 
-	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));
+
+	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;
@@ -181,18 +298,76 @@ 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, exists;
@@ -204,7 +379,7 @@ const char *find_unique_abbrev(const unsigned char *sha1, int len)
 		return hex;
 	while (len < 40) {
 		unsigned char sha1_ret[20];
-		status = get_short_sha1(hex, len, sha1_ret, 1);
+		status = get_short_sha1(hex, len, sha1_ret, GET_SHA1_QUIETLY);
 		if (exists
 		    ? !status
 		    : status == SHORT_NAME_NOT_FOUND) {
@@ -255,23 +430,52 @@ static inline int upstream_mark(const char *string, int len)
 	return 0;
 }
 
-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);
+static int interpret_nth_prior_checkout(const char *name, struct strbuf *buf);
 
 static int get_sha1_basic(const char *str, int len, unsigned char *sha1)
 {
 	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;
-
-	if (len == 40 && !get_sha1_hex(str, sha1))
+	int at, reflog_len, nth_prior = 0;
+
+	if (len == 40 && !get_sha1_hex(str, sha1)) {
+		if (warn_on_object_refname_ambiguity) {
+			refs_found = dwim_ref(str, len, tmp_sha1, &real_ref);
+			if (refs_found > 0 && warn_ambiguous_refs) {
+				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 (str[at+2] == '-') {
+					if (at != 0)
+						/* @{-N} not at start */
+						return -1;
+					nth_prior = 1;
+					continue;
+				}
 				if (!upstream_mark(str + at, len - at)) {
 					reflog_len = (len-1) - (at+2);
 					len = at;
@@ -285,20 +489,22 @@ 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 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, &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);
@@ -306,7 +512,9 @@ 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)
+	if (warn_ambiguous_refs &&
+	    (refs_found > 1 ||
+	     !get_short_sha1(str, len, tmp_sha1, GET_SHA1_QUIETLY)))
 		warning(warn_msg, len, str);
 
 	if (reflog_len) {
@@ -315,10 +523,6 @@ static int get_sha1_basic(const char *str, int len, unsigned char *sha1)
 		unsigned long co_time;
 		int co_tz, co_cnt;
 
-		/* a @{-N} placed anywhere except the start is an error */
-		if (str[at+2] == '-')
-			return -1;
-
 		/* Is it asking for N-th entry, or approxidate? */
 		for (i = nth = 0; 0 <= nth && i < reflog_len; i++) {
 			char ch = str[at+2+i];
@@ -342,12 +546,21 @@ static int get_sha1_basic(const char *str, int len, unsigned char *sha1)
 		}
 		if (read_ref_at(real_ref, at_time, nth, sha1, NULL,
 				&co_time, &co_tz, &co_cnt)) {
+			if (!len) {
+				if (!prefixcmp(real_ref, "refs/heads/")) {
+					str = real_ref + 11;
+					len = strlen(real_ref + 11);
+				} else {
+					/* detached HEAD */
+					str = "HEAD";
+					len = 4;
+				}
+			}
 			if (at_time)
 				warning("Log for '%.*s' only goes "
 					"back to %s.", len, str,
 					show_date(co_time, co_tz, DATE_RFC2822));
 			else {
-				free(real_ref);
 				die("Log for '%.*s' only has %d entries.",
 				    len, str, co_cnt);
 			}
@@ -362,7 +575,7 @@ 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;
 
@@ -395,7 +608,7 @@ static int get_nth_ancestor(const char *name, int len,
 	struct commit *commit;
 	int ret;
 
-	ret = get_sha1_1(name, len, sha1);
+	ret = get_sha1_1(name, len, sha1, GET_SHA1_COMMITTISH);
 	if (ret)
 		return ret;
 	commit = lookup_commit_reference(sha1);
@@ -419,7 +632,7 @@ struct object *peel_to_type(const char *name, int namelen,
 	while (1) {
 		if (!o || (!o->parsed && !parse_object(o->sha1)))
 			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;
@@ -441,6 +654,7 @@ 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;
 
 	/*
@@ -469,6 +683,8 @@ static int peel_onion(const char *name, int len, unsigned char *sha1)
 		expected_type = OBJ_TREE;
 	else if (!strncmp(blob_type, sp, 4) && sp[4] == '}')
 		expected_type = OBJ_BLOB;
+	else if (!prefixcmp(sp, "object}"))
+		expected_type = OBJ_ANY;
 	else if (sp[0] == '}')
 		expected_type = OBJ_NONE;
 	else if (sp[0] == '/')
@@ -476,7 +692,12 @@ static int peel_onion(const char *name, int len, unsigned char *sha1)
 	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);
@@ -525,6 +746,7 @@ 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;
@@ -535,14 +757,14 @@ static int get_describe_name(const char *name, int len, unsigned char *sha1)
 			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;
@@ -587,7 +809,7 @@ 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);
 }
 
 /*
@@ -676,8 +898,8 @@ 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,
@@ -687,7 +909,6 @@ static int grab_nth_branch_switch(unsigned char *osha1, unsigned char *nsha1,
 	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 ");
@@ -696,11 +917,12 @@ static int grab_nth_branch_switch(unsigned char *osha1, unsigned char *nsha1,
 
 	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;
 }
 
@@ -711,7 +933,7 @@ static int grab_nth_branch_switch(unsigned char *osha1, unsigned char *nsha1,
 static int interpret_nth_prior_checkout(const char *name, struct strbuf *buf)
 {
 	long nth;
-	int i, retval;
+	int retval;
 	struct grab_nth_branch_switch_cbdata cb;
 	const char *brace;
 	char *num_end;
@@ -721,34 +943,22 @@ static int interpret_nth_prior_checkout(const char *name, struct strbuf *buf)
 	brace = strchr(name, '}');
 	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_add(buf, cb.buf.buf, cb.buf.len);
+		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;
 }
 
@@ -769,7 +979,7 @@ int get_sha1_mb(const char *name, unsigned char *sha1)
 		struct strbuf sb;
 		strbuf_init(&sb, dots - name);
 		strbuf_add(&sb, name, dots - name);
-		st = get_sha1(sb.buf, sha1_tmp);
+		st = get_sha1_committish(sb.buf, sha1_tmp);
 		strbuf_release(&sb);
 	}
 	if (st)
@@ -778,7 +988,7 @@ int get_sha1_mb(const char *name, unsigned char *sha1)
 	if (!one)
 		return -1;
 
-	if (get_sha1(dots[3] ? (dots + 3) : "HEAD", sha1_tmp))
+	if (get_sha1_committish(dots[3] ? (dots + 3) : "HEAD", sha1_tmp))
 		return -1;
 	two = lookup_commit_reference_gently(sha1_tmp, 0);
 	if (!two)
@@ -794,6 +1004,27 @@ int get_sha1_mb(const char *name, unsigned char *sha1)
 	return st;
 }
 
+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, &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;
+}
+
 /*
  * 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
@@ -823,28 +1054,13 @@ int interpret_branch_name(const char *name, struct strbuf *buf)
 	int len = interpret_nth_prior_checkout(name, buf);
 	int tmp_len;
 
-	if (!len)
+	if (!len) {
 		return len; /* syntax Ok, not enough switches */
-	if (0 < len && len == namelen)
-		return len; /* consumed all */
-	else if (0 < len) {
-		/* we have extra data, which might need further processing */
-		struct strbuf tmp = STRBUF_INIT;
-		int used = buf->len;
-		int ret;
-
-		strbuf_add(buf, name + len, namelen - len);
-		ret = interpret_branch_name(buf->buf, &tmp);
-		/* that data was not interpreted, remove our cruft */
-		if (ret < 0) {
-			strbuf_setlen(buf, used);
-			return len;
-		}
-		strbuf_reset(buf);
-		strbuf_addbuf(buf, &tmp);
-		strbuf_release(&tmp);
-		/* tweak for size of {-N} versus expanded ref name */
-		return ret - used + len;
+	} else if (len > 0) {
+		if (len == namelen)
+			return len; /* consumed all */
+		else
+			return reinterpret(name, namelen, len, buf);
 	}
 
 	cp = strchr(name, '@');
@@ -856,10 +1072,23 @@ int interpret_branch_name(const char *name, struct strbuf *buf)
 	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);
+	/*
+	 * Upstream can be NULL only if cp refers to HEAD and HEAD
+	 * points to something different than a branch.
+	 */
+	if (!upstream)
+		die(_("HEAD does not point to a branch"));
+	if (!upstream->merge || !upstream->merge[0]->dst) {
+		if (!ref_exists(upstream->refname))
+			die(_("No such branch: '%s'"), cp);
+		if (!upstream->merge) {
+			die(_("No upstream configured for branch '%s'"),
+				upstream->name);
+		}
+		die(
+			_("Upstream branch '%s' not stored as a remote-tracking branch"),
+			upstream->merge[0]->src);
+	}
 	free(cp);
 	cp = shorten_unambiguous_ref(upstream->merge[0]->dst, 0);
 	strbuf_reset(buf);
@@ -871,9 +1100,13 @@ int interpret_branch_name(const char *name, struct strbuf *buf)
 int strbuf_branchname(struct strbuf *sb, const char *name)
 {
 	int len = strlen(name);
-	if (interpret_branch_name(name, sb) == len)
+	int used = interpret_branch_name(name, sb);
+
+	if (used == len)
 		return 0;
-	strbuf_add(sb, name, len);
+	if (used < 0)
+		used = 0;
+	strbuf_add(sb, name + used, len - used);
 	return len;
 }
 
@@ -893,14 +1126,60 @@ int strbuf_check_branch_ref(struct strbuf *sb, const char *name)
 int get_sha1(const char *name, unsigned char *sha1)
 {
 	struct object_context unused;
-	return get_sha1_with_context(name, sha1, &unused);
+	return get_sha1_with_context(name, 0, sha1, &unused);
+}
+
+/*
+ * Many callers know that the user meant to name a committish by
+ * syntactical positions where the object name appears.  Calling this
+ * function allows the machinery to disambiguate shorter-than-unique
+ * abbreviated object names between committish and others.
+ *
+ * Note that this does NOT error out when the named object is not a
+ * committish. 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)
+				       const char *object_name,
+				       int object_name_len)
 {
 	struct stat st;
 	unsigned char sha1[20];
@@ -910,8 +1189,8 @@ static void diagnose_invalid_sha1_path(const char *prefix,
 		prefix = "";
 
 	if (!lstat(filename, &st))
-		die("Path '%s' exists on disk, but not in '%s'.",
-		    filename, object_name);
+		die("Path '%s' exists on disk, but not in '%.*s'.",
+		    filename, object_name_len, object_name);
 	if (errno == ENOENT || errno == ENOTDIR) {
 		char *fullname = xmalloc(strlen(filename)
 					     + strlen(prefix) + 1);
@@ -921,16 +1200,16 @@ static void diagnose_invalid_sha1_path(const char *prefix,
 		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'?",
+			    "Did you mean '%.*s:%s' aka '%.*s:./%s'?",
 			    fullname,
 			    filename,
-			    object_name,
+			    object_name_len, object_name,
 			    fullname,
-			    object_name,
+			    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);
 	}
 }
 
@@ -940,7 +1219,7 @@ static void diagnose_invalid_index_path(int stage,
 					const char *filename)
 {
 	struct stat st;
-	struct cache_entry *ce;
+	const struct cache_entry *ce;
 	int pos;
 	unsigned namelen = strlen(filename);
 	unsigned fullnamelen;
@@ -992,16 +1271,6 @@ static void diagnose_invalid_index_path(int stage,
 }
 
 
-int get_sha1_with_mode_1(const char *name, unsigned char *sha1, unsigned *mode,
-			 int only_to_die, const char *prefix)
-{
-	struct object_context oc;
-	int ret;
-	ret = get_sha1_with_context_1(name, sha1, &oc, only_to_die, prefix);
-	*mode = oc.mode;
-	return ret;
-}
-
 static char *resolve_relative_path(const char *rel)
 {
 	if (prefixcmp(rel, "./") && prefixcmp(rel, "../"))
@@ -1019,20 +1288,24 @@ 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 only_to_die, const char *prefix)
+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;
 	int namelen = strlen(name);
 	const char *cp;
+	int only_to_die = flags & GET_SHA1_ONLY_TO_DIE;
 
 	memset(oc, 0, sizeof(*oc));
 	oc->mode = S_IFINVALID;
-	ret = get_sha1_1(name, namelen, sha1);
+	ret = get_sha1_1(name, namelen, sha1, 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
@@ -1040,7 +1313,7 @@ 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 (!only_to_die && namelen > 2 && name[1] == '/') {
@@ -1101,13 +1374,8 @@ int get_sha1_with_context_1(const char *name, unsigned char *sha1,
 	}
 	if (*cp == ':') {
 		unsigned char tree_sha1[20];
-		char *object_name = NULL;
-		if (only_to_die) {
-			object_name = xmalloc(cp-name+1);
-			strncpy(object_name, name, cp-name);
-			object_name[cp-name] = '\0';
-		}
-		if (!get_sha1_1(name, cp-name, tree_sha1)) {
+		int len = cp - name;
+		if (!get_sha1_1(name, len, tree_sha1, GET_SHA1_TREEISH)) {
 			const char *filename = cp+1;
 			char *new_filename = NULL;
 
@@ -1115,10 +1383,10 @@ int get_sha1_with_context_1(const char *name, unsigned char *sha1,
 			if (new_filename)
 				filename = new_filename;
 			ret = get_tree_entry(tree_sha1, filename, sha1, &oc->mode);
-			if (only_to_die) {
+			if (ret && only_to_die) {
 				diagnose_invalid_sha1_path(prefix, filename,
-							   tree_sha1, object_name);
-				free(object_name);
+							   tree_sha1,
+							   name, len);
 			}
 			hashcpy(oc->tree, tree_sha1);
 			strncpy(oc->path, filename,
@@ -1129,8 +1397,27 @@ int get_sha1_with_context_1(const char *name, unsigned char *sha1,
 			return ret;
 		} else {
 			if (only_to_die)
-				die("Invalid object name '%s'.", object_name);
+				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)
+{
+	return get_sha1_with_context_1(str, flags, NULL, sha1, orc);
+}