29 files changed, 833 insertions, 259 deletions

diff --git a/Documentation/config.txt b/Documentation/config.txt
index 7bc0e53848..a95e5a4ac9 100644
--- a/Documentation/config.txt
+++ b/Documentation/config.txt
@@ -177,6 +177,9 @@ advice.*::
 		Advice shown when you used linkgit:git-checkout[1] to
 		move to the detach HEAD state, to instruct how to create
 		a local branch after the fact.
+	amWorkDir::
+		Advice that shows the location of the patch file when
+		linkgit:git-am[1] fails to apply it.
 --
 
 core.fileMode::
diff --git a/Documentation/git-daemon.txt b/Documentation/git-daemon.txt
index 31b28fc29f..e8f757704c 100644
--- a/Documentation/git-daemon.txt
+++ b/Documentation/git-daemon.txt
@@ -204,7 +204,7 @@ receive-pack::
 	can push anything into the repository, including removal
 	of refs).  This is solely meant for a closed LAN setting
 	where everybody is friendly.  This service can be
-	enabled by `daemon.receivepack` configuration item to
+	enabled by setting `daemon.receivepack` configuration item to
 	`true`.
 
 EXAMPLES
diff --git a/Documentation/git-rev-parse.txt b/Documentation/git-rev-parse.txt
index 4cc3e9586f..3c63561f02 100644
--- a/Documentation/git-rev-parse.txt
+++ b/Documentation/git-rev-parse.txt
@@ -101,6 +101,12 @@ OPTIONS
 	The option core.warnAmbiguousRefs is used to select the strict
 	abbreviation mode.
 
+--disambiguate=<prefix>::
+	Show every object whose name begins with the given prefix.
+	The <prefix> must be at least 4 hexadecimal digits long to
+	avoid listing each and every object in the repository by
+	mistake.
+
 --all::
 	Show all refs found in `refs/`.
 
diff --git a/builtin/apply.c b/builtin/apply.c
index ace04c453b..069cf341b6 100644
--- a/builtin/apply.c
+++ b/builtin/apply.c
@@ -3589,7 +3589,7 @@ static void build_fake_ancestor(struct patch *list, const char *filename)
 		name = patch->old_name ? patch->old_name : patch->new_name;
 		if (0 < patch->is_new)
 			continue;
-		else if (get_sha1(patch->old_sha1_prefix, sha1))
+		else if (get_sha1_blob(patch->old_sha1_prefix, sha1))
 			/* git diff has no index line for mode/type changes */
 			if (!patch->lines_added && !patch->lines_deleted) {
 				if (get_current_sha1(patch->old_name, sha1))
diff --git a/builtin/cat-file.c b/builtin/cat-file.c
index 36a9104433..af74e775a1 100644
--- a/builtin/cat-file.c
+++ b/builtin/cat-file.c
@@ -91,7 +91,7 @@ static int cat_one_file(int opt, const char *exp_type, const char *obj_name)
 	unsigned long size;
 	struct object_context obj_context;
 
-	if (get_sha1_with_context(obj_name, sha1, &obj_context))
+	if (get_sha1_with_context(obj_name, 0, sha1, &obj_context))
 		die("Not a valid object name %s", obj_name);
 
 	buf = NULL;
diff --git a/builtin/commit-tree.c b/builtin/commit-tree.c
index 164b655df9..cb982c5503 100644
--- a/builtin/commit-tree.c
+++ b/builtin/commit-tree.c
@@ -48,8 +48,8 @@ int cmd_commit_tree(int argc, const char **argv, const char *prefix)
 	if (argc < 2 || !strcmp(argv[1], "-h"))
 		usage(commit_tree_usage);
 
-	if (get_sha1(argv[1], tree_sha1))
-		die("Not a valid object name %s", argv[1]);
+	if (get_sha1_tree(argv[1], tree_sha1))
+		die("Not a valid tree object name %s", argv[1]);
 
 	for (i = 1; i < argc; i++) {
 		const char *arg = argv[i];
@@ -57,7 +57,7 @@ int cmd_commit_tree(int argc, const char **argv, const char *prefix)
 			unsigned char sha1[20];
 			if (argc <= ++i)
 				usage(commit_tree_usage);
-			if (get_sha1(argv[i], sha1))
+			if (get_sha1_commit(argv[i], sha1))
 				die("Not a valid object name %s", argv[i]);
 			assert_sha1_type(sha1, OBJ_COMMIT);
 			new_parent(lookup_commit(sha1), &parents);
@@ -104,7 +104,7 @@ int cmd_commit_tree(int argc, const char **argv, const char *prefix)
 			continue;
 		}
 
-		if (get_sha1(arg, tree_sha1))
+		if (get_sha1_tree(arg, tree_sha1))
 			die("Not a valid object name %s", arg);
 		if (got_tree)
 			die("Cannot give more than one trees");
diff --git a/builtin/config.c b/builtin/config.c
index e8e1c0a456..8cd08da991 100644
--- a/builtin/config.c
+++ b/builtin/config.c
@@ -387,12 +387,20 @@ int cmd_config(int argc, const char **argv, const char *prefix)
 
 		home_config_paths(&user_config, &xdg_config, "config");
 
-		if (access(user_config, R_OK) && !access(xdg_config, R_OK))
+		if (!user_config)
+			/*
+			 * It is unknown if HOME/.gitconfig exists, so
+			 * we do not know if we should write to XDG
+			 * location; error out even if XDG_CONFIG_HOME
+			 * is set and points at a sane location.
+			 */
+			die("$HOME not set");
+
+		if (access(user_config, R_OK) &&
+		    xdg_config && !access(xdg_config, R_OK))
 			given_config_file = xdg_config;
-		else if (user_config)
-			given_config_file = user_config;
 		else
-			die("$HOME not set");
+			given_config_file = user_config;
 	}
 	else if (use_system_config)
 		given_config_file = git_etc_gitconfig();
diff --git a/builtin/log.c b/builtin/log.c
index adcbcf1f24..ecc2793690 100644
--- a/builtin/log.c
+++ b/builtin/log.c
@@ -367,6 +367,7 @@ int cmd_whatchanged(int argc, const char **argv, const char *prefix)
 	rev.simplify_history = 0;
 	memset(&opt, 0, sizeof(opt));
 	opt.def = "HEAD";
+	opt.revarg_opt = REVARG_COMMITTISH;
 	cmd_log_init(argc, argv, prefix, &rev, &opt);
 	if (!rev.diffopt.output_format)
 		rev.diffopt.output_format = DIFF_FORMAT_RAW;
@@ -557,6 +558,7 @@ int cmd_log(int argc, const char **argv, const char *prefix)
 	rev.always_show_header = 1;
 	memset(&opt, 0, sizeof(opt));
 	opt.def = "HEAD";
+	opt.revarg_opt = REVARG_COMMITTISH;
 	cmd_log_init(argc, argv, prefix, &rev, &opt);
 	return cmd_log_walk(&rev);
 }
@@ -1132,6 +1134,7 @@ int cmd_format_patch(int argc, const char **argv, const char *prefix)
 	rev.subject_prefix = fmt_patch_subject_prefix;
 	memset(&s_r_opt, 0, sizeof(s_r_opt));
 	s_r_opt.def = "HEAD";
+	s_r_opt.revarg_opt = REVARG_COMMITTISH;
 
 	if (default_attach) {
 		rev.mime_boundary = default_attach;
diff --git a/builtin/pack-objects.c b/builtin/pack-objects.c
index f3348208d8..782e7d0c38 100644
--- a/builtin/pack-objects.c
+++ b/builtin/pack-objects.c
@@ -2373,7 +2373,7 @@ static void get_object_list(int ac, const char **av)
 			}
 			die("not a rev '%s'", line);
 		}
-		if (handle_revision_arg(line, &revs, flags, 1))
+		if (handle_revision_arg(line, &revs, flags, REVARG_CANNOT_BE_FILENAME))
 			die("bad revision '%s'", line);
 	}
 
diff --git a/builtin/reset.c b/builtin/reset.c
index 4cc34c9084..74442bd766 100644
--- a/builtin/reset.c
+++ b/builtin/reset.c
@@ -276,7 +276,7 @@ int cmd_reset(int argc, const char **argv, const char *prefix)
 		 * Otherwise, argv[i] could be either <rev> or <paths> and
 		 * has to be unambiguous.
 		 */
-		else if (!get_sha1(argv[i], sha1)) {
+		else if (!get_sha1_committish(argv[i], sha1)) {
 			/*
 			 * Ok, argv[i] looks like a rev; it should not
 			 * be a filename.
@@ -289,9 +289,15 @@ int cmd_reset(int argc, const char **argv, const char *prefix)
 		}
 	}
 
-	if (get_sha1(rev, sha1))
+	if (get_sha1_committish(rev, sha1))
 		die(_("Failed to resolve '%s' as a valid ref."), rev);
 
+	/*
+	 * NOTE: As "git reset $treeish -- $path" should be usable on
+	 * any tree-ish, this is not strictly correct. We are not
+	 * moving the HEAD to any commit; we are merely resetting the
+	 * entries in the index to that of a treeish.
+	 */
 	commit = lookup_commit_reference(sha1);
 	if (!commit)
 		die(_("Could not parse object '%s'."), rev);
diff --git a/builtin/rev-parse.c b/builtin/rev-parse.c
index 13495b88f5..32788a9f86 100644
--- a/builtin/rev-parse.c
+++ b/builtin/rev-parse.c
@@ -195,6 +195,12 @@ static int anti_reference(const char *refname, const unsigned char *sha1, int fl
 	return 0;
 }
 
+static int show_abbrev(const unsigned char *sha1, void *cb_data)
+{
+	show_rev(NORMAL, sha1, NULL);
+	return 0;
+}
+
 static void show_datestring(const char *flag, const char *datestr)
 {
 	static char buffer[100];
@@ -238,7 +244,7 @@ static int try_difference(const char *arg)
 		next = "HEAD";
 	if (dotdot == arg)
 		this = "HEAD";
-	if (!get_sha1(this, sha1) && !get_sha1(next, end)) {
+	if (!get_sha1_committish(this, sha1) && !get_sha1_committish(next, end)) {
 		show_rev(NORMAL, end, next);
 		show_rev(symmetric ? NORMAL : REVERSED, sha1, this);
 		if (symmetric) {
@@ -278,7 +284,7 @@ static int try_parent_shorthands(const char *arg)
 		return 0;
 
 	*dotdot = 0;
-	if (get_sha1(arg, sha1))
+	if (get_sha1_committish(arg, sha1))
 		return 0;
 
 	if (!parents_only)
@@ -589,6 +595,10 @@ int cmd_rev_parse(int argc, const char **argv, const char *prefix)
 				for_each_ref(show_reference, NULL);
 				continue;
 			}
+			if (!prefixcmp(arg, "--disambiguate=")) {
+				for_each_abbrev(arg + 15, show_abbrev, NULL);
+				continue;
+			}
 			if (!strcmp(arg, "--bisect")) {
 				for_each_ref_in("refs/bisect/bad", show_reference, NULL);
 				for_each_ref_in("refs/bisect/good", anti_reference, NULL);
diff --git a/cache.h b/cache.h
index 6a1aff5e2a..2997b918e8 100644
--- a/cache.h
+++ b/cache.h
@@ -790,17 +790,25 @@ struct object_context {
 	unsigned mode;
 };
 
+#define GET_SHA1_QUIETLY        01
+#define GET_SHA1_COMMIT         02
+#define GET_SHA1_COMMITTISH     04
+#define GET_SHA1_TREE          010
+#define GET_SHA1_TREEISH       020
+#define GET_SHA1_BLOB	       040
+#define GET_SHA1_ONLY_TO_DIE 04000
+
 extern int get_sha1(const char *str, unsigned char *sha1);
-extern int get_sha1_with_mode_1(const char *str, unsigned char *sha1, unsigned *mode, int only_to_die, const char *prefix);
-static inline int get_sha1_with_mode(const char *str, unsigned char *sha1, unsigned *mode)
-{
-	return get_sha1_with_mode_1(str, sha1, mode, 0, NULL);
-}
-extern int get_sha1_with_context_1(const char *name, unsigned char *sha1, struct object_context *orc, int only_to_die, const char *prefix);
-static inline int get_sha1_with_context(const char *str, unsigned char *sha1, struct object_context *orc)
-{
-	return get_sha1_with_context_1(str, sha1, orc, 0, NULL);
-}
+extern int get_sha1_commit(const char *str, unsigned char *sha1);
+extern int get_sha1_committish(const char *str, unsigned char *sha1);
+extern int get_sha1_tree(const char *str, unsigned char *sha1);
+extern int get_sha1_treeish(const char *str, unsigned char *sha1);
+extern int get_sha1_blob(const char *str, unsigned char *sha1);
+extern void maybe_die_on_misspelt_object_name(const char *name, const char *prefix);
+extern int get_sha1_with_context(const char *str, unsigned flags, unsigned char *sha1, struct object_context *orc);
+
+typedef int each_abbrev_fn(const unsigned char *sha1, void *);
+extern int for_each_abbrev(const char *prefix, each_abbrev_fn, void *);
 
 /*
  * Try to read a SHA1 in hexadecimal format from the 40 characters
diff --git a/commit.c b/commit.c
index 8248a994a5..42af4c1f23 100644
--- a/commit.c
+++ b/commit.c
@@ -68,7 +68,7 @@ struct commit *lookup_commit_reference_by_name(const char *name)
 	unsigned char sha1[20];
 	struct commit *commit;
 
-	if (get_sha1(name, sha1))
+	if (get_sha1_committish(name, sha1))
 		return NULL;
 	commit = lookup_commit_reference(sha1);
 	if (!commit || parse_commit(commit))
diff --git a/config.c b/config.c
index 40818e872f..2b706ea205 100644
--- a/config.c
+++ b/config.c
@@ -945,12 +945,12 @@ int git_config_early(config_fn_t fn, void *data, const char *repo_config)
 		found += 1;
 	}
 
-	if (!access(xdg_config, R_OK)) {
+	if (xdg_config && !access(xdg_config, R_OK)) {
 		ret += git_config_from_file(fn, xdg_config, data);
 		found += 1;
 	}
 
-	if (!access(user_config, R_OK)) {
+	if (user_config && !access(user_config, R_OK)) {
 		ret += git_config_from_file(fn, user_config, data);
 		found += 1;
 	}
diff --git a/date.c b/date.c
index 1fdcf7c6ea..57331ed406 100644
--- a/date.c
+++ b/date.c
@@ -624,7 +624,7 @@ static int match_object_header_date(const char *date, unsigned long *timestamp,
 	unsigned long stamp;
 	int ofs;
 
-	if (*date < '0' || '9' <= *date)
+	if (*date < '0' || '9' < *date)
 		return -1;
 	stamp = strtoul(date, &end, 10);
 	if (*end != ' ' || stamp == ULONG_MAX || (end[1] != '+' && end[1] != '-'))
diff --git a/git-am.sh b/git-am.sh
index b6a530018e..c02e62d2aa 100755
--- a/git-am.sh
+++ b/git-am.sh
@@ -857,6 +857,11 @@ did you forget to use 'git add'?"
 	if test $apply_status != 0
 	then
 		eval_gettextln 'Patch failed at $msgnum $FIRSTLINE'
+		if test "$(git config --bool advice.amworkdir)" != false
+		then
+			eval_gettextln "The copy of the patch that failed is found in:
+   $dotest/patch"
+		fi
 		stop_here_user_resolve $this
 	fi
 
diff --git a/git-filter-branch.sh b/git-filter-branch.sh
index add2c0247f..178e45305d 100755
--- a/git-filter-branch.sh
+++ b/git-filter-branch.sh
@@ -84,7 +84,7 @@ set_ident () {
 			s/.*/GIT_'$uid'_EMAIL='\''&'\''; export GIT_'$uid'_EMAIL/p
 
 			g
-			s/^'$lid' [^<]* <[^>]*> \(.*\)$/\1/
+			s/^'$lid' [^<]* <[^>]*> \(.*\)$/@\1/
 			s/'\''/'\''\'\'\''/g
 			s/.*/GIT_'$uid'_DATE='\''&'\''; export GIT_'$uid'_DATE/p
 
diff --git a/git-submodule.sh b/git-submodule.sh
index 5629d875e6..dba4d39e1f 100755
--- a/git-submodule.sh
+++ b/git-submodule.sh
@@ -186,8 +186,10 @@ module_clone()
 		die "$(eval_gettext "Clone of '\$url' into submodule path '\$sm_path' failed")"
 	fi
 
-	a=$(cd "$gitdir" && pwd)/
-	b=$(cd "$sm_path" && pwd)/
+	# We already are at the root of the work tree but cd_to_toplevel will
+	# resolve any symlinks that might be present in $PWD
+	a=$(cd_to_toplevel && cd "$gitdir" && pwd)/
+	b=$(cd_to_toplevel && cd "$sm_path" && pwd)/
 	# normalize Windows-style absolute paths to POSIX-style absolute paths
 	case $a in [a-zA-Z]:/*) a=/${a%%:*}${a#*:} ;; esac
 	case $b in [a-zA-Z]:/*) b=/${b%%:*}${b#*:} ;; esac
diff --git a/revision.c b/revision.c
index 5b81a92e3a..9e8f47a25d 100644
--- a/revision.c
+++ b/revision.c
@@ -1000,7 +1000,7 @@ static int add_parents_only(struct rev_info *revs, const char *arg_, int flags)
 		flags ^= UNINTERESTING;
 		arg++;
 	}
-	if (get_sha1(arg, sha1))
+	if (get_sha1_committish(arg, sha1))
 		return 0;
 	while (1) {
 		it = get_reference(revs, arg, sha1, 0);
@@ -1114,16 +1114,16 @@ static void prepare_show_merge(struct rev_info *revs)
 	revs->limited = 1;
 }
 
-int handle_revision_arg(const char *arg_, struct rev_info *revs,
-			int flags,
-			int cant_be_filename)
+int handle_revision_arg(const char *arg_, struct rev_info *revs, int flags, unsigned revarg_opt)
 {
-	unsigned mode;
+	struct object_context oc;
 	char *dotdot;
 	struct object *object;
 	unsigned char sha1[20];
 	int local_flags;
 	const char *arg = arg_;
+	int cant_be_filename = revarg_opt & REVARG_CANNOT_BE_FILENAME;
+	unsigned get_sha1_flags = 0;
 
 	dotdot = strstr(arg, "..");
 	if (dotdot) {
@@ -1141,8 +1141,8 @@ int handle_revision_arg(const char *arg_, struct rev_info *revs,
 			next = "HEAD";
 		if (dotdot == arg)
 			this = "HEAD";
-		if (!get_sha1(this, from_sha1) &&
-		    !get_sha1(next, sha1)) {
+		if (!get_sha1_committish(this, from_sha1) &&
+		    !get_sha1_committish(next, sha1)) {
 			struct commit *a, *b;
 			struct commit_list *exclude;
 
@@ -1201,13 +1201,17 @@ int handle_revision_arg(const char *arg_, struct rev_info *revs,
 		local_flags = UNINTERESTING;
 		arg++;
 	}
-	if (get_sha1_with_mode(arg, sha1, &mode))
+
+	if (revarg_opt & REVARG_COMMITTISH)
+		get_sha1_flags = GET_SHA1_COMMITTISH;
+
+	if (get_sha1_with_context(arg, get_sha1_flags, sha1, &oc))
 		return revs->ignore_missing ? 0 : -1;
 	if (!cant_be_filename)
 		verify_non_filename(revs->prefix, arg);
 	object = get_reference(revs, arg, sha1, flags ^ local_flags);
 	add_rev_cmdline(revs, object, arg_, REV_CMD_REV, flags ^ local_flags);
-	add_pending_object_with_mode(revs, object, arg, mode);
+	add_pending_object_with_mode(revs, object, arg, oc.mode);
 	return 0;
 }
 
@@ -1257,7 +1261,7 @@ static void read_revisions_from_stdin(struct rev_info *revs,
 			}
 			die("options not supported in --stdin mode");
 		}
-		if (handle_revision_arg(sb.buf, revs, 0, 1))
+		if (handle_revision_arg(sb.buf, revs, 0, REVARG_CANNOT_BE_FILENAME))
 			die("bad revision '%s'", sb.buf);
 	}
 	if (seen_dashdash)
@@ -1708,7 +1712,7 @@ static int handle_revision_pseudo_opt(const char *submodule,
  */
 int setup_revisions(int argc, const char **argv, struct rev_info *revs, struct setup_revision_opt *opt)
 {
-	int i, flags, left, seen_dashdash, read_from_stdin, got_rev_arg = 0;
+	int i, flags, left, seen_dashdash, read_from_stdin, got_rev_arg = 0, revarg_opt;
 	struct cmdline_pathspec prune_data;
 	const char *submodule = NULL;
 
@@ -1736,6 +1740,9 @@ int setup_revisions(int argc, const char **argv, struct rev_info *revs, struct s
 
 	/* Second, deal with arguments and options */
 	flags = 0;
+	revarg_opt = opt ? opt->revarg_opt : 0;
+	if (seen_dashdash)
+		revarg_opt |= REVARG_CANNOT_BE_FILENAME;
 	read_from_stdin = 0;
 	for (left = i = 1; i < argc; i++) {
 		const char *arg = argv[i];
@@ -1771,7 +1778,8 @@ int setup_revisions(int argc, const char **argv, struct rev_info *revs, struct s
 			continue;
 		}
 
-		if (handle_revision_arg(arg, revs, flags, seen_dashdash)) {
+
+		if (handle_revision_arg(arg, revs, flags, revarg_opt)) {
 			int j;
 			if (seen_dashdash || *arg == '^')
 				die("bad revision '%s'", arg);
@@ -1822,11 +1830,11 @@ int setup_revisions(int argc, const char **argv, struct rev_info *revs, struct s
 	if (revs->def && !revs->pending.nr && !got_rev_arg) {
 		unsigned char sha1[20];
 		struct object *object;
-		unsigned mode;
-		if (get_sha1_with_mode(revs->def, sha1, &mode))
+		struct object_context oc;
+		if (get_sha1_with_context(revs->def, 0, sha1, &oc))
 			die("bad default revision '%s'", revs->def);
 		object = get_reference(revs, revs->def, sha1, 0);
-		add_pending_object_with_mode(revs, object, revs->def, mode);
+		add_pending_object_with_mode(revs, object, revs->def, oc.mode);
 	}
 
 	/* Did the user ask for any diff output? Run the diff! */
@@ -2361,29 +2369,28 @@ static struct commit *get_revision_internal(struct rev_info *revs)
 	}
 
 	/*
-	 * Now pick up what they want to give us
+	 * If our max_count counter has reached zero, then we are done. We
+	 * don't simply return NULL because we still might need to show
+	 * boundary commits. But we want to avoid calling get_revision_1, which
+	 * might do a considerable amount of work finding the next commit only
+	 * for us to throw it away.
+	 *
+	 * If it is non-zero, then either we don't have a max_count at all
+	 * (-1), or it is still counting, in which case we decrement.
 	 */
-	c = get_revision_1(revs);
-	if (c) {
-		while (0 < revs->skip_count) {
-			revs->skip_count--;
-			c = get_revision_1(revs);
-			if (!c)
-				break;
+	if (revs->max_count) {
+		c = get_revision_1(revs);
+		if (c) {
+			while (0 < revs->skip_count) {
+				revs->skip_count--;
+				c = get_revision_1(revs);
+				if (!c)
+					break;
+			}
 		}
-	}
 
-	/*
-	 * Check the max_count.
-	 */
-	switch (revs->max_count) {
-	case -1:
-		break;
-	case 0:
-		c = NULL;
-		break;
-	default:
-		revs->max_count--;
+		if (revs->max_count > 0)
+			revs->max_count--;
 	}
 
 	if (c)
diff --git a/revision.h b/revision.h
index 863f4f6454..cb5ab3513b 100644
--- a/revision.h
+++ b/revision.h
@@ -184,6 +184,7 @@ struct setup_revision_opt {
 	void (*tweak)(struct rev_info *, struct setup_revision_opt *);
 	const char *submodule;
 	int assume_dashdash;
+	unsigned revarg_opt;
 };
 
 extern void init_revisions(struct rev_info *revs, const char *prefix);
@@ -191,7 +192,9 @@ extern int setup_revisions(int argc, const char **argv, struct rev_info *revs, s
 extern void parse_revision_opt(struct rev_info *revs, struct parse_opt_ctx_t *ctx,
 				 const struct option *options,
 				 const char * const usagestr[]);
-extern int handle_revision_arg(const char *arg, struct rev_info *revs,int flags,int cant_be_filename);
+#define REVARG_CANNOT_BE_FILENAME 01
+#define REVARG_COMMITTISH 02
+extern int handle_revision_arg(const char *arg, struct rev_info *revs, int flags, unsigned revarg_opt);
 
 extern void reset_revision_walk(void);
 extern int prepare_revision_walk(struct rev_info *revs);
diff --git a/setup.c b/setup.c
index e11497720e..9139beefc7 100644
--- a/setup.c
+++ b/setup.c
@@ -77,9 +77,6 @@ static void NORETURN die_verify_filename(const char *prefix,
 					 const char *arg,
 					 int diagnose_misspelt_rev)
 {
-	unsigned char sha1[20];
-	unsigned mode;
-
 	if (!diagnose_misspelt_rev)
 		die("%s: no such path in the working tree.\n"
 		    "Use '-- <path>...' to specify paths that do not exist locally.",
@@ -88,11 +85,10 @@ static void NORETURN die_verify_filename(const char *prefix,
 	 * Saying "'(icase)foo' does not exist in the index" when the
 	 * user gave us ":(icase)foo" is just stupid.  A magic pathspec
 	 * begins with a colon and is followed by a non-alnum; do not
-	 * let get_sha1_with_mode_1(only_to_die=1) to even trigger.
+	 * let maybe_die_on_misspelt_object_name() even trigger.
 	 */
 	if (!(arg[0] == ':' && !isalnum(arg[1])))
-		/* try a detailed diagnostic ... */
-		get_sha1_with_mode_1(arg, sha1, &mode, 1, prefix);
+		maybe_die_on_misspelt_object_name(arg, prefix);
 
 	/* ... or fall back the most general message. */
 	die("ambiguous argument '%s': unknown revision or path not in the working tree.\n"
diff --git a/sha1_name.c b/sha1_name.c
index 5d81ea0564..95003c77ea 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 satisify 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)) {
-					/* uniqu