sha1_name.c: rename to use dash in file name

This is more consistent with the project style. The majority of Git's
source files use dashes in preference to underscores in their file names.

Signed-off-by: Stefan Beller <sbeller@google.com>

1 files changed, 1734 insertions, 0 deletions

diff --git a/sha1-name.c b/sha1-name.c
new file mode 100644
index 0000000..5b93bf8
--- /dev/null
+++ b/sha1-name.c
@@ -0,0 +1,1734 @@
+#include "cache.h"
+#include "config.h"
+#include "tag.h"
+#include "commit.h"
+#include "tree.h"
+#include "blob.h"
+#include "tree-walk.h"
+#include "refs.h"
+#include "remote.h"
+#include "dir.h"
+#include "sha1-array.h"
+#include "packfile.h"
+#include "object-store.h"
+#include "repository.h"
+
+static int get_oid_oneline(const char *, struct object_id *, struct commit_list *);
+
+typedef int (*disambiguate_hint_fn)(const struct object_id *, void *);
+
+struct disambiguate_state {
+	int len; /* length of prefix in hex chars */
+	char hex_pfx[GIT_MAX_HEXSZ + 1];
+	struct object_id bin_pfx;
+
+	disambiguate_hint_fn fn;
+	void *cb_data;
+	struct object_id candidate;
+	unsigned candidate_exists:1;
+	unsigned candidate_checked:1;
+	unsigned candidate_ok:1;
+	unsigned disambiguate_fn_used:1;
+	unsigned ambiguous:1;
+	unsigned always_call_fn:1;
+};
+
+static void update_candidates(struct disambiguate_state *ds, const struct object_id *current)
+{
+	if (ds->always_call_fn) {
+		ds->ambiguous = ds->fn(current, ds->cb_data) ? 1 : 0;
+		return;
+	}
+	if (!ds->candidate_exists) {
+		/* this is the first candidate */
+		oidcpy(&ds->candidate, current);
+		ds->candidate_exists = 1;
+		return;
+	} else if (!oidcmp(&ds->candidate, current)) {
+		/* the same as what we already have seen */
+		return;
+	}
+
+	if (!ds->fn) {
+		/* cannot disambiguate between ds->candidate and current */
+		ds->ambiguous = 1;
+		return;
+	}
+
+	if (!ds->candidate_checked) {
+		ds->candidate_ok = ds->fn(&ds->candidate, ds->cb_data);
+		ds->disambiguate_fn_used = 1;
+		ds->candidate_checked = 1;
+	}
+
+	if (!ds->candidate_ok) {
+		/* discard the candidate; we know it does not satisfy fn */
+		oidcpy(&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 int append_loose_object(const struct object_id *oid, const char *path,
+			       void *data)
+{
+	oid_array_append(data, oid);
+	return 0;
+}
+
+static int match_sha(unsigned, const unsigned char *, const unsigned char *);
+
+static void find_short_object_filename(struct disambiguate_state *ds)
+{
+	int subdir_nr = ds->bin_pfx.hash[0];
+	struct alternate_object_database *alt;
+	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.
+		 */
+		fakeent = alloc_alt_odb(get_object_directory());
+	}
+	fakeent->next = the_repository->objects->alt_odb_list;
+
+	for (alt = fakeent; alt && !ds->ambiguous; alt = alt->next) {
+		int pos;
+
+		if (!alt->loose_objects_subdir_seen[subdir_nr]) {
+			struct strbuf *buf = alt_scratch_buf(alt);
+			for_each_file_in_obj_subdir(subdir_nr, buf,
+						    append_loose_object,
+						    NULL, NULL,
+						    &alt->loose_objects_cache);
+			alt->loose_objects_subdir_seen[subdir_nr] = 1;
+		}
+
+		pos = oid_array_lookup(&alt->loose_objects_cache, &ds->bin_pfx);
+		if (pos < 0)
+			pos = -1 - pos;
+		while (!ds->ambiguous && pos < alt->loose_objects_cache.nr) {
+			const struct object_id *oid;
+			oid = alt->loose_objects_cache.oid + pos;
+			if (!match_sha(ds->len, ds->bin_pfx.hash, oid->hash))
+				break;
+			update_candidates(ds, oid);
+			pos++;
+		}
+	}
+}
+
+static int match_sha(unsigned len, const unsigned char *a, const unsigned char *b)
+{
+	do {
+		if (*a != *b)
+			return 0;
+		a++;
+		b++;
+		len -= 2;
+	} while (len > 1);
+	if (len)
+		if ((*a ^ *b) & 0xf0)
+			return 0;
+	return 1;
+}
+
+static void unique_in_pack(struct packed_git *p,
+			   struct disambiguate_state *ds)
+{
+	uint32_t num, i, first = 0;
+	const struct object_id *current = NULL;
+
+	if (open_pack_index(p) || !p->num_objects)
+		return;
+
+	num = p->num_objects;
+	bsearch_pack(&ds->bin_pfx, p, &first);
+
+	/*
+	 * At this point, "first" is the location of the lowest object
+	 * with an object name that could match "bin_pfx".  See if we have
+	 * 0, 1 or more objects that actually match(es).
+	 */
+	for (i = first; i < num && !ds->ambiguous; i++) {
+		struct object_id oid;
+		current = nth_packed_object_oid(&oid, p, i);
+		if (!match_sha(ds->len, ds->bin_pfx.hash, current->hash))
+			break;
+		update_candidates(ds, current);
+	}
+}
+
+static void find_short_packed_object(struct disambiguate_state *ds)
+{
+	struct packed_git *p;
+
+	for (p = get_packed_git(the_repository); p && !ds->ambiguous;
+	     p = p->next)
+		unique_in_pack(p, ds);
+}
+
+#define SHORT_NAME_NOT_FOUND (-1)
+#define SHORT_NAME_AMBIGUOUS (-2)
+
+static int finish_object_disambiguation(struct disambiguate_state *ds,
+					struct object_id *oid)
+{
+	if (ds->ambiguous)
+		return SHORT_NAME_AMBIGUOUS;
+
+	if (!ds->candidate_exists)
+		return SHORT_NAME_NOT_FOUND;
+
+	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;
+
+	oidcpy(oid, &ds->candidate);
+	return 0;
+}
+
+static int disambiguate_commit_only(const struct object_id *oid, void *cb_data_unused)
+{
+	int kind = oid_object_info(oid, NULL);
+	return kind == OBJ_COMMIT;
+}
+
+static int disambiguate_committish_only(const struct object_id *oid, void *cb_data_unused)
+{
+	struct object *obj;
+	int kind;
+
+	kind = oid_object_info(oid, NULL);
+	if (kind == OBJ_COMMIT)
+		return 1;
+	if (kind != OBJ_TAG)
+		return 0;
+
+	/* We need to do this the hard way... */
+	obj = deref_tag(parse_object(oid), NULL, 0);
+	if (obj && obj->type == OBJ_COMMIT)
+		return 1;
+	return 0;
+}
+
+static int disambiguate_tree_only(const struct object_id *oid, void *cb_data_unused)
+{
+	int kind = oid_object_info(oid, NULL);
+	return kind == OBJ_TREE;
+}
+
+static int disambiguate_treeish_only(const struct object_id *oid, void *cb_data_unused)
+{
+	struct object *obj;
+	int kind;
+
+	kind = oid_object_info(oid, NULL);
+	if (kind == OBJ_TREE || kind == OBJ_COMMIT)
+		return 1;
+	if (kind != OBJ_TAG)
+		return 0;
+
+	/* We need to do this the hard way... */
+	obj = deref_tag(parse_object(oid), NULL, 0);
+	if (obj && (obj->type == OBJ_TREE || obj->type == OBJ_COMMIT))
+		return 1;
+	return 0;
+}
+
+static int disambiguate_blob_only(const struct object_id *oid, void *cb_data_unused)
+{
+	int kind = oid_object_info(oid, NULL);
+	return kind == OBJ_BLOB;
+}
+
+static disambiguate_hint_fn default_disambiguate_hint;
+
+int set_disambiguate_hint_config(const char *var, const char *value)
+{
+	static const struct {
+		const char *name;
+		disambiguate_hint_fn fn;
+	} hints[] = {
+		{ "none", NULL },
+		{ "commit", disambiguate_commit_only },
+		{ "committish", disambiguate_committish_only },
+		{ "tree", disambiguate_tree_only },
+		{ "treeish", disambiguate_treeish_only },
+		{ "blob", disambiguate_blob_only }
+	};
+	int i;
+
+	if (!value)
+		return config_error_nonbool(var);
+
+	for (i = 0; i < ARRAY_SIZE(hints); i++) {
+		if (!strcasecmp(value, hints[i].name)) {
+			default_disambiguate_hint = hints[i].fn;
+			return 0;
+		}
+	}
+
+	return error("unknown hint type for '%s': %s", var, value);
+}
+
+static int init_object_disambiguation(const char *name, int len,
+				      struct disambiguate_state *ds)
+{
+	int i;
+
+	if (len < MINIMUM_ABBREV || len > GIT_SHA1_HEXSZ)
+		return -1;
+
+	memset(ds, 0, sizeof(*ds));
+
+	for (i = 0; i < len ;i++) {
+		unsigned char c = name[i];
+		unsigned char val;
+		if (c >= '0' && c <= '9')
+			val = c - '0';
+		else if (c >= 'a' && c <= 'f')
+			val = c - 'a' + 10;
+		else if (c >= 'A' && c <='F') {
+			val = c - 'A' + 10;
+			c -= 'A' - 'a';
+		}
+		else
+			return -1;
+		ds->hex_pfx[i] = c;
+		if (!(i & 1))
+			val <<= 4;
+		ds->bin_pfx.hash[i >> 1] |= val;
+	}
+
+	ds->len = len;
+	ds->hex_pfx[len] = '\0';
+	prepare_alt_odb(the_repository);
+	return 0;
+}
+
+static int show_ambiguous_object(const struct object_id *oid, void *data)
+{
+	const struct disambiguate_state *ds = data;
+	struct strbuf desc = STRBUF_INIT;
+	int type;
+
+
+	if (ds->fn && !ds->fn(oid, ds->cb_data))
+		return 0;
+
+	type = oid_object_info(oid, NULL);
+	if (type == OBJ_COMMIT) {
+		struct commit *commit = lookup_commit(oid);
+		if (commit) {
+			struct pretty_print_context pp = {0};
+			pp.date_mode.type = DATE_SHORT;
+			format_commit_message(commit, " %ad - %s", &desc, &pp);
+		}
+	} else if (type == OBJ_TAG) {
+		struct tag *tag = lookup_tag(oid);
+		if (!parse_tag(tag) && tag->tag)
+			strbuf_addf(&desc, " %s", tag->tag);
+	}
+
+	advise("  %s %s%s",
+	       find_unique_abbrev(oid, DEFAULT_ABBREV),
+	       type_name(type) ? type_name(type) : "unknown type",
+	       desc.buf);
+
+	strbuf_release(&desc);
+	return 0;
+}
+
+static int get_short_oid(const char *name, int len, struct object_id *oid,
+			  unsigned flags)
+{
+	int status;
+	struct disambiguate_state ds;
+	int quietly = !!(flags & GET_OID_QUIETLY);
+
+	if (init_object_disambiguation(name, len, &ds) < 0)
+		return -1;
+
+	if (HAS_MULTI_BITS(flags & GET_OID_DISAMBIGUATORS))
+		die("BUG: multiple get_short_oid disambiguator flags");
+
+	if (flags & GET_OID_COMMIT)
+		ds.fn = disambiguate_commit_only;
+	else if (flags & GET_OID_COMMITTISH)
+		ds.fn = disambiguate_committish_only;
+	else if (flags & GET_OID_TREE)
+		ds.fn = disambiguate_tree_only;
+	else if (flags & GET_OID_TREEISH)
+		ds.fn = disambiguate_treeish_only;
+	else if (flags & GET_OID_BLOB)
+		ds.fn = disambiguate_blob_only;
+	else
+		ds.fn = default_disambiguate_hint;
+
+	find_short_object_filename(&ds);
+	find_short_packed_object(&ds);
+	status = finish_object_disambiguation(&ds, oid);
+
+	if (!quietly && (status == SHORT_NAME_AMBIGUOUS)) {
+		error(_("short SHA1 %s is ambiguous"), ds.hex_pfx);
+
+		/*
+		 * We may still have ambiguity if we simply saw a series of
+		 * candidates that did not satisfy our hint function. In
+		 * that case, we still want to show them, so disable the hint
+		 * function entirely.
+		 */
+		if (!ds.ambiguous)
+			ds.fn = NULL;
+
+		advise(_("The candidates are:"));
+		for_each_abbrev(ds.hex_pfx, show_ambiguous_object, &ds);
+	}
+
+	return status;
+}
+
+static int collect_ambiguous(const struct object_id *oid, void *data)
+{
+	oid_array_append(data, oid);
+	return 0;
+}
+
+int for_each_abbrev(const char *prefix, each_abbrev_fn fn, void *cb_data)
+{
+	struct oid_array collect = OID_ARRAY_INIT;
+	struct disambiguate_state ds;
+	int ret;
+
+	if (init_object_disambiguation(prefix, strlen(prefix), &ds) < 0)
+		return -1;
+
+	ds.always_call_fn = 1;
+	ds.fn = collect_ambiguous;
+	ds.cb_data = &collect;
+	find_short_object_filename(&ds);
+	find_short_packed_object(&ds);
+
+	ret = oid_array_for_each_unique(&collect, fn, cb_data);
+	oid_array_clear(&collect);
+	return ret;
+}
+
+/*
+ * Return the slot of the most-significant bit set in "val". There are various
+ * ways to do this quickly with fls() or __builtin_clzl(), but speed is
+ * probably not a big deal here.
+ */
+static unsigned msb(unsigned long val)
+{
+	unsigned r = 0;
+	while (val >>= 1)
+		r++;
+	return r;
+}
+
+struct min_abbrev_data {
+	unsigned int init_len;
+	unsigned int cur_len;
+	char *hex;
+	const struct object_id *oid;
+};
+
+static inline char get_hex_char_from_oid(const struct object_id *oid,
+					 unsigned int pos)
+{
+	static const char hex[] = "0123456789abcdef";
+
+	if ((pos & 1) == 0)
+		return hex[oid->hash[pos >> 1] >> 4];
+	else
+		return hex[oid->hash[pos >> 1] & 0xf];
+}
+
+static int extend_abbrev_len(const struct object_id *oid, void *cb_data)
+{
+	struct min_abbrev_data *mad = cb_data;
+
+	unsigned int i = mad->init_len;
+	while (mad->hex[i] && mad->hex[i] == get_hex_char_from_oid(oid, i))
+		i++;
+
+	if (i < GIT_MAX_RAWSZ && i >= mad->cur_len)
+		mad->cur_len = i + 1;
+
+	return 0;
+}
+
+static void find_abbrev_len_for_pack(struct packed_git *p,
+				     struct min_abbrev_data *mad)
+{
+	int match = 0;
+	uint32_t num, first = 0;
+	struct object_id oid;
+	const struct object_id *mad_oid;
+
+	if (open_pack_index(p) || !p->num_objects)
+		return;
+
+	num = p->num_objects;
+	mad_oid = mad->oid;
+	match = bsearch_pack(mad_oid, p, &first);
+
+	/*
+	 * first is now the position in the packfile where we would insert
+	 * mad->hash if it does not exist (or the position of mad->hash if
+	 * it does exist). Hence, we consider a maximum of two objects
+	 * nearby for the abbreviation length.
+	 */
+	mad->init_len = 0;
+	if (!match) {
+		if (nth_packed_object_oid(&oid, p, first))
+			extend_abbrev_len(&oid, mad);
+	} else if (first < num - 1) {
+		if (nth_packed_object_oid(&oid, p, first + 1))
+			extend_abbrev_len(&oid, mad);
+	}
+	if (first > 0) {
+		if (nth_packed_object_oid(&oid, p, first - 1))
+			extend_abbrev_len(&oid, mad);
+	}
+	mad->init_len = mad->cur_len;
+}
+
+static void find_abbrev_len_packed(struct min_abbrev_data *mad)
+{
+	struct packed_git *p;
+
+	for (p = get_packed_git(the_repository); p; p = p->next)
+		find_abbrev_len_for_pack(p, mad);
+}
+
+int find_unique_abbrev_r(char *hex, const struct object_id *oid, int len)
+{
+	struct disambiguate_state ds;
+	struct min_abbrev_data mad;
+	struct object_id oid_ret;
+	if (len < 0) {
+		unsigned long count = approximate_object_count();
+		/*
+		 * Add one because the MSB only tells us the highest bit set,
+		 * not including the value of all the _other_ bits (so "15"
+		 * is only one off of 2^4, but the MSB is the 3rd bit.
+		 */
+		len = msb(count) + 1;
+		/*
+		 * We now know we have on the order of 2^len objects, which
+		 * expects a collision at 2^(len/2). But we also care about hex
+		 * chars, not bits, and there are 4 bits per hex. So all
+		 * together we need to divide by 2 and round up.
+		 */
+		len = DIV_ROUND_UP(len, 2);
+		/*
+		 * For very small repos, we stick with our regular fallback.
+		 */
+		if (len < FALLBACK_DEFAULT_ABBREV)
+			len = FALLBACK_DEFAULT_ABBREV;
+	}
+
+	oid_to_hex_r(hex, oid);
+	if (len == GIT_SHA1_HEXSZ || !len)
+		return GIT_SHA1_HEXSZ;
+
+	mad.init_len = len;
+	mad.cur_len = len;
+	mad.hex = hex;
+	mad.oid = oid;
+
+	find_abbrev_len_packed(&mad);
+
+	if (init_object_disambiguation(hex, mad.cur_len, &ds) < 0)
+		return -1;
+
+	ds.fn = extend_abbrev_len;
+	ds.always_call_fn = 1;
+	ds.cb_data = (void *)&mad;
+
+	find_short_object_filename(&ds);
+	(void)finish_object_disambiguation(&ds, &oid_ret);
+
+	hex[mad.cur_len] = 0;
+	return mad.cur_len;
+}
+
+const char *find_unique_abbrev(const struct object_id *oid, int len)
+{
+	static int bufno;
+	static char hexbuffer[4][GIT_MAX_HEXSZ + 1];
+	char *hex = hexbuffer[bufno];
+	bufno = (bufno + 1) % ARRAY_SIZE(hexbuffer);
+	find_unique_abbrev_r(hex, oid, len);
+	return hex;
+}
+
+static int ambiguous_path(const char *path, int len)
+{
+	int slash = 1;
+	int cnt;
+
+	for (cnt = 0; cnt < len; cnt++) {
+		switch (*path++) {
+		case '\0':
+			break;
+		case '/':
+			if (slash)
+				break;
+			slash = 1;
+			continue;
+		case '.':
+			continue;
+		default:
+			slash = 0;
+			continue;
+		}
+		break;
+	}
+	return slash;
+}
+
+static inline int at_mark(const char *string, int len,
+			  const char **suffix, int nr)
+{
+	int i;
+
+	for (i = 0; i < nr; i++) {
+		int suffix_len = strlen(suffix[i]);
+		if (suffix_len <= len
+		    && !strncasecmp(string, suffix[i], suffix_len))
+			return suffix_len;
+	}
+	return 0;
+}
+
+static inline int upstream_mark(const char *string, int len)
+{
+	const char *suffix[] = { "@{upstream}", "@{u}" };
+	return at_mark(string, len, suffix, ARRAY_SIZE(suffix));
+}
+
+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_oid_1(const char *name, int len, struct object_id *oid, unsigned lookup_flags);
+static int interpret_nth_prior_checkout(const char *name, int namelen, struct strbuf *buf);
+
+static int get_oid_basic(const char *str, int len, struct object_id *oid,
+			  unsigned int flags)
+{
+	static const char *warn_msg = "refname '%.*s' is ambiguous.";
+	static const char *object_name_msg = N_(
+	"Git normally never creates a ref that ends with 40 hex characters\n"
+	"because it will be ignored when you just specify 40-hex. These refs\n"
+	"may be created by mistake. For example,\n"
+	"\n"
+	"  git checkout -b $br $(git rev-parse ...)\n"
+	"\n"
+	"where \"$br\" is somehow empty and a 40-hex ref is created. Please\n"
+	"examine these refs and maybe delete them. Turn this message off by\n"
+	"running \"git config advice.objectNameWarning false\"");
+	struct object_id tmp_oid;
+	char *real_ref = NULL;
+	int refs_found = 0;
+	int at, reflog_len, nth_prior = 0;
+
+	if (len == GIT_SHA1_HEXSZ && !get_oid_hex(str, oid)) {
+		if (warn_ambiguous_refs && warn_on_object_refname_ambiguity) {
+			refs_found = dwim_ref(str, len, &tmp_oid, &real_ref);
+			if (refs_found > 0) {
+				warning(warn_msg, len, str);
+				if (advice_object_name_warning)
+					fprintf(stderr, "%s\n", _(object_name_msg));
+			}
+			free(real_ref);
+		}
+		return 0;
+	}
+
+	/* basic@{time or number or -number} format to query ref-log */
+	reflog_len = at = 0;
+	if (len && str[len-1] == '}') {
+		for (at = len-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) &&
+				    !push_mark(str + at, len - at)) {
+					reflog_len = (len-1) - (at+2);
+					len = at;
+				}
+				break;
+			}
+		}
+	}
+
+	/* Accept only unambiguous ref paths. */
+	if (len && ambiguous_path(str, len))
+		return -1;
+
+	if (nth_prior) {
+		struct strbuf buf = STRBUF_INIT;
+		int detached;
+
+		if (interpret_nth_prior_checkout(str, len, &buf) > 0) {
+			detached = (buf.len == GIT_SHA1_HEXSZ && !get_oid_hex(buf.buf, oid));
+			strbuf_release(&buf);
+			if (detached)
+				return 0;
+		}
+	}
+
+	if (!len && reflog_len)
+		/* allow "@{...}" to mean the current branch reflog */
+		refs_found = dwim_ref("HEAD", 4, oid, &real_ref);
+	else if (reflog_len)
+		refs_found = dwim_log(str, len, oid, &real_ref);
+	else
+		refs_found = dwim_ref(str, len, oid, &real_ref);
+
+	if (!refs_found)
+		return -1;
+
+	if (warn_ambiguous_refs && !(flags & GET_OID_QUIETLY) &&
+	    (refs_found > 1 ||
+	     !get_short_oid(str, len, &tmp_oid, GET_OID_QUIETLY)))
+		warning(warn_msg, len, str);
+
+	if (reflog_len) {
+		int nth, i;
+		timestamp_t at_time;
+		timestamp_t co_time;
+		int co_tz, co_cnt;
+
+		/* Is it asking for N-th entry, or approxidate? */
+		for (i = nth = 0; 0 <= nth && i < reflog_len; i++) {
+			char ch = str[at+2+i];
+			if ('0' <= ch && ch <= '9')
+				nth = nth * 10 + ch - '0';
+			else
+				nth = -1;
+		}
+		if (100000000 <= nth) {
+			at_time = nth;
+			nth = -1;
+		} else if (0 <= nth)
+			at_time = 0;
+		else {
+			int errors = 0;
+			char *tmp = xstrndup(str + at + 2, reflog_len);
+			at_time = approxidate_careful(tmp, &errors);
+			free(tmp);
+			if (errors) {
+				free(real_ref);
+				return -1;
+			}
+		}
+		if (read_ref_at(real_ref, flags, at_time, nth, oid, NULL,
+				&co_time, &co_tz, &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_OID_QUIETLY)) {
+					warning("Log for '%.*s' only goes "
+						"back to %s.", len, str,
+						show_date(co_time, co_tz, DATE_MODE(RFC2822)));
+				}
+			} else {
+				if (flags & GET_OID_QUIETLY) {
+					exit(128);
+				}
+				die("Log for '%.*s' only has %d entries.",
+				    len, str, co_cnt);
+			}
+		}
+	}
+
+	free(real_ref);
+	return 0;
+}
+
+static int get_parent(const char *name, int len,
+		      struct object_id *result, int idx)
+{
+	struct object_id oid;
+	int ret = get_oid_1(name, len, &oid, GET_OID_COMMITTISH);
+	struct commit *commit;
+	struct commit_list *p;
+
+	if (ret)
+		return ret;
+	commit = lookup_commit_reference(&oid);
+	if (parse_commit(commit))
+		return -1;
+	if (!idx) {
+		oidcpy(result, &commit->object.oid);
+		return 0;
+	}
+	p = commit->parents;
+	while (p) {
+		if (!--idx) {
+			oidcpy(result, &p->item->object.oid);
+			return 0;
+		}
+		p = p->next;
+	}
+	return -1;
+}
+
+static int get_nth_ancestor(const char *name, int len,
+			    struct object_id *result, int generation)
+{
+	struct object_id oid;
+	struct commit *commit;
+	int ret;
+
+	ret = get_oid_1(name, len, &oid, GET_OID_COMMITTISH);
+	if (ret)
+		return ret;
+	commit = lookup_commit_reference(&oid);
+	if (!commit)
+		return -1;
+
+	while (generation--) {
+		if (parse_commit(commit) || !commit->parents)
+			return -1;
+		commit = commit->parents->item;
+	}
+	oidcpy(result, &commit->object.oid);
+	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->oid)))
+			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, type_name(expected_type),
+				      type_name(o->type));
+			return NULL;
+		}
+	}
+}
+
+static int peel_onion(const char *name, int len, struct object_id *oid,
+		      unsigned lookup_flags)
+{
+	struct object_id outer;
+	const char *sp;
+	unsigned int expected_type = 0;
+	struct object *o;
+
+	/*
+	 * "ref^{type}" dereferences ref repeatedly until you cannot
+	 * dereference anymore, or you get an object of given type,
+	 * whichever comes first.  "ref^{}" means just dereference
+	 * tags until you get a non-tag.  "ref^0" is a shorthand for
+	 * "ref^{commit}".  "commit^{tree}" could be used to find the
+	 * top-level tree of the given commit.
+	 */
+	if (len < 4 || name[len-1] != '}')
+		return -1;
+
+	for (sp = name + len - 1; name <= sp; sp--) {
+		int ch = *sp;
+		if (ch == '{' && name < sp && sp[-1] == '^')
+			break;
+	}
+	if (sp <= name)
+		return -1;
+
+	sp++; /* beginning of type name, or closing brace for empty */
+	if (starts_with(sp, "commit}"))
+		expected_type = OBJ_COMMIT;
+	else if (starts_with(sp, "tag}"))
+		expected_type = OBJ_TAG;
+	else if (starts_with(sp, "tree}"))
+		expected_type = OBJ_TREE;
+	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;
+
+	lookup_flags &= ~GET_OID_DISAMBIGUATORS;
+	if (expected_type == OBJ_COMMIT)
+		lookup_flags |= GET_OID_COMMITTISH;
+	else if (expected_type == OBJ_TREE)
+		lookup_flags |= GET_OID_TREEISH;
+
+	if (get_oid_1(name, sp - name - 2, &outer, lookup_flags))
+		return -1;
+
+	o = parse_object(&outer);
+	if (!o)
+		return -1;
+	if (!expected_type) {
+		o = deref_tag(o, name, sp - name - 2);
+		if (!o || (!o->parsed && !parse_object(&o->oid)))
+			return -1;
+		oidcpy(oid, &o->oid);
+		return 0;
+	}
+
+	/*
+	 * 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;
+
+	oidcpy(oid, &o->oid);
+	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;
+
+		prefix = xstrndup(sp + 1, name + len - 1 - (sp + 1));
+		commit_list_insert((struct commit *)o, &list);
+		ret = get_oid_oneline(prefix, oid, list);
+		free(prefix);
+		return ret;
+	}
+	return 0;
+}
+
+static int get_describe_name(const char *name, int len, struct object_id *oid)
+{
+	const char *cp;
+	unsigned flags = GET_OID_QUIETLY | GET_OID_COMMIT;
+
+	for (cp = name + len - 1; name + 2 <= cp; cp--) {
+		char ch = *cp;
+		if (!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_oid(cp, len, oid, flags);
+			}
+		}
+	}
+	return -1;
+}
+
+static int get_oid_1(const char *name, int len, struct object_id *oid, unsigned lookup_flags)
+{
+	int ret, has_suffix;
+	const char *cp;
+
+	/*
+	 * "name~3" is "name^^^", "name~" is "name~1", and "name^" is "name^1".
+	 */
+	has_suffix = 0;
+	for (cp = name + len - 1; name <= cp; cp--) {
+		int ch = *cp;
+		if ('0' <= ch && ch <= '9')
+			continue;
+		if (ch == '~' || ch == '^')
+			has_suffix = ch;
+		break;
+	}
+
+	if (has_suffix) {
+		int num = 0;
+		int len1 = cp - name;
+		cp++;
+		while (cp < name + len)
+			num = num * 10 + *cp++ - '0';
+		if (!num && len1 == len - 1)
+			num = 1;
+		if (has_suffix == '^')
+			return get_parent(name, len1, oid, num);
+		/* else if (has_suffix == '~') -- goes without saying */
+		return get_nth_ancestor(name, len1, oid, num);
+	}
+
+	ret = peel_onion(name, len, oid, lookup_flags);
+	if (!ret)
+		return 0;
+
+	ret = get_oid_basic(name, len, oid, lookup_flags);
+	if (!ret)
+		return 0;
+
+	/* It could be describe output that is "SOMETHING-gXXXX" */
+	ret = get_describe_name(name, len, oid);
+	if (!ret)
+		return 0;
+
+	return get_short_oid(name, len, oid, lookup_flags);
+}
+
+/*
+ * 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 negative-matching, prefix the pattern-part with '!-', like: ':/!-WIP'.
+ *
+ * For a literal '!' character at the beginning of a pattern, you have to repeat
+ * that, like: ':/!!foo'
+ *
+ * For future extension, all other sequences beginning with ':/!' are reserved.
+ */
+
+/* Remember to update object flag allocation in object.h */
+#define ONELINE_SEEN (1u<<20)
+
+static int handle_one_ref(const char *path, const struct object_id *oid,
+			  int flag, void *cb_data)
+{
+	struct commit_list **list = cb_data;
+	struct object *object = parse_object(oid);
+	if (!object)
+		return 0;
+	if (object->type == OBJ_TAG) {
+		object = deref_tag(object, path, strlen(path));
+		if (!object)
+			return 0;
+	}
+	if (object->type != OBJ_COMMIT)
+		return 0;
+	commit_list_insert((struct commit *)object, list);
+	return 0;
+}
+
+static int get_oid_oneline(const char *prefix, struct object_id *oid,
+			    struct commit_list *list)
+{
+	struct commit_list *backup = NULL, *l;
+	int found = 0;
+	int negative = 0;
+	regex_t regex;
+
+	if (prefix[0] == '!') {
+		prefix++;
+
+		if (prefix[0] == '-') {
+			prefix++;
+			negative = 1;
+		} else if (prefix[0] != '!') {
+			return -1;
+		}
+	}
+
+	if (regcomp(&regex, prefix, REG_EXTENDED))
+		return -1;
+
+	for (l = list; l; l = l->next) {
+		l->item->object.flags |= ONELINE_SEEN;
+		commit_list_insert(l->item, &backup);
+	}
+	while (list) {
+		const char *p, *buf;
+		struct commit *commit;
+		int matches;
+
+		commit = pop_most_recent_commit(&list, ONELINE_SEEN);
+		if (!parse_object(&commit->object.oid))
+			continue;
+		buf = get_commit_buffer(commit, NULL);
+		p = strstr(buf, "\n\n");
+		matches = negative ^ (p && !regexec(&regex, p + 2, 0, NULL, 0));
+		unuse_commit_buffer(commit, buf);
+
+		if (matches) {
+			oidcpy(oid, &commit->object.oid);
+			found = 1;
+			break;
+		}
+	}
+	regfree(&regex);
+	free_commit_list(list);
+	for (l = backup; l; l = l->next)
+		clear_commit_marks(l->item, ONELINE_SEEN);
+	free_commit_list(backup);
+	return found ? 0 : -1;
+}
+
+struct grab_nth_branch_switch_cbdata {
+	int remaining;
+	struct strbuf buf;
+};
+
+static int grab_nth_branch_switch(struct object_id *ooid, struct object_id *noid,
+				  const char *email, timestamp_t timestamp, int tz,
+				  const char *message, void *cb_data)
+{
+	struct grab_nth_branch_switch_cbdata *cb = cb_data;
+	const char *match = NULL, *target = NULL;
+	size_t len;
+
+	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_oid_mb(const char *name, struct object_id *oid)
+{
+	struct commit *one, *two;
+	struct commit_list *mbs;
+	struct object_id oid_tmp;
+	const char *dots;
+	int st;
+
+	dots = strstr(name, "...");
+	if (!dots)
+		return get_oid(name, oid);
+	if (dots == name)
+		st = get_oid("HEAD", &oid_tmp);
+	else {
+		struct strbuf sb;
+		strbuf_init(&sb, dots - name);
+		strbuf_add(&sb, name, dots - name);
+		st = get_oid_committish(sb.buf, &oid_tmp);
+		strbuf_release(&sb);
+	}
+	if (st)
+		return st;
+	one = lookup_commit_reference_gently(&oid_tmp, 0);
+	if (!one)
+		return -1;
+
+	if (get_oid_committish(dots[3] ? (dots + 3) : "HEAD", &oid_tmp))
+		return -1;
+	two = lookup_commit_reference_gently(&oid_tmp, 0);
+	if (!two)
+		return -1;
+	mbs = get_merge_bases(one, two);
+	if (!mbs || mbs->next)
+		st = -1;
+	else {
+		st = 0;
+		oidcpy(oid, &mbs->item->object.oid);
+	}
+	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, unsigned allowed)
+{
+	/* we have extra data, which might need further processing */
+	struct strbuf tmp = STRBUF_INIT;
+	int used = buf->len;
+	int ret;
+
+	strbuf_add(buf, name + len, namelen - len);
+	ret = interpret_branch_name(buf->buf, buf->len, &tmp, allowed);
+	/* that data was not interpreted, remove our cruft */
+	if (ret < 0) {
+		strbuf_setlen(buf, used);
+		return len;
+	}
+	strbuf_reset(buf);
+	strbuf_addbuf(buf, &tmp);
+	strbuf_release(&tmp);
+	/* tweak for size of {-N} versus expanded ref name */
+	return ret - used + len;
+}
+
+static void set_shortened_ref(struct strbuf *buf, const char *ref)
+{
+	char *s = shorten_unambiguous_ref(ref, 0);
+	strbuf_reset(buf);
+	strbuf_addstr(buf, s);
+	free(s);
+}
+
+static int branch_interpret_allowed(const char *refname, unsigned allowed)
+{
+	if (!allowed)
+		return 1;
+
+	if ((allowed & INTERPRET_BRANCH_LOCAL) &&
+	    starts_with(refname, "refs/heads/"))
+		return 1;
+	if ((allowed & INTERPRET_BRANCH_REMOTE) &&
+	    starts_with(refname, "refs/remotes/"))
+		return 1;
+
+	return 0;
+}
+
+static int interpret_branch_mark(const char *name, int namelen,
+				 int at, struct strbuf *buf,
+				 int (*get_mark)(const char *, int),
+				 const char *(*get_data)(struct branch *,
+							 struct strbuf *),
+				 unsigned allowed)
+{
+	int len;
+	struct branch *branch;
+	struct strbuf err = STRBUF_INIT;
+	const char *value;
+
+	len = get_mark(name + at, namelen - at);
+	if (!len)
+		return -1;
+
+	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);
+
+	if (!branch_interpret_allowed(value, allowed))
+		return -1;
+
+	set_shortened_ref(buf, value);
+	return len + at;
+}
+
+int interpret_branch_name(const char *name, int namelen, struct strbuf *buf,
+			  unsigned allowed)
+{
+	char *at;
+	const char *start;
+	int len;
+
+	if (!namelen)
+		namelen = strlen(name);
+
+	if (!allowed || (allowed & INTERPRET_BRANCH_LOCAL)) {
+		len = interpret_nth_prior_checkout(name, namelen, buf);
+		if (!len) {
+			return len; /* syntax Ok, not enough switches */
+		} else if (len > 0) {
+			if (len == namelen)
+				return len; /* consumed all */
+			else
+				return reinterpret(name, namelen, len, buf, allowed);
+		}
+	}
+
+	for (start = name;
+	     (at = memchr(start, '@', namelen - (start - name)));
+	     start = at + 1) {
+
+		if (!allowed || (allowed & INTERPRET_BRANCH_HEAD)) {
+			len = interpret_empty_at(name, namelen, at - name, buf);
+			if (len > 0)
+				return reinterpret(name, namelen, len, buf,
+						   allowed);
+		}
+
+		len = interpret_branch_mark(name, namelen, at - name, buf,
+					    upstream_mark, branch_get_upstream,
+					    allowed);
+		if (len > 0)
+			return len;
+
+		len = interpret_branch_mark(name, namelen, at - name, buf,
+					    push_mark, branch_get_push,
+					    allowed);
+		if (len > 0)
+			return len;
+	}
+
+	return -1;
+}
+
+void strbuf_branchname(struct strbuf *sb, const char *name, unsigned allowed)
+{
+	int len = strlen(name);
+	int used = interpret_branch_name(name, len, sb, allowed);
+
+	if (used < 0)
+		used = 0;
+	strbuf_add(sb, name + used, len - used);
+}
+
+int strbuf_check_branch_ref(struct strbuf *sb, const char *name)
+{
+	if (startup_info->have_repository)
+		strbuf_branchname(sb, name, INTERPRET_BRANCH_LOCAL);
+	else
+		strbuf_addstr(sb, name);
+
+	/*
+	 * This splice must be done even if we end up rejecting the
+	 * name; builtin/branch.c::copy_or_rename_branch() still wants
+	 * to see what the name expanded to so that "branch -m" can be
+	 * used as a tool to correct earlier mistakes.
+	 */
+	strbuf_splice(sb, 0, 0, "refs/heads/", 11);
+
+	if (*name == '-' ||
+	    !strcmp(sb->buf, "refs/heads/HEAD"))
+		return -1;
+
+	return check_refname_format(sb->buf, 0);
+}
+
+/*
+ * This is like "get_oid_basic()", except it allows "object ID expressions",
+ * notably "xyz^" for "parent of xyz"
+ */
+int get_oid(const char *name, struct object_id *oid)
+{
+	struct object_context unused;
+	return get_oid_with_context(name, 0, oid, &unused);
+}
+
+
+/*
+ * Many callers know that the user meant to name a commit-ish by
+ * syntactical positions where the object name appears.  Calling this
+ * function allows the machinery to disambiguate shorter-than-unique
+ * abbreviated object names between commit-ish and others.
+ *
+ * Note that this does NOT error out when the named object is not a
+ * commit-ish. It is merely to give a hint to the disambiguation
+ * machinery.
+ */
+int get_oid_committish(const char *name, struct object_id *oid)
+{
+	struct object_context unused;
+	return get_oid_with_context(name, GET_OID_COMMITTISH,
+				    oid, &unused);
+}
+
+int get_oid_treeish(const char *name, struct object_id *oid)
+{
+	struct object_context unused;
+	return get_oid_with_context(name, GET_OID_TREEISH,
+				    oid, &unused);
+}
+
+int get_oid_commit(const char *name, struct object_id *oid)
+{
+	struct object_context unused;
+	return get_oid_with_context(name, GET_OID_COMMIT,
+				    oid, &unused);
+}
+
+int get_oid_tree(const char *name, struct object_id *oid)
+{
+	struct object_context unused;
+	return get_oid_with_context(name, GET_OID_TREE,
+				    oid, &unused);
+}
+
+int get_oid_blob(const char *name, struct object_id *oid)
+{
+	struct object_context unused;
+	return get_oid_with_context(name, GET_OID_BLOB,
+				    oid, &unused);
+}
+
+/* Must be called only when object_name:filename doesn't exist. */
+static void diagnose_invalid_oid_path(const char *prefix,
+				      const char *filename,
+				      const struct object_id *tree_oid,
+				      const char *object_name,
+				      int object_name_len)
+{
+	struct object_id oid;
+	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 (is_missing_file_error(errno)) {
+		char *fullname = xstrfmt("%s%s", prefix, filename);
+
+		if (!get_tree_entry(tree_oid, fullname, &oid, &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);
+	struct strbuf fullname = STRBUF_INIT;
+
+	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? */
+	strbuf_addstr(&fullname, prefix);
+	strbuf_addstr(&fullname, filename);
+	pos = cache_name_pos(fullname.buf, fullname.len);
+	if (pos < 0)
+		pos = -pos - 1;
+	if (pos < active_nr) {
+		ce = active_cache[pos];
+		if (ce_namelen(ce) == fullname.len &&
+		    !memcmp(ce->name, fullname.buf, fullname.len))
+			die("Path '%s' is in the index, but not '%s'.\n"
+			    "Did you mean ':%d:%s' aka ':%d:./%s'?",
+			    fullname.buf, filename,
+			    ce_stage(ce), fullname.buf,
+			    ce_stage(ce), filename);
+	}
+
+	if (file_exists(filename))
+		die("Path '%s' exists on disk, but not in the index.", filename);
+	if (is_missing_file_error(errno))
+		die("Path '%s' does not exist (neither on disk nor in the index).",
+		    filename);
+
+	strbuf_release(&fullname);
+}
+
+
+static char *resolve_relative_path(const char *rel)
+{
+	if (!starts_with(rel, "./") && !starts_with(rel, "../"))
+		return NULL;
+
+	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_oid_with_context_1(const char *name,
+				  unsigned flags,
+				  const char *prefix,
+				  struct object_id *oid,
+				  struct object_context *oc)
+{
+	int ret, bracket_depth;
+	int namelen = strlen(name);
+	const char *cp;
+	int only_to_die = flags & GET_OID_ONLY_TO_DIE;
+
+	if (only_to_die)
+		flags |= GET_OID_QUIETLY;
+
+	memset(oc, 0, sizeof(*oc));
+	oc->mode = S_IFINVALID;
+	strbuf_init(&oc->symlink_path, 0);
+	ret = get_oid_1(name, namelen, oid, flags);
+	if (!ret)
+		return ret;
+	/*
+	 * sha1:path --> object name of path in ent sha1
+	 * :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;
+		const struct cache_entry *ce;
+		char *new_path = NULL;
+		int pos;
+		if (!only_to_die && namelen > 2 && name[1] == '/') {
+			struct commit_list *list = NULL;
+
+			for_each_ref(handle_one_ref, &list);
+			commit_list_sort_by_date(&list);
+			return get_oid_oneline(name + 2, oid, list);
+		}
+		if (namelen < 3 ||
+		    name[2] != ':' ||
+		    name[1] < '0' || '3' < name[1])
+			cp = name + 1;
+		else {
+			stage = name[1] - '0';
+			cp = name + 3;
+		}
+		new_path = resolve_relative_path(cp);
+		if (!new_path) {
+			namelen = namelen - (cp - name);
+		} else {
+			cp = new_path;
+			namelen = strlen(cp);
+		}
+
+		if (flags & GET_OID_RECORD_PATH)
+			oc->path = xstrdup(cp);
+
+		if (!active_cache)
+			read_cache();
+		pos = cache_name_pos(cp, namelen);
+		if (pos < 0)
+			pos = -pos - 1;
+		while (pos < active_nr) {
+			ce = active_cache[pos];
+			if (ce_namelen(ce) != namelen ||
+			    memcmp(ce->name, cp, namelen))
+				break;
+			if (ce_stage(ce) == stage) {
+				oidcpy(oid, &ce->oid);
+				oc->mode = ce->ce_mode;
+				free(new_path);
+				return 0;
+			}
+			pos++;
+		}
+		if (only_to_die && name[1] && name[1] != '/')
+			diagnose_invalid_index_path(stage, prefix, cp);
+		free(new_path);
+		return -1;
+	}
+	for (cp = name, bracket_depth = 0; *cp; cp++) {
+		if (*cp == '{')
+			bracket_depth++;
+		else if (bracket_depth && *cp == '}')
+			bracket_depth--;
+		else if (!bracket_depth && *cp == ':')
+			break;
+	}
+	if (*cp == ':') {
+		struct object_id tree_oid;
+		int len = cp - name;
+		unsigned sub_flags = flags;
+
+		sub_flags &= ~GET_OID_DISAMBIGUATORS;
+		sub_flags |= GET_OID_TREEISH;
+
+		if (!get_oid_1(name, len, &tree_oid, sub_flags)) {
+			const char *filename = cp+1;
+			char *new_filename = NULL;
+
+			new_filename = resolve_relative_path(filename);
+			if (new_filename)
+				filename = new_filename;
+			if (flags & GET_OID_FOLLOW_SYMLINKS) {
+				ret = get_tree_entry_follow_symlinks(tree_oid.hash,
+					filename, oid->hash, &oc->symlink_path,
+					&oc->mode);
+			} else {
+				ret = get_tree_entry(&tree_oid, filename, oid,
+						     &oc->mode);
+				if (ret && only_to_die) {
+					diagnose_invalid_oid_path(prefix,
+								   filename,
+								   &tree_oid,
+								   name, len);
+				}
+			}
+			hashcpy(oc->tree, tree_oid.hash);
+			if (flags & GET_OID_RECORD_PATH)
+				oc->path = xstrdup(filename);
+
+			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;
+	struct object_id oid;
+	get_oid_with_context_1(name, GET_OID_ONLY_TO_DIE, prefix, &oid, &oc);
+}
+
+int get_oid_with_context(const char *str, unsigned flags, struct object_id *oid, struct object_context *oc)
+{
+	if (flags & GET_OID_FOLLOW_SYMLINKS && flags & GET_OID_ONLY_TO_DIE)
+		die("BUG: incompatible flags for get_sha1_with_context");
+	return get_oid_with_context_1(str, flags, NULL, oid, oc);
+}