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diff --git a/builtin/describe.c b/builtin/describe.c
--- /dev/null
+++ b/builtin/describe.c
@@ -0,0 +1,396 @@
+#include "cache.h"
+#include "commit.h"
+#include "tag.h"
+#include "refs.h"
+#include "builtin.h"
+#include "exec_cmd.h"
+#include "parse-options.h"
+#include "diff.h"
+
+#define SEEN (1u<<0)
+#define MAX_TAGS (FLAG_BITS - 1)
+
+static const char * const describe_usage[] = {
+ "git describe [options] <committish>*",
+ "git describe [options] --dirty",
+ NULL
+};
+
+static int debug; /* Display lots of verbose info */
+static int all; /* Any valid ref can be used */
+static int tags; /* Allow lightweight tags */
+static int longformat;
+static int abbrev = DEFAULT_ABBREV;
+static int max_candidates = 10;
+static int found_names;
+static const char *pattern;
+static int always;
+static const char *dirty;
+
+/* diff-index command arguments to check if working tree is dirty. */
+static const char *diff_index_args[] = {
+ "diff-index", "--quiet", "HEAD", "--", NULL
+};
+
+
+struct commit_name {
+ struct tag *tag;
+ int prio; /* annotated tag = 2, tag = 1, head = 0 */
+ unsigned char sha1[20];
+ char path[FLEX_ARRAY]; /* more */
+};
+static const char *prio_names[] = {
+ "head", "lightweight", "annotated",
+};
+
+static void add_to_known_names(const char *path,
+ struct commit *commit,
+ int prio,
+ const unsigned char *sha1)
+{
+ struct commit_name *e = commit->util;
+ if (!e || e->prio < prio) {
+ size_t len = strlen(path)+1;
+ free(e);
+ e = xmalloc(sizeof(struct commit_name) + len);
+ e->tag = NULL;
+ e->prio = prio;
+ hashcpy(e->sha1, sha1);
+ memcpy(e->path, path, len);
+ commit->util = e;
+ }
+ found_names = 1;
+}
+
+static int get_name(const char *path, const unsigned char *sha1, int flag, void *cb_data)
+{
+ int might_be_tag = !prefixcmp(path, "refs/tags/");
+ struct commit *commit;
+ struct object *object;
+ unsigned char peeled[20];
+ int is_tag, prio;
+
+ if (!all && !might_be_tag)
+ return 0;
+
+ if (!peel_ref(path, peeled) && !is_null_sha1(peeled)) {
+ commit = lookup_commit_reference_gently(peeled, 1);
+ if (!commit)
+ return 0;
+ is_tag = !!hashcmp(sha1, commit->object.sha1);
+ } else {
+ commit = lookup_commit_reference_gently(sha1, 1);
+ object = parse_object(sha1);
+ if (!commit || !object)
+ return 0;
+ is_tag = object->type == OBJ_TAG;
+ }
+
+ /* If --all, then any refs are used.
+ * If --tags, then any tags are used.
+ * Otherwise only annotated tags are used.
+ */
+ if (might_be_tag) {
+ if (is_tag)
+ prio = 2;
+ else
+ prio = 1;
+
+ if (pattern && fnmatch(pattern, path + 10, 0))
+ prio = 0;
+ }
+ else
+ prio = 0;
+
+ if (!all) {
+ if (!prio)
+ return 0;
+ }
+ add_to_known_names(all ? path + 5 : path + 10, commit, prio, sha1);
+ return 0;
+}
+
+struct possible_tag {
+ struct commit_name *name;
+ int depth;
+ int found_order;
+ unsigned flag_within;
+};
+
+static int compare_pt(const void *a_, const void *b_)
+{
+ struct possible_tag *a = (struct possible_tag *)a_;
+ struct possible_tag *b = (struct possible_tag *)b_;
+ if (a->depth != b->depth)
+ return a->depth - b->depth;
+ if (a->found_order != b->found_order)
+ return a->found_order - b->found_order;
+ return 0;
+}
+
+static unsigned long finish_depth_computation(
+ struct commit_list **list,
+ struct possible_tag *best)
+{
+ unsigned long seen_commits = 0;
+ while (*list) {
+ struct commit *c = pop_commit(list);
+ struct commit_list *parents = c->parents;
+ seen_commits++;
+ if (c->object.flags & best->flag_within) {
+ struct commit_list *a = *list;
+ while (a) {
+ struct commit *i = a->item;
+ if (!(i->object.flags & best->flag_within))
+ break;
+ a = a->next;
+ }
+ if (!a)
+ break;
+ } else
+ best->depth++;
+ while (parents) {
+ struct commit *p = parents->item;
+ parse_commit(p);
+ if (!(p->object.flags & SEEN))
+ insert_by_date(p, list);
+ p->object.flags |= c->object.flags;
+ parents = parents->next;
+ }
+ }
+ return seen_commits;
+}
+
+static void display_name(struct commit_name *n)
+{
+ if (n->prio == 2 && !n->tag) {
+ n->tag = lookup_tag(n->sha1);
+ if (!n->tag || parse_tag(n->tag) || !n->tag->tag)
+ die("annotated tag %s not available", n->path);
+ if (strcmp(n->tag->tag, all ? n->path + 5 : n->path))
+ warning("tag '%s' is really '%s' here", n->tag->tag, n->path);
+ }
+
+ if (n->tag)
+ printf("%s", n->tag->tag);
+ else
+ printf("%s", n->path);
+}
+
+static void show_suffix(int depth, const unsigned char *sha1)
+{
+ printf("-%d-g%s", depth, find_unique_abbrev(sha1, abbrev));
+}
+
+static void describe(const char *arg, int last_one)
+{
+ unsigned char sha1[20];
+ struct commit *cmit, *gave_up_on = NULL;
+ struct commit_list *list;
+ struct commit_name *n;
+ struct possible_tag all_matches[MAX_TAGS];
+ unsigned int match_cnt = 0, annotated_cnt = 0, cur_match;
+ unsigned long seen_commits = 0;
+ unsigned int unannotated_cnt = 0;
+
+ if (get_sha1(arg, sha1))
+ die("Not a valid object name %s", arg);
+ cmit = lookup_commit_reference(sha1);
+ if (!cmit)
+ die("%s is not a valid '%s' object", arg, commit_type);
+
+ n = cmit->util;
+ if (n && (tags || all || n->prio == 2)) {
+ /*
+ * Exact match to an existing ref.
+ */
+ display_name(n);
+ if (longformat)
+ show_suffix(0, n->tag ? n->tag->tagged->sha1 : sha1);
+ if (dirty)
+ printf("%s", dirty);
+ printf("\n");
+ return;
+ }
+
+ if (!max_candidates)
+ die("no tag exactly matches '%s'", sha1_to_hex(cmit->object.sha1));
+ if (debug)
+ fprintf(stderr, "searching to describe %s\n", arg);
+
+ list = NULL;
+ cmit->object.flags = SEEN;
+ commit_list_insert(cmit, &list);
+ while (list) {
+ struct commit *c = pop_commit(&list);
+ struct commit_list *parents = c->parents;
+ seen_commits++;
+ n = c->util;
+ if (n) {
+ if (!tags && !all && n->prio < 2) {
+ unannotated_cnt++;
+ } else if (match_cnt < max_candidates) {
+ struct possible_tag *t = &all_matches[match_cnt++];
+ t->name = n;
+ t->depth = seen_commits - 1;
+ t->flag_within = 1u << match_cnt;
+ t->found_order = match_cnt;
+ c->object.flags |= t->flag_within;
+ if (n->prio == 2)
+ annotated_cnt++;
+ }
+ else {
+ gave_up_on = c;
+ break;
+ }
+ }
+ for (cur_match = 0; cur_match < match_cnt; cur_match++) {
+ struct possible_tag *t = &all_matches[cur_match];
+ if (!(c->object.flags & t->flag_within))
+ t->depth++;
+ }
+ if (annotated_cnt && !list) {
+ if (debug)
+ fprintf(stderr, "finished search at %s\n",
+ sha1_to_hex(c->object.sha1));
+ break;
+ }
+ while (parents) {
+ struct commit *p = parents->item;
+ parse_commit(p);
+ if (!(p->object.flags & SEEN))
+ insert_by_date(p, &list);
+ p->object.flags |= c->object.flags;
+ parents = parents->next;
+ }
+ }
+
+ if (!match_cnt) {
+ const unsigned char *sha1 = cmit->object.sha1;
+ if (always) {
+ printf("%s", find_unique_abbrev(sha1, abbrev));
+ if (dirty)
+ printf("%s", dirty);
+ printf("\n");
+ return;
+ }
+ if (unannotated_cnt)
+ die("No annotated tags can describe '%s'.\n"
+ "However, there were unannotated tags: try --tags.",
+ sha1_to_hex(sha1));
+ else
+ die("No tags can describe '%s'.\n"
+ "Try --always, or create some tags.",
+ sha1_to_hex(sha1));
+ }
+
+ qsort(all_matches, match_cnt, sizeof(all_matches[0]), compare_pt);
+
+ if (gave_up_on) {
+ insert_by_date(gave_up_on, &list);
+ seen_commits--;
+ }
+ seen_commits += finish_depth_computation(&list, &all_matches[0]);
+ free_commit_list(list);
+
+ if (debug) {
+ for (cur_match = 0; cur_match < match_cnt; cur_match++) {
+ struct possible_tag *t = &all_matches[cur_match];
+ fprintf(stderr, " %-11s %8d %s\n",
+ prio_names[t->name->prio],
+ t->depth, t->name->path);
+ }
+ fprintf(stderr, "traversed %lu commits\n", seen_commits);
+ if (gave_up_on) {
+ fprintf(stderr,
+ "more than %i tags found; listed %i most recent\n"
+ "gave up search at %s\n",
+ max_candidates, max_candidates,
+ sha1_to_hex(gave_up_on->object.sha1));
+ }
+ }
+
+ display_name(all_matches[0].name);
+ if (abbrev)
+ show_suffix(all_matches[0].depth, cmit->object.sha1);
+ if (dirty)
+ printf("%s", dirty);
+ printf("\n");
+
+ if (!last_one)
+ clear_commit_marks(cmit, -1);
+}
+
+int cmd_describe(int argc, const char **argv, const char *prefix)
+{
+ int contains = 0;
+ struct option options[] = {
+ OPT_BOOLEAN(0, "contains", &contains, "find the tag that comes after the commit"),
+ OPT_BOOLEAN(0, "debug", &debug, "debug search strategy on stderr"),
+ OPT_BOOLEAN(0, "all", &all, "use any ref in .git/refs"),
+ OPT_BOOLEAN(0, "tags", &tags, "use any tag in .git/refs/tags"),
+ OPT_BOOLEAN(0, "long", &longformat, "always use long format"),
+ OPT__ABBREV(&abbrev),
+ OPT_SET_INT(0, "exact-match", &max_candidates,
+ "only output exact matches", 0),
+ OPT_INTEGER(0, "candidates", &max_candidates,
+ "consider <n> most recent tags (default: 10)"),
+ OPT_STRING(0, "match", &pattern, "pattern",
+ "only consider tags matching <pattern>"),
+ OPT_BOOLEAN(0, "always", &always,
+ "show abbreviated commit object as fallback"),
+ {OPTION_STRING, 0, "dirty", &dirty, "mark",
+ "append <mark> on dirty working tree (default: \"-dirty\")",
+ PARSE_OPT_OPTARG, NULL, (intptr_t) "-dirty"},
+ OPT_END(),
+ };
+
+ argc = parse_options(argc, argv, prefix, options, describe_usage, 0);
+ if (max_candidates < 0)
+ max_candidates = 0;
+ else if (max_candidates > MAX_TAGS)
+ max_candidates = MAX_TAGS;
+
+ save_commit_buffer = 0;
+
+ if (longformat && abbrev == 0)
+ die("--long is incompatible with --abbrev=0");
+
+ if (contains) {
+ const char **args = xmalloc((7 + argc) * sizeof(char *));
+ int i = 0;
+ args[i++] = "name-rev";
+ args[i++] = "--name-only";
+ args[i++] = "--no-undefined";
+ if (always)
+ args[i++] = "--always";
+ if (!all) {
+ args[i++] = "--tags";
+ if (pattern) {
+ char *s = xmalloc(strlen("--refs=refs/tags/") + strlen(pattern) + 1);
+ sprintf(s, "--refs=refs/tags/%s", pattern);
+ args[i++] = s;
+ }
+ }
+ memcpy(args + i, argv, argc * sizeof(char *));
+ args[i + argc] = NULL;
+ return cmd_name_rev(i + argc, args, prefix);
+ }
+
+ for_each_ref(get_name, NULL);
+ if (!found_names && !always)
+ die("No names found, cannot describe anything.");
+
+ if (argc == 0) {
+ if (dirty && !cmd_diff_index(ARRAY_SIZE(diff_index_args) - 1, diff_index_args, prefix))
+ dirty = NULL;
+ describe("HEAD", 1);
+ } else if (dirty) {
+ die("--dirty is incompatible with committishes");
+ } else {
+ while (argc-- > 0) {
+ describe(*argv++, argc == 0);
+ }
+ }
+ return 0;
+}