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![Taylor Blau](/assets/img/avatar_default.png)
When `show-ref` is combined with the `--heads` or `--tags` options, it
can avoid iterating parts of a repository's references that it doesn't
care about.
But it doesn't take advantage of this potential optimization. When this
command was introduced back in 358ddb62cf
(Add "git show-ref" builtin
command, 2006-09-15), `for_each_ref_in()` did exist. But since most
repositories don't have many (any?) references that aren't branches or
tags already, this makes little difference in practice.
Though for repositories with a large imbalance of branches and tags (or,
more likely in the case of server operators, many hidden references),
this can make quite a difference. Take, for example, a repository with
500,000 "hidden" references (all of the form "refs/__hidden__/N"), and
a single branch:
git commit --allow-empty -m "base" &&
seq 1 500000 | sed 's,\(.*\),create refs/__hidden__/\1 HEAD,' |
git update-ref --stdin &&
git pack-refs --all
Outputting the existence of that single branch currently takes on the
order of ~50ms on my machine. The vast majority of this time is wasted
iterating through references that we know we're going to discard.
Instead, teach `show-ref` that it can iterate just "refs/heads" and/or
"refs/tags" when given `--heads` and/or `--tags`, respectively. A few
small interesting things to note:
- When given either option, we can avoid the general-purpose
for_each_ref() call altogether, since we know that it won't give us
any references that we wouldn't filter out already.
- We can make two separate calls to `for_each_fullref_in()` (and
avoid, say, the more specialized `for_each_fullref_in_prefixes()`,
since we know that the set of references enumerated by each is
disjoint, so we'll never see the same reference appear in both
calls.
- We have to use the "fullref" variant (instead of just
`for_each_branch_ref()` and `for_each_tag_ref()`), since we expect
fully-qualified reference names to appear in `show-ref`'s output.
When either of `heads_only` or `tags_only` is set, we can eliminate the
strcmp() calls in `builtin/show-ref.c::show_ref()` altogether, since we
know that `show_ref()` will never see a non-branch or tag reference.
Unfortunately, we can't use `for_each_fullref_in_prefixes()` to enhance
`show-ref`'s pattern matching, since `show-ref` patterns match on the
_suffix_ (e.g., the pattern "foo" shows "refs/heads/foo",
"refs/tags/foo", and etc, not "foo/*").
Nonetheless, in our synthetic example above, this provides a significant
speed-up ("git" is roughly v2.36, "git.compile" is this patch):
$ hyperfine -N 'git show-ref --heads' 'git.compile show-ref --heads'
Benchmark 1: git show-ref --heads
Time (mean ± σ): 49.9 ms ± 6.2 ms [User: 45.6 ms, System: 4.1 ms]
Range (min … max): 46.1 ms … 73.6 ms 43 runs
Benchmark 2: git.compile show-ref --heads
Time (mean ± σ): 2.8 ms ± 0.4 ms [User: 1.4 ms, System: 1.2 ms]
Range (min … max): 1.3 ms … 5.6 ms 957 runs
Summary
'git.compile show-ref --heads' ran
18.03 ± 3.38 times faster than 'git show-ref --heads'
Signed-off-by: Taylor Blau <me@ttaylorr.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
226 lines
5.6 KiB
C
226 lines
5.6 KiB
C
#include "builtin.h"
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#include "cache.h"
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#include "config.h"
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#include "refs.h"
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#include "object-store.h"
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#include "object.h"
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#include "tag.h"
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#include "string-list.h"
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#include "parse-options.h"
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static const char * const show_ref_usage[] = {
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N_("git show-ref [-q | --quiet] [--verify] [--head] [-d | --dereference] [-s | --hash[=<n>]] [--abbrev[=<n>]] [--tags] [--heads] [--] [<pattern>...]"),
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N_("git show-ref --exclude-existing[=<pattern>]"),
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NULL
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};
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static int deref_tags, show_head, tags_only, heads_only, found_match, verify,
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quiet, hash_only, abbrev, exclude_arg;
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static const char **pattern;
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static const char *exclude_existing_arg;
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static void show_one(const char *refname, const struct object_id *oid)
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{
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const char *hex;
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struct object_id peeled;
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if (!has_object_file(oid))
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die("git show-ref: bad ref %s (%s)", refname,
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oid_to_hex(oid));
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if (quiet)
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return;
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hex = find_unique_abbrev(oid, abbrev);
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if (hash_only)
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printf("%s\n", hex);
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else
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printf("%s %s\n", hex, refname);
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if (!deref_tags)
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return;
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if (!peel_iterated_oid(oid, &peeled)) {
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hex = find_unique_abbrev(&peeled, abbrev);
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printf("%s %s^{}\n", hex, refname);
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}
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}
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static int show_ref(const char *refname, const struct object_id *oid,
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int flag, void *cbdata)
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{
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if (show_head && !strcmp(refname, "HEAD"))
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goto match;
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if (pattern) {
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int reflen = strlen(refname);
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const char **p = pattern, *m;
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while ((m = *p++) != NULL) {
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int len = strlen(m);
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if (len > reflen)
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continue;
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if (memcmp(m, refname + reflen - len, len))
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continue;
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if (len == reflen)
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goto match;
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if (refname[reflen - len - 1] == '/')
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goto match;
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}
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return 0;
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}
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match:
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found_match++;
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show_one(refname, oid);
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return 0;
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}
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static int add_existing(const char *refname, const struct object_id *oid,
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int flag, void *cbdata)
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{
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struct string_list *list = (struct string_list *)cbdata;
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string_list_insert(list, refname);
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return 0;
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}
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/*
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* read "^(?:<anything>\s)?<refname>(?:\^\{\})?$" from the standard input,
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* and
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* (1) strip "^{}" at the end of line if any;
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* (2) ignore if match is provided and does not head-match refname;
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* (3) warn if refname is not a well-formed refname and skip;
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* (4) ignore if refname is a ref that exists in the local repository;
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* (5) otherwise output the line.
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*/
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static int exclude_existing(const char *match)
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{
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static struct string_list existing_refs = STRING_LIST_INIT_DUP;
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char buf[1024];
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int matchlen = match ? strlen(match) : 0;
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for_each_ref(add_existing, &existing_refs);
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while (fgets(buf, sizeof(buf), stdin)) {
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char *ref;
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int len = strlen(buf);
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if (len > 0 && buf[len - 1] == '\n')
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buf[--len] = '\0';
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if (3 <= len && !strcmp(buf + len - 3, "^{}")) {
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len -= 3;
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buf[len] = '\0';
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}
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for (ref = buf + len; buf < ref; ref--)
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if (isspace(ref[-1]))
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break;
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if (match) {
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int reflen = buf + len - ref;
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if (reflen < matchlen)
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continue;
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if (strncmp(ref, match, matchlen))
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continue;
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}
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if (check_refname_format(ref, 0)) {
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warning("ref '%s' ignored", ref);
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continue;
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}
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if (!string_list_has_string(&existing_refs, ref)) {
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printf("%s\n", buf);
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}
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}
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return 0;
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}
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static int hash_callback(const struct option *opt, const char *arg, int unset)
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{
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hash_only = 1;
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/* Use full length SHA1 if no argument */
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if (!arg)
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return 0;
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return parse_opt_abbrev_cb(opt, arg, unset);
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}
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static int exclude_existing_callback(const struct option *opt, const char *arg,
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int unset)
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{
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BUG_ON_OPT_NEG(unset);
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exclude_arg = 1;
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*(const char **)opt->value = arg;
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return 0;
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}
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static const struct option show_ref_options[] = {
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OPT_BOOL(0, "tags", &tags_only, N_("only show tags (can be combined with heads)")),
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OPT_BOOL(0, "heads", &heads_only, N_("only show heads (can be combined with tags)")),
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OPT_BOOL(0, "verify", &verify, N_("stricter reference checking, "
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"requires exact ref path")),
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OPT_HIDDEN_BOOL('h', NULL, &show_head,
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N_("show the HEAD reference, even if it would be filtered out")),
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OPT_BOOL(0, "head", &show_head,
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N_("show the HEAD reference, even if it would be filtered out")),
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OPT_BOOL('d', "dereference", &deref_tags,
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N_("dereference tags into object IDs")),
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OPT_CALLBACK_F('s', "hash", &abbrev, N_("n"),
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N_("only show SHA1 hash using <n> digits"),
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PARSE_OPT_OPTARG, &hash_callback),
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OPT__ABBREV(&abbrev),
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OPT__QUIET(&quiet,
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N_("do not print results to stdout (useful with --verify)")),
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OPT_CALLBACK_F(0, "exclude-existing", &exclude_existing_arg,
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N_("pattern"), N_("show refs from stdin that aren't in local repository"),
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PARSE_OPT_OPTARG | PARSE_OPT_NONEG, exclude_existing_callback),
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OPT_END()
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};
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int cmd_show_ref(int argc, const char **argv, const char *prefix)
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{
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git_config(git_default_config, NULL);
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argc = parse_options(argc, argv, prefix, show_ref_options,
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show_ref_usage, 0);
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if (exclude_arg)
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return exclude_existing(exclude_existing_arg);
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pattern = argv;
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if (!*pattern)
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pattern = NULL;
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if (verify) {
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if (!pattern)
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die("--verify requires a reference");
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while (*pattern) {
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struct object_id oid;
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if ((starts_with(*pattern, "refs/") || !strcmp(*pattern, "HEAD")) &&
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!read_ref(*pattern, &oid)) {
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show_one(*pattern, &oid);
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}
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else if (!quiet)
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die("'%s' - not a valid ref", *pattern);
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else
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return 1;
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pattern++;
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}
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return 0;
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}
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if (show_head)
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head_ref(show_ref, NULL);
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if (heads_only || tags_only) {
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if (heads_only)
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for_each_fullref_in("refs/heads/", show_ref, NULL);
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if (tags_only)
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for_each_fullref_in("refs/tags/", show_ref, NULL);
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} else {
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for_each_ref(show_ref, NULL);
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}
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if (!found_match) {
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if (verify && !quiet)
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die("No match");
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return 1;
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}
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return 0;
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}
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