accept "git grep -- pattern"

[git/kirr.git] / builtin-grep.c

/*
 * Builtin "git grep"
 *
 * Copyright (c) 2006 Junio C Hamano
 */
#include "cache.h"
#include "blob.h"
#include "tree.h"
#include "commit.h"
#include "tag.h"
#include "tree-walk.h"
#include "builtin.h"
#include "parse-options.h"
#include "userdiff.h"
#include "grep.h"
#include "quote.h"

#ifndef NO_PTHREADS
#include "thread-utils.h"
#include <pthread.h>
#endif

static char const * const grep_usage[] = {
        "git grep [options] [-e] <pattern> [<rev>...] [[--] path...]",
        NULL
};

static int use_threads = 1;

#ifndef NO_PTHREADS
#define THREADS 8
static pthread_t threads[THREADS];

static void *load_sha1(const unsigned char *sha1, unsigned long *size,
                       const char *name);
static void *load_file(const char *filename, size_t *sz);

enum work_type {WORK_SHA1, WORK_FILE};

/* We use one producer thread and THREADS consumer
 * threads. The producer adds struct work_items to 'todo' and the
 * consumers pick work items from the same array.
 */
struct work_item
{
        enum work_type type;
        char *name;

        /* if type == WORK_SHA1, then 'identifier' is a SHA1,
         * otherwise type == WORK_FILE, and 'identifier' is a NUL
         * terminated filename.
         */
        void *identifier;
        char done;
        struct strbuf out;
};

/* In the range [todo_done, todo_start) in 'todo' we have work_items
 * that have been or are processed by a consumer thread. We haven't
 * written the result for these to stdout yet.
 *
 * The work_items in [todo_start, todo_end) are waiting to be picked
 * up by a consumer thread.
 *
 * The ranges are modulo TODO_SIZE.
 */
#define TODO_SIZE 128
static struct work_item todo[TODO_SIZE];
static int todo_start;
static int todo_end;
static int todo_done;

/* Has all work items been added? */
static int all_work_added;

/* This lock protects all the variables above. */
static pthread_mutex_t grep_mutex;

/* Used to serialize calls to read_sha1_file. */
static pthread_mutex_t read_sha1_mutex;

#define grep_lock() pthread_mutex_lock(&grep_mutex)
#define grep_unlock() pthread_mutex_unlock(&grep_mutex)
#define read_sha1_lock() pthread_mutex_lock(&read_sha1_mutex)
#define read_sha1_unlock() pthread_mutex_unlock(&read_sha1_mutex)

/* Signalled when a new work_item is added to todo. */
static pthread_cond_t cond_add;

/* Signalled when the result from one work_item is written to
 * stdout.
 */
static pthread_cond_t cond_write;

/* Signalled when we are finished with everything. */
static pthread_cond_t cond_result;

static void add_work(enum work_type type, char *name, void *id)
{
        grep_lock();

        while ((todo_end+1) % ARRAY_SIZE(todo) == todo_done) {
                pthread_cond_wait(&cond_write, &grep_mutex);
        }

        todo[todo_end].type = type;
        todo[todo_end].name = name;
        todo[todo_end].identifier = id;
        todo[todo_end].done = 0;
        strbuf_reset(&todo[todo_end].out);
        todo_end = (todo_end + 1) % ARRAY_SIZE(todo);

        pthread_cond_signal(&cond_add);
        grep_unlock();
}

static struct work_item *get_work(void)
{
        struct work_item *ret;

        grep_lock();
        while (todo_start == todo_end && !all_work_added) {
                pthread_cond_wait(&cond_add, &grep_mutex);
        }

        if (todo_start == todo_end && all_work_added) {
                ret = NULL;
        } else {
                ret = &todo[todo_start];
                todo_start = (todo_start + 1) % ARRAY_SIZE(todo);
        }
        grep_unlock();
        return ret;
}

static void grep_sha1_async(struct grep_opt *opt, char *name,
                            const unsigned char *sha1)
{
        unsigned char *s;
        s = xmalloc(20);
        memcpy(s, sha1, 20);
        add_work(WORK_SHA1, name, s);
}

static void grep_file_async(struct grep_opt *opt, char *name,
                            const char *filename)
{
        add_work(WORK_FILE, name, xstrdup(filename));
}

static void work_done(struct work_item *w)
{
        int old_done;

        grep_lock();
        w->done = 1;
        old_done = todo_done;
        for(; todo[todo_done].done && todo_done != todo_start;
            todo_done = (todo_done+1) % ARRAY_SIZE(todo)) {
                w = &todo[todo_done];
                write_or_die(1, w->out.buf, w->out.len);
                free(w->name);
                free(w->identifier);
        }

        if (old_done != todo_done)
                pthread_cond_signal(&cond_write);

        if (all_work_added && todo_done == todo_end)
                pthread_cond_signal(&cond_result);

        grep_unlock();
}

static void *run(void *arg)
{
        int hit = 0;
        struct grep_opt *opt = arg;

        while (1) {
                struct work_item *w = get_work();
                if (!w)
                        break;

                opt->output_priv = w;
                if (w->type == WORK_SHA1) {
                        unsigned long sz;
                        void* data = load_sha1(w->identifier, &sz, w->name);

                        if (data) {
                                hit |= grep_buffer(opt, w->name, data, sz);
                                free(data);
                        }
                } else if (w->type == WORK_FILE) {
                        size_t sz;
                        void* data = load_file(w->identifier, &sz);
                        if (data) {
                                hit |= grep_buffer(opt, w->name, data, sz);
                                free(data);
                        }
                } else {
                        assert(0);
                }

                work_done(w);
        }
        free_grep_patterns(arg);
        free(arg);

        return (void*) (intptr_t) hit;
}

static void strbuf_out(struct grep_opt *opt, const void *buf, size_t size)
{
        struct work_item *w = opt->output_priv;
        strbuf_add(&w->out, buf, size);
}

static void start_threads(struct grep_opt *opt)
{
        int i;

        pthread_mutex_init(&grep_mutex, NULL);
        pthread_mutex_init(&read_sha1_mutex, NULL);
        pthread_cond_init(&cond_add, NULL);
        pthread_cond_init(&cond_write, NULL);
        pthread_cond_init(&cond_result, NULL);

        for (i = 0; i < ARRAY_SIZE(todo); i++) {
                strbuf_init(&todo[i].out, 0);
        }

        for (i = 0; i < ARRAY_SIZE(threads); i++) {
                int err;
                struct grep_opt *o = grep_opt_dup(opt);
                o->output = strbuf_out;
                compile_grep_patterns(o);
                err = pthread_create(&threads[i], NULL, run, o);

                if (err)
                        die("grep: failed to create thread: %s",
                            strerror(err));
        }
}

static int wait_all(void)
{
        int hit = 0;
        int i;

        grep_lock();
        all_work_added = 1;

        /* Wait until all work is done. */
        while (todo_done != todo_end)
                pthread_cond_wait(&cond_result, &grep_mutex);

        /* Wake up all the consumer threads so they can see that there
         * is no more work to do.
         */
        pthread_cond_broadcast(&cond_add);
        grep_unlock();

        for (i = 0; i < ARRAY_SIZE(threads); i++) {
                void *h;
                pthread_join(threads[i], &h);
                hit |= (int) (intptr_t) h;
        }

        pthread_mutex_destroy(&grep_mutex);
        pthread_mutex_destroy(&read_sha1_mutex);
        pthread_cond_destroy(&cond_add);
        pthread_cond_destroy(&cond_write);
        pthread_cond_destroy(&cond_result);

        return hit;
}
#else /* !NO_PTHREADS */
#define read_sha1_lock()
#define read_sha1_unlock()

static int wait_all(void)
{
        return 0;
}
#endif

static int grep_config(const char *var, const char *value, void *cb)
{
        struct grep_opt *opt = cb;

        switch (userdiff_config(var, value)) {
        case 0: break;
        case -1: return -1;
        default: return 0;
        }

        if (!strcmp(var, "color.grep")) {
                opt->color = git_config_colorbool(var, value, -1);
                return 0;
        }
        if (!strcmp(var, "color.grep.match")) {
                if (!value)
                        return config_error_nonbool(var);
                color_parse(value, var, opt->color_match);
                return 0;
        }
        return git_color_default_config(var, value, cb);
}

/*
 * Return non-zero if max_depth is negative or path has no more then max_depth
 * slashes.
 */
static int accept_subdir(const char *path, int max_depth)
{
        if (max_depth < 0)
                return 1;

        while ((path = strchr(path, '/')) != NULL) {
                max_depth--;
                if (max_depth < 0)
                        return 0;
                path++;
        }
        return 1;
}

/*
 * Return non-zero if name is a subdirectory of match and is not too deep.
 */
static int is_subdir(const char *name, int namelen,
                const char *match, int matchlen, int max_depth)
{
        if (matchlen > namelen || strncmp(name, match, matchlen))
                return 0;

        if (name[matchlen] == '\0') /* exact match */
                return 1;

        if (!matchlen || match[matchlen-1] == '/' || name[matchlen] == '/')
                return accept_subdir(name + matchlen + 1, max_depth);

        return 0;
}

/*
 * git grep pathspecs are somewhat different from diff-tree pathspecs;
 * pathname wildcards are allowed.
 */
static int pathspec_matches(const char **paths, const char *name, int max_depth)
{
        int namelen, i;
        if (!paths || !*paths)
                return accept_subdir(name, max_depth);
        namelen = strlen(name);
        for (i = 0; paths[i]; i++) {
                const char *match = paths[i];
                int matchlen = strlen(match);
                const char *cp, *meta;

                if (is_subdir(name, namelen, match, matchlen, max_depth))
                        return 1;
                if (!fnmatch(match, name, 0))
                        return 1;
                if (name[namelen-1] != '/')
                        continue;

                /* We are being asked if the directory ("name") is worth
                 * descending into.
                 *
                 * Find the longest leading directory name that does
                 * not have metacharacter in the pathspec; the name
                 * we are looking at must overlap with that directory.
                 */
                for (cp = match, meta = NULL; cp - match < matchlen; cp++) {
                        char ch = *cp;
                        if (ch == '*' || ch == '[' || ch == '?') {
                                meta = cp;
                                break;
                        }
                }
                if (!meta)
                        meta = cp; /* fully literal */

                if (namelen <= meta - match) {
                        /* Looking at "Documentation/" and
                         * the pattern says "Documentation/howto/", or
                         * "Documentation/diff*.txt".  The name we
                         * have should match prefix.
                         */
                        if (!memcmp(match, name, namelen))
                                return 1;
                        continue;
                }

                if (meta - match < namelen) {
                        /* Looking at "Documentation/howto/" and
                         * the pattern says "Documentation/h*";
                         * match up to "Do.../h"; this avoids descending
                         * into "Documentation/technical/".
                         */
                        if (!memcmp(match, name, meta - match))
                                return 1;
                        continue;
                }
        }
        return 0;
}

static void *load_sha1(const unsigned char *sha1, unsigned long *size,
                       const char *name)
{
        enum object_type type;
        char *data;

        read_sha1_lock();
        data = read_sha1_file(sha1, &type, size);
        read_sha1_unlock();

        if (!data)
                error("'%s': unable to read %s", name, sha1_to_hex(sha1));

        return data;
}

static int grep_sha1(struct grep_opt *opt, const unsigned char *sha1,
                     const char *filename, int tree_name_len)
{
        struct strbuf pathbuf = STRBUF_INIT;
        char *name;

        if (opt->relative && opt->prefix_length) {
                quote_path_relative(filename + tree_name_len, -1, &pathbuf,
                                    opt->prefix);
                strbuf_insert(&pathbuf, 0, filename, tree_name_len);
        } else {
                strbuf_addstr(&pathbuf, filename);
        }

        name = strbuf_detach(&pathbuf, NULL);

#ifndef NO_PTHREADS
        if (use_threads) {
                grep_sha1_async(opt, name, sha1);
                return 0;
        } else
#endif
        {
                int hit;
                unsigned long sz;
                void *data = load_sha1(sha1, &sz, name);
                if (!data)
                        hit = 0;
                else
                        hit = grep_buffer(opt, name, data, sz);

                free(data);
                free(name);
                return hit;
        }
}

static void *load_file(const char *filename, size_t *sz)
{
        struct stat st;
        char *data;
        int i;

        if (lstat(filename, &st) < 0) {
        err_ret:
                if (errno != ENOENT)
                        error("'%s': %s", filename, strerror(errno));
                return 0;
        }
        if (!S_ISREG(st.st_mode))
                return 0;
        *sz = xsize_t(st.st_size);
        i = open(filename, O_RDONLY);
        if (i < 0)
                goto err_ret;
        data = xmalloc(*sz + 1);
        if (st.st_size != read_in_full(i, data, *sz)) {
                error("'%s': short read %s", filename, strerror(errno));
                close(i);
                free(data);
                return 0;
        }
        close(i);
        data[*sz] = 0;
        return data;
}

static int grep_file(struct grep_opt *opt, const char *filename)
{
        struct strbuf buf = STRBUF_INIT;
        char *name;

        if (opt->relative && opt->prefix_length)
                quote_path_relative(filename, -1, &buf, opt->prefix);
        else
                strbuf_addstr(&buf, filename);
        name = strbuf_detach(&buf, NULL);

#ifndef NO_PTHREADS
        if (use_threads) {
                grep_file_async(opt, name, filename);
                return 0;
        } else
#endif
        {
                int hit;
                size_t sz;
                void *data = load_file(filename, &sz);
                if (!data)
                        hit = 0;
                else
                        hit = grep_buffer(opt, name, data, sz);

                free(data);
                free(name);
                return hit;
        }
}

static int grep_cache(struct grep_opt *opt, const char **paths, int cached)
{
        int hit = 0;
        int nr;
        read_cache();

        for (nr = 0; nr < active_nr; nr++) {
                struct cache_entry *ce = active_cache[nr];
                if (!S_ISREG(ce->ce_mode))
                        continue;
                if (!pathspec_matches(paths, ce->name, opt->max_depth))
                        continue;
                /*
                 * If CE_VALID is on, we assume worktree file and its cache entry
                 * are identical, even if worktree file has been modified, so use
                 * cache version instead
                 */
                if (cached || (ce->ce_flags & CE_VALID) || ce_skip_worktree(ce)) {
                        if (ce_stage(ce))
                                continue;
                        hit |= grep_sha1(opt, ce->sha1, ce->name, 0);
                }
                else
                        hit |= grep_file(opt, ce->name);
                if (ce_stage(ce)) {
                        do {
                                nr++;
                        } while (nr < active_nr &&
                                 !strcmp(ce->name, active_cache[nr]->name));
                        nr--; /* compensate for loop control */
                }
                if (hit && opt->status_only)
                        break;
        }
        free_grep_patterns(opt);
        return hit;
}

static int grep_tree(struct grep_opt *opt, const char **paths,
                     struct tree_desc *tree,
                     const char *tree_name, const char *base)
{
        int len;
        int hit = 0;
        struct name_entry entry;
        char *down;
        int tn_len = strlen(tree_name);
        struct strbuf pathbuf;

        strbuf_init(&pathbuf, PATH_MAX + tn_len);

        if (tn_len) {
                strbuf_add(&pathbuf, tree_name, tn_len);
                strbuf_addch(&pathbuf, ':');
                tn_len = pathbuf.len;
        }
        strbuf_addstr(&pathbuf, base);
        len = pathbuf.len;

        while (tree_entry(tree, &entry)) {
                int te_len = tree_entry_len(entry.path, entry.sha1);
                pathbuf.len = len;
                strbuf_add(&pathbuf, entry.path, te_len);

                if (S_ISDIR(entry.mode))
                        /* Match "abc/" against pathspec to
                         * decide if we want to descend into "abc"
                         * directory.
                         */
                        strbuf_addch(&pathbuf, '/');

                down = pathbuf.buf + tn_len;
                if (!pathspec_matches(paths, down, opt->max_depth))
                        ;
                else if (S_ISREG(entry.mode))
                        hit |= grep_sha1(opt, entry.sha1, pathbuf.buf, tn_len);
                else if (S_ISDIR(entry.mode)) {
                        enum object_type type;
                        struct tree_desc sub;
                        void *data;
                        unsigned long size;

                        read_sha1_lock();
                        data = read_sha1_file(entry.sha1, &type, &size);
                        read_sha1_unlock();

                        if (!data)
                                die("unable to read tree (%s)",
                                    sha1_to_hex(entry.sha1));
                        init_tree_desc(&sub, data, size);
                        hit |= grep_tree(opt, paths, &sub, tree_name, down);
                        free(data);
                }
                if (hit && opt->status_only)
                        break;
        }
        strbuf_release(&pathbuf);
        return hit;
}

static int grep_object(struct grep_opt *opt, const char **paths,
                       struct object *obj, const char *name)
{
        if (obj->type == OBJ_BLOB)
                return grep_sha1(opt, obj->sha1, name, 0);
        if (obj->type == OBJ_COMMIT || obj->type == OBJ_TREE) {
                struct tree_desc tree;
                void *data;
                unsigned long size;
                int hit;
                data = read_object_with_reference(obj->sha1, tree_type,
                                                  &size, NULL);
                if (!data)
                        die("unable to read tree (%s)", sha1_to_hex(obj->sha1));
                init_tree_desc(&tree, data, size);
                hit = grep_tree(opt, paths, &tree, name, "");
                free(data);
                return hit;
        }
        die("unable to grep from object of type %s", typename(obj->type));
}

static int context_callback(const struct option *opt, const char *arg,
                            int unset)
{
        struct grep_opt *grep_opt = opt->value;
        int value;
        const char *endp;

        if (unset) {
                grep_opt->pre_context = grep_opt->post_context = 0;
                return 0;
        }
        value = strtol(arg, (char **)&endp, 10);
        if (*endp) {
                return error("switch `%c' expects a numerical value",
                             opt->short_name);
        }
        grep_opt->pre_context = grep_opt->post_context = value;
        return 0;
}

static int file_callback(const struct option *opt, const char *arg, int unset)
{
        struct grep_opt *grep_opt = opt->value;
        FILE *patterns;
        int lno = 0;
        struct strbuf sb = STRBUF_INIT;

        patterns = fopen(arg, "r");
        if (!patterns)
                die_errno("cannot open '%s'", arg);
        while (strbuf_getline(&sb, patterns, '\n') == 0) {
                /* ignore empty line like grep does */
                if (sb.len == 0)
                        continue;
                append_grep_pattern(grep_opt, strbuf_detach(&sb, NULL), arg,
                                    ++lno, GREP_PATTERN);
        }
        fclose(patterns);
        strbuf_release(&sb);
        return 0;
}

static int not_callback(const struct option *opt, const char *arg, int unset)
{
        struct grep_opt *grep_opt = opt->value;
        append_grep_pattern(grep_opt, "--not", "command line", 0, GREP_NOT);
        return 0;
}

static int and_callback(const struct option *opt, const char *arg, int unset)
{
        struct grep_opt *grep_opt = opt->value;
        append_grep_pattern(grep_opt, "--and", "command line", 0, GREP_AND);
        return 0;
}

static int open_callback(const struct option *opt, const char *arg, int unset)
{
        struct grep_opt *grep_opt = opt->value;
        append_grep_pattern(grep_opt, "(", "command line", 0, GREP_OPEN_PAREN);
        return 0;
}

static int close_callback(const struct option *opt, const char *arg, int unset)
{
        struct grep_opt *grep_opt = opt->value;
        append_grep_pattern(grep_opt, ")", "command line", 0, GREP_CLOSE_PAREN);
        return 0;
}

static int pattern_callback(const struct option *opt, const char *arg,
                            int unset)
{
        struct grep_opt *grep_opt = opt->value;
        append_grep_pattern(grep_opt, arg, "-e option", 0, GREP_PATTERN);
        return 0;
}

static int help_callback(const struct option *opt, const char *arg, int unset)
{
        return -1;
}

int cmd_grep(int argc, const char **argv, const char *prefix)
{
        int hit = 0;
        int cached = 0;
        int seen_dashdash = 0;
        int external_grep_allowed__ignored;
        struct grep_opt opt;
        struct object_array list = { 0, 0, NULL };
        const char **paths = NULL;
        int i;
        int dummy;
        struct option options[] = {
                OPT_BOOLEAN(0, "cached", &cached,
                        "search in index instead of in the work tree"),
                OPT_GROUP(""),
                OPT_BOOLEAN('v', "invert-match", &opt.invert,
                        "show non-matching lines"),
                OPT_BOOLEAN('i', "ignore-case", &opt.ignore_case,
                        "case insensitive matching"),
                OPT_BOOLEAN('w', "word-regexp", &opt.word_regexp,
                        "match patterns only at word boundaries"),
                OPT_SET_INT('a', "text", &opt.binary,
                        "process binary files as text", GREP_BINARY_TEXT),
                OPT_SET_INT('I', NULL, &opt.binary,
                        "don't match patterns in binary files",
                        GREP_BINARY_NOMATCH),
                { OPTION_INTEGER, 0, "max-depth", &opt.max_depth, "depth",
                        "descend at most <depth> levels", PARSE_OPT_NONEG,
                        NULL, 1 },
                OPT_GROUP(""),
                OPT_BIT('E', "extended-regexp", &opt.regflags,
                        "use extended POSIX regular expressions", REG_EXTENDED),
                OPT_NEGBIT('G', "basic-regexp", &opt.regflags,
                        "use basic POSIX regular expressions (default)",
                        REG_EXTENDED),
                OPT_BOOLEAN('F', "fixed-strings", &opt.fixed,
                        "interpret patterns as fixed strings"),
                OPT_GROUP(""),
                OPT_BOOLEAN('n', NULL, &opt.linenum, "show line numbers"),
                OPT_NEGBIT('h', NULL, &opt.pathname, "don't show filenames", 1),
                OPT_BIT('H', NULL, &opt.pathname, "show filenames", 1),
                OPT_NEGBIT(0, "full-name", &opt.relative,
                        "show filenames relative to top directory", 1),
                OPT_BOOLEAN('l', "files-with-matches", &opt.name_only,
                        "show only filenames instead of matching lines"),
                OPT_BOOLEAN(0, "name-only", &opt.name_only,
                        "synonym for --files-with-matches"),
                OPT_BOOLEAN('L', "files-without-match",
                        &opt.unmatch_name_only,
                        "show only the names of files without match"),
                OPT_BOOLEAN('z', "null", &opt.null_following_name,
                        "print NUL after filenames"),
                OPT_BOOLEAN('c', "count", &opt.count,
                        "show the number of matches instead of matching lines"),
                OPT_SET_INT(0, "color", &opt.color, "highlight matches", 1),
                OPT_GROUP(""),
                OPT_CALLBACK('C', NULL, &opt, "n",
                        "show <n> context lines before and after matches",
                        context_callback),
                OPT_INTEGER('B', NULL, &opt.pre_context,
                        "show <n> context lines before matches"),
                OPT_INTEGER('A', NULL, &opt.post_context,
                        "show <n> context lines after matches"),
                OPT_NUMBER_CALLBACK(&opt, "shortcut for -C NUM",
                        context_callback),
                OPT_BOOLEAN('p', "show-function", &opt.funcname,
                        "show a line with the function name before matches"),
                OPT_GROUP(""),
                OPT_CALLBACK('f', NULL, &opt, "file",
                        "read patterns from file", file_callback),
                { OPTION_CALLBACK, 'e', NULL, &opt, "pattern",
                        "match <pattern>", PARSE_OPT_NONEG, pattern_callback },
                { OPTION_CALLBACK, 0, "and", &opt, NULL,
                  "combine patterns specified with -e",
                  PARSE_OPT_NOARG | PARSE_OPT_NONEG, and_callback },
                OPT_BOOLEAN(0, "or", &dummy, ""),
                { OPTION_CALLBACK, 0, "not", &opt, NULL, "",
                  PARSE_OPT_NOARG | PARSE_OPT_NONEG, not_callback },
                { OPTION_CALLBACK, '(', NULL, &opt, NULL, "",
                  PARSE_OPT_NOARG | PARSE_OPT_NONEG | PARSE_OPT_NODASH,
                  open_callback },
                { OPTION_CALLBACK, ')', NULL, &opt, NULL, "",
                  PARSE_OPT_NOARG | PARSE_OPT_NONEG | PARSE_OPT_NODASH,
                  close_callback },
                OPT_BOOLEAN('q', "quiet", &opt.status_only,
                            "indicate hit with exit status without output"),
                OPT_BOOLEAN(0, "all-match", &opt.all_match,
                        "show only matches from files that match all patterns"),
                OPT_GROUP(""),
                OPT_BOOLEAN(0, "ext-grep", &external_grep_allowed__ignored,
                            "allow calling of grep(1) (ignored by this build)"),
                { OPTION_CALLBACK, 0, "help-all", &options, NULL, "show usage",
                  PARSE_OPT_HIDDEN | PARSE_OPT_NOARG, help_callback },
                OPT_END()
        };

        /*
         * 'git grep -h', unlike 'git grep -h <pattern>', is a request
         * to show usage information and exit.
         */
        if (argc == 2 && !strcmp(argv[1], "-h"))
                usage_with_options(grep_usage, options);

        memset(&opt, 0, sizeof(opt));
        opt.prefix = prefix;
        opt.prefix_length = (prefix && *prefix) ? strlen(prefix) : 0;
        opt.relative = 1;
        opt.pathname = 1;
        opt.pattern_tail = &opt.pattern_list;
        opt.regflags = REG_NEWLINE;
        opt.max_depth = -1;

        strcpy(opt.color_match, GIT_COLOR_RED GIT_COLOR_BOLD);
        opt.color = -1;
        git_config(grep_config, &opt);
        if (opt.color == -1)
                opt.color = git_use_color_default;

        /*
         * If there is no -- then the paths must exist in the working
         * tree.  If there is no explicit pattern specified with -e or
         * -f, we take the first unrecognized non option to be the
         * pattern, but then what follows it must be zero or more
         * valid refs up to the -- (if exists), and then existing
         * paths.  If there is an explicit pattern, then the first
         * unrecognized non option is the beginning of the refs list
         * that continues up to the -- (if exists), and then paths.
         */
        argc = parse_options(argc, argv, prefix, options, grep_usage,
                             PARSE_OPT_KEEP_DASHDASH |
                             PARSE_OPT_STOP_AT_NON_OPTION |
                             PARSE_OPT_NO_INTERNAL_HELP);

        /*
         * skip a -- separator; we know it cannot be
         * separating revisions from pathnames if
         * we haven't even had any patterns yet
         */
        if (argc > 0 && !opt.pattern_list && !strcmp(argv[0], "--")) {
                argv++;
                argc--;
        }

        /* First unrecognized non-option token */
        if (argc > 0 && !opt.pattern_list) {
                append_grep_pattern(&opt, argv[0], "command line", 0,
                                    GREP_PATTERN);
                argv++;
                argc--;
        }

        if (!opt.pattern_list)
                die("no pattern given.");
        if (!opt.fixed && opt.ignore_case)
                opt.regflags |= REG_ICASE;
        if ((opt.regflags != REG_NEWLINE) && opt.fixed)
                die("cannot mix --fixed-strings and regexp");

#ifndef NO_PTHREADS
        if (online_cpus() == 1 || !grep_threads_ok(&opt))
                use_threads = 0;

        if (use_threads)
                start_threads(&opt);
#else
        use_threads = 0;
#endif

        compile_grep_patterns(&opt);

        /* Check revs and then paths */
        for (i = 0; i < argc; i++) {
                const char *arg = argv[i];
                unsigned char sha1[20];
                /* Is it a rev? */
                if (!get_sha1(arg, sha1)) {
                        struct object *object = parse_object(sha1);
                        if (!object)
                                die("bad object %s", arg);
                        add_object_array(object, arg, &list);
                        continue;
                }
                if (!strcmp(arg, "--")) {
                        i++;
                        seen_dashdash = 1;
                }
                break;
        }

        /* The rest are paths */
        if (!seen_dashdash) {
                int j;
                for (j = i; j < argc; j++)
                        verify_filename(prefix, argv[j]);
        }

        if (i < argc)
                paths = get_pathspec(prefix, argv + i);
        else if (prefix) {
                paths = xcalloc(2, sizeof(const char *));
                paths[0] = prefix;
                paths[1] = NULL;
        }

        if (!list.nr) {
                int hit;
                if (!cached)
                        setup_work_tree();

                hit = grep_cache(&opt, paths, cached);
                if (use_threads)
                        hit |= wait_all();
                return !hit;
        }

        if (cached)
                die("both --cached and trees are given.");

        for (i = 0; i < list.nr; i++) {
                struct object *real_obj;
                real_obj = deref_tag(list.objects[i].item, NULL, 0);
                if (grep_object(&opt, paths, real_obj, list.objects[i].name)) {
                        hit = 1;
                        if (opt.status_only)
                                break;
                }
        }

        if (use_threads)
                hit |= wait_all();
        free_grep_patterns(&opt);
        return !hit;
}