/*
 * 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 "string-list.h"
#include "run-command.h"
#include "userdiff.h"
#include "grep.h"
#include "quote.h"
#include "dir.h"
#include "pathspec.h"

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

#define GREP_NUM_THREADS_DEFAULT 8
static int num_threads;

#ifndef NO_PTHREADS
static pthread_t *threads;

/* 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 {
	struct grep_source source;
	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;

static inline void grep_lock(void)
{
	if (num_threads)
		pthread_mutex_lock(&grep_mutex);
}

static inline void grep_unlock(void)
{
	if (num_threads)
		pthread_mutex_unlock(&grep_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 int skip_first_line;

static void add_work(struct grep_opt *opt, enum grep_source_type type,
		     const char *name, const char *path, const void *id)
{
	grep_lock();

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

	grep_source_init(&todo[todo_end].source, type, name, path, id);
	if (opt->binary != GREP_BINARY_TEXT)
		grep_source_load_driver(&todo[todo_end].source);
	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 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];
		if (w->out.len) {
			const char *p = w->out.buf;
			size_t len = w->out.len;

			/* Skip the leading hunk mark of the first file. */
			if (skip_first_line) {
				while (len) {
					len--;
					if (*p++ == '\n')
						break;
				}
				skip_first_line = 0;
			}

			write_or_die(1, p, len);
		}
		grep_source_clear(&w->source);
	}

	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;
		hit |= grep_source(opt, &w->source);
		grep_source_clear_data(&w->source);
		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(&grep_read_mutex, NULL);
	pthread_mutex_init(&grep_attr_mutex, NULL);
	pthread_cond_init(&cond_add, NULL);
	pthread_cond_init(&cond_write, NULL);
	pthread_cond_init(&cond_result, NULL);
	grep_use_locks = 1;

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

	threads = xcalloc(num_threads, sizeof(*threads));
	for (i = 0; i < num_threads; i++) {
		int err;
		struct grep_opt *o = grep_opt_dup(opt);
		o->output = strbuf_out;
		o->debug = 0;
		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 < num_threads; i++) {
		void *h;
		pthread_join(threads[i], &h);
		hit |= (int) (intptr_t) h;
	}

	free(threads);

	pthread_mutex_destroy(&grep_mutex);
	pthread_mutex_destroy(&grep_read_mutex);
	pthread_mutex_destroy(&grep_attr_mutex);
	pthread_cond_destroy(&cond_add);
	pthread_cond_destroy(&cond_write);
	pthread_cond_destroy(&cond_result);
	grep_use_locks = 0;

	return hit;
}
#else /* !NO_PTHREADS */

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

static int grep_cmd_config(const char *var, const char *value, void *cb)
{
	int st = grep_config(var, value, cb);
	if (git_color_default_config(var, value, cb) < 0)
		st = -1;

	if (!strcmp(var, "grep.threads")) {
		num_threads = git_config_int(var, value);
		if (num_threads < 0)
			die(_("invalid number of threads specified (%d) for %s"),
			    num_threads, var);
	}

	return st;
}

static void *lock_and_read_sha1_file(const unsigned char *sha1, enum object_type *type, unsigned long *size)
{
	void *data;

	grep_read_lock();
	data = read_sha1_file(sha1, type, size);
	grep_read_unlock();
	return data;
}

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

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

#ifndef NO_PTHREADS
	if (num_threads) {
		add_work(opt, GREP_SOURCE_SHA1, pathbuf.buf, path, sha1);
		strbuf_release(&pathbuf);
		return 0;
	} else
#endif
	{
		struct grep_source gs;
		int hit;

		grep_source_init(&gs, GREP_SOURCE_SHA1, pathbuf.buf, path, sha1);
		strbuf_release(&pathbuf);
		hit = grep_source(opt, &gs);

		grep_source_clear(&gs);
		return hit;
	}
}

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

	if (opt->relative && opt->prefix_length)
		quote_path_relative(filename, opt->prefix, &buf);
	else
		strbuf_addstr(&buf, filename);

#ifndef NO_PTHREADS
	if (num_threads) {
		add_work(opt, GREP_SOURCE_FILE, buf.buf, filename, filename);
		strbuf_release(&buf);
		return 0;
	} else
#endif
	{
		struct grep_source gs;
		int hit;

		grep_source_init(&gs, GREP_SOURCE_FILE, buf.buf, filename, filename);
		strbuf_release(&buf);
		hit = grep_source(opt, &gs);

		grep_source_clear(&gs);
		return hit;
	}
}

static void append_path(struct grep_opt *opt, const void *data, size_t len)
{
	struct string_list *path_list = opt->output_priv;

	if (len == 1 && *(const char *)data == '\0')
		return;
	string_list_append(path_list, xstrndup(data, len));
}

static void run_pager(struct grep_opt *opt, const char *prefix)
{
	struct string_list *path_list = opt->output_priv;
	const char **argv = xmalloc(sizeof(const char *) * (path_list->nr + 1));
	int i, status;

	for (i = 0; i < path_list->nr; i++)
		argv[i] = path_list->items[i].string;
	argv[path_list->nr] = NULL;

	status = run_command_v_opt_cd_env(argv, RUN_USING_SHELL, prefix, NULL);
	if (status)
		exit(status);
	free(argv);
}

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

	for (nr = 0; nr < active_nr; nr++) {
		const struct cache_entry *ce = active_cache[nr];
		if (!S_ISREG(ce->ce_mode) || ce_intent_to_add(ce))
			continue;
		if (!ce_path_match(ce, pathspec, NULL))
			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, ce->name);
		}
		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;
	}
	return hit;
}

static int grep_tree(struct grep_opt *opt, const struct pathspec *pathspec,
		     struct tree_desc *tree, struct strbuf *base, int tn_len,
		     int check_attr)
{
	int hit = 0;
	enum interesting match = entry_not_interesting;
	struct name_entry entry;
	int old_baselen = base->len;

	while (tree_entry(tree, &entry)) {
		int te_len = tree_entry_len(&entry);

		if (match != all_entries_interesting) {
			match = tree_entry_interesting(&entry, base, tn_len, pathspec);
			if (match == all_entries_not_interesting)
				break;
			if (match == entry_not_interesting)
				continue;
		}

		strbuf_add(base, entry.path, te_len);

		if (S_ISREG(entry.mode)) {
			hit |= grep_sha1(opt, entry.sha1, base->buf, tn_len,
					 check_attr ? base->buf + tn_len : NULL);
		}
		else if (S_ISDIR(entry.mode)) {
			enum object_type type;
			struct tree_desc sub;
			void *data;
			unsigned long size;

			data = lock_and_read_sha1_file(entry.sha1, &type, &size);
			if (!data)
				die(_("unable to read tree (%s)"),
				    sha1_to_hex(entry.sha1));

			strbuf_addch(base, '/');
			init_tree_desc(&sub, data, size);
			hit |= grep_tree(opt, pathspec, &sub, base, tn_len,
					 check_attr);
			free(data);
		}
		strbuf_setlen(base, old_baselen);

		if (hit && opt->status_only)
			break;
	}
	return hit;
}

static int grep_object(struct grep_opt *opt, const struct pathspec *pathspec,
		       struct object *obj, const char *name, const char *path)
{
	if (obj->type == OBJ_BLOB)
		return grep_sha1(opt, obj->oid.hash, name, 0, path);
	if (obj->type == OBJ_COMMIT || obj->type == OBJ_TREE) {
		struct tree_desc tree;
		void *data;
		unsigned long size;
		struct strbuf base;
		int hit, len;

		grep_read_lock();
		data = read_object_with_reference(obj->oid.hash, tree_type,
						  &size, NULL);
		grep_read_unlock();

		if (!data)
			die(_("unable to read tree (%s)"), oid_to_hex(&obj->oid));

		len = name ? strlen(name) : 0;
		strbuf_init(&base, PATH_MAX + len + 1);
		if (len) {
			strbuf_add(&base, name, len);
			strbuf_addch(&base, ':');
		}
		init_tree_desc(&tree, data, size);
		hit = grep_tree(opt, pathspec, &tree, &base, base.len,
				obj->type == OBJ_COMMIT);
		strbuf_release(&base);
		free(data);
		return hit;
	}
	die(_("unable to grep from object of type %s"), typename(obj->type));
}

static int grep_objects(struct grep_opt *opt, const struct pathspec *pathspec,
			const struct object_array *list)
{
	unsigned int i;
	int hit = 0;
	const unsigned int nr = list->nr;

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

static int grep_directory(struct grep_opt *opt, const struct pathspec *pathspec,
			  int exc_std)
{
	struct dir_struct dir;
	int i, hit = 0;

	memset(&dir, 0, sizeof(dir));
	if (exc_std)
		setup_standard_excludes(&dir);

	fill_directory(&dir, pathspec);
	for (i = 0; i < dir.nr; i++) {
		if (!dir_path_match(dir.entries[i], pathspec, 0, NULL))
			continue;
		hit |= grep_file(opt, dir.entries[i]->name);
		if (hit && opt->status_only)
			break;
	}
	return hit;
}

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;
	int from_stdin = !strcmp(arg, "-");
	FILE *patterns;
	int lno = 0;
	struct strbuf sb = STRBUF_INIT;

	patterns = from_stdin ? stdin : 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_pat(grep_opt, sb.buf, sb.len, arg, ++lno,
				GREP_PATTERN);
	}
	if (!from_stdin)
		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;
}

int cmd_grep(int argc, const char **argv, const char *prefix)
{
	int hit = 0;
	int cached = 0, untracked = 0, opt_exclude = -1;
	int seen_dashdash = 0;
	int external_grep_allowed__ignored;
	const char *show_in_pager = NULL, *default_pager = "dummy";
	struct grep_opt opt;
	struct object_array list = OBJECT_ARRAY_INIT;
	struct pathspec pathspec;
	struct string_list path_list = STRING_LIST_INIT_NODUP;
	int i;
	int dummy;
	int use_index = 1;
	int pattern_type_arg = GREP_PATTERN_TYPE_UNSPECIFIED;

	struct option options[] = {
		OPT_BOOL(0, "cached", &cached,
			N_("search in index instead of in the work tree")),
		OPT_NEGBIT(0, "no-index", &use_index,
			 N_("find in contents not managed by git"), 1),
		OPT_BOOL(0, "untracked", &untracked,
			N_("search in both tracked and untracked files")),
		OPT_SET_INT(0, "exclude-standard", &opt_exclude,
			    N_("ignore files specified via '.gitignore'"), 1),
		OPT_GROUP(""),
		OPT_BOOL('v', "invert-match", &opt.invert,
			N_("show non-matching lines")),
		OPT_BOOL('i', "ignore-case", &opt.ignore_case,
			N_("case insensitive matching")),
		OPT_BOOL('w', "word-regexp", &opt.word_regexp,
			N_("match patterns only at word boundaries")),
		OPT_SET_INT('a', "text", &opt.binary,
			N_("process binary files as text"), GREP_BINARY_TEXT),
		OPT_SET_INT('I', NULL, &opt.binary,
			N_("don't match patterns in binary files"),
			GREP_BINARY_NOMATCH),
		OPT_BOOL(0, "textconv", &opt.allow_textconv,
			 N_("process binary files with textconv filters")),
		{ OPTION_INTEGER, 0, "max-depth", &opt.max_depth, N_("depth"),
			N_("descend at most <depth> levels"), PARSE_OPT_NONEG,
			NULL, 1 },
		OPT_GROUP(""),
		OPT_SET_INT('E', "extended-regexp", &pattern_type_arg,
			    N_("use extended POSIX regular expressions"),
			    GREP_PATTERN_TYPE_ERE),
		OPT_SET_INT('G', "basic-regexp", &pattern_type_arg,
			    N_("use basic POSIX regular expressions (default)"),
			    GREP_PATTERN_TYPE_BRE),
		OPT_SET_INT('F', "fixed-strings", &pattern_type_arg,
			    N_("interpret patterns as fixed strings"),
			    GREP_PATTERN_TYPE_FIXED),
		OPT_SET_INT('P', "perl-regexp", &pattern_type_arg,
			    N_("use Perl-compatible regular expressions"),
			    GREP_PATTERN_TYPE_PCRE),
		OPT_GROUP(""),
		OPT_BOOL('n', "line-number", &opt.linenum, N_("show line numbers")),
		OPT_NEGBIT('h', NULL, &opt.pathname, N_("don't show filenames"), 1),
		OPT_BIT('H', NULL, &opt.pathname, N_("show filenames"), 1),
		OPT_NEGBIT(0, "full-name", &opt.relative,
			N_("show filenames relative to top directory"), 1),
		OPT_BOOL('l', "files-with-matches", &opt.name_only,
			N_("show only filenames instead of matching lines")),
		OPT_BOOL(0, "name-only", &opt.name_only,
			N_("synonym for --files-with-matches")),
		OPT_BOOL('L', "files-without-match",
			&opt.unmatch_name_only,
			N_("show only the names of files without match")),
		OPT_BOOL('z', "null", &opt.null_following_name,
			N_("print NUL after filenames")),
		OPT_BOOL('c', "count", &opt.count,
			N_("show the number of matches instead of matching lines")),
		OPT__COLOR(&opt.color, N_("highlight matches")),
		OPT_BOOL(0, "break", &opt.file_break,
			N_("print empty line between matches from different files")),
		OPT_BOOL(0, "heading", &opt.heading,
			N_("show filename only once above matches from same file")),
		OPT_GROUP(""),
		OPT_CALLBACK('C', "context", &opt, N_("n"),
			N_("show <n> context lines before and after matches"),
			context_callback),
		OPT_INTEGER('B', "before-context", &opt.pre_context,
			N_("show <n> context lines before matches")),
		OPT_INTEGER('A', "after-context", &opt.post_context,
			N_("show <n> context lines after matches")),
		OPT_INTEGER(0, "threads", &num_threads,
			N_("use <n> worker threads")),
		OPT_NUMBER_CALLBACK(&opt, N_("shortcut for -C NUM"),
			context_callback),
		OPT_BOOL('p', "show-function", &opt.funcname,
			N_("show a line with the function name before matches")),
		OPT_BOOL('W', "function-context", &opt.funcbody,
			N_("show the surrounding function")),
		OPT_GROUP(""),
		OPT_CALLBACK('f', NULL, &opt, N_("file"),
			N_("read patterns from file"), file_callback),
		{ OPTION_CALLBACK, 'e', NULL, &opt, N_("pattern"),
			N_("match <pattern>"), PARSE_OPT_NONEG, pattern_callback },
		{ OPTION_CALLBACK, 0, "and", &opt, NULL,
		  N_("combine patterns specified with -e"),
		  PARSE_OPT_NOARG | PARSE_OPT_NONEG, and_callback },
		OPT_BOOL(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__QUIET(&opt.status_only,
			   N_("indicate hit with exit status without output")),
		OPT_BOOL(0, "all-match", &opt.all_match,
			N_("show only matches from files that match all patterns")),
		{ OPTION_SET_INT, 0, "debug", &opt.debug, NULL,
		  N_("show parse tree for grep expression"),
		  PARSE_OPT_NOARG | PARSE_OPT_HIDDEN, NULL, 1 },
		OPT_GROUP(""),
		{ OPTION_STRING, 'O', "open-files-in-pager", &show_in_pager,
			N_("pager"), N_("show matching files in the pager"),
			PARSE_OPT_OPTARG, NULL, (intptr_t)default_pager },
		OPT_BOOL(0, "ext-grep", &external_grep_allowed__ignored,
			 N_("allow calling of grep(1) (ignored by this build)")),
		OPT_END()
	};

	init_grep_defaults();
	git_config(grep_cmd_config, NULL);
	grep_init(&opt, prefix);

	/*
	 * 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);
	grep_commit_pattern_type(pattern_type_arg, &opt);

	if (use_index && !startup_info->have_repository) {
		int fallback = 0;
		git_config_get_bool("grep.fallbacktonoindex", &fallback);
		if (fallback)
			use_index = 0;
		else
			/* die the same way as if we did it at the beginning */
			setup_git_directory();
	}

	/*
	 * 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 (show_in_pager == default_pager)
		show_in_pager = git_pager(1);
	if (show_in_pager) {
		opt.color = 0;
		opt.name_only = 1;
		opt.null_following_name = 1;
		opt.output_priv = &path_list;
		opt.output = append_path;
		string_list_append(&path_list, show_in_pager);
	}

	if (!opt.pattern_list)
		die(_("no pattern given."));
	if (!opt.fixed && opt.ignore_case)
		opt.regflags |= REG_ICASE;

	compile_grep_patterns(&opt);

	/* Check revs and then paths */
	for (i = 0; i < argc; i++) {
		const char *arg = argv[i];
		unsigned char sha1[20];
		struct object_context oc;
		/* Is it a rev? */
		if (!get_sha1_with_context(arg, 0, sha1, &oc)) {
			struct object *object = parse_object_or_die(sha1, arg);
			if (!seen_dashdash)
				verify_non_filename(prefix, arg);
			add_object_array_with_path(object, arg, &list, oc.mode, oc.path);
			continue;
		}
		if (!strcmp(arg, "--")) {
			i++;
			seen_dashdash = 1;
		}
		break;
	}

#ifndef NO_PTHREADS
	if (list.nr || cached || show_in_pager)
		num_threads = 0;
	else if (num_threads == 0)
		num_threads = GREP_NUM_THREADS_DEFAULT;
	else if (num_threads < 0)
		die(_("invalid number of threads specified (%d)"), num_threads);
#else
	num_threads = 0;
#endif

#ifndef NO_PTHREADS
	if (num_threads) {
		if (!(opt.name_only || opt.unmatch_name_only || opt.count)
		    && (opt.pre_context || opt.post_context ||
			opt.file_break || opt.funcbody))
			skip_first_line = 1;
		start_threads(&opt);
	}
#endif

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

	parse_pathspec(&pathspec, 0,
		       PATHSPEC_PREFER_CWD |
		       (opt.max_depth != -1 ? PATHSPEC_MAXDEPTH_VALID : 0),
		       prefix, argv + i);
	pathspec.max_depth = opt.max_depth;
	pathspec.recursive = 1;

	if (show_in_pager && (cached || list.nr))
		die(_("--open-files-in-pager only works on the worktree"));

	if (show_in_pager && opt.pattern_list && !opt.pattern_list->next) {
		const char *pager = path_list.items[0].string;
		int len = strlen(pager);

		if (len > 4 && is_dir_sep(pager[len - 5]))
			pager += len - 4;

		if (opt.ignore_case && !strcmp("less", pager))
			string_list_append(&path_list, "-I");

		if (!strcmp("less", pager) || !strcmp("vi", pager)) {
			struct strbuf buf = STRBUF_INIT;
			strbuf_addf(&buf, "+/%s%s",
					strcmp("less", pager) ? "" : "*",
					opt.pattern_list->pattern);
			string_list_append(&path_list, buf.buf);
			strbuf_detach(&buf, NULL);
		}
	}

	if (!show_in_pager && !opt.status_only)
		setup_pager();

	if (!use_index && (untracked || cached))
		die(_("--cached or --untracked cannot be used with --no-index."));

	if (!use_index || untracked) {
		int use_exclude = (opt_exclude < 0) ? use_index : !!opt_exclude;
		if (list.nr)
			die(_("--no-index or --untracked cannot be used with revs."));
		hit = grep_directory(&opt, &pathspec, use_exclude);
	} else if (0 <= opt_exclude) {
		die(_("--[no-]exclude-standard cannot be used for tracked contents."));
	} else if (!list.nr) {
		if (!cached)
			setup_work_tree();

		hit = grep_cache(&opt, &pathspec, cached);
	} else {
		if (cached)
			die(_("both --cached and trees are given."));
		hit = grep_objects(&opt, &pathspec, &list);
	}

	if (num_threads)
		hit |= wait_all();
	if (hit && show_in_pager)
		run_pager(&opt, prefix);
	free_grep_patterns(&opt);
	return !hit;
}