/*
 * 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_EXTERNAL_GREP
#ifdef __unix__
#define NO_EXTERNAL_GREP 0
#else
#define NO_EXTERNAL_GREP 1
#endif
#endif

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

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.external"))
		return git_config_string(&(opt->color_external), var, value);
	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 int grep_sha1(struct grep_opt *opt, const unsigned char *sha1, const char *name, int tree_name_len)
{
	unsigned long size;
	char *data;
	enum object_type type;
	int hit;
	struct strbuf pathbuf = STRBUF_INIT;

	data = read_sha1_file(sha1, &type, &size);
	if (!data) {
		error("'%s': unable to read %s", name, sha1_to_hex(sha1));
		return 0;
	}
	if (opt->relative && opt->prefix_length) {
		quote_path_relative(name + tree_name_len, -1, &pathbuf, opt->prefix);
		strbuf_insert(&pathbuf, 0, name, tree_name_len);
		name = pathbuf.buf;
	}
	hit = grep_buffer(opt, name, data, size);
	strbuf_release(&pathbuf);
	free(data);
	return hit;
}

static int grep_file(struct grep_opt *opt, const char *filename)
{
	struct stat st;
	int i;
	char *data;
	size_t sz;
	struct strbuf buf = STRBUF_INIT;

	if (lstat(filename, &st) < 0) {
	err_ret:
		if (errno != ENOENT)
			error("'%s': %s", filename, strerror(errno));
		return 0;
	}
	if (!st.st_size)
		return 0; /* empty file -- no grep hit */
	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);
	if (opt->relative && opt->prefix_length)
		filename = quote_path_relative(filename, -1, &buf, opt->prefix);
	i = grep_buffer(opt, filename, data, sz);
	strbuf_release(&buf);
	free(data);
	return i;
}

#if !NO_EXTERNAL_GREP
static int exec_grep(int argc, const char **argv)
{
	pid_t pid;
	int status;

	argv[argc] = NULL;
	pid = fork();
	if (pid < 0)
		return pid;
	if (!pid) {
		execvp("grep", (char **) argv);
		exit(255);
	}
	while (waitpid(pid, &status, 0) < 0) {
		if (errno == EINTR)
			continue;
		return -1;
	}
	if (WIFEXITED(status)) {
		if (!WEXITSTATUS(status))
			return 1;
		return 0;
	}
	return -1;
}

#define MAXARGS 1000
#define ARGBUF 4096
#define push_arg(a) do { \
	if (nr < MAXARGS) argv[nr++] = (a); \
	else die("maximum number of args exceeded"); \
	} while (0)

/*
 * If you send a singleton filename to grep, it does not give
 * the name of the file.  GNU grep has "-H" but we would want
 * that behaviour in a portable way.
 *
 * So we keep two pathnames in argv buffer unsent to grep in
 * the main loop if we need to do more than one grep.
 */
static int flush_grep(struct grep_opt *opt,
		      int argc, int arg0, const char **argv, int *kept)
{
	int status;
	int count = argc - arg0;
	const char *kept_0 = NULL;

	if (count <= 2) {
		/*
		 * Because we keep at least 2 paths in the call from
		 * the main loop (i.e. kept != NULL), and MAXARGS is
		 * far greater than 2, this usually is a call to
		 * conclude the grep.  However, the user could attempt
		 * to overflow the argv buffer by giving too many
		 * options to leave very small number of real
		 * arguments even for the call in the main loop.
		 */
		if (kept)
			die("insanely many options to grep");

		/*
		 * If we have two or more paths, we do not have to do
		 * anything special, but we need to push /dev/null to
		 * get "-H" behaviour of GNU grep portably but when we
		 * are not doing "-l" nor "-L" nor "-c".
		 */
		if (count == 1 &&
		    !opt->name_only &&
		    !opt->unmatch_name_only &&
		    !opt->count) {
			argv[argc++] = "/dev/null";
			argv[argc] = NULL;
		}
	}

	else if (kept) {
		/*
		 * Called because we found many paths and haven't finished
		 * iterating over the cache yet.  We keep two paths
		 * for the concluding call.  argv[argc-2] and argv[argc-1]
		 * has the last two paths, so save the first one away,
		 * replace it with NULL while sending the list to grep,
		 * and recover them after we are done.
		 */
		*kept = 2;
		kept_0 = argv[argc-2];
		argv[argc-2] = NULL;
		argc -= 2;
	}

	if (opt->pre_context || opt->post_context) {
		/*
		 * grep handles hunk marks between files, but we need to
		 * do that ourselves between multiple calls.
		 */
		if (opt->show_hunk_mark)
			write_or_die(1, "--\n", 3);
		else
			opt->show_hunk_mark = 1;
	}

	status = exec_grep(argc, argv);

	if (kept_0) {
		/*
		 * Then recover them.  Now the last arg is beyond the
		 * terminating NULL which is at argc, and the second
		 * from the last is what we saved away in kept_0
		 */
		argv[arg0++] = kept_0;
		argv[arg0] = argv[argc+1];
	}
	return status;
}

static void grep_add_color(struct strbuf *sb, const char *escape_seq)
{
	size_t orig_len = sb->len;

	while (*escape_seq) {
		if (*escape_seq == 'm')
			strbuf_addch(sb, ';');
		else if (*escape_seq != '\033' && *escape_seq  != '[')
			strbuf_addch(sb, *escape_seq);
		escape_seq++;
	}
	if (sb->len > orig_len && sb->buf[sb->len - 1] == ';')
		strbuf_setlen(sb, sb->len - 1);
}

static int external_grep(struct grep_opt *opt, const char **paths, int cached)
{
	int i, nr, argc, hit, len, status;
	const char *argv[MAXARGS+1];
	char randarg[ARGBUF];
	char *argptr = randarg;
	struct grep_pat *p;

	if (opt->extended || (opt->relative && opt->prefix_length))
		return -1;
	len = nr = 0;
	push_arg("grep");
	if (opt->fixed)
		push_arg("-F");
	if (opt->linenum)
		push_arg("-n");
	if (!opt->pathname)
		push_arg("-h");
	if (opt->regflags & REG_EXTENDED)
		push_arg("-E");
	if (opt->regflags & REG_ICASE)
		push_arg("-i");
	if (opt->binary == GREP_BINARY_NOMATCH)
		push_arg("-I");
	if (opt->word_regexp)
		push_arg("-w");
	if (opt->name_only)
		push_arg("-l");
	if (opt->unmatch_name_only)
		push_arg("-L");
	if (opt->null_following_name)
		/* in GNU grep git's "-z" translates to "-Z" */
		push_arg("-Z");
	if (opt->count)
		push_arg("-c");
	if (opt->post_context || opt->pre_context) {
		if (opt->post_context != opt->pre_context) {
			if (opt->pre_context) {
				push_arg("-B");
				len += snprintf(argptr, sizeof(randarg)-len,
						"%u", opt->pre_context) + 1;
				if (sizeof(randarg) <= len)
					die("maximum length of args exceeded");
				push_arg(argptr);
				argptr += len;
			}
			if (opt->post_context) {
				push_arg("-A");
				len += snprintf(argptr, sizeof(randarg)-len,
						"%u", opt->post_context) + 1;
				if (sizeof(randarg) <= len)
					die("maximum length of args exceeded");
				push_arg(argptr);
				argptr += len;
			}
		}
		else {
			push_arg("-C");
			len += snprintf(argptr, sizeof(randarg)-len,
					"%u", opt->post_context) + 1;
			if (sizeof(randarg) <= len)
				die("maximum length of args exceeded");
			push_arg(argptr);
			argptr += len;
		}
	}
	for (p = opt->pattern_list; p; p = p->next) {
		push_arg("-e");
		push_arg(p->pattern);
	}
	if (opt->color) {
		struct strbuf sb = STRBUF_INIT;

		grep_add_color(&sb, opt->color_match);
		setenv("GREP_COLOR", sb.buf, 1);

		strbuf_reset(&sb);
		strbuf_addstr(&sb, "mt=");
		grep_add_color(&sb, opt->color_match);
		strbuf_addstr(&sb, ":sl=:cx=:fn=:ln=:bn=:se=");
		setenv("GREP_COLORS", sb.buf, 1);

		strbuf_release(&sb);

		if (opt->color_external && strlen(opt->color_external) > 0)
			push_arg(opt->color_external);
	}

	hit = 0;
	argc = nr;
	for (i = 0; i < active_nr; i++) {
		struct cache_entry *ce = active_cache[i];
		char *name;
		int kept;
		if (!S_ISREG(ce->ce_mode))
			continue;
		if (!pathspec_matches(paths, ce->name, opt->max_depth))
			continue;
		name = ce->name;
		if (name[0] == '-') {
			int len = ce_namelen(ce);
			name = xmalloc(len + 3);
			memcpy(name, "./", 2);
			memcpy(name + 2, ce->name, len + 1);
		}
		argv[argc++] = name;
		if (MAXARGS <= argc) {
			status = flush_grep(opt, argc, nr, argv, &kept);
			if (0 < status)
				hit = 1;
			argc = nr + kept;
		}
		if (ce_stage(ce)) {
			do {
				i++;
			} while (i < active_nr &&
				 !strcmp(ce->name, active_cache[i]->name));
			i--; /* compensate for loop control */
		}
	}
	if (argc > nr) {
		status = flush_grep(opt, argc, nr, argv, NULL);
		if (0 < status)
			hit = 1;
	}
	return hit;
}
#endif

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

#if !NO_EXTERNAL_GREP
	/*
	 * Use the external "grep" command for the case where
	 * we grep through the checked-out files. It tends to
	 * be a lot more optimized
	 */
	if (!cached && external_grep_allowed) {
		hit = external_grep(opt, paths, cached);
		if (hit >= 0)
			return hit;
		hit = 0;
	}
#endif

	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)) {
			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 */
		}
	}
	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;

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

	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 external_grep_allowed = 1;
	int seen_dashdash = 0;
	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_BIT('i', "ignore-case", &opt.regflags,
			"case insensitive matching", REG_ICASE),
		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(0, "all-match", &opt.all_match,
			"show only matches from files that match all patterns"),
		OPT_GROUP(""),
#if NO_EXTERNAL_GREP
		OPT_BOOLEAN(0, "ext-grep", &external_grep_allowed,
			"allow calling of grep(1) (ignored by this build)"),
#else
		OPT_BOOLEAN(0, "ext-grep", &external_grep_allowed,
			"allow calling of grep(1) (default)"),
#endif
		{ OPTION_CALLBACK, 0, "help-all", &options, NULL, "show usage",
		  PARSE_OPT_HIDDEN | PARSE_OPT_NOARG, help_callback },
		OPT_END()
	};

	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);

	/* 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.color && !opt.color_external) || opt.funcname)
		external_grep_allowed = 0;
	if (!opt.pattern_list)
		die("no pattern given.");
	if ((opt.regflags != REG_NEWLINE) && opt.fixed)
		die("cannot mix --fixed-strings and regexp");
	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) {
		if (!cached)
			setup_work_tree();
		return !grep_cache(&opt, paths, cached, external_grep_allowed);
	}

	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;
	}
	free_grep_patterns(&opt);
	return !hit;
}