Merge branch 'nd/diff-parseopt'

The diff machinery, one of the oldest parts of the system, which
long predates the parse-options API, uses fairly long and complex
handcrafted option parser.  This is being rewritten to use the
parse-options API.

* nd/diff-parseopt:
  diff.c: convert --raw
  diff.c: convert -W|--[no-]function-context
  diff.c: convert -U|--unified
  diff.c: convert -u|-p|--patch
  diff.c: prepare to use parse_options() for parsing
  diff.h: avoid bit fields in struct diff_flags
  diff.h: keep forward struct declarations sorted
  parse-options: allow ll_callback with OPTION_CALLBACK
  parse-options: avoid magic return codes
  parse-options: stop abusing 'callback' for lowlevel callbacks
  parse-options: add OPT_BITOP()
  parse-options: disable option abbreviation with PARSE_OPT_KEEP_UNKNOWN
  parse-options: add one-shot mode
  parse-options.h: remove extern on function prototypes

10 files changed, 318 insertions, 158 deletions

diff --git a/Documentation/diff-options.txt b/Documentation/diff-options.txt
index 554a34080d..f37374165d 100644
--- a/Documentation/diff-options.txt
+++ b/Documentation/diff-options.txt
@@ -36,7 +36,7 @@ endif::git-format-patch[]
 -U<n>::
 --unified=<n>::
 	Generate diffs with <n> lines of context instead of
-	the usual three.
+	the usual three. Implies `--patch`.
 ifndef::git-format-patch[]
 	Implies `-p`.
 endif::git-format-patch[]
diff --git a/builtin/blame.c b/builtin/blame.c
index 581de0d832..177c1022a0 100644
--- a/builtin/blame.c
+++ b/builtin/blame.c
@@ -814,7 +814,7 @@ int cmd_blame(int argc, const char **argv, const char *prefix)
 		 * and are only included here to get included in the "-h"
 		 * output:
 		 */
-		{ OPTION_LOWLEVEL_CALLBACK, 0, "indent-heuristic", NULL, NULL, N_("Use an experimental heuristic to improve diffs"), PARSE_OPT_NOARG, parse_opt_unknown_cb },
+		{ OPTION_LOWLEVEL_CALLBACK, 0, "indent-heuristic", NULL, NULL, N_("Use an experimental heuristic to improve diffs"), PARSE_OPT_NOARG, NULL, 0, parse_opt_unknown_cb },
 
 		OPT_BIT(0, "minimal", &xdl_opts, N_("Spend extra cycles to find better match"), XDF_NEED_MINIMAL),
 		OPT_STRING('S', NULL, &revs_file, N_("file"), N_("Use revisions from <file> instead of calling git-rev-list")),
diff --git a/builtin/merge.c b/builtin/merge.c
index e47d77baee..5ce8946d39 100644
--- a/builtin/merge.c
+++ b/builtin/merge.c
@@ -113,12 +113,15 @@ static int option_parse_message(const struct option *opt,
 	return 0;
 }
 
-static int option_read_message(struct parse_opt_ctx_t *ctx,
-			       const struct option *opt, int unset)
+static enum parse_opt_result option_read_message(struct parse_opt_ctx_t *ctx,
+						 const struct option *opt,
+						 const char *arg_not_used,
+						 int unset)
 {
 	struct strbuf *buf = opt->value;
 	const char *arg;
 
+	BUG_ON_OPT_ARG(arg_not_used);
 	if (unset)
 		BUG("-F cannot be negated");
 
@@ -262,7 +265,7 @@ static struct option builtin_merge_options[] = {
 		option_parse_message),
 	{ OPTION_LOWLEVEL_CALLBACK, 'F', "file", &merge_msg, N_("path"),
 		N_("read message from file"), PARSE_OPT_NONEG,
-		(parse_opt_cb *) option_read_message },
+		NULL, 0, option_read_message },
 	OPT__VERBOSITY(&verbosity),
 	OPT_BOOL(0, "abort", &abort_current_merge,
 		N_("abort the current in-progress merge")),
diff --git a/builtin/update-index.c b/builtin/update-index.c
index 02ace602b9..1b6c42f748 100644
--- a/builtin/update-index.c
+++ b/builtin/update-index.c
@@ -848,14 +848,16 @@ static int parse_new_style_cacheinfo(const char *arg,
 	return 0;
 }
 
-static int cacheinfo_callback(struct parse_opt_ctx_t *ctx,
-				const struct option *opt, int unset)
+static enum parse_opt_result cacheinfo_callback(
+	struct parse_opt_ctx_t *ctx, const struct option *opt,
+	const char *arg, int unset)
 {
 	struct object_id oid;
 	unsigned int mode;
 	const char *path;
 
 	BUG_ON_OPT_NEG(unset);
+	BUG_ON_OPT_ARG(arg);
 
 	if (!parse_new_style_cacheinfo(ctx->argv[1], &mode, &oid, &path)) {
 		if (add_cacheinfo(mode, &oid, path, 0))
@@ -874,12 +876,14 @@ static int cacheinfo_callback(struct parse_opt_ctx_t *ctx,
 	return 0;
 }
 
-static int stdin_cacheinfo_callback(struct parse_opt_ctx_t *ctx,
-			      const struct option *opt, int unset)
+static enum parse_opt_result stdin_cacheinfo_callback(
+	struct parse_opt_ctx_t *ctx, const struct option *opt,
+	const char *arg, int unset)
 {
 	int *nul_term_line = opt->value;
 
 	BUG_ON_OPT_NEG(unset);
+	BUG_ON_OPT_ARG(arg);
 
 	if (ctx->argc != 1)
 		return error("option '%s' must be the last argument", opt->long_name);
@@ -888,12 +892,14 @@ static int stdin_cacheinfo_callback(struct parse_opt_ctx_t *ctx,
 	return 0;
 }
 
-static int stdin_callback(struct parse_opt_ctx_t *ctx,
-				const struct option *opt, int unset)
+static enum parse_opt_result stdin_callback(
+	struct parse_opt_ctx_t *ctx, const struct option *opt,
+	const char *arg, int unset)
 {
 	int *read_from_stdin = opt->value;
 
 	BUG_ON_OPT_NEG(unset);
+	BUG_ON_OPT_ARG(arg);
 
 	if (ctx->argc != 1)
 		return error("option '%s' must be the last argument", opt->long_name);
@@ -901,13 +907,15 @@ static int stdin_callback(struct parse_opt_ctx_t *ctx,
 	return 0;
 }
 
-static int unresolve_callback(struct parse_opt_ctx_t *ctx,
-				const struct option *opt, int unset)
+static enum parse_opt_result unresolve_callback(
+	struct parse_opt_ctx_t *ctx, const struct option *opt,
+	const char *arg, int unset)
 {
 	int *has_errors = opt->value;
 	const char *prefix = startup_info->prefix;
 
 	BUG_ON_OPT_NEG(unset);
+	BUG_ON_OPT_ARG(arg);
 
 	/* consume remaining arguments. */
 	*has_errors = do_unresolve(ctx->argc, ctx->argv,
@@ -920,13 +928,15 @@ static int unresolve_callback(struct parse_opt_ctx_t *ctx,
 	return 0;
 }
 
-static int reupdate_callback(struct parse_opt_ctx_t *ctx,
-				const struct option *opt, int unset)
+static enum parse_opt_result reupdate_callback(
+	struct parse_opt_ctx_t *ctx, const struct option *opt,
+	const char *arg, int unset)
 {
 	int *has_errors = opt->value;
 	const char *prefix = startup_info->prefix;
 
 	BUG_ON_OPT_NEG(unset);
+	BUG_ON_OPT_ARG(arg);
 
 	/* consume remaining arguments. */
 	setup_work_tree();
@@ -986,7 +996,8 @@ int cmd_update_index(int argc, const char **argv, const char *prefix)
 			N_("add the specified entry to the index"),
 			PARSE_OPT_NOARG | /* disallow --cacheinfo=<mode> form */
 			PARSE_OPT_NONEG | PARSE_OPT_LITERAL_ARGHELP,
-			(parse_opt_cb *) cacheinfo_callback},
+			NULL, 0,
+			cacheinfo_callback},
 		{OPTION_CALLBACK, 0, "chmod", &set_executable_bit, "(+|-)x",
 			N_("override the executable bit of the listed files"),
 			PARSE_OPT_NONEG,
@@ -1012,19 +1023,19 @@ int cmd_update_index(int argc, const char **argv, const char *prefix)
 		{OPTION_LOWLEVEL_CALLBACK, 0, "stdin", &read_from_stdin, NULL,
 			N_("read list of paths to be updated from standard input"),
 			PARSE_OPT_NONEG | PARSE_OPT_NOARG,
-			(parse_opt_cb *) stdin_callback},
+			NULL, 0, stdin_callback},
 		{OPTION_LOWLEVEL_CALLBACK, 0, "index-info", &nul_term_line, NULL,
 			N_("add entries from standard input to the index"),
 			PARSE_OPT_NONEG | PARSE_OPT_NOARG,
-			(parse_opt_cb *) stdin_cacheinfo_callback},
+			NULL, 0, stdin_cacheinfo_callback},
 		{OPTION_LOWLEVEL_CALLBACK, 0, "unresolve", &has_errors, NULL,
 			N_("repopulate stages #2 and #3 for the listed paths"),
 			PARSE_OPT_NONEG | PARSE_OPT_NOARG,
-			(parse_opt_cb *) unresolve_callback},
+			NULL, 0, unresolve_callback},
 		{OPTION_LOWLEVEL_CALLBACK, 'g', "again", &has_errors, NULL,
 			N_("only update entries that differ from HEAD"),
 			PARSE_OPT_NONEG | PARSE_OPT_NOARG,
-			(parse_opt_cb *) reupdate_callback},
+			NULL, 0, reupdate_callback},
 		OPT_BIT(0, "ignore-missing", &refresh_args.flags,
 			N_("ignore files missing from worktree"),
 			REFRESH_IGNORE_MISSING),
diff --git a/diff.c b/diff.c
index 5306c48652..1a1f215787 100644
--- a/diff.c
+++ b/diff.c
@@ -23,6 +23,7 @@
 #include "argv-array.h"
 #include "graph.h"
 #include "packfile.h"
+#include "parse-options.h"
 #include "help.h"
 
 #ifdef NO_FAST_WORKING_DIRECTORY
@@ -4491,6 +4492,8 @@ static void run_checkdiff(struct diff_filepair *p, struct diff_options *o)
 	builtin_checkdiff(name, other, attr_path, p->one, p->two, o);
 }
 
+static void prep_parse_options(struct diff_options *options);
+
 void repo_diff_setup(struct repository *r, struct diff_options *options)
 {
 	memcpy(options, &default_diff_options, sizeof(*options));
@@ -4532,6 +4535,8 @@ void repo_diff_setup(struct repository *r, struct diff_options *options)
 
 	options->color_moved = diff_color_moved_default;
 	options->color_moved_ws_handling = diff_color_moved_ws_default;
+
+	prep_parse_options(options);
 }
 
 void diff_setup_done(struct diff_options *options)
@@ -4635,6 +4640,8 @@ void diff_setup_done(struct diff_options *options)
 
 	if (!options->use_color || external_diff())
 		options->color_moved = 0;
+
+	FREE_AND_NULL(options->parseopts);
 }
 
 static int opt_arg(const char *arg, int arg_short, const char *arg_long, int *val)
@@ -4926,6 +4933,47 @@ static int parse_objfind_opt(struct diff_options *opt, const char *arg)
 	return 1;
 }
 
+static int diff_opt_unified(const struct option *opt,
+			    const char *arg, int unset)
+{
+	struct diff_options *options = opt->value;
+	char *s;
+
+	BUG_ON_OPT_NEG(unset);
+
+	options->context = strtol(arg, &s, 10);
+	if (*s)
+		return error(_("%s expects a numerical value"), "--unified");
+	enable_patch_output(&options->output_format);
+
+	return 0;
+}
+
+static void prep_parse_options(struct diff_options *options)
+{
+	struct option parseopts[] = {
+		OPT_GROUP(N_("Diff output format options")),
+		OPT_BITOP('p', "patch", &options->output_format,
+			  N_("generate patch"),
+			  DIFF_FORMAT_PATCH, DIFF_FORMAT_NO_OUTPUT),
+		OPT_BITOP('u', NULL, &options->output_format,
+			  N_("generate patch"),
+			  DIFF_FORMAT_PATCH, DIFF_FORMAT_NO_OUTPUT),
+		OPT_CALLBACK_F('U', "unified", options, N_("<n>"),
+			       N_("generate diffs with <n> lines context"),
+			       PARSE_OPT_NONEG, diff_opt_unified),
+		OPT_BOOL('W', "function-context", &options->flags.funccontext,
+			 N_("generate diffs with <n> lines context")),
+		OPT_BIT_F(0, "raw", &options->output_format,
+			  N_("generate the diff in raw format"),
+			  DIFF_FORMAT_RAW, PARSE_OPT_NONEG),
+		OPT_END()
+	};
+
+	ALLOC_ARRAY(options->parseopts, ARRAY_SIZE(parseopts));
+	memcpy(options->parseopts, parseopts, sizeof(parseopts));
+}
+
 int diff_opt_parse(struct diff_options *options,
 		   const char **av, int ac, const char *prefix)
 {
@@ -4936,13 +4984,18 @@ int diff_opt_parse(struct diff_options *options,
 	if (!prefix)
 		prefix = "";
 
+	ac = parse_options(ac, av, prefix, options->parseopts, NULL,
+			   PARSE_OPT_KEEP_DASHDASH |
+			   PARSE_OPT_KEEP_UNKNOWN |
+			   PARSE_OPT_NO_INTERNAL_HELP |
+			   PARSE_OPT_ONE_SHOT |
+			   PARSE_OPT_STOP_AT_NON_OPTION);
+
+	if (ac)
+		return ac;
+
 	/* Output format options */
-	if (!strcmp(arg, "-p") || !strcmp(arg, "-u") || !strcmp(arg, "--patch")
-	    || opt_arg(arg, 'U', "unified", &options->context))
-		enable_patch_output(&options->output_format);
-	else if (!strcmp(arg, "--raw"))
-		options->output_format |= DIFF_FORMAT_RAW;
-	else if (!strcmp(arg, "--patch-with-raw")) {
+	if (!strcmp(arg, "--patch-with-raw")) {
 		enable_patch_output(&options->output_format);
 		options->output_format |= DIFF_FORMAT_RAW;
 	} else if (!strcmp(arg, "--numstat"))
@@ -5230,12 +5283,6 @@ int diff_opt_parse(struct diff_options *options,
 	else if (opt_arg(arg, '\0', "inter-hunk-context",
 			 &options->interhunkcontext))
 		;
-	else if (!strcmp(arg, "-W"))
-		options->flags.funccontext = 1;
-	else if (!strcmp(arg, "--function-context"))
-		options->flags.funccontext = 1;
-	else if (!strcmp(arg, "--no-function-context"))
-		options->flags.funccontext = 0;
 	else if ((argcount = parse_long_opt("output", av, &optarg))) {
 		char *path = prefix_filename(prefix, optarg);
 		options->file = xfopen(path, "w");
diff --git a/diff.h b/diff.h
index b512d0477a..d9ad73f0e1 100644
--- a/diff.h
+++ b/diff.h
@@ -9,16 +9,17 @@
 #include "object.h"
 #include "oidset.h"
 
-struct rev_info;
+struct combine_diff_path;
+struct commit;
+struct diff_filespec;
 struct diff_options;
 struct diff_queue_struct;
-struct strbuf;
-struct diff_filespec;
-struct userdiff_driver;
 struct oid_array;
-struct commit;
-struct combine_diff_path;
+struct option;
 struct repository;
+struct rev_info;
+struct strbuf;
+struct userdiff_driver;
 
 typedef int (*pathchange_fn_t)(struct diff_options *options,
 		 struct combine_diff_path *path);
@@ -64,39 +65,39 @@ typedef struct strbuf *(*diff_prefix_fn_t)(struct diff_options *opt, void *data)
 
 #define DIFF_FLAGS_INIT { 0 }
 struct diff_flags {
-	unsigned recursive:1;
-	unsigned tree_in_recursive:1;
-	unsigned binary:1;
-	unsigned text:1;
-	unsigned full_index:1;
-	unsigned silent_on_remove:1;
-	unsigned find_copies_harder:1;
-	unsigned follow_renames:1;
-	unsigned rename_empty:1;
-	unsigned has_changes:1;
-	unsigned quick:1;
-	unsigned no_index:1;
-	unsigned allow_external:1;
-	unsigned exit_with_status:1;
-	unsigned reverse_diff:1;
-	unsigned check_failed:1;
-	unsigned relative_name:1;
-	unsigned ignore_submodules:1;
-	unsigned dirstat_cumulative:1;
-	unsigned dirstat_by_file:1;
-	unsigned allow_textconv:1;
-	unsigned textconv_set_via_cmdline:1;
-	unsigned diff_from_contents:1;
-	unsigned dirty_submodules:1;
-	unsigned ignore_untracked_in_submodules:1;
-	unsigned ignore_dirty_submodules:1;
-	unsigned override_submodule_config:1;
-	unsigned dirstat_by_line:1;
-	unsigned funccontext:1;
-	unsigned default_follow_renames:1;
-	unsigned stat_with_summary:1;
-	unsigned suppress_diff_headers:1;
-	unsigned dual_color_diffed_diffs:1;
+	unsigned recursive;
+	unsigned tree_in_recursive;
+	unsigned binary;
+	unsigned text;
+	unsigned full_index;
+	unsigned silent_on_remove;
+	unsigned find_copies_harder;
+	unsigned follow_renames;
+	unsigned rename_empty;
+	unsigned has_changes;
+	unsigned quick;
+	unsigned no_index;
+	unsigned allow_external;
+	unsigned exit_with_status;
+	unsigned reverse_diff;
+	unsigned check_failed;
+	unsigned relative_name;
+	unsigned ignore_submodules;
+	unsigned dirstat_cumulative;
+	unsigned dirstat_by_file;
+	unsigned allow_textconv;
+	unsigned textconv_set_via_cmdline;
+	unsigned diff_from_contents;
+	unsigned dirty_submodules;
+	unsigned ignore_untracked_in_submodules;
+	unsigned ignore_dirty_submodules;
+	unsigned override_submodule_config;
+	unsigned dirstat_by_line;
+	unsigned funccontext;
+	unsigned default_follow_renames;
+	unsigned stat_with_summary;
+	unsigned suppress_diff_headers;
+	unsigned dual_color_diffed_diffs;
 };
 
 static inline void diff_flags_or(struct diff_flags *a,
@@ -229,6 +230,7 @@ struct diff_options {
 	unsigned color_moved_ws_handling;
 
 	struct repository *repo;
+	struct option *parseopts;
 };
 
 void diff_emit_submodule_del(struct diff_options *o, const char *line);
diff --git a/parse-options-cb.c b/parse-options-cb.c
index e2f3eaed07..2733393546 100644
--- a/parse-options-cb.c
+++ b/parse-options-cb.c
@@ -170,9 +170,12 @@ int parse_opt_noop_cb(const struct option *opt, const char *arg, int unset)
  * "-h" output even if it's not being handled directly by
  * parse_options().
  */
-int parse_opt_unknown_cb(const struct option *opt, const char *arg, int unset)
+enum parse_opt_result parse_opt_unknown_cb(struct parse_opt_ctx_t *ctx,
+					   const struct option *opt,
+					   const char *arg, int unset)
 {
-	return -2;
+	BUG_ON_OPT_ARG(arg);
+	return PARSE_OPT_UNKNOWN;
 }
 
 /**
diff --git a/parse-options.c b/parse-options.c
index 9f84bacce6..cec74522e5 100644
--- a/parse-options.c
+++ b/parse-options.c
@@ -20,8 +20,9 @@ int optbug(const struct option *opt, const char *reason)
 	return error("BUG: switch '%c' %s", opt->short_name, reason);
 }
 
-static int get_arg(struct parse_opt_ctx_t *p, const struct option *opt,
-		   int flags, const char **arg)
+static enum parse_opt_result get_arg(struct parse_opt_ctx_t *p,
+				     const struct option *opt,
+				     int flags, const char **arg)
 {
 	if (p->opt) {
 		*arg = p->opt;
@@ -44,9 +45,10 @@ static void fix_filename(const char *prefix, const char **file)
 	*file = prefix_filename(prefix, *file);
 }
 
-static int opt_command_mode_error(const struct option *opt,
-				  const struct option *all_opts,
-				  int flags)
+static enum parse_opt_result opt_command_mode_error(
+	const struct option *opt,
+	const struct option *all_opts,
+	int flags)
 {
 	const struct option *that;
 	struct strbuf that_name = STRBUF_INIT;
@@ -69,16 +71,16 @@ static int opt_command_mode_error(const struct option *opt,
 		error(_("%s is incompatible with %s"),
 		      optname(opt, flags), that_name.buf);
 		strbuf_release(&that_name);
-		return -1;
+		return PARSE_OPT_ERROR;
 	}
 	return error(_("%s : incompatible with something else"),
 		     optname(opt, flags));
 }
 
-static int get_value(struct parse_opt_ctx_t *p,
-		     const struct option *opt,
-		     const struct option *all_opts,
-		     int flags)
+static enum parse_opt_result get_value(struct parse_opt_ctx_t *p,
+				       const struct option *opt,
+				       const struct option *all_opts,
+				       int flags)
 {
 	const char *s, *arg;
 	const int unset = flags & OPT_UNSET;
@@ -93,7 +95,7 @@ static int get_value(struct parse_opt_ctx_t *p,
 
 	switch (opt->type) {
 	case OPTION_LOWLEVEL_CALLBACK:
-		return (*(parse_opt_ll_cb *)opt->callback)(p, opt, unset);
+		return opt->ll_callback(p, opt, NULL, unset);
 
 	case OPTION_BIT:
 		if (unset)
@@ -109,6 +111,13 @@ static int get_value(struct parse_opt_ctx_t *p,
 			*(int *)opt->value &= ~opt->defval;
 		return 0;
 
+	case OPTION_BITOP:
+		if (unset)
+			BUG("BITOP can't have unset form");
+		*(int *)opt->value &= ~opt->extra;
+		*(int *)opt->value |= opt->defval;
+		return 0;
+
 	case OPTION_COUNTUP:
 		if (*(int *)opt->value < 0)
 			*(int *)opt->value = 0;
@@ -152,16 +161,27 @@ static int get_value(struct parse_opt_ctx_t *p,
 		return err;
 
 	case OPTION_CALLBACK:
+	{
+		const char *p_arg = NULL;
+		int p_unset;
+
 		if (unset)
-			return (*opt->callback)(opt, NULL, 1) ? (-1) : 0;
-		if (opt->flags & PARSE_OPT_NOARG)
-			return (*opt->callback)(opt, NULL, 0) ? (-1) : 0;
-		if (opt->flags & PARSE_OPT_OPTARG && !p->opt)
-			return (*opt->callback)(opt, NULL, 0) ? (-1) : 0;
-		if (get_arg(p, opt, flags, &arg))
+			p_unset = 1;
+		else if (opt->flags & PARSE_OPT_NOARG)
+			p_unset = 0;
+		else if (opt->flags & PARSE_OPT_OPTARG && !p->opt)
+			p_unset = 0;
+		else if (get_arg(p, opt, flags, &arg))
 			return -1;
-		return (*opt->callback)(opt, arg, 0) ? (-1) : 0;
-
+		else {
+			p_unset = 0;
+			p_arg = arg;
+		}
+		if (opt->callback)
+			return (*opt->callback)(opt, p_arg, p_unset) ? (-1) : 0;
+		else
+			return (*opt->ll_callback)(p, opt, p_arg, p_unset);
+	}
 	case OPTION_INTEGER:
 		if (unset) {
 			*(int *)opt->value = 0;
@@ -201,7 +221,8 @@ static int get_value(struct parse_opt_ctx_t *p,
 	}
 }
 
-static int parse_short_opt(struct parse_opt_ctx_t *p, const struct option *options)
+static enum parse_opt_result parse_short_opt(struct parse_opt_ctx_t *p,
+					     const struct option *options)
 {
 	const struct option *all_opts = options;
 	const struct option *numopt = NULL;
@@ -228,15 +249,19 @@ static int parse_short_opt(struct parse_opt_ctx_t *p, const struct option *optio
 			len++;
 		arg = xmemdupz(p->opt, len);
 		p->opt = p->opt[len] ? p->opt + len : NULL;
-		rc = (*numopt->callback)(numopt, arg, 0) ? (-1) : 0;
+		if (numopt->callback)
+			rc = (*numopt->callback)(numopt, arg, 0) ? (-1) : 0;
+		else
+			rc = (*numopt->ll_callback)(p, numopt, arg, 0);
 		free(arg);
 		return rc;
 	}
-	return -2;
+	return PARSE_OPT_UNKNOWN;
 }
 
-static int parse_long_opt(struct parse_opt_ctx_t *p, const char *arg,
-			  const struct option *options)
+static enum parse_opt_result parse_long_opt(
+	struct parse_opt_ctx_t *p, const char *arg,
+	const struct option *options)
 {
 	const struct option *all_opts = options;
 	const char *arg_end = strchrnul(arg, '=');
@@ -262,11 +287,12 @@ again:
 			if (*rest)
 				continue;
 			p->out[p->cpidx++] = arg - 2;
-			return 0;
+			return PARSE_OPT_DONE;
 		}
 		if (!rest) {
 			/* abbreviated? */
-			if (!strncmp(long_name, arg, arg_end - arg)) {
+			if (!(p->flags & PARSE_OPT_KEEP_UNKNOWN) &&
+			    !strncmp(long_name, arg, arg_end - arg)) {
 is_abbreviated:
 				if (abbrev_option) {
 					/*
@@ -326,11 +352,11 @@ is_abbreviated:
 			ambiguous_option->long_name,
 			(abbrev_flags & OPT_UNSET) ?  "no-" : "",
 			abbrev_option->long_name);
-		return -3;
+		return PARSE_OPT_HELP;
 	}
 	if (abbrev_option)
 		return get_value(p, abbrev_option, all_opts, abbrev_flags);
-	return -2;
+	return PARSE_OPT_UNKNOWN;
 }
 
 static int parse_nodash_opt(struct parse_opt_ctx_t *p, const char *arg,
@@ -400,6 +426,19 @@ static void parse_options_check(const struct option *opts)
 			if ((opts->flags & PARSE_OPT_OPTARG) ||
 			    !(opts->flags & PARSE_OPT_NOARG))
 				err |= optbug(opts, "should not accept an argument");
+			break;
+		case OPTION_CALLBACK:
+			if (!opts->callback && !opts->ll_callback)
+				BUG("OPTION_CALLBACK needs one callback");
+			if (opts->callback && opts->ll_callback)
+				BUG("OPTION_CALLBACK can't have two callbacks");
+			break;
+		case OPTION_LOWLEVEL_CALLBACK:
+			if (!opts->ll_callback)
+				BUG("OPTION_LOWLEVEL_CALLBACK needs a callback");
+			if (opts->callback)
+				BUG("OPTION_LOWLEVEL_CALLBACK needs no high level callback");
+			break;
 		default:
 			; /* ok. (usually accepts an argument) */
 		}
@@ -416,15 +455,24 @@ void parse_options_start(struct parse_opt_ctx_t *ctx,
 			 const struct option *options, int flags)
 {
 	memset(ctx, 0, sizeof(*ctx));
-	ctx->argc = ctx->total = argc - 1;
-	ctx->argv = argv + 1;
-	ctx->out  = argv;
+	ctx->argc = argc;
+	ctx->argv = argv;
+	if (!(flags & PARSE_OPT_ONE_SHOT)) {
+		ctx->argc--;
+		ctx->argv++;
+	}
+	ctx->total = ctx->argc;
+	ctx->out   = argv;
 	ctx->prefix = prefix;
 	ctx->cpidx = ((flags & PARSE_OPT_KEEP_ARGV0) != 0);
 	ctx->flags = flags;
 	if ((flags & PARSE_OPT_KEEP_UNKNOWN) &&
-	    (flags & PARSE_OPT_STOP_AT_NON_OPTION))
+	    (flags & PARSE_OPT_STOP_AT_NON_OPTION) &&
+	    !(flags & PARSE_OPT_ONE_SHOT))
 		BUG("STOP_AT_NON_OPTION and KEEP_UNKNOWN don't go together");
+	if ((flags & PARSE_OPT_ONE_SHOT) &&
+	    (flags & PARSE_OPT_KEEP_ARGV0))
+		BUG("Can't keep argv0 if you don't have it");
 	parse_options_check(options);
 }
 
@@ -536,6 +584,10 @@ int parse_options_step(struct parse_opt_ctx_t *ctx,
 	for (; ctx->argc; ctx->argc--, ctx->argv++) {
 		const char *arg = ctx->argv[0];
 
+		if (ctx->flags & PARSE_OPT_ONE_SHOT &&
+		    ctx->argc != ctx->total)
+			break;
+
 		if (*arg != '-' || !arg[1]) {
 			if (parse_nodash_opt(ctx, arg, options) == 0)
 				continue;
@@ -556,22 +608,28 @@ int parse_options_step(struct parse_opt_ctx_t *ctx,
 		if (arg[1] != '-') {
 			ctx->opt = arg + 1;
 			switch (parse_short_opt(ctx, options)) {
-			case -1:
+			case PARSE_OPT_ERROR:
 				return PARSE_OPT_ERROR;
-			case -2:
+			case PARSE_OPT_UNKNOWN:
 				if (ctx->opt)
 					check_typos(arg + 1, options);
 				if (internal_help && *ctx->opt == 'h')
 					goto show_usage;
 				goto unknown;
+			case PARSE_OPT_NON_OPTION:
+			case PARSE_OPT_HELP:
+			case PARSE_OPT_COMPLETE:
+				BUG("parse_short_opt() cannot return these");
+			case PARSE_OPT_DONE:
+				break;
 			}
 			if (ctx->opt)
 				check_typos(arg + 1, options);
 			while (ctx->opt) {
 				switch (parse_short_opt(ctx, options)) {
-				case -1:
+				case PARSE_OPT_ERROR:
 					return PARSE_OPT_ERROR;
-				case -2:
+				case PARSE_OPT_UNKNOWN:
 					if (internal_help && *ctx->opt == 'h')
 						goto show_usage;
 
@@ -583,6 +641,12 @@ int parse_options_step(struct parse_opt_ctx_t *ctx,
 					ctx->argv[0] = xstrdup(ctx->opt - 1);
 					*(char *)ctx->argv[0] = '-';
 					goto unknown;
+				case PARSE_OPT_NON_OPTION:
+				case PARSE_OPT_COMPLETE:
+				case PARSE_OPT_HELP:
+					BUG("parse_short_opt() cannot return these");
+				case PARSE_OPT_DONE:
+					break;
 				}
 			}
 			continue;
@@ -601,15 +665,22 @@ int parse_options_step(struct parse_opt_ctx_t *ctx,
 		if (internal_help && !strcmp(arg + 2, "help"))
 			goto show_usage;
 		switch (parse_long_opt(ctx, arg + 2, options)) {
-		case -1:
+		case PARSE_OPT_ERROR:
 			return PARSE_OPT_ERROR;
-		case -2:
+		case PARSE_OPT_UNKNOWN:
 			goto unknown;
-		case -3:
+		case PARSE_OPT_HELP:
 			goto show_usage;
+		case PARSE_OPT_NON_OPTION:
+		case PARSE_OPT_COMPLETE:
+			BUG("parse_long_opt() cannot return these");
+		case PARSE_OPT_DONE:
+			break;
 		}
 		continue;
 unknown:
+		if (ctx->flags & PARSE_OPT_ONE_SHOT)
+			break;
 		if (!(ctx->flags & PARSE_OPT_KEEP_UNKNOWN))
 			return PARSE_OPT_UNKNOWN;
 		ctx->out[ctx->cpidx++] = ctx->argv[0];
@@ -623,6 +694,9 @@ unknown:
 
 int parse_options_end(struct parse_opt_ctx_t *ctx)
 {
+	if (ctx->flags & PARSE_OPT_ONE_SHOT)
+		return ctx->total - ctx->argc;
+
 	MOVE_ARRAY(ctx->out + ctx->cpidx, ctx->argv, ctx->argc);
 	ctx->out[ctx->cpidx + ctx->argc] = NULL;
 	return ctx->cpidx + ctx->argc;
diff --git a/parse-options.h b/parse-options.h
index 14fe32428e..7d83e2971d 100644
--- a/parse-options.h
+++ b/parse-options.h
@@ -10,6 +10,7 @@ enum parse_opt_type {
 	/* options with no arguments */
 	OPTION_BIT,
 	OPTION_NEGBIT,
+	OPTION_BITOP,
 	OPTION_COUNTUP,
 	OPTION_SET_INT,
 	OPTION_CMDMODE,
@@ -27,7 +28,8 @@ enum parse_opt_flags {
 	PARSE_OPT_STOP_AT_NON_OPTION = 2,
 	PARSE_OPT_KEEP_ARGV0 = 4,
 	PARSE_OPT_KEEP_UNKNOWN = 8,
-	PARSE_OPT_NO_INTERNAL_HELP = 16
+	PARSE_OPT_NO_INTERNAL_HELP = 16,
+	PARSE_OPT_ONE_SHOT = 32
 };
 
 enum parse_opt_option_flags {
@@ -47,8 +49,9 @@ struct option;
 typedef int parse_opt_cb(const struct option *, const char *arg, int unset);
 
 struct parse_opt_ctx_t;
-typedef int parse_opt_ll_cb(struct parse_opt_ctx_t *ctx,
-				const struct option *opt, int unset);
+typedef enum parse_opt_result parse_opt_ll_cb(struct parse_opt_ctx_t *ctx,
+					      const struct option *opt,
+					      const char *arg, int unset);
 
 /*
  * `type`::
@@ -98,13 +101,16 @@ typedef int parse_opt_ll_cb(struct parse_opt_ctx_t *ctx,
  *			 the option takes optional argument.
  *
  * `callback`::
- *   pointer to the callback to use for OPTION_CALLBACK or
- *   OPTION_LOWLEVEL_CALLBACK.
+ *   pointer to the callback to use for OPTION_CALLBACK
  *
  * `defval`::
  *   default value to fill (*->value) with for PARSE_OPT_OPTARG.
  *   OPTION_{BIT,SET_INT} store the {mask,integer} to put in the value when met.
  *   CALLBACKS can use it like they want.
+ *
+ * `ll_callback`::
+ *   pointer to the callback to use for OPTION_LOWLEVEL_CALLBACK
+ *
  */
 struct option {
 	enum parse_opt_type type;
@@ -117,6 +123,8 @@ struct option {
 	int flags;
 	parse_opt_cb *callback;
 	intptr_t defval;
+	parse_opt_ll_cb *ll_callback;
+	intptr_t extra;
 };
 
 #define OPT_BIT_F(s, l, v, h, b, f) { OPTION_BIT, (s), (l), (v), NULL, (h), \
@@ -126,12 +134,17 @@ struct option {
 #define OPT_SET_INT_F(s, l, v, h, i, f) { OPTION_SET_INT, (s), (l), (v), NULL, \
 					  (h), PARSE_OPT_NOARG | (f), NULL, (i) }
 #define OPT_BOOL_F(s, l, v, h, f)   OPT_SET_INT_F(s, l, v, h, 1, f)
+#define OPT_CALLBACK_F(s, l, v, a, h, f, cb)			\
+	{ OPTION_CALLBACK, (s), (l), (v), (a), (h), (f), (cb) }
 
 #define OPT_END()                   { OPTION_END }
 #define OPT_ARGUMENT(l, h)          { OPTION_ARGUMENT, 0, (l), NULL, NULL, \
 				      (h), PARSE_OPT_NOARG}
 #define OPT_GROUP(h)                { OPTION_GROUP, 0, NULL, NULL, NULL, (h) }
 #define OPT_BIT(s, l, v, h, b)      OPT_BIT_F(s, l, v, h, b, 0)
+#define OPT_BITOP(s, l, v, h, set, clear) { OPTION_BITOP, (s), (l), (v), NULL, (h), \
+					    PARSE_OPT_NOARG|PARSE_OPT_NONEG, NULL, \
+					    (set), NULL, (clear) }
 #define OPT_NEGBIT(s, l, v, h, b)   { OPTION_NEGBIT, (s), (l), (v), NULL, \
 				      (h), PARSE_OPT_NOARG, NULL, (b) }
 #define OPT_COUNTUP(s, l, v, h)     OPT_COUNTUP_F(s, l, v, h, 0)
@@ -153,8 +166,7 @@ struct option {
 #define OPT_EXPIRY_DATE(s, l, v, h) \
 	{ OPTION_CALLBACK, (s), (l), (v), N_("expiry-date"),(h), 0,	\
 	  parse_opt_expiry_date_cb }
-#define OPT_CALLBACK(s, l, v, a, h, f) \
-	{ OPTION_CALLBACK, (s), (l), (v), (a), (h), 0, (f) }
+#define OPT_CALLBACK(s, l, v, a, h, f) OPT_CALLBACK_F(s, l, v, a, h, 0, f)
 #define OPT_NUMBER_CALLBACK(v, h, f) \
 	{ OPTION_NUMBER, 0, NULL, (v), NULL, (h), \
 	  PARSE_OPT_NOARG | PARSE_OPT_NONEG, (f) }
@@ -169,23 +181,31 @@ struct option {
 	  N_("no-op (backward compatibility)"),		\
 	  PARSE_OPT_HIDDEN | PARSE_OPT_NOARG, parse_opt_noop_cb }
 
-/* parse_options() will filter out the processed options and leave the
- * non-option arguments in argv[]. usagestr strings should be marked
- * for translation with N_().
+/*
+ * parse_options() will filter out the processed options and leave the
+ * non-option arguments in argv[]. argv0 is assumed program name and
+ * skipped.
+ *
+ * usagestr strings should be marked for translation with N_().
+ *
  * Returns the number of arguments left in argv[].
+ *
+ * In one-shot mode, argv0 is not a program name, argv[] is left
+ * untouched and parse_options() returns the number of options
+ * processed.
  */
-extern int parse_options(int argc, const char **argv, const char *prefix,
-			 const struct option *options,
-			 const char * const usagestr[], int flags);
+int parse_options(int argc, const char **argv, const char *prefix,
+		  const struct option *options,
+		  const char * const usagestr[], int flags);
 
-extern NORETURN void usage_with_options(const char * const *usagestr,
-					const struct option *options);
+NORETURN void usage_with_options(const char * const *usagestr,
+				 const struct option *options);
 
-extern NORETURN void usage_msg_opt(const char *msg,
-				   const char * const *usagestr,
-				   const struct option *options);
+NORETURN void usage_msg_opt(const char *msg,
+			    const char * const *usagestr,
+			    const struct option *options);
 
-extern int optbug(const struct option *opt, const char *reason);
+int optbug(const struct option *opt, const char *reason);
 const char *optname(const struct option *opt, int flags);
 
 /*
@@ -204,12 +224,12 @@ const char *optname(const struct option *opt, int flags);
 
 /*----- incremental advanced APIs -----*/
 
-enum {
-	PARSE_OPT_COMPLETE = -2,
-	PARSE_OPT_HELP = -1,
-	PARSE_OPT_DONE,
+enum parse_opt_result {
+	PARSE_OPT_COMPLETE = -3,
+	PARSE_OPT_HELP = -2,
+	PARSE_OPT_ERROR = -1,	/* must be the same as error() */
+	PARSE_OPT_DONE = 0,	/* fixed so that "return 0" works */
 	PARSE_OPT_NON_OPTION,
-	PARSE_OPT_ERROR,
 	PARSE_OPT_UNKNOWN
 };
 
@@ -227,31 +247,31 @@ struct parse_opt_ctx_t {
 	const char *prefix;
 };
 
-extern void parse_options_start(struct parse_opt_ctx_t *ctx,
-				int argc, const char **argv, const char *prefix,
-				const struct option *options, int flags);
+void parse_options_start(struct parse_opt_ctx_t *ctx,
+			 int argc, const char **argv, const char *prefix,
+			 const struct option *options, int flags);
 
-extern int parse_options_step(struct parse_opt_ctx_t *ctx,
-			      const struct option *options,
-			      const char * const usagestr[]);
+int parse_options_step(struct parse_opt_ctx_t *ctx,
+		       const struct option *options,
+		       const char * const usagestr[]);
 
-extern int parse_options_end(struct parse_opt_ctx_t *ctx);
+int parse_options_end(struct parse_opt_ctx_t *ctx);
 
-extern struct option *parse_options_concat(struct option *a, struct option *b);
+struct option *parse_options_concat(struct option *a, struct option *b);
 
 /*----- some often used options -----*/
-extern int parse_opt_abbrev_cb(const struct option *, const char *, int);
-extern int parse_opt_expiry_date_cb(const struct option *, const char *, int);
-extern int parse_opt_color_flag_cb(const struct option *, const char *, int);
-extern int parse_opt_verbosity_cb(const struct option *, const char *, int);
-extern int parse_opt_object_name(const struct option *, const char *, int);
-extern int parse_opt_commits(const struct option *, const char *, int);
-extern int parse_opt_tertiary(const struct option *, const char *, int);
-extern int parse_opt_string_list(const struct option *, const char *, int);
-extern int parse_opt_noop_cb(const struct option *, const char *, int);
-extern int parse_opt_unknown_cb(const struct option *, const char *, int);
-extern int parse_opt_passthru(const struct option *, const char *, int);
-extern int parse_opt_passthru_argv(const struct option *, const char *, int);
+int parse_opt_abbrev_cb(const struct option *, const char *, int);
+int parse_opt_expiry_date_cb(const struct option *, const char *, int);
+int parse_opt_color_flag_cb(const struct option *, const char *, int);
+int parse_opt_verbosity_cb(const struct option *, const char *, int);
+int parse_opt_object_name(const struct option *, const char *, int);
+int parse_opt_commits(const struct option *, const char *, int);
+int parse_opt_tertiary(const struct option *, const char *, int);
+int parse_opt_string_list(const struct option *, const char *, int);
+int parse_opt_noop_cb(const struct option *, const char *, int);
+int parse_opt_unknown_cb(struct parse_opt_ctx_t *ctx, const struct option *, const char *, int);
+int parse_opt_passthru(const struct option *, const char *, int);
+int parse_opt_passthru_argv(const struct option *, const char *, int);
 
 #define OPT__VERBOSE(var, h)  OPT_COUNTUP('v', "verbose", (var), (h))
 #define OPT__QUIET(var, h)    OPT_COUNTUP('q', "quiet",   (var), (h))
diff --git a/t/t7800-difftool.sh b/t/t7800-difftool.sh
index 22b9199d59..bb9a7f4ff9 100755
--- a/t/t7800-difftool.sh
+++ b/t/t7800-difftool.sh
@@ -546,7 +546,7 @@ do
 done >actual
 EOF
 
-test_expect_success SYMLINKS 'difftool --dir-diff --symlink without unstaged changes' '
+test_expect_success SYMLINKS 'difftool --dir-diff --symlinks without unstaged changes' '
 	cat >expect <<-EOF &&
 	file
 	$PWD/file
@@ -555,7 +555,7 @@ test_expect_success SYMLINKS 'difftool --dir-diff --symlink without unstaged cha
 	sub/sub
 	$PWD/sub/sub
 	EOF
-	git difftool --dir-diff --symlink \
+	git difftool --dir-diff --symlinks \
 		--extcmd "./.git/CHECK_SYMLINKS" branch HEAD &&
 	test_cmp expect actual
 '