[PATCH 5/6] parse-options: build early scan options from a struct option array

@@ -1323,6 +1323,45 @@ int early_scan_options(int argc, const char **argv,
 	return argc;
 }
 
+struct early_scan_option *
+early_scan_options_from_options(const struct option *options,
+				const char **wanted)
+{
+	struct early_scan_option *early;
+	size_t nr = 0;
+
+	for (const struct option *opt = options; opt->type != OPTION_END; opt++)
+		if (opt->long_name)
+			nr++;
+
+	CALLOC_ARRAY(early, nr + 1);
+
+	nr = 0;
+	for (const struct option *opt = options; opt->type != OPTION_END; opt++) {
+		if (!opt->long_name)
+			continue;
+		early[nr].name = opt->long_name;
+		early[nr].takes_value = !!parse_options_takes_argument(opt);
+		nr++;
+	}
+
+	for (; wanted && *wanted; wanted++) {
+		size_t i;
+
+		for (i = 0; i < nr; i++) {
+			if (strcmp(early[i].name, *wanted))
+				continue;
+			early[i].wanted = 1;
+			break;
+		}
+		if (i == nr)
+			BUG("wanted option '%s' is not in the options array",
+			    *wanted);
+	}
+
+	return early;
+}
+
 static int usage_argh(const struct option *opts, FILE *outfile)
 {
 	const char *s;

@@ -561,6 +561,28 @@ int early_scan_options(int argc, const char **argv,
 		       enum early_scan_flags flags,
 		       early_scan_fn *fn, void *data);
 
+/*
+ * Build the `struct early_scan_option` array to pass to
+ * early_scan_options() from the `options` array that the actual option
+ * parsing uses, so that both agree on which options take a value.
+ *
+ * Note some intentional limitations to keep the scan simple and fast:
+ * short options are ignored, options with PARSE_OPT_LASTARG_DEFAULT or
+ * PARSE_OPT_OPTARG are treated as not taking a separate value, negated
+ * options ("--no-...") are not automatically generated, and abbreviated
+ * options will not be matched.
+ *
+ * The options named in the NULL terminated `wanted` array get their
+ * `wanted` bit set, the other ones are only there to be skipped along
+ * with their value. It is a BUG() for a name in `wanted` not to appear
+ * in `options`.
+ *
+ * The returned array is allocated and should be free()d by the caller.
+ */
+struct early_scan_option *
+early_scan_options_from_options(const struct option *options,
+				const char **wanted);
+
 /*----- incremental advanced APIs -----*/
 
 struct parse_opt_cmdmode_list;

@@ -422,3 +422,35 @@ int cmd__early_scan_options(int argc, const char **argv)
 
 	return 0;
 }
+
+int cmd__early_scan_from_options(int argc, const char **argv)
+{
+	int an_int = 0, a_bool = 0;
+	char *a_string = NULL;
+	const struct option options[] = {
+		OPT_STRING(0, "string", &a_string, "str", "get a string"),
+		OPT_INTEGER(0, "int", &an_int, "get an integer"),
+		OPT_BOOL(0, "bool", &a_bool, "get a boolean"),
+		OPT_STRING_F(0, "optarg", &a_string, "str",
+			     "string with an optional value",
+			     PARSE_OPT_OPTARG),
+		OPT_END()
+	};
+	static const char *wanted[] = { "bool", NULL };
+	struct early_scan_option *early;
+	int stopped;
+
+	early = early_scan_options_from_options(options, wanted);
+
+	for (const struct early_scan_option *o = early; o->name; o++)
+		printf("option: %s takes_value: %d wanted: %d\n",
+		       o->name, o->takes_value, o->wanted);
+
+	stopped = early_scan_options(argc - 1, argv + 1, early, 0,
+				     show_early_option, NULL);
+	printf("stopped at: %d of %d\n", stopped, argc - 1);
+
+	free(early);
+
+	return 0;
+}

@@ -51,6 +51,7 @@ static struct test_cmd cmds[] = {
 	{ "parse-options", cmd__parse_options },
 	{ "parse-options-flags", cmd__parse_options_flags },
 	{ "early-scan-options", cmd__early_scan_options },
+	{ "early-scan-from-options", cmd__early_scan_from_options },
 	{ "parse-pathspec-file", cmd__parse_pathspec_file },
 	{ "parse-subcommand", cmd__parse_subcommand },
 	{ "partial-clone", cmd__partial_clone },

@@ -44,6 +44,7 @@ int cmd__pack_mtimes(int argc, const char **argv);
 int cmd__parse_options(int argc, const char **argv);
 int cmd__parse_options_flags(int argc, const char **argv);
 int cmd__early_scan_options(int argc, const char **argv);
+int cmd__early_scan_from_options(int argc, const char **argv);
 int cmd__parse_pathspec_file(int argc, const char** argv);
 int cmd__parse_subcommand(int argc, const char **argv);
 int cmd__partial_clone(int argc, const char **argv);

@@ -922,4 +922,30 @@ test_expect_success 'early_scan_options() ignores abbreviated options' '
 	test_cmp expect actual
 '
 
+test_expect_success 'early_scan_options_from_options() derives takes_value' '
+	test-tool early-scan-from-options >actual &&
+	cat >expect <<-\EOF &&
+	option: string takes_value: 1 wanted: 0
+	option: int takes_value: 1 wanted: 0
+	option: bool takes_value: 0 wanted: 1
+	option: optarg takes_value: 0 wanted: 0
+	stopped at: 0 of 0
+	EOF
+	test_cmp expect actual
+'
+
+test_expect_success 'early_scan_options_from_options() skips values' '
+	test-tool early-scan-from-options --string --bool >out &&
+	tail -1 out >actual &&
+	echo "stopped at: 2 of 2" >expect &&
+	test_cmp expect actual &&
+	test-tool early-scan-from-options --string v --bool >out &&
+	tail -2 out >actual &&
+	cat >expect <<-\EOF &&
+	found: bool at 2
+	stopped at: 3 of 3
+	EOF
+	test_cmp expect actual
+'
+
 test_done