for-each-ref: delay parsing of --sort=<atom> options

The for-each-ref family of commands invoke parsers immediately when
it sees each --sort=<atom> option, and die before even seeing the
other options on the command line when the <atom> is unrecognised.

Instead, accumulate them in a string list, and have them parsed into
a ref_sorting structure after the command line parsing is done.  As
a consequence, "git branch --sort=bogus -h" used to fail to give the
brief help, which arguably may have been a feature, now does so,
which is more consistent with how other options work.

The patch is smaller than the actual extent of the "damage" to the
codebase, thanks to the fact that the original code consistently
used OPT_REF_SORT() macro to handle command line options.  We only
needed to replace the variable used for the list, and implementation
of the callback function used in the macro.

The old rule was for the users of the API to:

 - Declare ref_sorting and ref_sorting_tail variables;

 - OPT_REF_SORT() macro will instantiate ref_sorting instance (which
   may barf and die) and append it to the tail;

 - Append to the tail each ref_sorting read from the configuration
   by parsing in the config callback (which may barf and die);

 - See if ref_sorting is null and use ref_sorting_default() instead.

Now the rule is not all that different but is simpler:

 - Declare ref_sorting_options string list.

 - OPT_REF_SORT() macro will append it to the string list;

 - Append to the string list the sort key read from the
   configuration;

 - call ref_sorting_options() to turn the string list to ref_sorting
   structure (which also deals with the default value).

As side effects, this change also cleans up a few issues:

 - 95be717c (parse_opt_ref_sorting: always use with NONEG flag,
   2019-03-20) muses that "git for-each-ref --no-sort" should simply
   clear the sort keys accumulated so far; it now does.

 - The implementation detail of "struct ref_sorting" and the helper
   function parse_ref_sorting() can now be private to the ref-filter
   API implementation.

 - If you set branch.sort to a bogus value, the any "git branch"
   invocation, not only the listing mode, would abort with the
   original code; now it doesn't

Signed-off-by: Junio C Hamano <gitster@pobox.com>

1 files changed, 24 insertions, 10 deletions

diff --git a/ref-filter.c b/ref-filter.c
index 282cdad103..afed03472f 100644
--- a/ref-filter.c
+++ b/ref-filter.c
@@ -2470,6 +2470,12 @@ static int memcasecmp(const void *vs1, const void *vs2, size_t n)
 	return 0;
 }
 
+struct ref_sorting {
+	struct ref_sorting *next;
+	int atom; /* index into used_atom array (internal) */
+	enum ref_sorting_order sort_flags;
+};
+
 static int cmp_ref_sorting(struct ref_sorting *s, struct ref_array_item *a, struct ref_array_item *b)
 {
 	struct atom_value *va, *vb;
@@ -2663,7 +2669,7 @@ static int parse_sorting_atom(const char *atom)
 }
 
 /*  If no sorting option is given, use refname to sort as default */
-struct ref_sorting *ref_default_sorting(void)
+static struct ref_sorting *ref_default_sorting(void)
 {
 	static const char cstr_name[] = "refname";
 
@@ -2674,7 +2680,7 @@ struct ref_sorting *ref_default_sorting(void)
 	return sorting;
 }
 
-void parse_ref_sorting(struct ref_sorting **sorting_tail, const char *arg)
+static void parse_ref_sorting(struct ref_sorting **sorting_tail, const char *arg)
 {
 	struct ref_sorting *s;
 
@@ -2692,17 +2698,25 @@ void parse_ref_sorting(struct ref_sorting **sorting_tail, const char *arg)
 	s->atom = parse_sorting_atom(arg);
 }
 
-int parse_opt_ref_sorting(const struct option *opt, const char *arg, int unset)
+struct ref_sorting *ref_sorting_options(struct string_list *options)
 {
+	struct string_list_item *item;
+	struct ref_sorting *sorting = NULL, **tail = &sorting;
+
+	if (!options->nr) {
+		sorting = ref_default_sorting();
+	} else {
+		for_each_string_list_item(item, options)
+			parse_ref_sorting(tail, item->string);
+	}
+
 	/*
-	 * NEEDSWORK: We should probably clear the list in this case, but we've
-	 * already munged the global used_atoms list, which would need to be
-	 * undone.
+	 * From here on, the ref_sorting list should be used to talk
+	 * about the sort order used for the output.  The caller
+	 * should not touch the string form anymore.
 	 */
-	BUG_ON_OPT_NEG(unset);
-
-	parse_ref_sorting(opt->value, arg);
-	return 0;
+	string_list_clear(options, 0);
+	return sorting;
 }
 
 void ref_sorting_release(struct ref_sorting *sorting)