command: export some option metadata

This might be interesting for GUIs and such.

It's probably still a little bit insufficient. For example, the filter
and audio/video output lists are not available through this.

DOCS/man/input.rst

@@ -1446,7 +1446,15 @@ Property list
     Additional per-option information.
 
     This has a number of sub-properties. Replace ``<name>`` with the name of
-    a top-level option.
+    a top-level option. No guarantee of stability is given to any of these
+    sub-properties - they may change radically in the feature.
+
+    ``option-info/<name>/name``
+        Returns the name of the option.
+
+    ``option-info/<name>/type``
+        Return the name of the option type, like ``String`` or ``Integer``.
+        For many complex types, this isn't very accurate.
 
     ``option-info/<name>/set-from-commandline``
 
@@ -1454,6 +1462,21 @@ Property list
         ``no`` otherwise. What this is set to if the option is e.g. changed
         at runtime is left undefined (meaning it could change in the future).
 
+    ``option-info/<name>/default-value``
+        The default value of the option. May not always be available.
+
+    ``option-info/<name>/min``, ``option-info/<name>/max``
+        Integer minimum and maximum values allowed for the option. Only
+        available if the options are numeric, and the minimum/maximum has been
+        set internally. It's also possible that only one of these is set.
+
+    ``option-info/<name>/choices``
+        If the option is a choice option, the possible choices. Choices that
+        are integers may or may not be included (they can be implied by ``min``
+        and ``max``). Note that options which behave like choice options, but
+        are not actual choice options internally, may not have this info
+        available.
+
 ``property-list``
     Return the list of top-level properties.
 

options/m_option.c

@@ -696,7 +696,7 @@ static char *print_choice(const m_option_t *opt, const void *val)
 }
 
 const struct m_option_type m_option_type_choice = {
-    .name  = "String",  // same as arbitrary strings in option list for now
+    .name  = "Choice",
     .size  = sizeof(int),
     .parse = parse_choice,
     .print = print_choice,

options/m_property.h

@@ -189,6 +189,8 @@ struct m_sub_property {
     .type = {.type = CONF_TYPE_STRING}, .value = {.string = (char *)(s)}
 #define SUB_PROP_FLOAT(f) \
     .type = {.type = CONF_TYPE_FLOAT}, .value = {.float_ = (f)}
+#define SUB_PROP_DOUBLE(f) \
+    .type = {.type = CONF_TYPE_DOUBLE}, .value = {.double_ = (f)}
 #define SUB_PROP_FLAG(f) \
     .type = {.type = CONF_TYPE_FLAG}, .value = {.flag = (f)}
 

player/command.c

@@ -3017,14 +3017,46 @@ static int mp_property_option_info(void *ctx, struct m_property *prop,
         if (!co)
             return M_PROPERTY_UNKNOWN;
 
+        union m_option_value def = {0};
+        if (co->default_data)
+            memcpy(&def, co->default_data, co->opt->type->size);
+
+        const struct m_option *opt = co->opt;
+        bool has_minmax =
+            opt->type == &m_option_type_int ||
+            opt->type == &m_option_type_int64 ||
+            opt->type == &m_option_type_float ||
+            opt->type == &m_option_type_double;
+        char **choices = NULL;
+
+        if (opt->type == &m_option_type_choice) {
+            has_minmax = true;
+            struct m_opt_choice_alternatives *alt = opt->priv;
+            int num = 0;
+            for ( ; alt->name; alt++)
+                MP_TARRAY_APPEND(NULL, choices, num, alt->name);
+            MP_TARRAY_APPEND(NULL, choices, num, NULL);
+        }
+
         struct m_sub_property props[] = {
+            {"name",                    SUB_PROP_STR(co->name)},
+            {"type",                    SUB_PROP_STR(opt->type->name)},
             {"set-from-commandline",    SUB_PROP_FLAG(co->is_set_from_cmdline)},
+            {"default-value",           *opt, def},
+            {"min",                     SUB_PROP_DOUBLE(opt->min),
+             .unavailable = !(has_minmax && (opt->flags & M_OPT_MIN))},
+            {"max",                     SUB_PROP_DOUBLE(opt->max),
+             .unavailable = !(has_minmax && (opt->flags & M_OPT_MAX))},
+            {"choices", .type = {.type = CONF_TYPE_STRING_LIST},
+             .value = {.string_list = choices}, .unavailable = !choices},
             {0}
         };
 
         struct m_property_action_arg next_ka = *ka;
         next_ka.key = rem;
-        return m_property_read_sub(props, M_PROPERTY_KEY_ACTION, &next_ka);
+        int r = m_property_read_sub(props, M_PROPERTY_KEY_ACTION, &next_ka);
+        talloc_free(choices);
+        return r;
     }
     }
     return M_PROPERTY_NOT_IMPLEMENTED;