Thanks for the contribution. You need to squash the commits together (as described in http://docs.godotengine.org/en/latest/community/contributing/pr_workflow.html#mastering-the-pr-workflow-the-rebase).

Sure - no problem. Just squashed my commits.

For the reference, so far there seems to be only three uses of this undocumented feature:

servers/physics_server.cpp
244:    ADD_PROPERTY(PropertyInfo(Variant::ARRAY, "exclude", PROPERTY_HINT_NONE, itos(Variant::_RID) + ":"), "set_exclude", "get_exclude");

servers/physics_2d_server.cpp
251:    ADD_PROPERTY(PropertyInfo(Variant::ARRAY, "exclude", PROPERTY_HINT_NONE, itos(Variant::_RID) + ":"), "set_exclude", "get_exclude");

scene/gui/rich_text_label.cpp
2720:   ADD_PROPERTY(PropertyInfo(Variant::ARRAY, "custom_effects", PROPERTY_HINT_RESOURCE_TYPE, "17/17:RichTextEffect", (PROPERTY_USAGE_DEFAULT | PROPERTY_USAGE_SCRIPT_VARIABLE), "RichTextEffect"), "set_effects", "get_effects");

The syntax is quite non-obvious.

It was implemented by @bojidar-bg in #6930, fixing #3586.

Are you sure that those changes don't break the GDScript export hints?

Thank you for looking into it.

So I did check use-cases you have mentioned - and my fix crashes editor for one of them (resource hint), and doesn't fix every other case (sub-property hint).

I think we need to step back and re-think it a bit - since we have more than one format here.

Summary:

ADD_PROPERTY(PropertyInfo(Variant::ARRAY, "hints_array", PROPERTY_HINT_NONE, itos(Variant::NODE_PATH)+":"+itos(PROPERTY_HINT_NODE_PATH_VALID_TYPES)+"/RigidBody"), "set_hints", "get_hints");

master: sub-hint not working
my fix: works as expected

ADD_PROPERTY(PropertyInfo(Variant::ARRAY, "hints_array2", PROPERTY_HINT_NONE, itos(Variant::NODE_PATH)+":"), "set_hints2", "get_hints2");

master: works as expected
my fix: works as expected

ADD_PROPERTY(PropertyInfo(Variant::ARRAY, "hints_array3", PROPERTY_HINT_NONE, itos(Variant::NODE_PATH)+":Path2D/PathFollow2D/Sprite:texture:size"), "set_hints3", "get_hints3");

master: sub-hint not working
my fix: sub-hint not working

I need to look into it more - colon is used in more than one context. It seems, the first colon is hint/sub-hint separator - and any following colon is property descriptor - but I can't confirm this easily.

ADD_PROPERTY(PropertyInfo(Variant::ARRAY, "hints_array4", PROPERTY_HINT_NONE, itos(Variant::_RID) + ":"), "set_hints4", "get_hints4");

master: can't add any element to this array via editor
my fix: can't add any element to this array via editor
but I guess this is correct behavior, since RID's are not(?) persistent

ADD_PROPERTY(PropertyInfo(Variant::ARRAY, "hints_array5", PROPERTY_HINT_RESOURCE_TYPE, "17/17:RichTextEffect", (PROPERTY_USAGE_DEFAULT | PROPERTY_USAGE_SCRIPT_VARIABLE), "RichTextEffect"), "set_hints5", "get_hints5");

master: works as expected
my fix: editor crashes :(

ERROR: Variant::construct: Index p_type=1717 out of size (VARIANT_MAX=27)

The slash left of colon is probably what original code expected.

If I understand this correctly - we can have sub-types left of the colon sign so:
17 = Variant::Object
17 = Resource(?) I'm not sure where it comes from.

Could you confirm this?

Still I think this case can be fixed fairly easily.
btw. perhaps we should create some kind of C++ macro for generating hint strings? This would be a good point of reference.

Hey, sorry for the late comment.

Looking at what I implemented in GDScript and what the previous code was, seems like the format is:
itos(Type(sub_type)) + "/" + itos(PropertyHint(sub_hint)) + ":" + String(sub_hint_string)
or, when not needing a hint:
itos(Type(sub_type)) + ":" + String(sub_hint_string)

While the examples given the above comment (and the new code) expect:
itos(Type(sub_type)) + ":" + itos(PropertyHint(sub_hint)) + "/" + String(sub_hint_string)
or, when not needing a hint:
itos(Type(sub_type)) + ":" + String(sub_hint_string)

Now, in general, the first option should be better since we already require that the colon is there, but the "/" can be ambiguous in the second case (and thus, if the sub_hint_string includes a slash, you would need to add "0/" before it)

@lonegamedev Is this still desired? If so, it needs to be rebased on the latest master branch.

Closing as this is stale. This use case is likely better handled in 4.0 using typed arrays, but this can be reopened if there is still a need for what it implemented.