Formspec: Show a player inventory using core.show_formspec

[SmallJoker]

'core.show_formspec' now shows a temporary inventory formspec as if it was opened using the hotkey on client-side.

Fixes luanti-org/minetest_game#3188 as soon both server and client are >= 5.13.0.

To do

This PR is Ready for Review.

How to test

core.register_chatcommand("fs", {
	func = function(name, param)
		local player = core.get_player_by_name(name)
		if not player then return end -- ncurses

		if core.get_player_information(name).protocol_version < (core.protocol_versions["5.13.0"] or 0) then
			return false, "Not supported by client; formspec inputs are not sent to the server"
		end

		local fs = player:get_inventory_formspec()
		core.show_formspec(name, "", "size[8,8]button[4,4;5,1;x;I do nothing]")

		assert(fs == player:get_inventory_formspec(), "formspecs must still match")

		core.after(2, function()
			-- Force update to the regular inventory formspec
			core.chat_send_player(name, "*** PREVIOUS FORMSPEC RESTORED ***")
			player:set_inventory_formspec(fs)
		end)

		core.after(5, function()
			-- Force close
			core.chat_send_player(name, "*** FORCE CLOSE FORMSPEC TEST ***")
			core.show_formspec(name, "", "")
		end)
		return true
	end
})

1. Open the inventory. Navigate a bit
2. Use /fs. The formspec must show the same thing that you saw last
3. Navigate in the formspec before it closes after 5 seconds
4. Open the inventory using the hotkey. It must show the same formspec that you saw last.

[SmallJoker]

Just realized that my test script misses the point. Updated it to show the advantage, which is in fact inventory mod-independent:

local fs = player:get_inventory_formspec(fs)
core.show_formspec(name, "", fs)

This opens the inventory, although any custom formspec may be provided.

[grorp]

I wonder whether this change is going to be break someone's mod. Currently, you could do core.show_formspec(player:get_player_name(), "", ...) when receiving an event from the inventory formspec to update it temporarily, e.g. to open a dialog. If the user opens the inventory again later, it will still be the inventory formspec set earlier. With this PR, the change will be permanent. Obviously you could just use a different formspec name for the temporary formspec to avoid this.

With grep -P -r 'show_formspec\(.*?, "",' ../games ../mods, I can't see a case in my locally installed content where this would be a problem.

[SmallJoker]

to update it temporarily, e.g. to open a dialog.

On the other hand: if the formspec looks like an inventory formspec, then it would be weird to revert back to the original formspec when re-opening. e.g. when navigating to a recipe when hitting a node with a special tool.
Mods could address this by sending the same formspec twice: 1x for core.show_formspec and 1x for player:set_inventory_formspec(fs).

[SmallJoker]

Changed the implementation to become popup-like.

[grorp]

Changed the implementation to become popup-like.

If I do:

//lua core.show_formspec(core.get_connected_players()[1]:get_player_name(), "", "formspec_version[8]size[3,3]label[0,0.5;Rhododendron]")

then close the formspec and press I to open the regular inventory, I still see the "Rhododendron" formspec. Is that an accident?

[SmallJoker]

@grorp I see. Fixed that. Here's a few more commands for testing:

# Open popup
//lua core.after(3, function() core.show_formspec(core.get_connected_players()[1]:get_player_name(), "", "formspec_version[8]size[3,3]label[0,0.5;Rhododendron]") end)

# Force close inventory
//lua core.after(3, function() core.show_formspec(core.get_connected_players()[1]:get_player_name(), "", "") end)

[grorp]

Looks good. Two nitpicks attached, feel free to change or not.

See also my comment regarding the more explicit documentation, but my approval applies regardless