[1894] Fix a bug allowing for upgradin a green city that you don't have access to

[Galatolol]

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Implementation Notes

Explanation of Change

Currently a corporation can upgrade a green city tile it is next to but doesn't have access to the city (like Ouest on the first screenshot). It shouldn't be possible, it first has to connect to the city.

⚠️ This requires pinning ⚠️

Screenshots

[ollybh]

This isn't the correct way to do this. The player shouldn't be offered the option to place those tiles if the corporation does not have access to any paths on the placed tile.

1894’s implementation of Step::Tracker::legal_tile_rotation? is, for brown city tiles, only checking whether the replacement tile has track connected to the same exits. It should also be checking that one of the paths on the tile is connected to an exit on the corporation’s graph.

This is the test in Engine::Step::Tracker::legal_tile_rotation? that you need to keep:

18xx/lib/engine/step/tracker.rb

Lines 424 to 425 in 4d661ea

	entity_reaches_a_new_exit = !(new_exits & hex_neighbors(entity, hex)).empty?
	return false unless entity_reaches_a_new_exit

[Galatolol]

@ollybh Thank you for the suggestion, I agree that it's better to not offer upgrades at all.

[ollybh]

The logic here looks correct. The only thing I would change is to use a slightly more efficient way for testing for array intersection: arr1.intersect?(arr2) instead of (arr1 & arr2).empty?. You could also stick it as a single liner, but Rubocop might object to the line length.

Suggested change

	if @game.class::GREEN_CITY_TILES.include?(hex.tile.name)
	entity_reaches_a_new_exit = !(tile.exits & hex_neighbors(entity, hex)).empty?
	return false unless entity_reaches_a_new_exit
	end
	return false if @game.class::GREEN_CITY_TILES.include?(hex.tile.name) && !tile.exits.intersect?(hex_neighbors(entity, hex))

[Galatolol]

Robocop accepts the "one-liner" divided in two: