Lambda parameters get an extra "," at the end, causing syntax errors (v0.23.0)

[blabdouze]

If for exemple I want to use a lambda as argument, let's say for filter function :

func _my_func() -> void:
	[0, 2, 3].filter(
		func(value: int):
			match value:
				0:
					return false
				_:
					return true
	)

It will be formated as :

func _my_func() -> void:
	[0, 2, 3].filter(
		func(value: int):
			match value:
				0:
					return false
				_:
					return true,
	)

Notice the extra , added by the formater after return true causing a syntax error.

Same code is correctly formated on 0.21.0.

Related to #287 I think ?

[NathanLovato]

Thanks for the report. Okay that's good to know, parsing of lambdas in function arguments (maybe not only) is quite quirky in GDScript. The trailing comma is usually reliable but, for some reason, maybe because of the match statement, it doesn't work here. I'll have to investigate.

In other situations if you removed the comma you'd get a parse error that GDScript expects the indentation of the closing parenthesis of the function call to match the last statement of the lambda and you'd have to write this:

func _my_func() -> void:
	[0, 2, 3].filter(
		func(value: int):
			match value:
				0:
					return false
				_:
					return true
					)

Another option is always having the closing parentheses tight to a lambda if it ends a list of arguments, like this:

func _my_func() -> void:
	[0, 2, 3].filter(
		func(value: int):
			match value:
				0:
					return false
				_:
					return true)

If you encounter any other cases where the formatter produces a code that has a parse error, please let me know. It's always really useful because there are some syntaxes in GDScript that are finicky and we need all the variants that GDScript does not support to find the right set of rules to work reliably around its quirks.

[blabdouze]

Ok thanks a lot for the tool & the workaround !

[NathanLovato]

Fixed by 9982a81, but the Godot parser is bugged actually and while we can omit the lambda, I think for this specific pattern (lambda ending with match statement) we'll have to wrap in parentheses. The bug is that Godot tries to parse the comma as if it was part of the match statement, it doesn't recognize that it's in an argument list and that the comma means the end of the argument.