GDScript 2.0: "Trying to return a typed array with an array of a different type"

[1xch]

Godot version

4.0.alpha6.official.e4f0fc50f

System information

Linux Ubuntu 20.04

Issue description

Project launched with F5 stops running with breakpoint error:

trying to return a typed array with an array of a diffent type.'

Steps to reproduce

In short for illustration purposes here, this function:

func build(s:Session, c:ConfigFile):
	set_session(s)
	build_arrays(c, _build_test())
	print("BUILD_TEST")

func _build_test() -> Array[Array]:
	return [
		["test", ["test-unmodifiable"], "test", Operator.SYNC],
		["test", ["test-unsyncable"], "test", Operator.READ|Operator.WRITE],
		["test", ["test-string", "test-stringmulti"], "test", Operator.caching_full],
		["test", ["test-bool", "test-boolmulti"], "test", Operator.caching_full],
		["test", ["test-int", "test-intmulti"], "test", Operator.caching_full],
		["test", ["test-float", "test-floatmulti"], "test", Operator.caching_full],
		["test", ["test-vec", "test-vecmulti"], "test", Operator.caching_full],
		["test", ["test-tooltip"], "test", Operator.caching_full],
		["test", ["aaaa", "bbbb", "cccc", "xxxx"],  "test", Operator.caching_full],
	]

goes through the below funcs:

static func build_arrays(c:ConfigFile, d:Array[Array]) -> Array[CNF]:
	var accum:Array[CNF]
	for v in d:
		accum = build_array(c, v, accum)
	return accum

static func build_array(c:ConfigFile, d:Array, accum:Array[CNF]) -> Array[CNF]:
	var get_section = d[0] as String
	var keys = d[1] as Array[String]
	var put_section = d[2] as String
	var flagged = d[3] as int
	return build_keys(keys, c, get_section, put_section, flagged, accum)

static func build_keys(
	keys, # :Array[String],
	c:ConfigFile,
	get_section:String,
	put_section:String,
	flagged:int,
	accum:Array[CNF]) -> Array[CNF]:
	for k in keys:
		var nc = build_cnf(
				c,
				get_section,
				put_section,
				k,
				flagged)
		accum.append(nc)
	return accum  # !!!!!!!!!! ERROR IS HERE in editor 

static func build_cnf(c:ConfigFile, gs:String, ps:String, k:String, cf:int) -> CNF:
	var cnf_val = c.get_value(gs, k, null)
	var pad_val = c.get_value("pad", k, {})
	return CNF.new([gs, k], [ps, k], cnf_val, cf, pad_val)

editor breakpoint error occurs at the return of build_keys with the cooccuring terminal output is:

ERROR: Assignment of arrays of incompatible types.
   at: _assign (core/variant/array.cpp:221)

The accumulator is going in as Array[CNF] and coming out as Array[CNF].

Minimal reproduction project

No response

[1xch]

Likely duplicate or relative of #59879, #59721, #59485

Removal of typed arrays allows processing to continue.

[NoodleSushi]

Encountered this issue in 4.0.alpha6
I made a Array[BaseTag] variable catch a function that returns Array[BaseTag], yet the error occurs. It works when I made the function return an untyped Array.