GDScript: Add return type covariance and parameter type contravariance

modules/gdscript/tests/scripts/analyzer/errors/function_param_type_invalid_contravariance_1.gd

@@ -0,0 +1,10 @@
+class A:
+	func f(_p: Object):
+		pass
+
+class B extends A:
+	func f(_p: Node):
+		pass
+
+func test():
+	pass

modules/gdscript/tests/scripts/analyzer/errors/function_param_type_invalid_contravariance_1.out

@@ -0,0 +1,2 @@
+GDTEST_ANALYZER_ERROR
+The function signature doesn't match the parent. Parent signature is "f(Object) -> Variant".

modules/gdscript/tests/scripts/analyzer/errors/function_param_type_invalid_contravariance_2.gd

@@ -0,0 +1,10 @@
+class A:
+	func f(_p: Variant):
+		pass
+
+class B extends A:
+	func f(_p: Node): # No `is_type_compatible()` misuse.
+		pass
+
+func test():
+	pass

modules/gdscript/tests/scripts/analyzer/errors/function_param_type_invalid_contravariance_2.out

@@ -0,0 +1,2 @@
+GDTEST_ANALYZER_ERROR
+The function signature doesn't match the parent. Parent signature is "f(Variant) -> Variant".

modules/gdscript/tests/scripts/analyzer/errors/function_param_type_invalid_contravariance_3.gd

@@ -0,0 +1,10 @@
+class A:
+	func f(_p: int):
+		pass
+
+class B extends A:
+	func f(_p: float): # No implicit conversion.
+		pass
+
+func test():
+	pass

modules/gdscript/tests/scripts/analyzer/errors/function_param_type_invalid_contravariance_3.out

@@ -0,0 +1,2 @@
+GDTEST_ANALYZER_ERROR
+The function signature doesn't match the parent. Parent signature is "f(int) -> Variant".

modules/gdscript/tests/scripts/analyzer/errors/function_return_type_invalid_covariance_1.gd

@@ -0,0 +1,10 @@
+class A:
+	func f() -> Node:
+		return null
+
+class B extends A:
+	func f() -> Object:
+		return null
+
+func test():
+	pass

modules/gdscript/tests/scripts/analyzer/errors/function_return_type_invalid_covariance_1.out

@@ -0,0 +1,2 @@
+GDTEST_ANALYZER_ERROR
+The function signature doesn't match the parent. Parent signature is "f() -> Node".

modules/gdscript/tests/scripts/analyzer/errors/function_return_type_invalid_covariance_2.gd

@@ -0,0 +1,10 @@
+class A:
+	func f() -> Node:
+		return null
+
+class B extends A:
+	func f() -> Variant: # No `is_type_compatible()` misuse.
+		return null
+
+func test():
+	pass

modules/gdscript/tests/scripts/analyzer/errors/function_return_type_invalid_covariance_2.out

@@ -0,0 +1,2 @@
+GDTEST_ANALYZER_ERROR
+The function signature doesn't match the parent. Parent signature is "f() -> Node".

modules/gdscript/tests/scripts/analyzer/errors/function_return_type_invalid_covariance_3.gd

@@ -0,0 +1,10 @@
+class A:
+	func f() -> Node:
+		return null
+
+class B extends A:
+	func f() -> void: # No `is_type_compatible()` misuse.
+		return
+
+func test():
+	pass

modules/gdscript/tests/scripts/analyzer/errors/function_return_type_invalid_covariance_3.out

@@ -0,0 +1,2 @@
+GDTEST_ANALYZER_ERROR
+The function signature doesn't match the parent. Parent signature is "f() -> Node".

modules/gdscript/tests/scripts/analyzer/errors/function_return_type_invalid_covariance_4.gd

@@ -0,0 +1,10 @@
+class A:
+	func f() -> float:
+		return 0.0
+
+class B extends A:
+	func f() -> int: # No implicit conversion.
+		return 0
+
+func test():
+	pass

modules/gdscript/tests/scripts/analyzer/errors/function_return_type_invalid_covariance_4.out

@@ -0,0 +1,2 @@
+GDTEST_ANALYZER_ERROR
+The function signature doesn't match the parent. Parent signature is "f() -> float".