Check using the type annotation for default parameter value and try-catch variable

[kaleidawave]

putting these together because they are pretty much the same implementation

Default parameter value

currently no exception is raised here

function x(a: number = "hi") {}

it should raise an exception for the default parameter value, as the RHS is not subtype-able under number

the code is here, using type_is_subtype with parameter_constraint against value (default_value) and sending the result to checking_data.diagnostics_container with the position using A::expression_position

ezno/checker/src/features/functions.rs

Lines 136 to 147 in b6ead3e

	parameter_constraint: TypeId,
	environment: &mut Environment,
	checking_data: &mut CheckingData<T, A>,
	expression: &'a A::Expression<'a>,
	) -> TypeId {
	let (value, out, ..) = environment.new_lexical_environment_fold_into_parent(
	Scope::DefaultFunctionParameter {},
	checking_data,
	|environment, checking_data| {
	A::synthesise_expression(expression, parameter_constraint, environment, checking_data)
	},
	);

Catch variable

currently no exception is raised here

try {
	throw 5
} catch (e: string) {
	
}

it should raise an exception here 5 is RHS is not subtype-able under number

the code should go here

ezno/checker/src/synthesis/statements.rs

Line 250 in b6ead3e

// TODO subtype thrown here with catch_variable_type

The shape of code

Here you can see how it is done for x satisfies Type. You simply want to import the type_is_subtype function and give the type from the annotation as the LHS type/first argument, then follow the rest.

ezno/checker/src/types/subtyping.rs

Lines 760 to 764 in b6ead3e

	let mut basic_equality = BasicEquality {
	add_property_restrictions: false,
	position: source_map::Nullable::NULL,
	};
	let result = type_is_subtype(to_satisfy, expr_ty, &mut basic_equality, environment, types);

and emitting the error diagnostic

ezno/checker/src/lib.rs

Lines 382 to 400 in b6ead3e

	if !check_satisfies(expr_ty, to_satisfy, &self.types, environment) {
	let expected = diagnostics::TypeStringRepresentation::from_type_id(
	to_satisfy,
	&environment.as_general_context(),
	&self.types,
	false,
	);
	let found = diagnostics::TypeStringRepresentation::from_type_id(
	expr_ty,
	&environment.as_general_context(),
	&self.types,
	false,
	);
	self.diagnostics_container.add_error(TypeCheckError::NotSatisfied {
	at,
	expected,
	found,
	});
	}

---

You want to create custom TypeCheckErrors for both these scenarios, to annotate that it was a InvalidDefaultValue or ThrowDoesNotMatchCatchVariableAnnotation

You also want to add tests to specification.md for the cases above.

As with any issue, if you want more help or questions feel free to ask

[n-keerthi-gayathri]

@kaleidawave please assign me this issue

[CharlesTaylor7]

@kaleidawave @n-keerthi-gayathri
Hey, I'm interested in taking on this task as my first contribution. I'll be following the detailed steps in the issue description, but I'll post again if I run into any issues.