Repository navigation
Expressions in JS special assignments don't use jsdoc for contextual type #25571
Description
TypeScript Version: 3.0.0-dev.20180710
Search Terms: tagged discriminated union property this jsdoc checkjs allowjs literal
The following typescript works great:
type DoneStatus = {
status: 'done';
count: number;
};
type ErrorStatus = {
status: 'error';
error: Error;
};
type Status = DoneStatus | ErrorStatus;
class Thing {
s: Status;
constructor() {
this.s = { status: 'done', count: 3 };
}
fail() {
this.s = { status: 'error', error: new Error() };
}
}However, the equivalent JS does not:
/**
* @typedef DoneStatus
* @property {'done'} status
* @property {number} count
*/
/**
* @typedef ErrorStatus
* @property {'error'} status
* @property {Error} error
*/
/** @typedef {DoneStatus | ErrorStatus} Status */
class Thing {
constructor() {
/** @type {Status} */
this.s = { status: 'done', count: 3 }; // ts error
}
fail() {
this.s = { status: 'error', error: new Error() }; // ts error
}
}Both assignments give the error:
[ts] Type 'string' is not assignable to type '"error" | "done"'.
test.js(3, 4): The expected type comes from property 'status' which is declared here on type 'DoneStatus | ErrorStatus'
(property) status: string
Expected behavior:
JS behaves the same as TS version
Activity
mhegazy commentedon Jul 11, 2018
looks like the contextual type is not picked up correctly for the special property assignment case.
[-]Can't assign immediate values to tagged union properties in JS mode[/-][+]Expressions in JS special assignments don't use jsdoc for contextual type[/+]sandersn commentedon Jul 12, 2018
I'm going to make a partial fix that makes these assignments appropriately context sensitive, which fixes this bug, but then work on a permanent fix that makes the type of other assignments, like
correctly assign
{ status: 'done' }as the type ofF.prototype. This a bigger change that is probably not appropriate for 3.0.1. Hard to say without trying it first.Explicitly typed js assignments: context sensitive
Explicitly typed special assignments are context sensitive (#25619)
akdor1154 commentedon Jul 13, 2018
Nathan Shively-Sanders (@sandersn) is this the best way of asserting member types? i.e. the one thing I wasn't sure of was should I be using some
@propertyassertion instead? I just couldn't find a way to get it to work - if I add a@propertytag to myclassthen TS interprets it as a static property, not instance.On my reading of jsdoc docs it seems using
@typeat the assignment point is considered correct, just wanted to check :)sandersn commentedon Jul 16, 2018
In Javascript, the pattern that the compiler expects is modelled on Closure:
Basically it's just looking for assignments to
this.propertyName. If the assignment has an initialiser, it will use its type unless there is a type annotation. The compiler actually looks in any method, not just constructors, but assignments in the constructor are definite -- they don't include undefined in the type like assignments in methods do.We have a proposal for a
@propertytags that would go above the class, but those would result in slower code than just initialising properties in the constructor since the VM will end up creating fewer hidden classes for classes with uniform sets of properties.