Bug description

Found via StackOverflow: https://stackoverflow.com/q/79232050/634824

TypeScript allows the this keyword to be used as a type.

• https://www.typescriptlang.org/docs/handbook/2/classes.html#this-types
• https://www.typescriptlang.org/docs/handbook/advanced-types.html#polymorphic-this-types

AssemblyScript seems to recognize this syntax and compiles fine:

class X {
 doSomething(): this {
 return this;
 }
}

However, in AssemblyScript, it always is treated as the class where this is used - which is not necessarily the type of the instance when the object is extended.

class Y extends X {
 doSomethingElse(): string {
 return "You made it!";
 }
}

Steps to reproduce

With the above code,

console.log(new Y().doSomething().doSomethingElse());

fails to compile. The error is:

ERROR TS2339: Property 'doSomethingElse' does not exist on type 'assembly/index/X'.
 :
 12 │ console.log(new Y().doSomething().doSomethingElse());
 │ ~~~~~~~~~~~~~~~
 └─ in assembly/index.ts(12,35)

Essentially, y.doSomething() is returning a type X where it should return a type Y.

TypeScript tooling believes the value should be Y, but AssemblyScript thinks it's X.

Image

Casting the value using <Y> or as Y works, but the point is that one may have full awareness of the original type when making the call.

AssemblyScript version

v0.27.32