Template Method Pattern does not work with @override

[mlhaufe]

import {Contracted, override} from "@final-hill/decorator-contracts"

@Contracted()
class A {
    constructor() {
        this.method()
    }

    method() {
        console.log('A.method()')
    }
}


class B extends A {
    @override
    method() {
        console.log('B.method()')
    }
}

new B() // No output

[mlhaufe]

Looks like the underlying issue is that super() is called (which then calls a method) before the feature can be restored to it's
implementation.

// Contracted.ts
abstract class InnerContracted extends Base {
    ...
    constructor(...args: any[]) {
        super(...args);
        ...
    }
    ...
}

TypeScript 4.6 is wanted here as it supports code before super() but this release is still in beta:

https://devblogs.microsoft.com/typescript/announcing-typescript-4-6-beta/#code-before-super

A near-term ugly alternative is to use an IIFE in the super call itself:

super(
    ...((...args) => { 
        ...
        return args
    })(...args)
)

In either case there is a challenge due to the this references in the current constructor body.

Is there an alternative approach through the @override stub?

//override.ts
...

// method decorators are evaluated before class decorators
return {
    enumerable: true,
    configurable: true,
    ...(!feature.isAccessor ? {writable: true} : {}),
    ...(feature.hasGetter ? {get(){ assert((this.constructor as any)[isContracted], MSG_NOT_CONTRACTED); } } : {}),
    ...(feature.hasSetter ? {set(_){ assert((this.constructor as any)[isContracted], MSG_NOT_CONTRACTED); } } : {}),
    ...(feature.isMethod ? {value() { assert((this.constructor as any)[isContracted], MSG_NOT_CONTRACTED); } } : {})
};

[mlhaufe]

Looks like the semantics of decorators is changing soon (breaking change), so this fix will need to be delayed a bit:

microsoft/TypeScript#50820