Code Action Idea: Fix Missing Argument From Context

[hediet]

class MyService {}

class Foo {
    constructor(
        private readonly myService: MyService
    ) {}

    blah() {
        bar('hello'); // Cursor is here
    }
}

function bar(baz: string, service: MyService) {
    // ...
}

Cursor is on the squiggles.

---

- Use missing argument from context ->

class MyService {}

class Foo {
    constructor(
        private readonly myService: MyService
    ) {}

    blah() {
        bar('hello', this.myService);
    }
}

function bar(baz: string, service: MyService) {
    // ...
}

- Use missing argument from parameter ->

class MyService {}

class Foo {
    constructor(
        private readonly myService: MyService
    ) {}

    blah(myService: MyServic) {
        bar('hello', myService);
    }
}

function bar(baz: string, service: MyService) {
    // ...
}

---

If you could record my code changes, you would see that parameter "wiring" is a task I do very often.

[hediet]

Resharper has an entire Wizard for this. When you use "Introduce parameter", it will go through all callers an offers options to fix those.

Basically, these are the resolution options:

• For functions and methods: Use/Introduce parameter (and go to callers of this method when a new parameter has been added)
• For classes: Use/Introduce field (and go to callers of the constructor when a new constructor parameter is added)
• Use variable in scope

Ideally you could use breadth search on all symbols in scope to find valid expressions.

Also, if there are multiple possible expressions, pre-select the one that has the best levenshtein distance to parameter name (e.g. parameter name is input1: ITextModel, in scope are this.input1TextModel: ITextModel and this.input2TextModel: ITextModel - then you should suggest this.input1TextModel as first option).

I think this feature could be a wow-factor.

[lgrammel]

Wow, thanks for this awesome writeup! "Introduce parameter" is one of the refactorings I was thinking about :)

Just for me to understand your flow better (because the title says "Fix missing argument"), would you primarily need to

• just fix missing argument issues
• or run an "introduce parameter" refactoring on a function/method/constructor
• or both?

[hediet]

I would use this for both. If this recorder tool existed, I could show you exactly what I did and in which way automatisation would have helped me! (and how much time I spent on doing it manually)

[hediet]

Another code example where it would have saved me some seconds:

This feature could find all three missing arguments from the context.

[hediet]

My prototype works nicely:

It is a ts server plugin and heavily uses type checking.

[lgrammel]

This is pretty cool!

P42 is currently limited to type information from a single file for performance reasons - I would need to extend the architecture to be able to get type information that's comparable to what the TS service offers. Do you know if there is a way to access the TS type information from other extensions?