Error messages are vague when types have the same name

[DanielRosenwasser]

Consider the following:

module ts {
    export interface Node {
        kind: SyntaxKind;
        pos: number;
        end: number;
    }
}

function f(n: Node) {
    ts.forEachChild(n, () => { /* ... */ });
}

The subtlety is that the user meant to declare ts.Node as the type of n.

Here you'll get the error on n within the forEachChild call, with the message

TS2345 Argument of type 'Node' is not assignable to parameter of type 'Node'.

which is unhelpful because it makes the user feel like they've completely lost their mind.

We should use a qualified name in such cases.

[NoelAbrahams]

which is unhelpful because it makes the user feel like they've completely lost their mind.

true 😃

[DanielRosenwasser]

It reminds me of this Steve Yegge post from way back.

There's nothing more fun than having your compiler tell you: "Error: expected type (int, int, int) but got type (int, int, int)". Sheesh.

You might note the irony of the section that appears in. 😄

[chrisbubernak]

Did anyone ever end up working on this? I took a look at it this morning and it doesn't seem too bad. I'll send out a PR when I get a chance to finish it up & test.

[DickvdBrink]

@chrisbubernak, I worked on this a few weeks back, was a pretty minor change but it ended up breaking some other things (when I looked at the baselines, I believe it was something with the require paths now gone from the baseline), and I never had the time to actually look at it more. :(

[NoelAbrahams]

@DanielRosenwasser /@chrisbubernak,

I ran into this gem today using 1.4:

Class 'Baz' incorrectly implements interface 'BazInternal'.
  Types of property 'equals' are incompatible.
    Type '(other: Baz) => boolean' is not assignable to type '(other: Baz) => boolean'.
      Types of parameters 'other' and 'other' are incompatible.
        Type 'Baz' is not assignable to type 'Baz'.
          Types of property 'bar' are incompatible.
            Type '(handler: (event: DragEvent) => void) => void' is not assignable to type '(handler: (event: DragEvent) => void) => void'.
              Types of parameters 'handler' and 'handler' are incompatible.
                Type '(event: DragEvent) => void' is not assignable to type '(event: DragEvent) => void'.
                  Types of parameters 'event' and 'event' are incompatible.
                    Type 'DragEvent' is not assignable to type 'DragEvent'.
                      Property 'foo' is missing in type 'DragEvent'.

I mean Types of parameters 'other' and 'other' are incompatible might be a candidate for the error messages hall of fame? 😄

[RyanCavanaugh]

That error looks like a bug. Do you have a repro? Or is it that there are two different DomElements?

[NoelAbrahams]

@RyanCavanaugh, there's only one DomElement. While implementing the interface there was a parameter clash with a type in lib.d.ts. Seems to be in the same ball park as this issue, but will take a look at producing a repro.

[DanielRosenwasser]

We're almost there; #1798 is probably the next pain-point to tackle.