Incomprehensible error message when parameter clashes with type in Lib.d.ts

[NoelAbrahams]

Hi,

TS: 1.4

The following code:

declare module foo {

    interface DragEvent {

        foo(): void;
        dataTransfer: DataTransfer;
    }

    interface Baz {

        bar(handler: (event: foo.DragEvent) => void): void;
    }

    interface BazInternal {

        equals(other: Baz): boolean;
    }
}

class Baz implements foo.BazInternal {

    public equals(other: Baz) {
        return true;
    }

    public bar(handler: (event: DragEvent) => void) {
    }
}

Causes the compiler to issue an incomprehensible error message:

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'.    

The relevant items are:

• The signature for public bar should have been public bar(handler: (event: foo.DragEvent) => void)
• To reproduce the error, the interface foo.DragEvent should have an additional method foo(): void; (in order to distinguish it from the type in lib.d.ts)
• For the line Type 'Baz' is not assignable to type 'Baz' to be printed there should be both a class and an interface called Baz.

Related issues: #1419 #1796

[DanielRosenwasser]

Type 'Baz' is not assignable to type 'Baz'.

As this is related to #1419, #1575 should partially help with some of what you're seeing here.

[DanielRosenwasser]

If we could actually get the Type 'Baz' is not assignable to type 'Baz'. portion fixed, then this would at least not be quite as crazy. Unfortunately we"re not doing that somewhere.

[mhegazy]

this shoudl be fixed now. it shows:

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 'foo.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 'foo.DragEvent'.
Property 'foo' is missing in type 'DragEvent'.