"Class XXX used before its declaration" breaking change in 2.3.0

[s-panferov]

TypeScript Version: typescript@rc 2.3.0

Code

export interface IconProps {
    size?: number;
}

// I use this to create a type that has `size` non-nullable 
// (because it always present due to `defaultProps`
type SafeProps = IconProps & typeof Icon.defaultProps;

export default class Icon extends React.Component<IconProps, any> {
    static defaultProps = {
       size: 10
    };

    render() {
        // cast to SafeProps to safely extract `size`
        const { size } = this.props as SafeProps
        return <div style={{ size }} />
    }
}

Expected behavior:
It compiles. This actually works in 2.2.2

Actual behavior:

Class 'Icon' used before its declaration on line type SafeProps = IconProps & typeof Icon.defaultProps;

Is this an intended breaking change?

[sandersn]

Looks like references to block-scoped variables should be allowed inside typeof in a type.

[gcnew]

There is a similar PR for const - #14700. May it get merged as well?

[sandersn]

Yes, I'll go ahead and merge it after resolving conflicts.

This is still showing errors if the class and its use are in separate files.

a.ts

let foo: typeof C;

b.ts

class C {}

tsconfig.json

{
  "compilerOptions": {
      "outFile": "foo"
  }
}

Shows: src/a.ts(1,17): error TS2449: Class 'C' used before its declaration.

[mhegazy]

tracking as #15998