JS declarations for an export assigned class expression can conflict with local names

[weswigham]

Per this comment on the PR, the JS declaration emitter currently has a known issue where an export assigned class expression with a name can cause a conflict with another named declaration in the file and produce an invalid declaration file.

So, for example, this:

class A { member = new Q(); };
class Q { x = 12 };
module.exports = class Q { x = new A(); }

currently emits along the lines of

declare class A { member: Q; };
declare class Q { x: number };
declare class Q { x: A; }
exports = Q;

(because it reused the anonymous class's name for the hoisted class declaration) which isn't quite right.

[Bnaya]

I have a similar issue with esm default export:
code:

import React from "react";
/**
 * @type {React.FunctionComponent}
 */
const TabbedShowLayout = ({
    classes: classesOverride,
    className,
    version,
}) => {
    return (
        <div className={className} key={version}>
            {className}
        </div>
    );
};


TabbedShowLayout.defaultProps = {
    tabs: "default value"
};

export default TabbedShowLayout;

emitted declarations:

export default TabbedShowLayout;
/**
 * @type {React.FunctionComponent}
 */
declare const TabbedShowLayout: React.FunctionComponent;
declare namespace TabbedShowLayout {
    export const defaultProps: Partial<any> | undefined;
}
import React from "react";

Errors:
Cannot redeclare block-scoped variable 'TabbedShowLayout'.

[Bnaya]

Additional breakage with javascript:

import React from "react";
import PropTypes from "prop-types"

const TabbedShowLayout = ({
}) => {
    return (
        <div />
    );
};

TabbedShowLayout.propTypes = {
    version: PropTypes.number,

};

TabbedShowLayout.defaultProps = {
    tabs: undefined
};

export default TabbedShowLayout;

d.ts:

export default TabbedShowLayout;
declare function TabbedShowLayout({}: {}): JSX.Element;
declare namespace TabbedShowLayout {
    export namespace propTypes {
        import version = PropTypes.number;
        export { version };
    }
    export namespace defaultProps {
// Cannot export 'undefined'. Only local declarations can be exported from a module
        export { undefined as tabs };
    }
// Import declarations in a namespace cannot reference a module.ts(1147)
// Cannot find module 'prop-types'.ts(2307)
    import PropTypes from "prop-types";
}

[Bnaya]

I'm not sure how common is it to emit invalid types
But i think it will be very useful if the emitter would check the declarations it emits as a fail safe,
and warn the user what something went wrong. maybe prompt to open an issue or so.

[Bnaya]

Is it on the roadmap to 3.7 final?

[weswigham]

It should be, yeah - I'm just on vacation this week, so probably won't progress on it for a bit.

[Bnaya]

I hope this issue won't be forgotten for 3.7 🙏😰

[weswigham]

@Bnaya I have a build over in #34786 that I'd love if you could give a try.

[Bnaya]

Thank you very much!
seems like most of the issues are gone

some of the findings:

import React from 'react';
import PropTypes from 'prop-types';

function Tree({ allowDropOnRoot }) {
  return <div />
}

Tree.propTypes = {
    classes: PropTypes.object,
};

Tree.defaultProps = {
    classes: {},
    parentSource: 'parent_id',
};

export default Tree;

emits broken:

export default Tree;
declare function Tree({ allowDropOnRoot }: {
    allowDropOnRoot: any;
}): JSX.Element;
declare namespace Tree {
    export namespace propTypes {
        export const classes: PropTypes.Requireable<object>;
    }
    export namespace defaultProps {
 // Cannot find name 'classes_1'
        export { classes_1 as classes };
        export const parentSource: string;
    }
}
import PropTypes from "prop-types";
//# sourceMappingURL=Tree.d.ts.map

When removing the propTypes.classes the problem is gone.

EDIT:
Also it depends on the namespace for the prop-types module and not importing it,
even that on the source, its importing it