Missing support for namespaces in JSDoc types

[remcohaszing]

Steps to reproduce

Example code taken from CHANGES.md:

/** @typedef {1} NS.T */

Practical example: simplematter

Behavior with typescript@6.0

Nested typedef names are supported and translate to a type-only namespace.

Behavior with tsgo

This is explicitly no longer supported.

I like type-only namespaces. I also like being able to use them in JSDoc. It appears to be a deliberate choice to no longer support that, so I wanted to provide some feedback that some people actually like this feature.

The proposed substitute is to translate it to a .d.ts file. This is not a substitute however.

• This means the types and implementation can no longer live in the same file.
• This conflicts with the use of "rootDir" and "outDir", because declaration files are not compiled.
• This conflicts with tsc --init, which now emits skipLibCheck: true by default. This means declaration files are not type checked.

So really, there’s no substitute for this syntax.

[DanielRosenwasser]

• This conflicts with the use of "rootDir" and "outDir", because declaration files are not compiled.
• This conflicts with tsc --init, which now emits skipLibCheck: true by default. This means declaration files are not type checked.

To weigh in specifically on these points - if you're doing declaration emit, you can do a non-declaration TypeScript file that only contains ambient/emitless code.

[DanielRosenwasser]

In this code, are you relying on others on the outside to reference simplematter as a type? Or is it just for local clarity?

[remcohaszing]

To weigh in specifically on these points - if you're doing declaration emit, you can do a non-declaration TypeScript file that only contains ambient/emitless code.

This doesn’t allow you to merge a value and type-only namespace in the package exports.

In this code, are you relying on others on the outside to reference simplematter as a type?

It’s a deliberate choice to export the type like this. I like to attach types that are closely related to a value like this, so when the value is imported, the type related types available too. Typically these are names like Options or Props, but even the JSX classic runtime namespace works similarly.

Or is it just for local clarity?

This question does highlight the older issue that @typedef means to both define a type and to export it. It would be great if support for local types is implemented somehow, and TypeScript 7 is an opportunity to make a breaking change for this if necessary.