JSDoc present in mapped types is not output in generated type literals in declaration files

🔎 Search Terms

generated declaration files mapped types jsdoc missing

🕗 Version & Regression Information

• This is the behavior in every version I tried, and I reviewed the FAQ for entries about: I don't believe the FAQ contains anything applicable to this.

⏯ Playground Link

https://www.typescriptlang.org/play/?#code/JYWwDg9gTgLgBALzgMyhEcDkCIBNMBQBApgB6SxwDGEAdgM7z1UAWxIAhnALyIB0EAEYArYlRgAKAN4E4cAPQAqRbLmK4AZXTE4tYFR0ApDQBEIVVXEXzVyCBABc-RlGC0A5hICUAGgIBfLyIaBnhSHjhmNk4+MA4oemJpO0csDkxAvhTLOVy8-ILCuXl5OAA9CrgWCAA3YlcPFHtI6oB3ejgYNjhjMwsgA

💻 Code

This is not the same issue as https://github.com/microsoft/typescript/issues/50715, that issue is about type mappings that lose the JSDoc period.

I'm talking about what happens in the .d.ts file generated for source like this where JSDoc does survive type mapping:

import z from 'zod'

export const schema = z.object({
  /**
   * Some nice JSDoc
   */
  foo: z.string(),
})

const x = schema.parse({foo: 'a'}).foo
                                // ^^^ hovering foo shows the JSDoc

🙁 Actual behavior

Hovering the parsed .foo in the source file displays the JSDoc for the property:

But if I consume the same type from the generated .d.ts file, I don't get the JSDoc:

🙂 Expected behavior

We should get the same JSDoc when consuming the .d.ts file as we do when consuming the source file it was generated from.

Additional information about the issue

If we look at the generated .d.ts the problem is clear: tsc isn't outputting JSDoc it has in memory for mapped type properties to the generated type literals:

import z from 'zod';
export declare const schema: z.ZodObject<{
  /**
   * Some nice JSDoc
   */
  foo: z.ZodString;
}, "strip", z.ZodTypeAny, {
  foo: string; // (tsc should have copied the JSDoc to this property)
}, {
  foo: string; // (and to this one)
}>;
//# sourceMappingURL=Schema.d.ts.map

It would at least be nice to have an option to output these copies of JSDoc, even though it would make the declaration file bigger.

Reproduce the mapped-type declaration output using the linked TypeScript Playground and compare the generated .d.ts with the source JSDoc. Trace the declaration emitter and mapped-type property handling, then add coverage showing that generated type literals preserve the JSDoc and verify the expected declarations.