JSDocs @typedef parsing runs into infinite loop

[clshortfuse]

TypeScript Version: v4.1.0-dev.20200824

Search Terms:

Code

TS:

export type XMLObject<T> = {
  $A: {
    [K in keyof T]?: XMLObject<T[K]>[]
  },
  $O: {
    [K in keyof T]?: {
      $$?: Record<string, string>
    } & (T[K] extends string ? {$:string} : XMLObject<T[K]>)
  },
  $$?: Record<string, string>,
  } & {
  [K in keyof T]?: (
    T[K] extends string ? string
      : XMLObject<T[K]>
  )
};

const p:XMLObject<{foo:string}> = {};

JS:

/**
 * @template T
 * @typedef {{
  $A: {
    [K in keyof T]?: XMLObject<T[K]>[]
  },
  $O: {
    [K in keyof T]?: {
      $$?: Record<string, string>
    } & (T[K] extends string ? {$:string} : XMLObject<T[K]>)
  },
  $$?: Record<string, string>,
  } & {
  [K in keyof T]?: (
    T[K] extends string ? string
      : XMLObject<T[K]>
  )
}} XMLObject<T> */

/** @type {XMLObject<{foo:string}>} */
const p = {};

Expected behavior:

VSCode Intellisense outputs should match and results should somewhat as fast in JS as in TS.

Actual behavior:

Extremely long parsing time, Intellisense mismatch and long, infinitely looping type details. Hovering over XMLObject in the playground link takes a very long time on JS.

JS:

TS:

Playground Link:

JS: https://www.typescriptlang.org/play?ts=4.1.0-dev.20200824&useJavaScript=true#code/PQKhCgAIUgBAXApgWwA4BsCGTIBUowICeqiAJogGaQDeNUkAJAIIBctDkkA2gNKQBLAHaQA1oiIB7argC6AfnYANALIAZAPIAjAFaIAxvAA8uPrIB83WQwC+AGgaMN7ely59BI8VJkKXnN0ZGRUgAJQNJACcyIwBneEjhAHM7SHjEoSTzAJtIADJIAApTXllIRAAPJCEyWLSE5Mh5WkZWdOTc5XVtPUMTM3MASlsHLiCQ8P0omPbM1Nms0chcgtcefmExCWk8PyKAkrLK6tr6jKSms+SAri7NXQNjQ+yuYZtc1Xvep-NoYHBwKBCPASIhaJ8eo8jDRKJJJG0GpkbOZciB-lMhPFIKhIABeWg2ADc4CAA

TS: https://www.typescriptlang.org/play?ts=4.1.0-dev.20200824#code/KYDwDg9gTgLgBDAnmYcAaBZAMgeQEYBWwAxjADwAqAfHALxwDeAUHHACQCCAXIy63AG0A0nACWAOzgBrYIggAzOBQC6Afh6ZchEuQrDlVAcr4BfADR82OHs36CRE6bIVK1NvnbZt1cAEoloABMyAGcYKAkAczM4MIjxSKoPOBM4ADI4AAo9IWU4UBhgcUCQ2PCouFVGNi44qNSNbHwiUkp9KgBKUwtWLx9-YiDQ8oSYuoSqHpT03lZhMUkZOUUVH0zknLyCopKy+MjKvajk1katFt12vi6TAG4mJkHxMLgwLk1mnTIGeQgIWpGkRMNHoDDuTCAA

Related Issues:

[clshortfuse]

I see what's going on. The JSDocs parser is including $A and $O as part of T when it runs the last [K in keyof T].

I can work around the issue by breaking apart the first part into its own type first.

export type XMLObjectBase<T> = {
  $A: {
    [P in keyof T]?: XMLObject<T[P]>[]
  },
  $O: {
    [P in keyof T]?: {
      $$?: Record<string, string>
    } & (T[P] extends string ? {$:string} : XMLObject<T[P]>)
  },
  $$?: Record<string, string>,
};

export type XMLObject<T> = XMLObjectBase<T> & {
  [K in keyof T]?: (T[K] extends string ? string : XMLObject<T[K]>)
};

The parser is probably compiling a type as one big one on the fly and getting stuck in an infinite loop.

[sandersn]

I thought this might be the result of changing ? to parse as a type postfix only when no other interpretation is possible, but the bad behaviour repros on 3.9 and 4.0 too.

[sandersn]

The code that makes recursive type aliases work failed on typedefs. #40861 fixes this.