getting "error TS2677: A type predicate's type must be assignable to its parameter's type."

Versions

• System: linux
• NodeJS: 14.18.0
• Typescript: 4.9.3
• Compiler / Transpiler: tsc
• Typegoose(NPM): ^9.13.0
• Typegoose(GIT): commithash
• mongoose: 6.7.3

What is the Problem?

npm run tsc fails to build with this error:

node_modules/@typegoose/typegoose/lib/typeguards.d.ts:8:82 - error TS2677: A type predicate's type must be assignable to its parameter's type.
  Type 'T extends DocumentType<infer T1, infer T2> ? DocumentType<T1, T2> : T extends object ? DocumentType<T, BeAnObject> : never' is not assignable to type 'Ref<T, S>'.
    Type 'DocumentType<unknown, unknown> | (T extends object ? DocumentType<T, BeAnObject> : never)' is not assignable to type 'Ref<T, S>'.
      Type 'DocumentType<unknown, unknown>' is not assignable to type 'Ref<T, S>'.
        Type 'DocumentType<unknown, unknown>' is not assignable to type 'S'.
          'S' could be instantiated with an arbitrary type which could be unrelated to 'DocumentType<unknown, unknown>'.

8 export declare function isDocument<T, S extends RefType>(doc: Ref<T, S>): doc is T extends DocumentType<infer T1, infer T2> ? DocumentType<T1, T2> : T extends object ? DocumentType<T> : never;

Do you know why it happens?

no

---

[hasezoey]

i just noticed that the hotfix works as long as the source-file is directly used, but the declaration file (compiled output) does not work because it did not actually transfer the @ts-ignore

so the only workaround is to use a older typescript version (being 4.8) and waiting for typegoose 10.0 (beta build coming soon) which updated those types to work on typescript 4.9

[hasezoey]

The Typescript issue i had opened has been closed as “not planned” (and more or less “working as intended”), so there will be no fix for typescript 4.9 for typegoose 9.x, see https://github.com/microsoft/TypeScript/issues/51638; continue to use typescript 4.8 as a workaround

Note: typegoose 10.0 will have typescript 4.9 support (and minimal requirement) and a beta has already been released