Fix types resolved from InferSchemaType

[HiiiiD]

Summary

Currently InferSchemaType<> returns weird types when using Schema.Types.*, check #12431 for better explanation

Examples

[hasezoey]

This change seems to break some existing types tests (see test runs), could you maybe fix those and add new ones that this change is meant to address?

Note: in case you dont know how to run those types tests locally:

• install everything with npm install
• and run the types test with npm run test-tsd

[HiiiiD]

Yes, I'm testing right now
I'll add new tests asap

[HiiiiD]

I've rebased on top of master, but I have an issue that I don't know how to fix
I've tried for an hour to find out why required: true with Schema.Types.Decimal128 breaks the types but I haven't found a solution. (So the test at line 725 fails)
Any clues @hasezoey?

[hasezoey]

The following would fix it for now as mentioned in #12431 (comment), though i dont know why it happens (probably a typescript bug?)

index 7c0038a869..ff9914217c 100644
--- a/types/inferschematype.d.ts
+++ b/types/inferschematype.d.ts
@@ -38,7 +38,16 @@ declare module 'mongoose' {
    * // result
    * type UserType = {userName?: string}
    */
-  type InferSchemaType<SchemaType> = ObtainSchemaGeneric<SchemaType, 'DocType'>;
+  type InferSchemaType<SchemaType> = ObtainDocType<SchemaType>; // "ObtainDocType" is used over "ObtainSchemaGeneric", because "ObtainSchemaGeneric" would return a modified result
+
+  /**
+   * @summary Obtains the "DocType" generic of a Schema, has to be used because with "ObtainSchemaGeneric" it would return a modified type
+   * @param {TSchema} TSchema A generic of schema type instance
+   */
+  type ObtainDocType<TSchema> =
+    TSchema extends Schema<any, any, any, any, any, any, any, infer DocType>
+      ? DocType
+      : unknown;
 
   /**
    * @summary Obtains schema Generic type by using generic alias.

inferschematype.patch.txt

[HiiiiD]

I've applied your changes @hasezoey but have failing tests

[hasezoey]

i have updated my comment at #12431 (comment) because it (after some more testing) contained "wrong" information.

it seems like if we dont do infer TPathTypeKey but instead any, then the DocType for the thing this PR is meant to solve, solves it but creates other issues in other places, but as soon as infer SomeName is done again for the TPathTypeKey generic, then the type this PR is trying to solve, breaks again
but i have no clue what that generic is there for or what it affects or why typescript does not give the correct type

[vkarpov15]

I suspect this will be fixed by #12352, I'll check a little later.

[vkarpov15]

Don't do this. For some reason, not inferring all the generics (there's one in particular that is important that I forget) breaks stuff. There's a little more info on this PR: #12352 . I don't know why, TypeScript is filled with delightful little surprises like that.

[vkarpov15]

Confirmed this is fixed by #12352, without any test failures. I'm going to add the test to #12352 and close this issue. Thanks for pointing out this issue 👍