fix: deep partial working with active records create and merge

[bellstrand]

Description of change

#8817 partially broke create & merge functions in Active Record setups.

@Entity()
export class Item extends BaseEntity {
    @PrimaryColumn()
    id: string
    @Column()
    value: number
}

const input: Pick<Item, "value"> = { value: 42 }
const item = Item.create(input)

currently fails to compile because of

No overload matches this call.
  Overload 1 of 3, '(this: (new () => Item) & typeof BaseEntity, entityLikeArray: DeepPartial<Item>[]): Item[]', gave the following error.
    Argument of type 'Pick<Item, "value">' is not assignable to parameter of type 'DeepPartial<Item>[]'.
      Type 'Pick<Item, "value">' is missing the following properties from type 'DeepPartial<Item>[]': length, pop, push, concat, and 26 more.
  Overload 2 of 3, '(this: (new () => BaseEntity) & typeof BaseEntity, entityLike: DeepPartial<BaseEntity>): BaseEntity', gave the following error.
    Argument of type 'Pick<Item, "value">' is not assignable to parameter of type 'DeepPartial<BaseEntity>'.ts(2769)
BaseEntity.ts(185, 12): The call would have succeeded against this implementation, but implementation signatures of overloads are not externally visible.

Pull-Request Checklist

• Code is up-to-date with the master branch
• npm run format to apply prettier formatting
• npm run test passes with this change
• This pull request links relevant issues as Fixes #9150
• There are new or updated unit tests validating the change
• Documentation has been updated to reflect this change - N/A
• The new commits follow conventions explained in CONTRIBUTING.md

[pleerock]

Thanks for the contribution.

We need a better solution that solves all the issues. Now it breaks DeepPartial<Item> usage and solves Pick<Item, "value"> issue. But DeepPartial<Item> also a valid issue.

So the question is what other usages currently break? Maybe root cause is different and we should seek for a different solution?

[pleerock]

I think current implementation is just a hack it doesn't really solve the issue.

Solution to the issue is to explicitly specify Item to a generic parameter T:

Item.create<Item>(input)

I don't think this issue can be resolved until microsoft/TypeScript#5863 would be.

[pleerock]

Closing as there is no answer from author.