The inferred type of 'createTestModel' references an inaccessible 'unique symbol' type.

[cdauth]

Issue Creation Checklist

• I understand that my issue will be automatically closed if I don't fill in the requested information
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Bug Description

I am in the process of upgrading from Sequelize 6.3.5 to 6.30.0 (and from TypeScript 4.1.3 to 5.0.3). In my code I use functions that return model classes. While these functions previously worked, TypeScript is now throwing the following error:

The inferred type of 'createTestModel' references an inaccessible 'unique symbol' type. A type annotation is necessary.ts(2527)

This only happens when the function (or a type derived from it) is exported. If it is exclusively used within the model, no error is raised.

It seems that Sequelize 6.13.0 is that last version where this works without an error.

Reproducible Example

export function createTestModel() {
	return class TestModel extends Model {
		declare id: string;
	};
}

What do you expect to happen?

I expect the type to be inferred automatically, as it was possible in the previous version.

Environment

• Sequelize version: 6.30.0
• Node.js version: 19.7.0
• TypeScript version: 5.0.3
• Database & Version: (not relevant)
• Connector library & Version: (not relevant)

Would you be willing to resolve this issue by submitting a Pull Request?

• Yes, I have the time and I know how to start.
• Yes, I have the time but I will need guidance.
• No, I don't have the time, but my company or I are supporting Sequelize through donations on OpenCollective.
• No, I don't have the time, and I understand that I will need to wait until someone from the community or maintainers is interested in resolving my issue.

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[WikiRik]

I've removed the stale label to give us a bit more time to get to this report. There's been quite some changes under the hood since 6.13.0 due to our initial TypeScript migration which probably caused this issue

[cdauth]

This is still a blocker for me.

I have found the following workaround, which seems to work for me:

export interface TestModel extends Model<InferAttributes<TestModel>, InferCreationAttributes<TestModel>> {
    id: string;
}

export function createTestModel(): ModelStatic<TestModel> {
    return class TestModel extends Model {} as any;
}

[ToTheHit]

Same problem with follow code:

function SomeFn() {
  class AnimalModel extends Model {}
  return AnimalModel;
}

export type TAnimalStatic = ReturnType<typeof SomeFn>;
export type TAnimalInstance = InstanceType<TAnimalStatic>;

Typescript throw error only when exporting at least one type.

Sequelize version: 6.35.2
Node.js version: 20.8.0
TypeScript version: 5.2.2

[ToTheHit]

This bug will be fixed after removing follow code

sequelize/packages/core/src/model-typescript.ts

Lines 353 to 356 in 1f99151

	// TODO [>7]: Remove this
	private static get _indexes(): never {
	throw new Error('Model._indexes has been replaced with Model.getIndexes()');
	}

[WikiRik]

This bug will be fixed after removing follow code

sequelize/packages/core/src/model-typescript.ts

Lines 353 to 356 in 1f99151

	// TODO [>7]: Remove this
	private static get _indexes(): never {
	throw new Error('Model._indexes has been replaced with Model.getIndexes()');
	}

That's code from v7, and the original issue is for an issue in v6 where we do not have a model-typescript.ts file

[ToTheHit]

This bug will be fixed after removing follow code

sequelize/packages/core/src/model-typescript.ts

Lines 353 to 356 in 1f99151

	// TODO [>7]: Remove this
	private static get _indexes(): never {
	throw new Error('Model._indexes has been replaced with Model.getIndexes()');
	}

That's code from v7, and the original issue is for an issue in v6 where we do not have a model-typescript.ts file

Oops.. My bad, sorry...

There is also a error in v7 with same code examples. Maybe I will create issue for that later

For v6 I created a PR. I don't know why there was a comment "Do not export", but if we export ForeignKeyBrand TypeScript's error will be fixed.

[ephys]

I'm trying to replicate the issue in https://github.com/sequelize/sequelize-sscce, I tried against Sequelize 6.36 and 7.0.0-alpha.36, with TypeScript 5.0.3 and 5.3.3, but I can't manage to get the error

Could you fork that repo and try to replicate the bug there?

[ToTheHit]

I'm trying to replicate the issue in https://github.com/sequelize/sequelize-sscce, I tried against Sequelize 6.36 and 7.0.0-alpha.36, with TypeScript 5.0.3 and 5.3.3, but I can't manage to get the error

Could you fork that repo and try to replicate the bug there?

You need to add option "declaration": true in tsconfig.json.

Before fix (#16933)

Screenshot before fix

After fix

Screenshot after fix

For sequelize vesrion 7.0.0+ typescript throw error TS4094: Property _indexes of exported class expression may not be private or protected.. In previous comment I suggested how to fix it.
BTW this is not a sequelize bug, but typescript:

1. Allow .d.ts files to represent anonymous class expressions with private members microsoft/TypeScript#36060
2. False error TS4094: ... exported class expression may not be private or protected. microsoft/TypeScript#30355