Error not issued when global type is an alias of an object type literal

[rotu]

🔎 Search Terms

array, constructor, bracket

🕗 Version & Regression Information

• This is a crash

⏯ Playground Link

https://www.typescriptlang.org/dev/bug-workbench/?noLib=true&target=99&ts=5.5.0-dev.20240227#code/PTAEAEDsHsBkEsBGAuUAXATgVwKYCgQI0BDDAcxzVRwGdIcAPNPPAExwGMAbUnUMrtETEuoAN55QoDtEg00oAIIYMxAJ6oJUqQB4AKqAC8oLJADWMAO6QAfAAoAdE9JkayYpDUBtALoBKVGVVNX0bSW16S1B9IxNzK0gAGnsnBxc3D29-QJV1UPCAXxYpNDUABz4gvL0bWK1tL3hUSCwAW0QcDB9UPXCpLhxIMjQAC2a2joxCvCKCMBFRaAAzdBG+DsEosngANz4AIgAFDGgKjFLQAHIBodHL0HgaUFbHmnghh8h0cr5LsQLLql9sg8ABuUB2LwARkSoAATLCAMz+UA0YhoR5LeC0JS5EItdqdGygsEQ6GwhGgZF+VHozHYp5iUA3YZjUAEyagAok9jcXjSWTyUCkKHNHB7DC+Uki2kYmhYnFMlmjcaEjBcnmcHgYPgyOQKUhw1WTKXgw2y+mK5mDVnGzpclhzVaPVEjaBYLisVYnKIeUCdE7qxBYBTwBSsaC0SCXZiEcBoGgAWkYFQ4aGTKmgU3BkJ8wqeHM6vhpaLlCqe8gw7zIUrwKazCiZBSAA

💻 Code

// @noLib: true
// @target: esnext

declare global {
  const Array: {
    <T = unknown>(...args:any[]): Array<T>
    new <T = unknown,>(...args:any[]): Array<T>
  }

  type Array<T> = {
    [i: number]: T
    length: number
  }
}

// all of the below give "Property 'length' is missing in type '{}'...":
; ([1, 2, 3]) satisfies Array<number>;
; ([1, 2, 3]) satisfies { length: number };
declare const ar1: never[]
; ar1 satisfies { length: number };
declare const ar2: number[]
; ar2 satisfies { length: number }

// this should throw an error but it doesn't
// @ts-expect-error
; ([] as number[]) satisfies string[]

export { }

🙁 Actual behavior

Types created with the T[] and objects created with the [x as T] syntax are not typed as Array<T> but instead as {}.

🙂 Expected behavior

I expect either:

• T[] syntax and Array<T> to be completely synonymous
• A compiler error that the Array type is not an instantiable type

Additional information about the issue

Related to #57009.

[RyanCavanaugh]

This is not supported. Array<T> must be an interface.

You're the only person trying to do this, please stop 😅

[rotu]

This is not supported. Array<T> must be an interface.

You're the only person trying to do this, please stop 😅

lol - gotcha. Wasn't sure if "this isn't going to work" was referring to the circular definition or using a type alias. Now I know!

I'm suprised there's not a compiler error - it seems like checker.ts should be checking the presence and the arity of the global Array type. There's even a check in there (that doesn't seem to be working) that global types are declared as a class or interface.

globalArrayType = getGlobalType("Array" as __String, /*arity*/ 1, /*reportErrors*/ true);

// ...

function getGlobalType(name: __String, arity: number, reportErrors: boolean): ObjectType | undefined {
    const symbol = getGlobalTypeSymbol(name, reportErrors);
    return symbol || reportErrors ? getTypeOfGlobalSymbol(symbol, arity) : undefined;
}

// ...

function getTypeOfGlobalSymbol(symbol: Symbol | undefined, arity: number): ObjectType {
    function getTypeDeclaration(symbol: Symbol): Declaration | undefined {
        const declarations = symbol.declarations;
        if (declarations) {
            for (const declaration of declarations) {
                switch (declaration.kind) {
                    case SyntaxKind.ClassDeclaration:
                    case SyntaxKind.InterfaceDeclaration:
                    case SyntaxKind.EnumDeclaration:
                        return declaration;
                }
            }
        }
    }

    if (!symbol) {
        return arity ? emptyGenericType : emptyObjectType;
    }
    const type = getDeclaredTypeOfSymbol(symbol);
    if (!(type.flags & TypeFlags.Object)) {
        error(getTypeDeclaration(symbol), Diagnostics.Global_type_0_must_be_a_class_or_interface_type, symbolName(symbol));
        return arity ? emptyGenericType : emptyObjectType;
    }
    if (length((type as InterfaceType).typeParameters) !== arity) {
        error(getTypeDeclaration(symbol), Diagnostics.Global_type_0_must_have_1_type_parameter_s, symbolName(symbol), arity);
        return arity ? emptyGenericType : emptyObjectType;
    }
    return type as ObjectType;
}

[RyanCavanaugh]

Good catch; I think we changed how eagerly type aliases are resolved in some cases and broke that check.

[RyanCavanaugh]

Gonna hijack this one

[RyanCavanaugh]

It looks like we created an unintentional dependency on this codepath not flagging type aliases when we added PromiseConstructorLike, which is defined as

declare type PromiseConstructorLike = new <T>(executor: (resolve: (value: T | PromiseLike<T>) => void, reject: (reason?: any) => void) => void) => PromiseLike<T>;

Maybe just telling people to not do this when they try to is sufficient; this function is now quite a bit indirected from different call sites that do/do not have the class/interface distinction.

[typescript-bot]

:wave: Hi, I'm the Repro bot. I can help narrow down and track compiler bugs across releases! This comment reflects the current state of the repro in the issue body running against the nightly TypeScript.

---

Issue body code block by @rotu

:x: Failed: -

• Type '{}' does not satisfy the expected type 'Array'. Property 'length' is missing in type '{}' but required in type 'Array'.
• Type '{}' does not satisfy the expected type '{ length: number; }'. Property 'length' is missing in type '{}' but required in type '{ length: number; }'.
• Type '{}' does not satisfy the expected type '{ length: number; }'. Property 'length' is missing in type '{}' but required in type '{ length: number; }'.
• Type '{}' does not satisfy the expected type '{ length: number; }'. Property 'length' is missing in type '{}' but required in type '{ length: number; }'.
• Unused '@ts-expect-error' directive.

Historical Information

Version

Reproduction Outputs

4.9.3, 5.0.2, 5.1.3, 5.2.2, 5.3.2

:x: Failed: - Type '{}' does not satisfy the expected type 'Array'. Property 'length' is missing in type '{}' but required in type 'Array'. Type '{}' does not satisfy the expected type '{ length: number; }'. Property 'length' is missing in type '{}' but required in type '{ length: number; }'. Type '{}' does not satisfy the expected type '{ length: number; }'. Property 'length' is missing in type '{}' but required in type '{ length: number; }'. Type '{}' does not satisfy the expected type '{ length: number; }'. Property 'length' is missing in type '{}' but required in type '{ length: number; }'. Unused '@ts-expect-error' directive.