unique symbols from the global SymbolConstructor widen way too eagerly

Given

const a = Symbol.toStringTag;

class F {
    [a](){ return "" }
}

(new F())[a];

we currently issue a Element implicitly has an 'any' type because expression of type 'symbol' can't be used to index type 'F'.(7053) error on the access.

There should be no errors, as with

const a = Symbol();

class F {
    [a](){ return "" }
}

(new F())[a];

since Symbol.toStringTag is a unique symbol just like what Symbol() makes.

Wait, why is a well-known symbol typed as unique symbol? That feels wrong to me.

Because it's a specific, unique symbol. As a matter of fact, we don't even have the concept of a "well-known" symbol anymore - unique symbols subsumed them as the more general concept (the term well known no longer appears anywhere in the checker's code, just some old comments!).

I guess I just always saw unique symbol as this special nominal type that every time it's mentioned, refers to a distinct type, so it feels weird to apply that to values that are predefined by the runtime. IOW unique symbol implies to me a value that can't be forged

The original example is fixed. With --strict --lib es2015, it produced TS7053 through 5.7.0-dev.20240923 and is clean in 5.7.0-dev.20240924, TypeScript 6.0.3, and current native TypeScript.

The change is PR #59860, which makes non-literal computed class members participate in the class type rather than being dropped.

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`unique symbol`s from the global `SymbolConstructor` widen way too eagerly #53276

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unique symbols from the global SymbolConstructor widen way too eagerly #53276

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fatcerberus commented on Mar 15, 2023

weswigham commented on Mar 16, 2023

fatcerberus commented on Mar 16, 2023

RyanCavanaugh commented on Sep 19, 2026

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`unique symbol`s from the global `SymbolConstructor` widen way too eagerly #53276