Explicitly encode keyof behaviors for never and unknown into getIndexType #30753
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@typescript-bot test this & @typescript-bot run dt - I honestly have no idea what this will affect in the wild. Historically people haven't really relied on incorrect boundary relations in TS, so we shall see. |
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Heya @weswigham, I've started to run the extended test suite on this PR at d147a0d. You can monitor the build here. It should now contribute to this PR's status checks. |
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Heya @weswigham, I've started to run the Definitely Typed test suite on this PR at d147a0d. You can monitor the build here. It should now contribute to this PR's status checks. |
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This is great change IMO. One semi-related question. Is there a reason for the following, mainly regarding type A = keyof Object; // "constructor" | "toString" | "toLocaleString" | "valueOf" | "hasOwnProperty" | "isPrototypeOf" | "propertyIsEnumerable"
type B = keyof number; // "toString" | "toFixed" | "toExponential" | "toPrecision" | "valueOf" | "toLocaleString"
type C = keyof object; // never; |
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@RyanCavanaugh @ahejlsberg no DT or RWC changes 😸 |
…t to need @rbuckton's union product checking to fully work again
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keyof never->string | number | symbol(changed fromnever)keyof unknown->never(unchanged, but no longer derived fromunknown's empty apparent type)The reasoning for the first is pretty simple - we know
keyofis contravariant, so the more specialized the input type is, the broader the output type is. For each key we add on the input type, we specify a smaller and smaller set of inputs, while the output set of keys grows. Once the input is the empty set of types (never), our result should encompass every possible key.Fixes #30657