Fixed contextual types within generic tuple mapped types#53042
Fixed contextual types within generic tuple mapped types#53042Andarist wants to merge 4 commits intomicrosoft:mainfrom
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This is the comment where you describe the bug, right? |
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Yep, it mentions this and related things |
src/compiler/checker.ts
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| return isCircularMappedProperty(prop) ? undefined : getTypeOfSymbol(prop); | ||
| } | ||
| if (isTupleType(t) && isNumericLiteralName(name) && +name >= 0) { | ||
| if (t.target.hasRestElement) { |
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The tuple type could be [...T] where T extends [] and, thus, should not have a contextual type for a numbered element (at all), so I'm not sure checking this field is correct.
src/compiler/checker.ts
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| if (t.target.hasRestElement) { | ||
| const restElement = getTypeArguments(t)[t.target.fixedLength]; | ||
| if (restElement !== type) { | ||
| const propType = getTypeOfPropertyOfContextualType(restElement, name); |
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Erm, name needs to be offset by the length of the preceding fixed elements of the tuple, no? And even that's thrown into question with multiple variadic tuple elements? Eg, if t is [...T, ...U] and name is 0, where T extends [] | [number] and U extends [] | [string], this is just going to lookup 0 on T, which is, at best, a partial result. (You'd want the contextual type to be something like string | number | undefined or something constrained to such). Seems like something a bit more complete is needed to handle variadic tuples fully.
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It's a case that I came up with when reviewing #53036