Fixed an issue with optionality not being stripped from generic mapped types on indexed access - #59921
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…d types on indexed access
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| const mapper = createTypeMapper([getTypeParameterFromMappedType(objectType)], [index]); | ||
| const templateMapper = combineTypeMappers(objectType.mapper, mapper); | ||
| const instantiatedTemplateType = instantiateType(getTemplateTypeFromMappedType(objectType.target as MappedType || objectType), templateMapper); | ||
| const isOptional = getMappedTypeOptionality(objectType) > 0 || (isGenericType(objectType) ? |
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In the given repro the immediate modifiers type has -? for which getMappedTypeOptionality returns -1. So the first condition was not satisfied and the compiler proceeded to compute getCombinedMappedTypeOptionality. This time it was called with the modifiers type and not the original object type. Since that was a mapped type too it got its modifiers type etc.
Essentially this was skipping the outermost mapped type modifiers in this scenario - the ones that were supposed strip the optionality.
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fixes #59902