Fixes to inference and mapped types in --strictOptionalProperties mode #44595
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typescript-bot
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Author: Team
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weswigham
approved these changes
Jun 15, 2021
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| function removeType(type: Type, targetType: Type) { | ||
| return filterType(type, t => t !== targetType); |
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This is maybe a micro-optimization, but because unions are sorted, and all the undefined type variants are such low type IDs, if targetType is a union, we only need to check the first union element, rather than all of them exhaustively, IIRC.
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Yeah, but filterType also does stuff for the (denormalized) origin type and we'd have to duplicate that as well.
RyanCavanaugh
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Jun 15, 2021
DanielRosenwasser
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This PR fixes the following two issues:
--strictOptionalPropertiesmode, inference from an optional property to an index signature simply infers the property type as written. For example, inferring from{ a?: number }to{ [key: string]: T }infersnumberforT, and inferring from{ a?: number | undefined }to{ [key: string]: T }infersnumber | undefinedforT.--strictOptionalPropertiesmode, a mapped type that strips optionality doesn't strip explicitly includedundefinedtypes. For example,Required<{ a?: number }>is{ a: number }andRequired<{ a?: number | undefined }>is{ a: number | undefined }.Fixes parts of #44494.