Better Inference for mapped array and tuple types #50046
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This is my attempt to fix #29841.
The checker now checks if a mapped type is an interface that extends an array or tuple, and if it is, only the elements of it are mapped and other non-array-prototype properties are discarded, behaving like the ES map method.
It also fixes
Mapper<[number, ...string[], number]>
being incorrectly mapped to[Mapper<number>, ...Mapper<string | number>[], Mapper<string | number>]
instead of[Mapper<number>, ...Mapper<string>[], Mapper<number>]
, and[0, ...1[], 2]
instead of[0, ...number[], number]
whentype Mapper<T> = { [P in keyof T]: P }
.I am new to the checker and the
src
code in general, so please, guide and correct me for anything weird.