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Chris Tate
6bbabd5fc9
Converting a dynamic value into a union (`JSON.parse(text) as T`, a cast from `any`) tries the arms in order and builds the first arm whose literal discriminator and whole structure match. The builder of that arm converts its members, and a member typed as another union matched its arm's structure again. Every value was matched once per union around it, so converting a tree of depth d cost about d times as much as a flat one. The arm a union matched now builds as a trusted conversion (scr_dyn_trust_enter). Inside it, a nested union picks an arm without matching the arm's structure, which the enclosing match already checked, when the value's arm is known: a plain object's arm by its literal, when the arms' literals are disjoint and no arm without a literal takes plain objects, or the only arm that takes plain objects (a record) or arrays (an array), as in an optional or nullable member. Other unions, and values that are not plain objects or arrays, match as before. Getters and proxy traps run outside the trusted conversion. Failed conversions throw the same TypeError with the same path.