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// @strict: true
type ADT = {
tag: "A",
a1: string
} | {
tag: "D",
d20: 1 | 2 | 3 | 4 | 5 | 6 | 7 | 8 | 9 | 10 | 11 | 12 | 13 | 14 | 15 | 16 | 17 | 18 | 19 | 20
} | {
tag: "T",
}
let wrong: ADT = { tag: "T", a1: "extra" }
wrong = { tag: "A", d20: 12 }
wrong = { tag: "D" }
type Ambiguous = {
tag: "A",
x: string
} | {
tag: "A",
y: number
} | {
tag: "B",
z: boolean
} | {
tag: "C"
}
let amb: Ambiguous
// no error for ambiguous tag, even when it could satisfy both constituents at once
amb = { tag: "A", x: "hi" }
amb = { tag: "A", y: 12 }
amb = { tag: "A", x: "hi", y: 12 }
// correctly error on excess property 'extra', even when ambiguous
amb = { tag: "A", x: "hi", extra: 12 }
amb = { tag: "A", y: 12, extra: 12 }
// assignability errors still work.
// But note that the error for `z: true` is the fallback one of reporting on
// the last constituent since assignability error reporting can't find a single best discriminant either.
amb = { tag: "A" }
amb = { tag: "A", z: true }
type Overlapping =
| { a: 1, b: 1, first: string }
| { a: 2, second: string }
| { b: 3, third: string }
let over: Overlapping
// these two are still errors despite their doubled up discriminants
over = { a: 1, b: 1, first: "ok", second: "error" }
over = { a: 1, b: 1, first: "ok", third: "error" }
// Freshness disappears after spreading a union
declare let t0: { a: any, b: any } | { d: any, e: any }
declare let t1: { a: any, b: any, c: any } | { c: any, d: any, e: any }
let t2 = { ...t1 }
t0 = t2
// Nested excess property checks work with discriminated unions
type AN = { a: string } | { c: string }
type BN = { b: string }
type AB = { kind: "A", n: AN } | { kind: "B", n: BN }
const abab: AB = {
kind: "A",
n: {
a: "a",
b: "b", // excess -- kind: "A"
}
}
const abac: AB = {
kind: "A",
n: {
a: "a",
c: "c", // ok -- kind: "A", an: { a: string } | { c: string }
}
}
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