b24050aefd
* Target types in excess property checking must match all discriminable properties This allows fewer types to be discriminated in excess properties, which fixes some examples. * Add excess property test * Fix semicolon lint * Remove extra semicolon! * Improve EPC for unions with multiple discriminants
90 lines
2.2 KiB
TypeScript
90 lines
2.2 KiB
TypeScript
// @strict: true
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type ADT = {
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tag: "A",
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a1: string
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} | {
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tag: "D",
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d20: 1 | 2 | 3 | 4 | 5 | 6 | 7 | 8 | 9 | 10 | 11 | 12 | 13 | 14 | 15 | 16 | 17 | 18 | 19 | 20
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} | {
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tag: "T",
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}
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let wrong: ADT = { tag: "T", a1: "extra" }
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wrong = { tag: "A", d20: 12 }
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wrong = { tag: "D" }
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type Ambiguous = {
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tag: "A",
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x: string
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} | {
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tag: "A",
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y: number
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} | {
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tag: "B",
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z: boolean
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} | {
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tag: "C"
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}
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let amb: Ambiguous
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// no error for ambiguous tag, even when it could satisfy both constituents at once
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amb = { tag: "A", x: "hi" }
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amb = { tag: "A", y: 12 }
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amb = { tag: "A", x: "hi", y: 12 }
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// correctly error on excess property 'extra', even when ambiguous
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amb = { tag: "A", x: "hi", extra: 12 }
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amb = { tag: "A", y: 12, extra: 12 }
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// assignability errors still work.
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// But note that the error for `z: true` is the fallback one of reporting on
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// the last constituent since assignability error reporting can't find a single best discriminant either.
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amb = { tag: "A" }
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amb = { tag: "A", z: true }
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type Overlapping =
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| { a: 1, b: 1, first: string }
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| { a: 2, second: string }
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| { b: 3, third: string }
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let over: Overlapping
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// these two are still errors despite their doubled up discriminants
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over = { a: 1, b: 1, first: "ok", second: "error" }
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over = { a: 1, b: 1, first: "ok", third: "error" }
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// Freshness disappears after spreading a union
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declare let t0: { a: any, b: any } | { d: any, e: any }
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declare let t1: { a: any, b: any, c: any } | { c: any, d: any, e: any }
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let t2 = { ...t1 }
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t0 = t2
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// Nested excess property checks work with discriminated unions
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type AN = { a: string } | { c: string }
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type BN = { b: string }
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type AB = { kind: "A", n: AN } | { kind: "B", n: BN }
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const abab: AB = {
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kind: "A",
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n: {
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a: "a",
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b: "b", // excess -- kind: "A"
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}
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}
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const abac: AB = {
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kind: "A",
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n: {
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a: "a",
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c: "c", // ok -- kind: "A", an: { a: string } | { c: string }
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}
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}
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// Excess property checks must match all discriminable properties
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type Button = { tag: 'button'; type?: 'submit'; };
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type Anchor = { tag: 'a'; type?: string; href: string };
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type Union = Button | Anchor;
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const obj: Union = {
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tag: 'button',
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type: 'submit',
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// should have error here
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href: 'foo',
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};
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