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Malte UblandClaude Opus 5.5
acb0a4c9ed
A record width copy such as Provider<"beta"> into Provider<Api> failed on method fields whose parameter record depends on the instantiation: TypeScript admits them by method bivariance, but the adapter only took mechanical parameter conversions. Inside a record's field plan, such a field now takes a checked adapter: parameters convert with the record width plans, and union arms without a home throw the catchable TypeError. Top-level function conversions and every pair that planned before are unchanged. The safe direction lifts too: record-width's method field whose parameter record widens now plans, so its SC2002 refusal gives way to the later honest SC1090 (a function value has no inspect lowering). Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
42 lines
1.6 KiB
TypeScript
42 lines
1.6 KiB
TypeScript
// SC2002: the RESIDUE of the width-copy family — record shapes that
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// neither match exactly nor width-coerce. Each fence names the first
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// blocking rule. (The width copies themselves — field-subset narrowing,
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// hybrid captures, per-field lifts — are differential corpus.)
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// An index-signature source cannot complete an absent optional field:
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// the overflow could hold the key at runtime, and a completed undefined
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// would drop that value.
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type Loose = { [k: string]: number };
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type PickedA = { a?: number };
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const loose: Loose = { a: 1 };
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const picked: PickedA = loose;
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console.log(picked);
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// A method field whose parameter shapes relate only BIVARIANTLY: the field
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// lifts as a checked adapter, so only the console.log below refuses (a
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// function value has no inspect lowering).
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type SrcM = { m(x: { a: number }): void; extra: number };
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type DstM = { m(x: { a: number; b: number }): void };
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const srcM: SrcM = {
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m: (x) => {
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console.log(x.a);
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},
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extra: 1,
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};
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const dstM: DstM = srcM;
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console.log(dstM);
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// A source field that cannot enter the target's value slot (a Map has no
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// dyn conversion into an 'unknown' signature slot).
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type WithMap = { m: Map<string, number>; n: number };
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const withMap: WithMap = { m: new Map(), n: 1 };
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const bag: Record<string, unknown> = withMap;
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console.log(bag);
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// A declared target field that cannot take a runtime key collision from
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// the signature slot (its type is narrower than the slot's).
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type Odd = { a?: boolean; [k: string]: boolean | string | undefined };
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const plain = { b: "hi" };
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const odd: Odd = plain;
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console.log(odd);
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