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Infer from type arguments of the same alias in inferFromObjectTypes #57895

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Infer from type arguments of the same alias in inferFromObjectTypes #57895

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Infer from type arguments of the same alias in `inferFromObjectTypes`
Andarist Mar 21, 2024
925bb5d
Merge remote-tracking branch 'origin/main' into infer-between-same-al…
Andarist May 1, 2024
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13 changes: 13 additions & 0 deletions src/compiler/checker.ts
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Original file line number Diff line number Diff line change
Expand Up @@ -26073,6 +26073,19 @@ export function createTypeChecker(host: TypeCheckerHost): TypeChecker {
}

function inferFromObjectTypes(source: Type, target: Type) {
if (source.aliasSymbol && source.aliasSymbol === target.aliasSymbol) {
if (source.aliasTypeArguments) {
// Source and target are types originating in the same generic type alias declaration.
// Simply infer from source type arguments to target type arguments, with defaults applied.
const params = getSymbolLinks(source.aliasSymbol).typeParameters!;
const minParams = getMinTypeArgumentCount(params);
const sourceTypes = fillMissingTypeArguments(source.aliasTypeArguments, params, minParams, isInJSFile(source.aliasSymbol.valueDeclaration));
const targetTypes = fillMissingTypeArguments(target.aliasTypeArguments, params, minParams, isInJSFile(source.aliasSymbol.valueDeclaration));
inferFromTypeArguments(sourceTypes, targetTypes!, getAliasVariances(source.aliasSymbol));
}
// And if there weren't any type arguments, there's no reason to run inference as the types must be the same.
return;
}
if (
getObjectFlags(source) & ObjectFlags.Reference && getObjectFlags(target) & ObjectFlags.Reference && (
(source as TypeReference).target === (target as TypeReference).target || isArrayType(source) && isArrayType(target)
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