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Fixed type predicate inference for discriminated union parameters (#57952)

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This commit is contained in:
Mateusz Burzyński
2024-04-02 20:49:21 +02:00
committed by GitHub
parent 4cedfe40b0
commit 42a215c8fb
6 changed files with 133 additions and 3 deletions
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7
src/compiler/checker.ts
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@@ -37690,8 +37690,8 @@ export function createTypeChecker(host: TypeCheckerHost): TypeChecker {
{ flags: FlowFlags.Start };
const trueCondition: FlowCondition = {
flags: FlowFlags.TrueCondition,
node: expr,
antecedent,
node: expr,
};
const trueType = getFlowTypeOfReference(param.name, initType, initType, func, trueCondition);
@@ -37700,10 +37700,11 @@ export function createTypeChecker(host: TypeCheckerHost): TypeChecker {
// "x is T" means that x is T if and only if it returns true. If it returns false then x is not T.
// This means that if the function is called with an argument of type trueType, there can't be anything left in the `else` branch. It must reduce to `never`.
const falseCondition: FlowCondition = {
...trueCondition,
flags: FlowFlags.FalseCondition,
antecedent,
node: expr,
};
const falseSubtype = getFlowTypeOfReference(param.name, trueType, trueType, func, falseCondition);
const falseSubtype = getFlowTypeOfReference(param.name, initType, trueType, func, falseCondition);
return falseSubtype.flags & TypeFlags.Never ? trueType : undefined;
}