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Make exception for synthetic 'this.x' in narrowTypeByInstanceof

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This commit is contained in:
Anders Hejlsberg 2019-02-03 15:23:07 -08:00
parent dcfbe5a7a7
commit 415c725bb9
1 changed files with 11 additions and 2 deletions
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13
src/compiler/checker.ts
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@ -15045,6 +15045,10 @@ namespace ts {
return false;
}
function isSyntheticThisPropertyAccess(expr: Node) {
return isAccessExpression(expr) && expr.expression.kind === SyntaxKind.ThisKeyword && !!(expr.expression.flags & NodeFlags.Synthesized);
}
function findDiscriminantProperties(sourceProperties: Symbol[], target: Type): Symbol[] | undefined {
let result: Symbol[] | undefined;
for (const sourceProperty of sourceProperties) {
@ -16260,8 +16264,13 @@ namespace ts {
const left = getReferenceCandidate(expr.left);
if (!isMatchingReference(reference, left)) {
// For a reference of the form 'x.y', an 'x instanceof T' type guard resets the
// narrowed type of 'y' to its declared type.
if (containsMatchingReference(reference, left)) {
// narrowed type of 'y' to its declared type. We do this because preceding 'x.y'
// references might reference a different 'y' property. However, we make an exception
// for property accesses where x is a synthetic 'this' expression, indicating that we
// were called from isPropertyInitializedInConstructor. Without this exception,
// initializations of 'this' properties that occur before a 'this instanceof XXX'
// check would not be considered.
if (containsMatchingReference(reference, left) && !isSyntheticThisPropertyAccess(reference)) {
return declaredType;
}
return type;