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Reflect CFA effects of optional chains in equality checks

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This commit is contained in:
Anders Hejlsberg 2019-10-04 15:27:32 -07:00
parent 3c794e9f9b
commit 719b779b6b
1 changed files with 28 additions and 0 deletions
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28
src/compiler/checker.ts
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@ -18124,6 +18124,16 @@ namespace ts {
return false;
}
function optionalChainContainsReference(source: Node, target: Node) {
while (isOptionalChain(source)) {
source = source.expression;
if (isMatchingReference(source, target)) {
return true;
}
}
return false;
}
// Return true if target is a property access xxx.yyy, source is a property access xxx.zzz, the declared
// type of xxx is a union type, and yyy is a property that is possibly a discriminant. We consider a property
// a possible discriminant if its type differs in the constituents of containing union type, and if every
@ -19350,6 +19360,14 @@ namespace ts {
if (isMatchingReference(reference, right)) {
return narrowTypeByEquality(type, operator, left, assumeTrue);
}
if (assumeTrue && (operator === SyntaxKind.EqualsEqualsEqualsToken || operator === SyntaxKind.ExclamationEqualsEqualsToken)) {
if (optionalChainContainsReference(left, reference)) {
type = narrowTypeByOptionalChainContainment(type, operator, right);
}
else if (optionalChainContainsReference(right, reference)) {
type = narrowTypeByOptionalChainContainment(type, operator, left);
}
}
if (isMatchingReferenceDiscriminant(left, declaredType)) {
return narrowTypeByDiscriminant(type, <AccessExpression>left, t => narrowTypeByEquality(t, operator, right, assumeTrue));
}
@ -19374,6 +19392,16 @@ namespace ts {
return type;
}
function narrowTypeByOptionalChainContainment(type: Type, operator: SyntaxKind, value: Expression): Type {
// We are in the true branch of obj?.foo === value or obj?.foo !== value. We remove undefined and null from
// the type of obj if (a) the operator is === and the type of value doesn't include undefined or (b) the
// operator is !== and the type of value is undefined.
const valueType = getTypeOfExpression(value);
return operator === SyntaxKind.EqualsEqualsEqualsToken && !(getTypeFacts(valueType) & TypeFacts.EQUndefined) ||
operator === SyntaxKind.ExclamationEqualsEqualsToken && valueType.flags & TypeFlags.Undefined ?
getTypeWithFacts(type, TypeFacts.NEUndefinedOrNull) : type;
}
function narrowTypeByEquality(type: Type, operator: SyntaxKind, value: Expression, assumeTrue: boolean): Type {
if (type.flags & TypeFlags.Any) {
return type;