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Fix narrowing of optional chains (#36089)

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* Check for definitely not undefined instead of maybe not undefined

* Fix comment

* Add tests
This commit is contained in:
Anders Hejlsberg
2020-01-08 15:37:27 -08:00
committed by GitHub
parent 3e4578c9f4
commit 0aab63b7ff
6 changed files with 666 additions and 158 deletions
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23
src/compiler/checker.ts
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@@ -19777,13 +19777,22 @@ namespace ts {
}
function narrowTypeByOptionalChainContainment(type: Type, operator: SyntaxKind, value: Expression, assumeTrue: boolean): Type {
// We are in a 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 effectiveTrue = operator === SyntaxKind.EqualsEqualsToken || operator === SyntaxKind.EqualsEqualsEqualsToken ? assumeTrue : !assumeTrue;
const doubleEquals = operator === SyntaxKind.EqualsEqualsToken || operator === SyntaxKind.ExclamationEqualsToken;
const valueNonNullish = !(getTypeFacts(getTypeOfExpression(value)) & (doubleEquals ? TypeFacts.EQUndefinedOrNull : TypeFacts.EQUndefined));
return effectiveTrue === valueNonNullish ? getTypeWithFacts(type, TypeFacts.NEUndefinedOrNull) : type;
// We are in a branch of obj?.foo === value (or any one of the other equality operators). We narrow obj as follows:
// When operator is === and type of value excludes undefined, null and undefined is removed from type of obj in true branch.
// When operator is !== and type of value excludes undefined, null and undefined is removed from type of obj in false branch.
// When operator is == and type of value excludes null and undefined, null and undefined is removed from type of obj in true branch.
// When operator is != and type of value excludes null and undefined, null and undefined is removed from type of obj in false branch.
// When operator is === and type of value is undefined, null and undefined is removed from type of obj in false branch.
// When operator is !== and type of value is undefined, null and undefined is removed from type of obj in true branch.
// When operator is == and type of value is null or undefined, null and undefined is removed from type of obj in false branch.
// When operator is != and type of value is null or undefined, null and undefined is removed from type of obj in true branch.
const equalsOperator = operator === SyntaxKind.EqualsEqualsToken || operator === SyntaxKind.EqualsEqualsEqualsToken;
const nullableFlags = operator === SyntaxKind.EqualsEqualsToken || operator === SyntaxKind.ExclamationEqualsToken ? TypeFlags.Nullable : TypeFlags.Undefined;
const valueType = getTypeOfExpression(value);
// Note that we include any and unknown in the exclusion test because their domain includes null and undefined.
const removeNullable = equalsOperator !== assumeTrue && everyType(valueType, t => !!(t.flags & nullableFlags)) ||
equalsOperator === assumeTrue && everyType(valueType, t => !(t.flags & (TypeFlags.AnyOrUnknown | nullableFlags)));
return removeNullable ? getTypeWithFacts(type, TypeFacts.NEUndefinedOrNull) : type;
}
function narrowTypeByEquality(type: Type, operator: SyntaxKind, value: Expression, assumeTrue: boolean): Type {