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Implement constructor check type guard #32256

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Implement constructor check type guard #32256

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49 changes: 49 additions & 0 deletions src/compiler/checker.ts
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Original file line number Diff line number Diff line change
Expand Up @@ -17247,6 +17247,12 @@ namespace ts {
if (right.kind === SyntaxKind.TypeOfExpression && isStringLiteralLike(left)) {
return narrowTypeByTypeof(type, <TypeOfExpression>right, operator, left, assumeTrue);
}
if (isConstructorAccessExpression(left) && right.kind === SyntaxKind.Identifier) {
return narrowTypeByConstructor(type, left, operator, right, assumeTrue);
}
if (isConstructorAccessExpression(right) && left.kind === SyntaxKind.Identifier) {
return narrowTypeByConstructor(type, right, operator, left, assumeTrue);
}
if (isMatchingReference(reference, left)) {
return narrowTypeByEquality(type, operator, right, assumeTrue);
}
Expand Down Expand Up @@ -17275,6 +17281,13 @@ namespace ts {
return narrowType(type, expr.right, assumeTrue);
}
return type;

function isConstructorAccessExpression(expr: Expression): expr is AccessExpression {
return (
isPropertyAccessEntityNameExpression(expr) && idText(expr.name) === "constructor"
|| isElementAccessExpression(expr) && isStringLiteralLike(expr.argumentExpression) && expr.argumentExpression.text === "constructor"
);
}
}

function narrowTypeByEquality(type: Type, operator: SyntaxKind, value: Expression, assumeTrue: boolean): Type {
Expand Down Expand Up @@ -17505,6 +17518,42 @@ namespace ts {
return getTypeWithFacts(mapType(type, narrowTypeForTypeofSwitch(impliedType)), switchFacts);
}

function narrowTypeByConstructor(type: Type, constructorAccessExpr: AccessExpression, operator: SyntaxKind, identifier: Expression, assumeTrue: boolean): Type {
if (!assumeTrue || operator !== SyntaxKind.EqualsEqualsToken && operator !== SyntaxKind.EqualsEqualsEqualsToken) {
return type;
}

if (!isMatchingReference(reference, constructorAccessExpr.expression)) {
return declaredType;
}

const identifierType = getTypeOfExpression(identifier);
if (!isTypeSubtypeOf(identifierType, globalFunctionType)) {
return type;
}

const prototypeProperty = getPropertyOfType(identifierType, "prototype" as __String);
if (!prototypeProperty) {
return type;
}

const prototypeType = getTypeOfSymbol(prototypeProperty);
const candidate = !isTypeAny(prototypeType) ? prototypeType : undefined;
if (!candidate || candidate === globalObjectType || candidate === globalFunctionType) {
return type;
}

return getNarrowedType(type, candidate, assumeTrue, isConstructedBy);

function isConstructedBy(source: Type, target: Type) {
if (source.flags & TypeFlags.Primitive) {
return areTypesComparable(source, target);
}

return isTypeDerivedFrom(source, target);
}
}

function narrowTypeByInstanceof(type: Type, expr: BinaryExpression, assumeTrue: boolean): Type {
const left = getReferenceCandidate(expr.left);
if (!isMatchingReference(reference, left)) {
Expand Down
170 changes: 170 additions & 0 deletions tests/baselines/reference/typeGuardConstructor.errors.txt
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Original file line number Diff line number Diff line change
@@ -0,0 +1,170 @@
tests/cases/compiler/typeGuardConstructor.ts(33,9): error TS2339: Property 'prop1' does not exist on type 'number | Foo'.
Property 'prop1' does not exist on type 'number'.
tests/cases/compiler/typeGuardConstructor.ts(36,9): error TS2339: Property 'prop1' does not exist on type 'number | Foo'.
Property 'prop1' does not exist on type 'number'.
tests/cases/compiler/typeGuardConstructor.ts(39,9): error TS2339: Property 'prop1' does not exist on type 'number | Foo'.
Property 'prop1' does not exist on type 'number'.
tests/cases/compiler/typeGuardConstructor.ts(42,9): error TS2339: Property 'prop1' does not exist on type 'number | Foo'.
Property 'prop1' does not exist on type 'number'.
tests/cases/compiler/typeGuardConstructor.ts(45,9): error TS2339: Property 'prop1' does not exist on type 'number | Foo'.
Property 'prop1' does not exist on type 'number'.
tests/cases/compiler/typeGuardConstructor.ts(48,9): error TS2339: Property 'prop1' does not exist on type 'number | Foo'.
Property 'prop1' does not exist on type 'number'.
tests/cases/compiler/typeGuardConstructor.ts(51,9): error TS2339: Property 'prop1' does not exist on type 'number | Foo'.
Property 'prop1' does not exist on type 'number'.
tests/cases/compiler/typeGuardConstructor.ts(54,9): error TS2339: Property 'prop1' does not exist on type 'number | Foo'.
Property 'prop1' does not exist on type 'number'.


==== tests/cases/compiler/typeGuardConstructor.ts (8 errors) ====
// Typical case
class Foo {
prop1: string;
}

let foo: Foo | number;
if (foo.constructor == Foo) {
foo.prop1; // string
}
if (foo["constructor"] == Foo) {
foo.prop1; // string
}
if (foo.constructor === Foo) {
foo.prop1; // string
}
if (foo["constructor"] === Foo) {
foo.prop1; // string
}
if (Foo == foo.constructor) {
foo.prop1; // string
}
if (Foo == foo["constructor"]) {
foo.prop1; // string
}
if (Foo === foo.constructor) {
foo.prop1; // string
}
if (Foo === foo["constructor"]) {
foo.prop1; // string
}

if (foo.constructor != Foo) {
foo.prop1; // ERROR
~~~~~
!!! error TS2339: Property 'prop1' does not exist on type 'number | Foo'.
!!! error TS2339: Property 'prop1' does not exist on type 'number'.
}
if (foo["constructor"] != Foo) {
foo.prop1; // ERROR
~~~~~
!!! error TS2339: Property 'prop1' does not exist on type 'number | Foo'.
!!! error TS2339: Property 'prop1' does not exist on type 'number'.
}
if (foo.constructor !== Foo) {
foo.prop1; // ERROR
~~~~~
!!! error TS2339: Property 'prop1' does not exist on type 'number | Foo'.
!!! error TS2339: Property 'prop1' does not exist on type 'number'.
}
if (foo["constructor"] !== Foo) {
foo.prop1; // ERROR
~~~~~
!!! error TS2339: Property 'prop1' does not exist on type 'number | Foo'.
!!! error TS2339: Property 'prop1' does not exist on type 'number'.
}
if (Foo != foo.constructor) {
foo.prop1; // ERROR
~~~~~
!!! error TS2339: Property 'prop1' does not exist on type 'number | Foo'.
!!! error TS2339: Property 'prop1' does not exist on type 'number'.
}
if (Foo != foo["constructor"]) {
foo.prop1; // ERROR
~~~~~
!!! error TS2339: Property 'prop1' does not exist on type 'number | Foo'.
!!! error TS2339: Property 'prop1' does not exist on type 'number'.
}
if (Foo !== foo.constructor) {
foo.prop1; // ERROR
~~~~~
!!! error TS2339: Property 'prop1' does not exist on type 'number | Foo'.
!!! error TS2339: Property 'prop1' does not exist on type 'number'.
}
if (Foo !== foo["constructor"]) {
foo.prop1; // ERROR
~~~~~
!!! error TS2339: Property 'prop1' does not exist on type 'number | Foo'.
!!! error TS2339: Property 'prop1' does not exist on type 'number'.
}


// Derived class case
class Bar extends Foo {
prop2: number;
}

let bar: Bar | boolean;
if (bar.constructor === Bar) {
bar.prop1; // string
bar.prop2; // number
}
if (bar.constructor === Foo) {
bar.prop1; // string
bar.prop2; // number
}


// Union of primitives, number, arrays, and Foo
var x: number | "hello" | "world" | true | false | number[] | string[] | Foo;

if (x.constructor === Number) {
x; // number
}

if (x.constructor === String) {
x; // "hello" | "world"
}

if (x.constructor === Boolean) {
x; // boolean
}

if (x.constructor === Array) {
x; // number[] | string[]
}

if (x.constructor === Function) {
x; // declaredType
}

if (x.constructor === Foo) {
x; // Foo
x.prop1; // string
}


// Narrowing any
let a: any;

if (a.constructor === Foo) {
a; // Foo
}
if (a.constructor === "hello") {
a; // any
}
if (a.constructor === Function) {
a; // any
}


// If for some reason someone defines a type with it's own constructor property
type S = {
constructor: () => void;
};

let s: S | string;

if (s.constructor === String) {
s; // string
}

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