Don't narrow against unions of constructor functions with instanceof (#38099)

* WIP * Only narrows when the union is not all constructors
2026-02-05 16:38:05 -06:00 · 2020-07-07 11:34:10 -04:00 · 2020-07-07 11:34:10 -04:00 · 6ebd73c84f
commit 6ebd73c84f
parent 9a65658b28
5 changed files with 237 additions and 0 deletions
--- a/src/compiler/checker.ts
+++ b/src/compiler/checker.ts
@ -21800,6 +21800,12 @@ namespace ts {
                        emptyObjectType;
                }

+                // We can't narrow a union based off instanceof without negated types see #31576 for more info
+                if (!assumeTrue && rightType.flags & TypeFlags.Union) {
+                    const nonConstructorTypeInUnion = find((<UnionType>rightType).types, (t) => !isConstructorType(t));
+                    if (!nonConstructorTypeInUnion) return type;
+                }
+
                return getNarrowedType(type, targetType, assumeTrue, isTypeDerivedFrom);
            }

--- a/tests/baselines/reference/doesNotNarrowUnionOfConstructorsWithInstanceof.js
+++ b/tests/baselines/reference/doesNotNarrowUnionOfConstructorsWithInstanceof.js
@ -0,0 +1,53 @@
+//// [doesNotNarrowUnionOfConstructorsWithInstanceof.ts]
+class A {
+    length: 1
+    constructor() {
+      this.length = 1
+    }
+}
+
+class B {
+    length: 2
+    constructor() {
+      this.length = 2
+    }
+}
+
+function getTypedArray(flag: boolean) {
+  return flag ? new A() : new B();
+}
+function getTypedArrayConstructor(flag: boolean) {
+  return flag ? A : B;
+}
+const a = getTypedArray(true);              // A | B
+const b = getTypedArrayConstructor(false);  // A constructor | B constructor
+
+if (!(a instanceof b)) {
+  console.log(a.length);  // Used to be property 'length' does not exist on type 'never'.
+}
+
+
+//// [doesNotNarrowUnionOfConstructorsWithInstanceof.js]
+var A = /** @class */ (function () {
+    function A() {
+        this.length = 1;
+    }
+    return A;
+}());
+var B = /** @class */ (function () {
+    function B() {
+        this.length = 2;
+    }
+    return B;
+}());
+function getTypedArray(flag) {
+    return flag ? new A() : new B();
+}
+function getTypedArrayConstructor(flag) {
+    return flag ? A : B;
+}
+var a = getTypedArray(true); // A | B
+var b = getTypedArrayConstructor(false); // A constructor | B constructor
+if (!(a instanceof b)) {
+    console.log(a.length); // Used to be property 'length' does not exist on type 'never'.
+}
--- a/tests/baselines/reference/doesNotNarrowUnionOfConstructorsWithInstanceof.symbols
+++ b/tests/baselines/reference/doesNotNarrowUnionOfConstructorsWithInstanceof.symbols
@ -0,0 +1,68 @@
+=== tests/cases/compiler/doesNotNarrowUnionOfConstructorsWithInstanceof.ts ===
+class A {
+>A : Symbol(A, Decl(doesNotNarrowUnionOfConstructorsWithInstanceof.ts, 0, 0))
+
+    length: 1
+>length : Symbol(A.length, Decl(doesNotNarrowUnionOfConstructorsWithInstanceof.ts, 0, 9))
+
+    constructor() {
+      this.length = 1
+>this.length : Symbol(A.length, Decl(doesNotNarrowUnionOfConstructorsWithInstanceof.ts, 0, 9))
+>this : Symbol(A, Decl(doesNotNarrowUnionOfConstructorsWithInstanceof.ts, 0, 0))
+>length : Symbol(A.length, Decl(doesNotNarrowUnionOfConstructorsWithInstanceof.ts, 0, 9))
+    }
+}
+
+class B {
+>B : Symbol(B, Decl(doesNotNarrowUnionOfConstructorsWithInstanceof.ts, 5, 1))
+
+    length: 2
+>length : Symbol(B.length, Decl(doesNotNarrowUnionOfConstructorsWithInstanceof.ts, 7, 9))
+
+    constructor() {
+      this.length = 2
+>this.length : Symbol(B.length, Decl(doesNotNarrowUnionOfConstructorsWithInstanceof.ts, 7, 9))
+>this : Symbol(B, Decl(doesNotNarrowUnionOfConstructorsWithInstanceof.ts, 5, 1))
+>length : Symbol(B.length, Decl(doesNotNarrowUnionOfConstructorsWithInstanceof.ts, 7, 9))
+    }
+}
+
+function getTypedArray(flag: boolean) {
+>getTypedArray : Symbol(getTypedArray, Decl(doesNotNarrowUnionOfConstructorsWithInstanceof.ts, 12, 1))
+>flag : Symbol(flag, Decl(doesNotNarrowUnionOfConstructorsWithInstanceof.ts, 14, 23))
+
+  return flag ? new A() : new B();
+>flag : Symbol(flag, Decl(doesNotNarrowUnionOfConstructorsWithInstanceof.ts, 14, 23))
+>A : Symbol(A, Decl(doesNotNarrowUnionOfConstructorsWithInstanceof.ts, 0, 0))
+>B : Symbol(B, Decl(doesNotNarrowUnionOfConstructorsWithInstanceof.ts, 5, 1))
+}
+function getTypedArrayConstructor(flag: boolean) {
+>getTypedArrayConstructor : Symbol(getTypedArrayConstructor, Decl(doesNotNarrowUnionOfConstructorsWithInstanceof.ts, 16, 1))
+>flag : Symbol(flag, Decl(doesNotNarrowUnionOfConstructorsWithInstanceof.ts, 17, 34))
+
+  return flag ? A : B;
+>flag : Symbol(flag, Decl(doesNotNarrowUnionOfConstructorsWithInstanceof.ts, 17, 34))
+>A : Symbol(A, Decl(doesNotNarrowUnionOfConstructorsWithInstanceof.ts, 0, 0))
+>B : Symbol(B, Decl(doesNotNarrowUnionOfConstructorsWithInstanceof.ts, 5, 1))
+}
+const a = getTypedArray(true);              // A | B
+>a : Symbol(a, Decl(doesNotNarrowUnionOfConstructorsWithInstanceof.ts, 20, 5))
+>getTypedArray : Symbol(getTypedArray, Decl(doesNotNarrowUnionOfConstructorsWithInstanceof.ts, 12, 1))
+
+const b = getTypedArrayConstructor(false);  // A constructor | B constructor
+>b : Symbol(b, Decl(doesNotNarrowUnionOfConstructorsWithInstanceof.ts, 21, 5))
+>getTypedArrayConstructor : Symbol(getTypedArrayConstructor, Decl(doesNotNarrowUnionOfConstructorsWithInstanceof.ts, 16, 1))
+
+if (!(a instanceof b)) {
+>a : Symbol(a, Decl(doesNotNarrowUnionOfConstructorsWithInstanceof.ts, 20, 5))
+>b : Symbol(b, Decl(doesNotNarrowUnionOfConstructorsWithInstanceof.ts, 21, 5))
+
+  console.log(a.length);  // Used to be property 'length' does not exist on type 'never'.
+>console.log : Symbol(Console.log, Decl(lib.dom.d.ts, --, --))
+>console : Symbol(console, Decl(lib.dom.d.ts, --, --))
+>log : Symbol(Console.log, Decl(lib.dom.d.ts, --, --))
+>a.length : Symbol(length, Decl(doesNotNarrowUnionOfConstructorsWithInstanceof.ts, 0, 9), Decl(doesNotNarrowUnionOfConstructorsWithInstanceof.ts, 7, 9))
+>a : Symbol(a, Decl(doesNotNarrowUnionOfConstructorsWithInstanceof.ts, 20, 5))
+>length : Symbol(length, Decl(doesNotNarrowUnionOfConstructorsWithInstanceof.ts, 0, 9), Decl(doesNotNarrowUnionOfConstructorsWithInstanceof.ts, 7, 9))
+}
+
--- a/tests/baselines/reference/doesNotNarrowUnionOfConstructorsWithInstanceof.types
+++ b/tests/baselines/reference/doesNotNarrowUnionOfConstructorsWithInstanceof.types
@ -0,0 +1,84 @@
+=== tests/cases/compiler/doesNotNarrowUnionOfConstructorsWithInstanceof.ts ===
+class A {
+>A : A
+
+    length: 1
+>length : 1
+
+    constructor() {
+      this.length = 1
+>this.length = 1 : 1
+>this.length : 1
+>this : this
+>length : 1
+>1 : 1
+    }
+}
+
+class B {
+>B : B
+
+    length: 2
+>length : 2
+
+    constructor() {
+      this.length = 2
+>this.length = 2 : 2
+>this.length : 2
+>this : this
+>length : 2
+>2 : 2
+    }
+}
+
+function getTypedArray(flag: boolean) {
+>getTypedArray : (flag: boolean) => A | B
+>flag : boolean
+
+  return flag ? new A() : new B();
+>flag ? new A() : new B() : A | B
+>flag : boolean
+>new A() : A
+>A : typeof A
+>new B() : B
+>B : typeof B
+}
+function getTypedArrayConstructor(flag: boolean) {
+>getTypedArrayConstructor : (flag: boolean) => typeof A | typeof B
+>flag : boolean
+
+  return flag ? A : B;
+>flag ? A : B : typeof A | typeof B
+>flag : boolean
+>A : typeof A
+>B : typeof B
+}
+const a = getTypedArray(true);              // A | B
+>a : A | B
+>getTypedArray(true) : A | B
+>getTypedArray : (flag: boolean) => A | B
+>true : true
+
+const b = getTypedArrayConstructor(false);  // A constructor | B constructor
+>b : typeof A | typeof B
+>getTypedArrayConstructor(false) : typeof A | typeof B
+>getTypedArrayConstructor : (flag: boolean) => typeof A | typeof B
+>false : false
+
+if (!(a instanceof b)) {
+>!(a instanceof b) : boolean
+>(a instanceof b) : boolean
+>a instanceof b : boolean
+>a : A | B
+>b : typeof A | typeof B
+
+  console.log(a.length);  // Used to be property 'length' does not exist on type 'never'.
+>console.log(a.length) : void
+>console.log : (...data: any[]) => void
+>console : Console
+>log : (...data: any[]) => void
+>a.length : 1 | 2
+>a : A | B
+>length : 1 | 2
+}
+
--- a/tests/cases/compiler/doesNotNarrowUnionOfConstructorsWithInstanceof.ts
+++ b/tests/cases/compiler/doesNotNarrowUnionOfConstructorsWithInstanceof.ts
@ -0,0 +1,26 @@
+class A {
+    length: 1
+    constructor() {
+      this.length = 1
+    }
+}
+
+class B {
+    length: 2
+    constructor() {
+      this.length = 2
+    }
+}
+
+function getTypedArray(flag: boolean) {
+  return flag ? new A() : new B();
+}
+function getTypedArrayConstructor(flag: boolean) {
+  return flag ? A : B;
+}
+const a = getTypedArray(true);              // A | B
+const b = getTypedArrayConstructor(false);  // A constructor | B constructor
+
+if (!(a instanceof b)) {
+  console.log(a.length);  // Used to be property 'length' does not exist on type 'never'.
+}