Error when LHS of instanceof is Union of Primitives #18519

src/compiler/checker.ts

@@ -17587,6 +17587,12 @@ namespace ts {
                 (kind & TypeFlags.NonPrimitive && isTypeAssignableTo(source, nonPrimitiveType));
         }
 
+        function allTypesAssignableToKind(source: Type, kind: TypeFlags, strict?: boolean): boolean {
+            return source.flags & TypeFlags.Union ?
+                every((source as UnionType).types, subType => allTypesAssignableToKind(subType, kind, strict)) :
+                isTypeAssignableToKind(source, kind, strict);
+        }
+
         function isConstEnumObjectType(type: Type): boolean {
             return getObjectFlags(type) & ObjectFlags.Anonymous && type.symbol && isConstEnumSymbol(type.symbol);
         }
@@ -17604,7 +17610,8 @@ namespace ts {
             // and the right operand to be of type Any, a subtype of the 'Function' interface type, or have a call or construct signature.
             // The result is always of the Boolean primitive type.
             // NOTE: do not raise error if leftType is unknown as related error was already reported
-            if (!isTypeAny(leftType) && isTypeAssignableToKind(leftType, TypeFlags.Primitive)) {
+            if (!isTypeAny(leftType) &&
+                allTypesAssignableToKind(leftType, TypeFlags.Primitive)) {
                 error(left, Diagnostics.The_left_hand_side_of_an_instanceof_expression_must_be_of_type_any_an_object_type_or_a_type_parameter);
             }
             // NOTE: do not raise error if right is unknown as related error was already reported

tests/baselines/reference/instanceofWithPrimitiveUnion.errors.txt

@@ -0,0 +1,21 @@
+tests/cases/compiler/instanceofWithPrimitiveUnion.ts(2,9): error TS2358: The left-hand side of an 'instanceof' expression must be of type 'any', an object type or a type parameter.
+tests/cases/compiler/instanceofWithPrimitiveUnion.ts(8,9): error TS2358: The left-hand side of an 'instanceof' expression must be of type 'any', an object type or a type parameter.
+
+
+==== tests/cases/compiler/instanceofWithPrimitiveUnion.ts (2 errors) ====
+    function test1(x: number | string) {
+        if (x instanceof Object) {
+            ~
+!!! error TS2358: The left-hand side of an 'instanceof' expression must be of type 'any', an object type or a type parameter.
+            x;
+        }
+    }
+
+    function test2(x: (number | string) | number) {
+        if (x instanceof Object) {
+            ~
+!!! error TS2358: The left-hand side of an 'instanceof' expression must be of type 'any', an object type or a type parameter.
+            x;
+        }
+    }
+

tests/baselines/reference/instanceofWithPrimitiveUnion.js

@@ -0,0 +1,25 @@
+//// [instanceofWithPrimitiveUnion.ts]
+function test1(x: number | string) {
+    if (x instanceof Object) {
+        x;
+    }
+}
+
+function test2(x: (number | string) | number) {
+    if (x instanceof Object) {
+        x;
+    }
+}
+
+
+//// [instanceofWithPrimitiveUnion.js]
+function test1(x) {
+    if (x instanceof Object) {
+        x;
+    }
+}
+function test2(x) {
+    if (x instanceof Object) {
+        x;
+    }
+}

tests/baselines/reference/instanceofWithPrimitiveUnion.symbols

@@ -0,0 +1,27 @@
+=== tests/cases/compiler/instanceofWithPrimitiveUnion.ts ===
+function test1(x: number | string) {
+>test1 : Symbol(test1, Decl(instanceofWithPrimitiveUnion.ts, 0, 0))
+>x : Symbol(x, Decl(instanceofWithPrimitiveUnion.ts, 0, 15))
+
+    if (x instanceof Object) {
+>x : Symbol(x, Decl(instanceofWithPrimitiveUnion.ts, 0, 15))
+>Object : Symbol(Object, Decl(lib.d.ts, --, --), Decl(lib.d.ts, --, --))
+
+        x;
+>x : Symbol(x, Decl(instanceofWithPrimitiveUnion.ts, 0, 15))
+    }
+}
+
+function test2(x: (number | string) | number) {
+>test2 : Symbol(test2, Decl(instanceofWithPrimitiveUnion.ts, 4, 1))
+>x : Symbol(x, Decl(instanceofWithPrimitiveUnion.ts, 6, 15))
+
+    if (x instanceof Object) {
+>x : Symbol(x, Decl(instanceofWithPrimitiveUnion.ts, 6, 15))
+>Object : Symbol(Object, Decl(lib.d.ts, --, --), Decl(lib.d.ts, --, --))
+
+        x;
+>x : Symbol(x, Decl(instanceofWithPrimitiveUnion.ts, 6, 15))
+    }
+}
+

tests/baselines/reference/instanceofWithPrimitiveUnion.types

@@ -0,0 +1,29 @@
+=== tests/cases/compiler/instanceofWithPrimitiveUnion.ts ===
+function test1(x: number | string) {
+>test1 : (x: string | number) => void
+>x : string | number
+
+    if (x instanceof Object) {
+>x instanceof Object : boolean
+>x : string | number
+>Object : ObjectConstructor
+
+        x;
+>x : string | number
+    }
+}
+
+function test2(x: (number | string) | number) {
+>test2 : (x: string | number) => void
+>x : string | number
+
+    if (x instanceof Object) {
+>x instanceof Object : boolean
+>x : string | number
+>Object : ObjectConstructor
+
+        x;
+>x : string | number
+    }
+}
+

tests/cases/compiler/instanceofWithPrimitiveUnion.ts

@@ -0,0 +1,11 @@
+function test1(x: number | string) {
+    if (x instanceof Object) {
+        x;
+    }
+}
+
+function test2(x: (number | string) | number) {
+    if (x instanceof Object) {
+        x;
+    }
+}