Fix isTypeDerivedFrom to properly handle {} and intersections (#51631)

* Fix isTypeDerivedFrom to properly handle {} and intersections

* Add tests

Author: ahejlsberg

src/compiler/checker.ts

@@ -18759,16 +18759,20 @@ export function createTypeChecker(host: TypeCheckerHost): TypeChecker {
     // An object type S is considered to be derived from an object type T if
     // S is a union type and every constituent of S is derived from T,
     // T is a union type and S is derived from at least one constituent of T, or
-    // S is a type variable with a base constraint that is derived from T,
+    // S is an intersection type and some constituent of S is derived from T, or
+    // S is a type variable with a base constraint that is derived from T, or
+    // T is {} and S is an object-like type (ensuring {} is less derived than Object), or
     // T is one of the global types Object and Function and S is a subtype of T, or
     // T occurs directly or indirectly in an 'extends' clause of S.
     // Note that this check ignores type parameters and only considers the
     // inheritance hierarchy.
     function isTypeDerivedFrom(source: Type, target: Type): boolean {
         return source.flags & TypeFlags.Union ? every((source as UnionType).types, t => isTypeDerivedFrom(t, target)) :
             target.flags & TypeFlags.Union ? some((target as UnionType).types, t => isTypeDerivedFrom(source, t)) :
+            source.flags & TypeFlags.Intersection ? some((source as IntersectionType).types, t => isTypeDerivedFrom(t, target)) :
             source.flags & TypeFlags.InstantiableNonPrimitive ? isTypeDerivedFrom(getBaseConstraintOfType(source) || unknownType, target) :
-            target === globalObjectType ? !!(source.flags & (TypeFlags.Object | TypeFlags.NonPrimitive)) :
+            isEmptyAnonymousObjectType(target) ? !!(source.flags & (TypeFlags.Object | TypeFlags.NonPrimitive)) :
+            target === globalObjectType ? !!(source.flags & (TypeFlags.Object | TypeFlags.NonPrimitive)) && !isEmptyAnonymousObjectType(source) :
             target === globalFunctionType ? !!(source.flags & TypeFlags.Object) && isFunctionObjectType(source as ObjectType) :
             hasBaseType(source, getTargetType(target)) || (isArrayType(target) && !isReadonlyArrayType(target) && isTypeDerivedFrom(source, globalReadonlyArrayType));
     }

tests/baselines/reference/inKeywordAndIntersection.js

@@ -0,0 +1,59 @@
+//// [inKeywordAndIntersection.ts]
+class A { a = 0 }
+class B { b = 0 }
+
+function f10(obj: A & { x: string } | B) {
+    if (obj instanceof Object) {
+        obj;  // A & { x: string } | B
+    }
+    else {
+        obj;  // Error
+    }
+}
+
+// Repro from #50844
+
+interface InstanceOne {
+    one(): void
+}
+
+interface InstanceTwo {
+    two(): void
+}
+
+const instance = {} as InstanceOne | InstanceTwo
+
+const ClassOne = {} as { new(): InstanceOne } & { foo: true };
+
+if (instance instanceof ClassOne) {
+    instance.one();
+}
+
+
+//// [inKeywordAndIntersection.js]
+"use strict";
+var A = /** @class */ (function () {
+    function A() {
+        this.a = 0;
+    }
+    return A;
+}());
+var B = /** @class */ (function () {
+    function B() {
+        this.b = 0;
+    }
+    return B;
+}());
+function f10(obj) {
+    if (obj instanceof Object) {
+        obj; // A & { x: string } | B
+    }
+    else {
+        obj; // Error
+    }
+}
+var instance = {};
+var ClassOne = {};
+if (instance instanceof ClassOne) {
+    instance.one();
+}

tests/baselines/reference/inKeywordAndIntersection.symbols

@@ -0,0 +1,65 @@
+=== tests/cases/compiler/inKeywordAndIntersection.ts ===
+class A { a = 0 }
+>A : Symbol(A, Decl(inKeywordAndIntersection.ts, 0, 0))
+>a : Symbol(A.a, Decl(inKeywordAndIntersection.ts, 0, 9))
+
+class B { b = 0 }
+>B : Symbol(B, Decl(inKeywordAndIntersection.ts, 0, 17))
+>b : Symbol(B.b, Decl(inKeywordAndIntersection.ts, 1, 9))
+
+function f10(obj: A & { x: string } | B) {
+>f10 : Symbol(f10, Decl(inKeywordAndIntersection.ts, 1, 17))
+>obj : Symbol(obj, Decl(inKeywordAndIntersection.ts, 3, 13))
+>A : Symbol(A, Decl(inKeywordAndIntersection.ts, 0, 0))
+>x : Symbol(x, Decl(inKeywordAndIntersection.ts, 3, 23))
+>B : Symbol(B, Decl(inKeywordAndIntersection.ts, 0, 17))
+
+    if (obj instanceof Object) {
+>obj : Symbol(obj, Decl(inKeywordAndIntersection.ts, 3, 13))
+>Object : Symbol(Object, Decl(lib.es5.d.ts, --, --), Decl(lib.es5.d.ts, --, --))
+
+        obj;  // A & { x: string } | B
+>obj : Symbol(obj, Decl(inKeywordAndIntersection.ts, 3, 13))
+    }
+    else {
+        obj;  // Error
+>obj : Symbol(obj, Decl(inKeywordAndIntersection.ts, 3, 13))
+    }
+}
+
+// Repro from #50844
+
+interface InstanceOne {
+>InstanceOne : Symbol(InstanceOne, Decl(inKeywordAndIntersection.ts, 10, 1))
+
+    one(): void
+>one : Symbol(InstanceOne.one, Decl(inKeywordAndIntersection.ts, 14, 23))
+}
+
+interface InstanceTwo {
+>InstanceTwo : Symbol(InstanceTwo, Decl(inKeywordAndIntersection.ts, 16, 1))
+
+    two(): void
+>two : Symbol(InstanceTwo.two, Decl(inKeywordAndIntersection.ts, 18, 23))
+}
+
+const instance = {} as InstanceOne | InstanceTwo
+>instance : Symbol(instance, Decl(inKeywordAndIntersection.ts, 22, 5))
+>InstanceOne : Symbol(InstanceOne, Decl(inKeywordAndIntersection.ts, 10, 1))
+>InstanceTwo : Symbol(InstanceTwo, Decl(inKeywordAndIntersection.ts, 16, 1))
+
+const ClassOne = {} as { new(): InstanceOne } & { foo: true };
+>ClassOne : Symbol(ClassOne, Decl(inKeywordAndIntersection.ts, 24, 5))
+>InstanceOne : Symbol(InstanceOne, Decl(inKeywordAndIntersection.ts, 10, 1))
+>foo : Symbol(foo, Decl(inKeywordAndIntersection.ts, 24, 49))
+
+if (instance instanceof ClassOne) {
+>instance : Symbol(instance, Decl(inKeywordAndIntersection.ts, 22, 5))
+>ClassOne : Symbol(ClassOne, Decl(inKeywordAndIntersection.ts, 24, 5))
+
+    instance.one();
+>instance.one : Symbol(InstanceOne.one, Decl(inKeywordAndIntersection.ts, 14, 23))
+>instance : Symbol(instance, Decl(inKeywordAndIntersection.ts, 22, 5))
+>one : Symbol(InstanceOne.one, Decl(inKeywordAndIntersection.ts, 14, 23))
+}
+

tests/baselines/reference/inKeywordAndIntersection.types

@@ -0,0 +1,66 @@
+=== tests/cases/compiler/inKeywordAndIntersection.ts ===
+class A { a = 0 }
+>A : A
+>a : number
+>0 : 0
+
+class B { b = 0 }
+>B : B
+>b : number
+>0 : 0
+
+function f10(obj: A & { x: string } | B) {
+>f10 : (obj: (A & {    x: string;}) | B) => void
+>obj : B | (A & { x: string; })
+>x : string
+
+    if (obj instanceof Object) {
+>obj instanceof Object : boolean
+>obj : B | (A & { x: string; })
+>Object : ObjectConstructor
+
+        obj;  // A & { x: string } | B
+>obj : B | (A & { x: string; })
+    }
+    else {
+        obj;  // Error
+>obj : never
+    }
+}
+
+// Repro from #50844
+
+interface InstanceOne {
+    one(): void
+>one : () => void
+}
+
+interface InstanceTwo {
+    two(): void
+>two : () => void
+}
+
+const instance = {} as InstanceOne | InstanceTwo
+>instance : InstanceOne | InstanceTwo
+>{} as InstanceOne | InstanceTwo : InstanceOne | InstanceTwo
+>{} : {}
+
+const ClassOne = {} as { new(): InstanceOne } & { foo: true };
+>ClassOne : (new () => InstanceOne) & { foo: true; }
+>{} as { new(): InstanceOne } & { foo: true } : (new () => InstanceOne) & { foo: true; }
+>{} : {}
+>foo : true
+>true : true
+
+if (instance instanceof ClassOne) {
+>instance instanceof ClassOne : boolean
+>instance : InstanceOne | InstanceTwo
+>ClassOne : (new () => InstanceOne) & { foo: true; }
+
+    instance.one();
+>instance.one() : void
+>instance.one : () => void
+>instance : InstanceOne
+>one : () => void
+}
+

tests/baselines/reference/inKeywordAndUnknown.errors.txt

@@ -20,4 +20,38 @@ tests/cases/compiler/inKeywordAndUnknown.ts(12,18): error TS2638: Type '{}' may
         }
         y;  // {}
     }
+    
+    // Repro from #51007
+    
+    function isHTMLTable(table: unknown): boolean {
+        return !!table && table instanceof Object && 'html' in table;
+    }
+    
+    function f1(x: unknown) {
+        return x && x instanceof Object && 'a' in x;
+    }
+    
+    function f2<T>(x: T) {
+        return x && x instanceof Object && 'a' in x;
+    }
+    
+    function f3(x: {}) {
+        return x instanceof Object && 'a' in x;
+    }
+    
+    function f4<T extends {}>(x: T) {
+        return x instanceof Object && 'a' in x;
+    }
+    
+    function f5<T>(x: T & {}) {
+        return x instanceof Object && 'a' in x;
+    }
+    
+    function f6<T extends {}>(x: T & {}) {
+        return x instanceof Object && 'a' in x;
+    }
+    
+    function f7<T extends object>(x: T & {}) {
+        return x instanceof Object && 'a' in x;
+    }
 

tests/baselines/reference/inKeywordAndUnknown.js

@@ -15,6 +15,40 @@ function f(x: {}, y: unknown) {
     }
     y;  // {}
 }
+
+// Repro from #51007
+
+function isHTMLTable(table: unknown): boolean {
+    return !!table && table instanceof Object && 'html' in table;
+}
+
+function f1(x: unknown) {
+    return x && x instanceof Object && 'a' in x;
+}
+
+function f2<T>(x: T) {
+    return x && x instanceof Object && 'a' in x;
+}
+
+function f3(x: {}) {
+    return x instanceof Object && 'a' in x;
+}
+
+function f4<T extends {}>(x: T) {
+    return x instanceof Object && 'a' in x;
+}
+
+function f5<T>(x: T & {}) {
+    return x instanceof Object && 'a' in x;
+}
+
+function f6<T extends {}>(x: T & {}) {
+    return x instanceof Object && 'a' in x;
+}
+
+function f7<T extends object>(x: T & {}) {
+    return x instanceof Object && 'a' in x;
+}
 
 
 //// [inKeywordAndUnknown.js]
@@ -34,3 +68,28 @@ function f(x, y) {
     }
     y; // {}
 }
+// Repro from #51007
+function isHTMLTable(table) {
+    return !!table && table instanceof Object && 'html' in table;
+}
+function f1(x) {
+    return x && x instanceof Object && 'a' in x;
+}
+function f2(x) {
+    return x && x instanceof Object && 'a' in x;
+}
+function f3(x) {
+    return x instanceof Object && 'a' in x;
+}
+function f4(x) {
+    return x instanceof Object && 'a' in x;
+}
+function f5(x) {
+    return x instanceof Object && 'a' in x;
+}
+function f6(x) {
+    return x instanceof Object && 'a' in x;
+}
+function f7(x) {
+    return x instanceof Object && 'a' in x;
+}