Improved handling of structurally identical classes

src/compiler/checker.ts

@@ -7440,9 +7440,12 @@ namespace ts {
             return false;
         }
 
-        function isSubtypeOfAny(candidate: Type, types: Type[]): boolean {
-            for (const type of types) {
-                if (candidate !== type && isTypeSubtypeOf(candidate, type)) {
+        function isSubtypeOfAny(source: Type, targets: Type[]): boolean {
+            for (const target of targets) {
+                if (source !== target && isTypeSubtypeOf(source, target) && (
+                    !(getObjectFlags(getTargetType(source)) & ObjectFlags.Class) ||
+                    !(getObjectFlags(getTargetType(target)) & ObjectFlags.Class) ||
+                    isTypeDerivedFrom(source, target))) {
                     return true;
                 }
             }
@@ -8565,12 +8568,19 @@ namespace ts {
             return isTypeRelatedTo(source, target, assignableRelation);
         }
 
-        // A type S is considered to be an instance of a type T if S and T are the same type or if S is a
-        // subtype of T but not structurally identical to T. This specifically means that two distinct but
-        // structurally identical types (such as two classes) are not considered instances of each other.
-        function isTypeInstanceOf(source: Type, target: Type): boolean {
-            return getTargetType(source) === getTargetType(target) || isTypeSubtypeOf(source, target) && !isTypeIdenticalTo(source, target);
-        }
+        // 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
+        // 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((<UnionType>source).types, t => isTypeDerivedFrom(t, target)) :
+                target.flags & TypeFlags.Union ? some((<UnionType>target).types, t => isTypeDerivedFrom(source, t)) :
+                target === globalObjectType || target === globalFunctionType ? isTypeSubtypeOf(source, target) :
+                hasBaseType(source, getTargetType(target));
+            }
 
         /**
          * This is *not* a bi-directional relationship.
@@ -9604,7 +9614,7 @@ namespace ts {
                 if (relation === identityRelation) {
                     return propertiesIdenticalTo(source, target);
                 }
-                const requireOptionalProperties = relation === subtypeRelation && !isObjectLiteralType(source);
+                const requireOptionalProperties = relation === subtypeRelation && !isObjectLiteralType(source) && !isEmptyArrayLiteralType(source);
                 const unmatchedProperty = getUnmatchedProperty(source, target, requireOptionalProperties);
                 if (unmatchedProperty) {
                     if (reportErrors) {
@@ -10312,6 +10322,11 @@ namespace ts {
                 !(type.flags & TypeFlags.Nullable) && isTypeAssignableTo(type, anyReadonlyArrayType);
         }
 
+        function isEmptyArrayLiteralType(type: Type): boolean {
+            const elementType = isArrayType(type) ? (<TypeReference>type).typeArguments[0] : undefined;
+            return elementType === undefinedWideningType || elementType === neverType;
+        }
+
         function isTupleLikeType(type: Type): boolean {
             return !!getPropertyOfType(type, "0" as __String);
         }
@@ -12415,7 +12430,7 @@ namespace ts {
                 }
 
                 if (targetType) {
-                    return getNarrowedType(type, targetType, assumeTrue, isTypeInstanceOf);
+                    return getNarrowedType(type, targetType, assumeTrue, isTypeDerivedFrom);
                 }
 
                 return type;
@@ -13883,7 +13898,6 @@ namespace ts {
                     type.pattern = node;
                     return type;
                 }
-                const contextualType = getApparentTypeOfContextualType(node);
                 if (contextualType && contextualTypeIsTupleLikeType(contextualType)) {
                     const pattern = contextualType.pattern;
                     // If array literal is contextually typed by a binding pattern or an assignment pattern, pad the resulting
@@ -18087,14 +18101,6 @@ namespace ts {
             return (target.flags & TypeFlags.Nullable) !== 0 || isTypeComparableTo(source, target);
         }
 
-        function getBestChoiceType(type1: Type, type2: Type): Type {
-            const firstAssignableToSecond = isTypeAssignableTo(type1, type2);
-            const secondAssignableToFirst = isTypeAssignableTo(type2, type1);
-            return secondAssignableToFirst && !firstAssignableToSecond ? type1 :
-                firstAssignableToSecond && !secondAssignableToFirst ? type2 :
-                getUnionType([type1, type2], /*subtypeReduction*/ true);
-        }
-
         function checkBinaryExpression(node: BinaryExpression, checkMode?: CheckMode) {
             return checkBinaryLikeExpression(node.left, node.operatorToken, node.right, checkMode, node);
         }
@@ -18231,7 +18237,7 @@ namespace ts {
                         leftType;
                 case SyntaxKind.BarBarToken:
                     return getTypeFacts(leftType) & TypeFacts.Falsy ?
-                        getBestChoiceType(removeDefinitelyFalsyTypes(leftType), rightType) :
+                        getUnionType([removeDefinitelyFalsyTypes(leftType), rightType], /*subtypeReduction*/ true) :
                         leftType;
                 case SyntaxKind.EqualsToken:
                     checkAssignmentOperator(rightType);
@@ -18391,7 +18397,7 @@ namespace ts {
             checkExpression(node.condition);
             const type1 = checkExpression(node.whenTrue, checkMode);
             const type2 = checkExpression(node.whenFalse, checkMode);
-            return getBestChoiceType(type1, type2);
+            return getUnionType([type1, type2], /*subtypeReduction*/ true);
         }
 
         function checkTemplateExpression(node: TemplateExpression): Type {

src/compiler/factory.ts

@@ -2641,7 +2641,7 @@ namespace ts {
     /**
      * Gets a custom text range to use when emitting source maps.
      */
-    export function getSourceMapRange(node: Node) {
+    export function getSourceMapRange(node: Node): SourceMapRange {
         const emitNode = node.emitNode;
         return (emitNode && emitNode.sourceMapRange) || node;
     }

tests/baselines/reference/arrayLiteralsWithRecursiveGenerics.types

@@ -55,8 +55,8 @@ var myList: MyList<number>;
 >MyList : MyList<T>
 
 var xs = [list, myList]; // {}[]
->xs : List<number>[]
->[list, myList] : List<number>[]
+>xs : (List<number> | MyList<number>)[]
+>[list, myList] : (List<number> | MyList<number>)[]
 >list : List<number>
 >myList : MyList<number>
 

tests/baselines/reference/fixSignatureCaching.types

@@ -866,9 +866,9 @@ define(function () {
 >'UnknownMobile' : "UnknownMobile"
 
     isArray = ('isArray' in Array) ?
->isArray = ('isArray' in Array) ?        Array.isArray : function (value) { return Object.prototype.toString.call(value) === '[object Array]'; } : (value: any) => boolean
+>isArray = ('isArray' in Array) ?        Array.isArray : function (value) { return Object.prototype.toString.call(value) === '[object Array]'; } : (arg: any) => arg is any[]
 >isArray : any
->('isArray' in Array) ?        Array.isArray : function (value) { return Object.prototype.toString.call(value) === '[object Array]'; } : (value: any) => boolean
+>('isArray' in Array) ?        Array.isArray : function (value) { return Object.prototype.toString.call(value) === '[object Array]'; } : (arg: any) => arg is any[]
 >('isArray' in Array) : boolean
 >'isArray' in Array : boolean
 >'isArray' : "isArray"

tests/baselines/reference/narrowingGenericTypeFromInstanceof01.errors.txt

@@ -1,6 +1,5 @@
-tests/cases/conformance/types/typeRelationships/instanceOf/narrowingGenericTypeFromInstanceof01.ts(13,17): error TS2345: Argument of type 'A<T> | B<T>' is not assignable to parameter of type 'A<T>'.
-  Type 'B<T>' is not assignable to type 'A<T>'.
-    Property 'a' is missing in type 'B<T>'.
+tests/cases/conformance/types/typeRelationships/instanceOf/narrowingGenericTypeFromInstanceof01.ts(13,17): error TS2345: Argument of type 'B<T>' is not assignable to parameter of type 'A<{}>'.
+  Property 'a' is missing in type 'B<T>'.
 
 
 ==== tests/cases/conformance/types/typeRelationships/instanceOf/narrowingGenericTypeFromInstanceof01.ts (1 errors) ====
@@ -18,9 +17,8 @@ tests/cases/conformance/types/typeRelationships/instanceOf/narrowingGenericTypeF
         if (x instanceof B) {
             acceptA(x);
                     ~
-!!! error TS2345: Argument of type 'A<T> | B<T>' is not assignable to parameter of type 'A<T>'.
-!!! error TS2345:   Type 'B<T>' is not assignable to type 'A<T>'.
-!!! error TS2345:     Property 'a' is missing in type 'B<T>'.
+!!! error TS2345: Argument of type 'B<T>' is not assignable to parameter of type 'A<{}>'.
+!!! error TS2345:   Property 'a' is missing in type 'B<T>'.
         }
 
         if (x instanceof A) {

tests/baselines/reference/narrowingGenericTypeFromInstanceof01.types

@@ -43,7 +43,7 @@ function test<T>(x: A<T> | B<T>) {
         acceptA(x);
 >acceptA(x) : any
 >acceptA : <T>(a: A<T>) => void
->x : A<T> | B<T>
+>x : B<T>
     }
 
     if (x instanceof A) {
@@ -65,7 +65,7 @@ function test<T>(x: A<T> | B<T>) {
         acceptB(x);
 >acceptB(x) : void
 >acceptB : <T>(b: B<T>) => void
->x : A<T> | B<T>
+>x : B<T>
     }
 
     if (x instanceof B) {
@@ -76,6 +76,6 @@ function test<T>(x: A<T> | B<T>) {
         acceptB(x);
 >acceptB(x) : void
 >acceptB : <T>(b: B<T>) => void
->x : A<T> | B<T>
+>x : B<T>
     }
 }

tests/baselines/reference/nonContextuallyTypedLogicalOr.symbols

@@ -28,8 +28,8 @@ var e: Ellement;
 >Ellement : Symbol(Ellement, Decl(nonContextuallyTypedLogicalOr.ts, 3, 1))
 
 (c || e).dummy;
->(c || e).dummy : Symbol(Contextual.dummy, Decl(nonContextuallyTypedLogicalOr.ts, 0, 22))
+>(c || e).dummy : Symbol(dummy, Decl(nonContextuallyTypedLogicalOr.ts, 0, 22), Decl(nonContextuallyTypedLogicalOr.ts, 5, 20))
 >c : Symbol(c, Decl(nonContextuallyTypedLogicalOr.ts, 10, 3))
 >e : Symbol(e, Decl(nonContextuallyTypedLogicalOr.ts, 11, 3))
->dummy : Symbol(Contextual.dummy, Decl(nonContextuallyTypedLogicalOr.ts, 0, 22))
+>dummy : Symbol(dummy, Decl(nonContextuallyTypedLogicalOr.ts, 0, 22), Decl(nonContextuallyTypedLogicalOr.ts, 5, 20))
 

tests/baselines/reference/nonContextuallyTypedLogicalOr.types

@@ -29,8 +29,8 @@ var e: Ellement;
 
 (c || e).dummy;
 >(c || e).dummy : any
->(c || e) : Contextual
->c || e : Contextual
+>(c || e) : Contextual | Ellement
+>c || e : Contextual | Ellement
 >c : Contextual
 >e : Ellement
 >dummy : any