Code review comments

src/compiler/checker.ts

@@ -16247,10 +16247,8 @@ namespace ts {
         function writeBaseConstructorTypeOfClass(node: ClassLikeDeclaration, enclosingDeclaration: Node, flags: TypeFormatFlags, writer: SymbolWriter) {
             const classType = <InterfaceType>getDeclaredTypeOfSymbol(getSymbolOfNode(node));
             resolveBaseTypesOfClass(classType);
-            const baseType = classType.resolvedBaseTypes[0];
-            if (baseType) {
-                getSymbolDisplayBuilder().buildTypeDisplay(baseType, writer, enclosingDeclaration, flags);
-            }
+            const baseType = classType.resolvedBaseTypes.length ? classType.resolvedBaseTypes[0] : unknownType;
+            getSymbolDisplayBuilder().buildTypeDisplay(baseType, writer, enclosingDeclaration, flags);
         }
 
         function hasGlobalName(name: string): boolean {

tests/baselines/reference/declarationEmit_expressionInExtends4.errors.txt

@@ -0,0 +1,35 @@
+tests/cases/compiler/declarationEmit_expressionInExtends4.ts(2,10): error TS4060: Return type of exported function has or is using private name 'D'.
+tests/cases/compiler/declarationEmit_expressionInExtends4.ts(6,17): error TS2315: Type 'D' is not generic.
+tests/cases/compiler/declarationEmit_expressionInExtends4.ts(10,18): error TS2304: Cannot find name 'SomeUndefinedFunction'.
+tests/cases/compiler/declarationEmit_expressionInExtends4.ts(15,18): error TS2304: Cannot find name 'SomeUndefinedFunction'.
+tests/cases/compiler/declarationEmit_expressionInExtends4.ts(15,18): error TS4020: Extends clause of exported class 'C3' has or is using private name 'SomeUndefinedFunction'.
+
+
+==== tests/cases/compiler/declarationEmit_expressionInExtends4.ts (5 errors) ====
+    
+    function getSomething() {
+             ~~~~~~~~~~~~
+!!! error TS4060: Return type of exported function has or is using private name 'D'.
+        return class D { }
+    }
+    
+    class C extends getSomething()<number, string> {
+                    ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+!!! error TS2315: Type 'D' is not generic.
+    
+    }
+    
+    class C2 extends SomeUndefinedFunction()<number, string> {
+                     ~~~~~~~~~~~~~~~~~~~~~
+!!! error TS2304: Cannot find name 'SomeUndefinedFunction'.
+    
+    }
+    
+    
+    class C3 extends SomeUndefinedFunction {
+                     ~~~~~~~~~~~~~~~~~~~~~
+!!! error TS2304: Cannot find name 'SomeUndefinedFunction'.
+                     ~~~~~~~~~~~~~~~~~~~~~
+!!! error TS4020: Extends clause of exported class 'C3' has or is using private name 'SomeUndefinedFunction'.
+    
+    }

tests/baselines/reference/declarationEmit_expressionInExtends4.js

@@ -0,0 +1,53 @@
+//// [declarationEmit_expressionInExtends4.ts]
+
+function getSomething() {
+    return class D { }
+}
+
+class C extends getSomething()<number, string> {
+
+}
+
+class C2 extends SomeUndefinedFunction()<number, string> {
+
+}
+
+
+class C3 extends SomeUndefinedFunction {
+
+}
+
+//// [declarationEmit_expressionInExtends4.js]
+var __extends = (this && this.__extends) || function (d, b) {
+    for (var p in b) if (b.hasOwnProperty(p)) d[p] = b[p];
+    function __() { this.constructor = d; }
+    d.prototype = b === null ? Object.create(b) : (__.prototype = b.prototype, new __());
+};
+function getSomething() {
+    return (function () {
+        function D() {
+        }
+        return D;
+    }());
+}
+var C = (function (_super) {
+    __extends(C, _super);
+    function C() {
+        _super.apply(this, arguments);
+    }
+    return C;
+}(getSomething()));
+var C2 = (function (_super) {
+    __extends(C2, _super);
+    function C2() {
+        _super.apply(this, arguments);
+    }
+    return C2;
+}(SomeUndefinedFunction()));
+var C3 = (function (_super) {
+    __extends(C3, _super);
+    function C3() {
+        _super.apply(this, arguments);
+    }
+    return C3;
+}(SomeUndefinedFunction));

tests/cases/compiler/declarationEmit_expressionInExtends4.ts

@@ -0,0 +1,18 @@
+// @declaration: true
+
+function getSomething() {
+    return class D { }
+}
+
+class C extends getSomething()<number, string> {
+
+}
+
+class C2 extends SomeUndefinedFunction()<number, string> {
+
+}
+
+
+class C3 extends SomeUndefinedFunction {
+
+}