emit top level classes as class expressions when target=ES6 and module=System

src/compiler/emitter.ts

@@ -5278,9 +5278,11 @@ const _super = (function (geti, seti) {
 
             function emitClassLikeDeclarationForES6AndHigher(node: ClassLikeDeclaration) {
                 let decoratedClassAlias: string;
-                const thisNodeIsDecorated = nodeIsDecorated(node);
+                const isHoistedDeclarationInSystemModule = shouldHoistDeclarationInSystemJsModule(node);
+                const isDecorated = nodeIsDecorated(node);
+                const rewriteAsClassExpression = isDecorated || isHoistedDeclarationInSystemModule;
                 if (node.kind === SyntaxKind.ClassDeclaration) {
-                    if (thisNodeIsDecorated) {
+                    if (rewriteAsClassExpression) {
                         // When we emit an ES6 class that has a class decorator, we must tailor the
                         // emit to certain specific cases.
                         //
@@ -5361,7 +5363,10 @@ const _super = (function (geti, seti) {
                         //  [Example 4]
                         //
 
-                        if (resolver.getNodeCheckFlags(node) & NodeCheckFlags.ClassWithBodyScopedClassBinding) {
+                        // NOTE: we reuse the same rewriting logic for cases when targeting ES6 and module kind is System.
+                        // Because of hoisting top level class declaration need to be emitted as class expressions. 
+                        // Double bind case is only required if node is decorated.
+                        if (isDecorated && resolver.getNodeCheckFlags(node) & NodeCheckFlags.ClassWithBodyScopedClassBinding) {
                             decoratedClassAlias = unescapeIdentifier(makeUniqueName(node.name ? node.name.text : "default"));
                             decoratedClassAliases[getNodeId(node)] = decoratedClassAlias;
                             write(`let ${decoratedClassAlias};`);
@@ -5372,7 +5377,9 @@ const _super = (function (geti, seti) {
                             write("export ");
                         }
 
-                        write("let ");
+                        if (!isHoistedDeclarationInSystemModule) {
+                            write("let ");
+                        }
                         emitDeclarationName(node);
                         if (decoratedClassAlias !== undefined) {
                             write(` = ${decoratedClassAlias}`);
@@ -5416,7 +5423,7 @@ const _super = (function (geti, seti) {
                 // emit name if
                 // - node has a name
                 // - this is default export with static initializers
-                if (node.name || (node.flags & NodeFlags.Default && (staticProperties.length > 0 || modulekind !== ModuleKind.ES6) && !thisNodeIsDecorated)) {
+                if (node.name || (node.flags & NodeFlags.Default && (staticProperties.length > 0 || modulekind !== ModuleKind.ES6) && !rewriteAsClassExpression)) {
                     write(" ");
                     emitDeclarationName(node);
                 }
@@ -5436,7 +5443,7 @@ const _super = (function (geti, seti) {
                 writeLine();
                 emitToken(SyntaxKind.CloseBraceToken, node.members.end);
 
-                if (thisNodeIsDecorated) {
+                if (rewriteAsClassExpression) {
                     decoratedClassAliases[getNodeId(node)] = undefined;
                     write(";");
                 }
@@ -5476,7 +5483,7 @@ const _super = (function (geti, seti) {
                     // module), export it
                     if (node.flags & NodeFlags.Default) {
                         // if this is a top level default export of decorated class, write the export after the declaration.
-                        if (thisNodeIsDecorated) {
+                        if (isDecorated) {
                             writeLine();
                             write("export default ");
                             emitDeclarationName(node);

tests/baselines/reference/anonymousDefaultExportsSystem.js

@@ -14,8 +14,8 @@ System.register([], function(exports_1, context_1) {
     return {
         setters:[],
         execute: function() {
-            class default_1 {
-            }
+            default_1 = class {
+            };
             exports_1("default", default_1);
         }
     }

tests/baselines/reference/decoratedDefaultExportsGetExportedSystem.js

@@ -26,7 +26,7 @@ System.register([], function(exports_1, context_1) {
     return {
         setters:[],
         execute: function() {
-            let Foo = class Foo {
+            Foo = class Foo {
             };
             Foo = __decorate([
                 decorator
@@ -49,7 +49,7 @@ System.register([], function(exports_1, context_1) {
     return {
         setters:[],
         execute: function() {
-            let default_1 = class {
+            default_1 = class {
             };
             default_1 = __decorate([
                 decorator

tests/baselines/reference/defaultExportsGetExportedSystem.js

@@ -15,8 +15,8 @@ System.register([], function(exports_1, context_1) {
     return {
         setters:[],
         execute: function() {
-            class Foo {
-            }
+            Foo = class Foo {
+            };
             exports_1("default", Foo);
         }
     }

tests/baselines/reference/outFilerootDirModuleNamesSystem.js

@@ -37,8 +37,8 @@ System.register("a", ["b"], function(exports_2, context_2) {
                 b_1 = b_1_1;
             }],
         execute: function() {
-            class Foo {
-            }
+            Foo = class Foo {
+            };
             exports_2("default", Foo);
             b_1.default();
         }

tests/baselines/reference/systemModuleTargetES6.js

@@ -0,0 +1,42 @@
+//// [systemModuleTargetES6.ts]
+export class MyClass { }
+export class MyClass2 {
+    static value = 42;
+    static getInstance() { return MyClass2.value; }
+}
+
+export function myFunction() {
+    return new MyClass();
+}
+
+export function myFunction2() {
+    return new MyClass2();
+}
+
+//// [systemModuleTargetES6.js]
+System.register([], function(exports_1, context_1) {
+    "use strict";
+    var __moduleName = context_1 && context_1.id;
+    var MyClass, MyClass2;
+    function myFunction() {
+        return new MyClass();
+    }
+    exports_1("myFunction", myFunction);
+    function myFunction2() {
+        return new MyClass2();
+    }
+    exports_1("myFunction2", myFunction2);
+    return {
+        setters:[],
+        execute: function() {
+            MyClass = class MyClass {
+            };
+            exports_1("MyClass", MyClass);
+            MyClass2 = class MyClass2 {
+                static getInstance() { return MyClass2.value; }
+            };
+            MyClass2.value = 42;
+            exports_1("MyClass2", MyClass2);
+        }
+    }
+});

tests/baselines/reference/systemModuleTargetES6.symbols

@@ -0,0 +1,30 @@
+=== tests/cases/compiler/systemModuleTargetES6.ts ===
+export class MyClass { }
+>MyClass : Symbol(MyClass, Decl(systemModuleTargetES6.ts, 0, 0))
+
+export class MyClass2 {
+>MyClass2 : Symbol(MyClass2, Decl(systemModuleTargetES6.ts, 0, 24))
+
+    static value = 42;
+>value : Symbol(MyClass2.value, Decl(systemModuleTargetES6.ts, 1, 23))
+
+    static getInstance() { return MyClass2.value; }
+>getInstance : Symbol(MyClass2.getInstance, Decl(systemModuleTargetES6.ts, 2, 22))
+>MyClass2.value : Symbol(MyClass2.value, Decl(systemModuleTargetES6.ts, 1, 23))
+>MyClass2 : Symbol(MyClass2, Decl(systemModuleTargetES6.ts, 0, 24))
+>value : Symbol(MyClass2.value, Decl(systemModuleTargetES6.ts, 1, 23))
+}
+
+export function myFunction() {
+>myFunction : Symbol(myFunction, Decl(systemModuleTargetES6.ts, 4, 1))
+
+    return new MyClass();
+>MyClass : Symbol(MyClass, Decl(systemModuleTargetES6.ts, 0, 0))
+}
+
+export function myFunction2() {
+>myFunction2 : Symbol(myFunction2, Decl(systemModuleTargetES6.ts, 8, 1))
+
+    return new MyClass2();
+>MyClass2 : Symbol(MyClass2, Decl(systemModuleTargetES6.ts, 0, 24))
+}

tests/baselines/reference/systemModuleTargetES6.types

@@ -0,0 +1,33 @@
+=== tests/cases/compiler/systemModuleTargetES6.ts ===
+export class MyClass { }
+>MyClass : MyClass
+
+export class MyClass2 {
+>MyClass2 : MyClass2
+
+    static value = 42;
+>value : number
+>42 : number
+
+    static getInstance() { return MyClass2.value; }
+>getInstance : () => number
+>MyClass2.value : number
+>MyClass2 : typeof MyClass2
+>value : number
+}
+
+export function myFunction() {
+>myFunction : () => MyClass
+
+    return new MyClass();
+>new MyClass() : MyClass
+>MyClass : typeof MyClass
+}
+
+export function myFunction2() {
+>myFunction2 : () => MyClass2
+
+    return new MyClass2();
+>new MyClass2() : MyClass2
+>MyClass2 : typeof MyClass2
+}

tests/cases/compiler/systemModuleTargetES6.ts

@@ -0,0 +1,15 @@
+// @target: ES6
+// @module: System
+export class MyClass { }
+export class MyClass2 {
+    static value = 42;
+    static getInstance() { return MyClass2.value; }
+}
+
+export function myFunction() {
+    return new MyClass();
+}
+
+export function myFunction2() {
+    return new MyClass2();
+}