Merge pull request #10 from joeywatts/class-properties-esnext

Moves the transformation of class properties to the ESNext transformer.

Property initializers are moved to the constructor by the TypeScript transformer only if there is constructor parameter properties. This is to preserve property initialization order.

It currently does not produce void 0 initializers for property declarations that have no initializer due to ESNext and TypeScript having different runtime behaviors. TS completely elides property declarations with no initializer, while I believe the ESNext would define that property on the instance with an undefined value (which is observable at runtime - propertyName in instance or for (var prop in instance) {}).

Author: mheiber

src/compiler/binder.ts

@@ -3189,8 +3189,7 @@ namespace ts {
             // A ClassDeclaration is ES6 syntax.
             transformFlags = subtreeFlags | TransformFlags.AssertES2015;
 
-            // A class with a parameter property assignment, property initializer, computed property name, or decorator is
-            // TypeScript syntax.
+            // A class with a parameter property assignment or decorator is TypeScript syntax.
             // An exported declaration may be TypeScript syntax, but is handled by the visitor
             // for a namespace declaration.
             if ((subtreeFlags & TransformFlags.ContainsTypeScriptClassSyntax)
@@ -3213,8 +3212,7 @@ namespace ts {
         // A ClassExpression is ES6 syntax.
         let transformFlags = subtreeFlags | TransformFlags.AssertES2015;
 
-        // A class with a parameter property assignment, property initializer, or decorator is
-        // TypeScript syntax.
+        // A class with a parameter property assignment or decorator is TypeScript syntax.
         if (subtreeFlags & TransformFlags.ContainsTypeScriptClassSyntax
             || node.typeParameters) {
             transformFlags |= TransformFlags.AssertTypeScript;
@@ -3310,7 +3308,6 @@ namespace ts {
             || hasModifier(node, ModifierFlags.TypeScriptModifier)
             || node.typeParameters
             || node.type
-            || (node.name && isComputedPropertyName(node.name)) // While computed method names aren't typescript, the TS transform must visit them to emit property declarations correctly
             || !node.body) {
             transformFlags |= TransformFlags.AssertTypeScript;
         }
@@ -3341,7 +3338,6 @@ namespace ts {
         if (node.decorators
             || hasModifier(node, ModifierFlags.TypeScriptModifier)
             || node.type
-            || (node.name && isComputedPropertyName(node.name)) // While computed accessor names aren't typescript, the TS transform must visit them to emit property declarations correctly
             || !node.body) {
             transformFlags |= TransformFlags.AssertTypeScript;
         }
@@ -3356,12 +3352,16 @@ namespace ts {
     }
 
     function computePropertyDeclaration(node: PropertyDeclaration, subtreeFlags: TransformFlags) {
-        // A PropertyDeclaration is TypeScript syntax.
-        let transformFlags = subtreeFlags | TransformFlags.AssertTypeScript;
+        // A PropertyDeclaration is ESnext syntax.
+        let transformFlags = subtreeFlags | TransformFlags.AssertESNext;
 
-        // If the PropertyDeclaration has an initializer or a computed name, we need to inform its ancestor
-        // so that it handle the transformation.
-        if (node.initializer || isComputedPropertyName(node.name)) {
+        // Decorators, TypeScript-specific modifiers, and type annotations are TypeScript syntax.
+        if (some(node.decorators) || hasModifier(node, ModifierFlags.TypeScriptModifier) || node.type) {
+            transformFlags |= TransformFlags.AssertTypeScript;
+        }
+
+        // Hoisted variables related to class properties should live within the TypeScript class wrapper.
+        if (isComputedPropertyName(node.name) || (hasStaticModifier(node) && node.initializer)) {
             transformFlags |= TransformFlags.ContainsTypeScriptClassSyntax;
         }
 
@@ -3762,6 +3762,8 @@ namespace ts {
                 break;
 
             case SyntaxKind.ComputedPropertyName:
+                // Computed property names are transformed by the ESNext transformer.
+                transformFlags |= TransformFlags.AssertESNext;
                 // Even though computed property names are ES6, we don't treat them as such.
                 // This is so that they can flow through PropertyName transforms unaffected.
                 // Instead, we mark the container as ES6, so that it can properly handle the transform.

src/compiler/transformers/esnext.ts

@@ -240,6 +240,47 @@ namespace ts {
             isIdentifier(expression);
     }
 
+    /**
+     * A simple inlinable expression is an expression which can be copied into multiple locations
+     * without risk of repeating any sideeffects and whose value could not possibly change between
+     * any such locations
+     */
+    export function isSimpleInlineableExpression(expression: Expression) {
+        return !isIdentifier(expression) && isSimpleCopiableExpression(expression) ||
+            isWellKnownSymbolSyntactically(expression);
+    }
+
+    /**
+     * Adds super call and preceding prologue directives into the list of statements.
+     *
+     * @param ctor The constructor node.
+     * @param result The list of statements.
+     * @param visitor The visitor to apply to each node added to the result array.
+     * @returns index of the statement that follows super call
+     */
+    export function addPrologueDirectivesAndInitialSuperCall(ctor: ConstructorDeclaration, result: Statement[], visitor: Visitor): number {
+        if (ctor.body) {
+            const statements = ctor.body.statements;
+            // add prologue directives to the list (if any)
+            const index = addPrologue(result, statements, /*ensureUseStrict*/ false, visitor);
+            if (index === statements.length) {
+                // list contains nothing but prologue directives (or empty) - exit
+                return index;
+            }
+
+            const statement = statements[index];
+            if (statement.kind === SyntaxKind.ExpressionStatement && isSuperCall((<ExpressionStatement>statement).expression)) {
+                result.push(visitNode(statement, visitor, isStatement));
+                return index + 1;
+            }
+
+            return index;
+        }
+
+        return 0;
+    }
+
+
     /**
      * @param input Template string input strings
      * @param args Names which need to be made file-level unique
@@ -255,4 +296,43 @@ namespace ts {
             return result;
         };
     }
+
+    /**
+     * Gets all property declarations with initializers on either the static or instance side of a class.
+     *
+     * @param node The class node.
+     * @param isStatic A value indicating whether to get properties from the static or instance side of the class.
+     */
+    export function getInitializedProperties(node: ClassExpression | ClassDeclaration, isStatic: boolean): ReadonlyArray<PropertyDeclaration> {
+        return filter(node.members, isStatic ? isStaticInitializedProperty : isInstanceInitializedProperty);
+    }
+
+    /**
+     * Gets a value indicating whether a class element is a static property declaration with an initializer.
+     *
+     * @param member The class element node.
+     */
+    export function isStaticInitializedProperty(member: ClassElement): member is PropertyDeclaration & { initializer: Expression; } {
+        return isInitializedProperty(member) && hasStaticModifier(member);
+    }
+
+    /**
+     * Gets a value indicating whether a class element is an instance property declaration with an initializer.
+     *
+     * @param member The class element node.
+     */
+    export function isInstanceInitializedProperty(member: ClassElement): member is PropertyDeclaration & { initializer: Expression; } {
+        return isInitializedProperty(member) && !hasStaticModifier(member);
+    }
+
+    /**
+     * Gets a value indicating whether a class element is either a static or an instance property declaration with an initializer.
+     *
+     * @param member The class element node.
+     * @param isStatic A value indicating whether the member should be a static or instance member.
+     */
+    export function isInitializedProperty(member: ClassElement): member is PropertyDeclaration & { initializer: Expression; } {
+        return member.kind === SyntaxKind.PropertyDeclaration
+            && (<PropertyDeclaration>member).initializer !== undefined;
+    }
 }

src/compiler/transformers/ts.ts

@@ -34,8 +34,8 @@ var C = /** @class */ (function () {
     }
     return C;
 }());
-_a = a_1.x;
 exports.C = C;
+_a = a_1.x;
 //// [c.js]
 "use strict";
 var __extends = (this && this.__extends) || (function () {
@@ -64,8 +64,8 @@ var D = /** @class */ (function (_super) {
     }
     return D;
 }(b_1.C));
-_a = a_1.x;
 exports.D = D;
+_a = a_1.x;
 
 
 //// [a.d.ts]