Implement TDZ for ClassFieldDefinitionEvaluation (#6855)

* First implementation sketch and testcase

* Use helper instead of inline IIFE's

* minNodeVersion 6.0.0

* Hoisted visitor for subtraversal and fixed edgest case

* Resolve merge conflicts in helpers

* Remove duplicated helper from messing up Git

packages/babel-helpers/src/helpers.js

@@ -633,6 +633,12 @@ helpers.readOnlyError = defineHelper(`
   }
 `);
 
+helpers.classNameTDZError = defineHelper(`
+  export default function _classNameTDZError(name) {
+    throw new Error("Class \\"" + name + "\\" cannot be referenced in computed property keys.");
+  }
+`);
+
 helpers.temporalUndefined = defineHelper(`
   export default {};
 `);

packages/babel-plugin-proposal-class-properties/src/index.js

@@ -25,6 +25,26 @@ export default function(api, options) {
     },
   };
 
+  const ClassFieldDefinitionEvaluationTDZVisitor = {
+    Expression(path) {
+      if (path === this.shouldSkip) {
+        path.skip();
+      }
+    },
+
+    ReferencedIdentifier(path) {
+      if (this.classRef === path.scope.getBinding(path.node.name)) {
+        const classNameTDZError = this.file.addHelper("classNameTDZError");
+        const throwNode = t.callExpression(classNameTDZError, [
+          t.stringLiteral(path.node.name),
+        ]);
+
+        path.replaceWith(t.sequenceExpression([throwNode, path.node]));
+        path.skip();
+      }
+    },
+  };
+
   const buildClassPropertySpec = (ref, { key, value, computed }, scope) => {
     return template.statement`
       Object.defineProperty(REF, KEY, {
@@ -95,6 +115,11 @@ export default function(api, options) {
           // Make sure computed property names are only evaluated once (upon class definition)
           // and in the right order in combination with static properties
           if (!computedPath.get("key").isConstantExpression()) {
+            computedPath.traverse(ClassFieldDefinitionEvaluationTDZVisitor, {
+              classRef: path.scope.getBinding(ref.name),
+              file: this.file,
+              shouldSkip: computedPath.get("value"),
+            });
             const ident = path.scope.generateUidIdentifierBasedOnNode(
               computedNode.key,
             );

packages/babel-plugin-proposal-class-properties/test/fixtures/static-property-tdz/edgest-case/actual.js

@@ -0,0 +1,3 @@
+class A {
+  static [{ x: A || 0 }.x];
+}

packages/babel-plugin-proposal-class-properties/test/fixtures/static-property-tdz/edgest-case/expected.js

@@ -0,0 +1,17 @@
+function _classCallCheck(instance, Constructor) { if (!(instance instanceof Constructor)) { throw new TypeError("Cannot call a class as a function"); } }
+
+function _classNameTDZError(name) { throw new Error("Class \"" + name + "\" cannot be referenced in computed property keys."); }
+
+let A = function A() {
+  _classCallCheck(this, A);
+};
+
+var _x$x = {
+  x: (_classNameTDZError("A"), A) || 0
+}.x;
+Object.defineProperty(A, _x$x, {
+  configurable: true,
+  enumerable: true,
+  writable: true,
+  value: void 0
+});

packages/babel-plugin-proposal-class-properties/test/fixtures/static-property-tdz/general/actual.js

@@ -0,0 +1,3 @@
+class C {
+  static [C + 3] = 3;
+}

packages/babel-plugin-proposal-class-properties/test/fixtures/static-property-tdz/general/exec.js

@@ -0,0 +1,3 @@
+class C {
+  static [C + 3] = 3;
+}

packages/babel-plugin-proposal-class-properties/test/fixtures/static-property-tdz/general/expected.js

@@ -0,0 +1,16 @@
+function _classCallCheck(instance, Constructor) { if (!(instance instanceof Constructor)) { throw new TypeError("Cannot call a class as a function"); } }
+
+function _classNameTDZError(name) { throw new Error("Class \"" + name + "\" cannot be referenced in computed property keys."); }
+
+let C = function C() {
+  _classCallCheck(this, C);
+};
+
+var _ref = (_classNameTDZError("C"), C) + 3;
+
+Object.defineProperty(C, _ref, {
+  configurable: true,
+  enumerable: true,
+  writable: true,
+  value: 3
+});

packages/babel-plugin-proposal-class-properties/test/fixtures/static-property-tdz/general/options.json

@@ -0,0 +1,3 @@
+{
+  "throws": "Class \"C\" cannot be referenced in computed property keys."
+}

packages/babel-plugin-proposal-class-properties/test/fixtures/static-property-tdz/loose/actual.js

@@ -0,0 +1,3 @@
+class C {
+  static [C + 3] = 3;
+}

packages/babel-plugin-proposal-class-properties/test/fixtures/static-property-tdz/loose/exec.js

@@ -0,0 +1,3 @@
+class C {
+  static [C + 3] = 3;
+}

packages/babel-plugin-proposal-class-properties/test/fixtures/static-property-tdz/loose/expected.js

@@ -0,0 +1,7 @@
+function _classNameTDZError(name) { throw new Error("Class \"" + name + "\" cannot be referenced in computed property keys."); }
+
+class C {}
+
+var _ref = (_classNameTDZError("C"), C) + 3;
+
+C[_ref] = 3;

packages/babel-plugin-proposal-class-properties/test/fixtures/static-property-tdz/loose/options.json

@@ -0,0 +1,4 @@
+{
+  "throws": "Class \"C\" cannot be referenced in computed property keys.",
+  "plugins": [["proposal-class-properties", {"loose": true}]]
+}

packages/babel-plugin-proposal-class-properties/test/fixtures/static-property-tdz/options.json

@@ -0,0 +1,4 @@
+{
+  "plugins": ["proposal-class-properties", "transform-classes"],
+  "minNodeVersion": "6.0.0"
+}