[decorators] Only transform declarations to expressions when needed (#7124)

packages/babel-plugin-proposal-decorators/src/index.js

@@ -63,11 +63,11 @@ export default function() {
    * with the proper decorated behavior.
    */
   function applyClassDecorators(classPath) {
+    if (!hasClassDecorators(classPath.node)) return;
+
     const decorators = classPath.node.decorators || [];
     classPath.node.decorators = null;
 
-    if (decorators.length === 0) return;
-
     const name = classPath.scope.generateDeclaredUidIdentifier("class");
 
     return decorators
@@ -82,30 +82,30 @@ export default function() {
       }, classPath.node);
   }
 
+  function hasClassDecorators(classNode) {
+    return !!(classNode.decorators && classNode.decorators.length);
+  }
+
   /**
    * Given a class expression with method-level decorators, create a new expression
    * with the proper decorated behavior.
    */
   function applyMethodDecorators(path, state) {
-    const hasMethodDecorators = path.node.body.body.some(function(node) {
-      return (node.decorators || []).length > 0;
-    });
-
-    if (!hasMethodDecorators) return;
+    if (!hasMethodDecorators(path.node.body.body)) return;
 
     return applyTargetDecorators(path, state, path.node.body.body);
   }
 
+  function hasMethodDecorators(body) {
+    return body.some(node => node.decorators && node.decorators.length);
+  }
+
   /**
    * Given an object expression with property decorators, create a new expression
    * with the proper decorated behavior.
    */
   function applyObjectDecorators(path, state) {
-    const hasMethodDecorators = path.node.properties.some(function(node) {
-      return (node.decorators || []).length > 0;
-    });
-
-    if (!hasMethodDecorators) return;
+    if (!hasMethodDecorators(path.node.properties)) return;
 
     return applyTargetDecorators(path, state, path.node.properties);
   }
@@ -215,32 +215,29 @@ export default function() {
     inherits: syntaxDecorators,
 
     visitor: {
-      ExportDefaultDeclaration(path) {
-        if (!path.get("declaration").isClassDeclaration()) return;
-
-        const { node } = path;
-        const ref =
-          node.declaration.id || path.scope.generateUidIdentifier("default");
-        node.declaration.id = ref;
-
-        // Split the class declaration and the export into two separate statements.
-        path.replaceWith(node.declaration);
-        path.insertAfter(
-          t.exportNamedDeclaration(null, [
-            t.exportSpecifier(ref, t.identifier("default")),
-          ]),
-        );
-      },
       ClassDeclaration(path) {
         const { node } = path;
 
-        const ref = node.id || path.scope.generateUidIdentifier("class");
+        if (!hasClassDecorators(node) && !hasMethodDecorators(node.body.body)) {
+          return;
+        }
 
-        path.replaceWith(
-          t.variableDeclaration("let", [
-            t.variableDeclarator(ref, t.toExpression(node)),
-          ]),
-        );
+        const ref = node.id || path.scope.generateUidIdentifier("class");
+        const letDeclaration = t.variableDeclaration("let", [
+          t.variableDeclarator(ref, t.toExpression(node)),
+        ]);
+
+        if (path.parentPath.isExportDefaultDeclaration()) {
+          // Split the class declaration and the export into two separate statements.
+          path.parentPath.replaceWithMultiple([
+            letDeclaration,
+            t.exportNamedDeclaration(null, [
+              t.exportSpecifier(ref, t.identifier("default")),
+            ]),
+          ]);
+        } else {
+          path.replaceWith(letDeclaration);
+        }
       },
       ClassExpression(path, state) {
         // Create a replacement for the class node if there is one. We do one pass to replace classes with

packages/babel-plugin-proposal-decorators/test/fixtures/decl-to-expression/class-decorators/actual.js

@@ -0,0 +1,2 @@
+export default @dec class A {}
+@dec class B {}

packages/babel-plugin-proposal-decorators/test/fixtures/decl-to-expression/class-decorators/expected.js

@@ -0,0 +1,5 @@
+var _class, _class2;
+
+export default dec(_class = class A {}) || _class;
+
+let B = dec(_class2 = class B {}) || _class2;

packages/babel-plugin-proposal-decorators/test/fixtures/decl-to-expression/method-decorators/actual.js

@@ -0,0 +1,6 @@
+export default class A {
+  @dec foo() {}
+}
+class B {
+  @dec foo() {}
+}

packages/babel-plugin-proposal-decorators/test/fixtures/decl-to-expression/method-decorators/expected.js

@@ -0,0 +1,13 @@
+var _class, _class2;
+
+function _applyDecoratedDescriptor(target, property, decorators, descriptor, context) { var desc = {}; Object['ke' + 'ys'](descriptor).forEach(function (key) { desc[key] = descriptor[key]; }); desc.enumerable = !!desc.enumerable; desc.configurable = !!desc.configurable; if ('value' in desc || desc.initializer) { desc.writable = true; } desc = decorators.slice().reverse().reduce(function (desc, decorator) { return decorator(target, property, desc) || desc; }, desc); if (context && desc.initializer !== void 0) { desc.value = desc.initializer ? desc.initializer.call(context) : void 0; desc.initializer = undefined; } if (desc.initializer === void 0) { Object['define' + 'Property'](target, property, desc); desc = null; } return desc; }
+
+let A = (_class2 = class A {
+  foo() {}
+
+}, (_applyDecoratedDescriptor(_class2.prototype, "foo", [dec], Object.getOwnPropertyDescriptor(_class2.prototype, "foo"), _class2.prototype)), _class2);
+export { A as default };
+let B = (_class = class B {
+  foo() {}
+
+}, (_applyDecoratedDescriptor(_class.prototype, "foo", [dec], Object.getOwnPropertyDescriptor(_class.prototype, "foo"), _class.prototype)), _class);

packages/babel-plugin-proposal-decorators/test/fixtures/decl-to-expression/no-decorators/actual.js

@@ -0,0 +1,6 @@
+export default class A {
+  foo() {}
+}
+class B {
+  foo() {}
+}

packages/babel-plugin-proposal-decorators/test/fixtures/decl-to-expression/no-decorators/expected.js

@@ -0,0 +1,9 @@
+export default class A {
+  foo() {}
+
+}
+
+class B {
+  foo() {}
+
+}

packages/babel-plugin-proposal-decorators/test/fixtures/decl-to-expression/options.json

@@ -0,0 +1,4 @@
+{
+  "presets": [],
+  "plugins": ["proposal-decorators"]
+}