fix transform-classes

Author: wardpeet

packages/babel-preset-gatsby/package.json

@@ -13,6 +13,7 @@
     "@babel/plugin-proposal-nullish-coalescing-operator": "^7.12.1",
     "@babel/plugin-proposal-optional-chaining": "^7.12.1",
     "@babel/plugin-syntax-dynamic-import": "^7.8.3",
+    "@babel/plugin-transform-classes": "^7.12.1",
     "@babel/plugin-transform-runtime": "^7.12.1",
     "@babel/plugin-transform-spread": "^7.12.1",
     "@babel/preset-env": "^7.12.1",

packages/babel-preset-gatsby/src/__tests__/__snapshots__/index.js.snap

@@ -298,6 +298,12 @@ Object {
         "loose": false,
       },
     ],
+    Array [
+      "<PROJECT_ROOT>/node_modules/@babel/plugin-transform-classes/lib/index.js",
+      Object {
+        "loose": true,
+      },
+    ],
     "<PROJECT_ROOT>/node_modules/babel-plugin-dynamic-import-node/lib/index.js",
     Array [
       "<PROJECT_ROOT>/node_modules/babel-plugin-transform-react-remove-prop-types/lib/index.js",
@@ -568,6 +574,12 @@ Object {
         "loose": false,
       },
     ],
+    Array [
+      "<PROJECT_ROOT>/node_modules/@babel/plugin-transform-classes/lib/index.js",
+      Object {
+        "loose": true,
+      },
+    ],
     "<PROJECT_ROOT>/node_modules/babel-plugin-dynamic-import-node/lib/index.js",
   ],
   "presets": Array [

packages/babel-preset-gatsby/src/index.js

@@ -119,12 +119,19 @@ export default function preset(_, options = {}) {
           // absoluteRuntime: absoluteRuntimePath,
         },
       ],
+      // TODO allow loose mode as an option in v3
       isBrowser && [
         resolve(`@babel/plugin-transform-spread`),
         {
           loose: false, // Fixes #14848
         },
       ],
+      isBrowser && [
+        resolve(`@babel/plugin-transform-classes`),
+        {
+          loose: true,
+        },
+      ],
       IS_TEST && resolve(`babel-plugin-dynamic-import-node`),
       stage === `build-javascript` && [
         // Remove PropTypes from production build