feat(gatsby): Support React 17's new JSX Transform

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

@@ -258,6 +258,7 @@ Object {
       Object {
         "development": false,
         "pragma": "React.createElement",
+        "runtime": "classic",
         "useBuiltIns": true,
       },
     ],
@@ -527,6 +528,7 @@ Object {
       Object {
         "development": false,
         "pragma": "React.createElement",
+        "runtime": "classic",
         "useBuiltIns": true,
       },
     ],
@@ -790,6 +792,7 @@ Object {
       Object {
         "development": false,
         "pragma": "React.createElement",
+        "runtime": "classic",
         "useBuiltIns": true,
       },
     ],
@@ -1053,6 +1056,7 @@ Object {
       Object {
         "development": true,
         "pragma": "React.createElement",
+        "runtime": "classic",
         "useBuiltIns": true,
       },
     ],

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

@@ -26,4 +26,18 @@ describe(`babel-preset-gatsby`, () => {
       }),
     ])
   })
+
+  it(`Allows to configure react runtime`, () => {
+    const { presets } = preset(null, {
+      reactRuntime: `automatic`,
+    })
+
+    expect(presets[1]).toEqual([
+      expect.stringContaining(path.join(`@babel`, `preset-react`)),
+      expect.objectContaining({
+        pragma: undefined,
+        runtime: `automatic`,
+      }),
+    ])
+  })
 })

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

@@ -77,8 +77,12 @@ export default function preset(_, options = {}) {
         resolve(`@babel/preset-react`),
         {
           useBuiltIns: true,
-          pragma: `React.createElement`,
+          pragma:
+            options.reactRuntime === `automatic`
+              ? undefined
+              : `React.createElement`,
           development: stage === `develop`,
+          runtime: options.reactRuntime || `classic`,
         },
       ],
     ],

packages/gatsby/src/redux/__tests__/__snapshots__/babelrc.ts.snap

@@ -173,6 +173,7 @@ Array [
     Array [
       "/path/to/module/babel-preset-gatsby",
       Object {
+        "reactRuntime": undefined,
         "stage": "test",
       },
     ],

packages/gatsby/src/utils/__tests__/__snapshots__/webpack-utils.ts.snap

@@ -41,6 +41,7 @@ Object {
         "cacheDirectory": "<TEMP_DIR>/test/.cache/webpack/babel",
         "compact": false,
         "configFile": true,
+        "reactRuntime": "classic",
         "stage": "develop",
       },
     },

packages/gatsby/src/utils/babel-loader-helpers.js

@@ -24,7 +24,7 @@ const getCustomOptions = stage => {
 const prepareOptions = (babel, options = {}, resolve = require.resolve) => {
   const pluginBabelConfig = loadCachedConfig()
 
-  const { stage } = options
+  const { stage, reactRuntime } = options
 
   // Required plugins/presets
   const requiredPlugins = [
@@ -67,6 +67,7 @@ const prepareOptions = (babel, options = {}, resolve = require.resolve) => {
         resolve(`babel-preset-gatsby`),
         {
           stage,
+          reactRuntime,
         },
       ],
       {

packages/gatsby/src/utils/babel-loader.js

@@ -24,10 +24,11 @@ const {
 module.exports = babelLoader.custom(babel => {
   const toReturn = {
     // Passed the loader options.
-    customOptions({ stage = `test`, ...options }) {
+    customOptions({ stage = `test`, reactRuntime = `classic`, ...options }) {
       return {
         custom: {
           stage,
+          reactRuntime,
         },
         loader: {
           sourceType: `unambiguous`,

packages/gatsby/src/utils/eslint-config.ts

@@ -1,7 +1,10 @@
 import { printSchema, GraphQLSchema } from "graphql"
 import { CLIEngine } from "eslint"
 
-export const eslintConfig = (schema: GraphQLSchema): CLIEngine.Options => {
+export const eslintConfig = (
+  schema: GraphQLSchema,
+  usingJsxRuntime: boolean
+): CLIEngine.Options => {
   return {
     useEslintrc: false,
     resolvePluginsRelativeTo: __dirname,
@@ -14,6 +17,12 @@ export const eslintConfig = (schema: GraphQLSchema): CLIEngine.Options => {
       extends: [require.resolve(`eslint-config-react-app`)],
       plugins: [`graphql`],
       rules: {
+        // New versions of react use a special jsx runtime that remove the requirement
+        // for having react in scope for jsx. Once the jsx runtime is backported to all
+        // versions of react we can make this always be `off`.
+        // I would also assume that eslint-config-react-app will switch their flag to `off`
+        // when jsx runtime is stable in all common versions of React.
+        "react/react-in-jsx-scope": usingJsxRuntime ? `off` : `error`, // Conditionally apply for reactRuntime?
         "import/no-webpack-loader-syntax": [0],
         "graphql/template-strings": [
           `error`,

packages/gatsby/src/utils/webpack-utils.ts

@@ -137,6 +137,7 @@ export const createWebpackUtils = (
 
   const isSSR = stage.includes(`html`)
 
+  const jsxRuntimeExists = reactHasJsxRuntime()
   const makeExternalOnly = (original: RuleFactory) => (
     options = {}
   ): RuleSetRule => {
@@ -273,6 +274,7 @@ export const createWebpackUtils = (
       return {
         options: {
           stage,
+          reactRuntime: jsxRuntimeExists ? `automatic` : `classic`,
           // TODO add proper cache keys
           cacheDirectory: path.join(
             program.directory,
@@ -303,7 +305,7 @@ export const createWebpackUtils = (
     },
 
     eslint: (schema: GraphQLSchema) => {
-      const options = eslintConfig(schema)
+      const options = eslintConfig(schema, jsxRuntimeExists)
 
       return {
         options,
@@ -710,3 +712,19 @@ export const createWebpackUtils = (
     plugins,
   }
 }
+
+function reactHasJsxRuntime(): boolean {
+  try {
+    // React is shipping a new jsx runtime that is to be used with
+    // an option on @babel/preset-react called `runtime: automatic`
+    // Not every version of React has this jsx-runtime yet. Eventually,
+    // it will be backported to older versions of react and this check
+    // will become unnecessary.
+    return !!require.resolve(`react/jsx-runtime.js`)
+  } catch (e) {
+    // If the require.resolve throws, that means this version of React
+    // does not support the jsx runtime.
+  }
+
+  return false
+}