feat(gatsby-plugin-typescript): Supports linting

packages/gatsby-plugin-typescript/README.md

@@ -77,3 +77,9 @@ Visual Studio Code is very good in this regard.
 
 In addition, you can see the instructions in [TypeScript-Babel-Starter](https://github.com/Microsoft/TypeScript-Babel-Starter)
 for setting up a `type-check` task.
+
+## ESLint
+
+This plugin supports linting TSX with [typescript-eslint](https://typescript-eslint.io) using [Gatsby's default ESLint config](https://www.gatsbyjs.org/docs/eslint/). To enable linting TSX, install `typescript`.
+
+`npm install typescript`

packages/gatsby-plugin-typescript/package.json

@@ -33,7 +33,13 @@
   "license": "MIT",
   "main": "index.js",
   "peerDependencies": {
-    "gatsby": "^2.0.0"
+    "gatsby": "^2.0.0",
+    "typescript": "^3.2.1"
+  },
+  "peerDependenciesMeta": {
+    "typescript": {
+      "optional": true
+    }
   },
   "repository": {
     "type": "git",

packages/gatsby-plugin-typescript/src/__tests__/gatsby-node.js

@@ -49,7 +49,22 @@ describe(`gatsby-plugin-typescript`, () => {
       const actions = { setWebpackConfig: jest.fn() }
       const jsLoader = {}
       const loaders = { js: jest.fn(() => jsLoader) }
-      onCreateWebpackConfig({ actions, loaders })
+      const stage = `develop`
+      const eslintLoader = { loader: `eslint-loader` }
+      const webpackConfig = {
+        module: {
+          rules: [
+            {
+              enforce: `pre`,
+              test: /\.jsx?$/,
+              exclude: /(node_modules|bower_components)/,
+              use: [eslintLoader],
+            },
+          ],
+        },
+      }
+      const getConfig = jest.fn(() => webpackConfig)
+      onCreateWebpackConfig({ actions, getConfig, loaders, stage })
       expect(actions.setWebpackConfig).toHaveBeenCalledWith({
         module: {
           rules: [
@@ -60,13 +75,116 @@ describe(`gatsby-plugin-typescript`, () => {
           ],
         },
       })
+      expect(actions.setWebpackConfig).toHaveBeenCalledWith({
+        module: {
+          rules: [
+            {
+              enforce: `pre`,
+              test: /\.tsx?$/,
+              exclude: /(node_modules|bower_components)/,
+              use: [eslintLoader],
+            },
+          ],
+        },
+      })
     })
 
     it(`does not set the webpack config if there isn't a js loader`, () => {
       const actions = { setWebpackConfig: jest.fn() }
       const loaders = { js: jest.fn() }
-      onCreateWebpackConfig({ actions, loaders })
+      const stage = `develop`
+      const getConfig = jest.fn()
+      onCreateWebpackConfig({ actions, getConfig, loaders, stage })
       expect(actions.setWebpackConfig).not.toHaveBeenCalled()
     })
+
+    it(`does not set the typescript-eslint webpack config if the built-in eslint-loader isn't set`, () => {
+      const actions = { setWebpackConfig: jest.fn() }
+      const jsLoader = {}
+      const loaders = {
+        js: jest.fn(() => jsLoader),
+      }
+      const stage = `develop`
+      const webpackConfig = {
+        module: {
+          rules: [
+            {
+              enforce: `pre`,
+              test: /\.jsx?$/,
+              exclude: /(node_modules|bower_components)/,
+              use: [],
+            },
+          ],
+        },
+      }
+      const getConfig = jest.fn(() => webpackConfig)
+      onCreateWebpackConfig({ actions, getConfig, loaders, stage })
+      expect(actions.setWebpackConfig).toHaveBeenCalledWith({
+        module: {
+          rules: [
+            {
+              test: /\.tsx?$/,
+              use: jsLoader,
+            },
+          ],
+        },
+      })
+      expect(actions.setWebpackConfig).not.toHaveBeenCalledWith({
+        module: {
+          rules: [
+            {
+              enforce: `pre`,
+              test: /\.tsx?$/,
+              exclude: /(node_modules|bower_components)/,
+              use: [],
+            },
+          ],
+        },
+      })
+    })
+
+    it(`set the typescript-eslint webpack config only if in develop stage`, () => {
+      const actions = { setWebpackConfig: jest.fn() }
+      const jsLoader = {}
+      const loaders = { js: jest.fn(() => jsLoader) }
+      const stage = `build-html`
+      const eslintLoader = { loader: `eslint-loader` }
+      const webpackConfig = {
+        module: {
+          rules: [
+            {
+              enforce: `pre`,
+              test: /\.jsx?$/,
+              exclude: /(node_modules|bower_components)/,
+              use: [eslintLoader],
+            },
+          ],
+        },
+      }
+      const getConfig = jest.fn(() => webpackConfig)
+      onCreateWebpackConfig({ actions, getConfig, loaders, stage })
+      expect(actions.setWebpackConfig).toHaveBeenCalledWith({
+        module: {
+          rules: [
+            {
+              test: /\.tsx?$/,
+              use: jsLoader,
+            },
+          ],
+        },
+      })
+      expect(actions.setWebpackConfig).not.toHaveBeenCalledWith({
+        module: {
+          rules: [
+            {
+              enforce: `pre`,
+              test: /\.tsx?$/,
+              exclude: /(node_modules|bower_components)/,
+              use: [eslintLoader],
+            },
+          ],
+        },
+      })
+    })
   })
 })

packages/gatsby-plugin-typescript/src/gatsby-node.js

@@ -16,7 +16,13 @@ function onCreateBabelConfig({ actions }, options) {
   })
 }
 
-function onCreateWebpackConfig({ actions, loaders }) {
+function onCreateWebpackConfig({
+  actions,
+  getConfig,
+  loaders,
+  stage,
+  reporter,
+}) {
   const jsLoader = loaders.js()
 
   if (!jsLoader) {
@@ -33,6 +39,38 @@ function onCreateWebpackConfig({ actions, loaders }) {
       ],
     },
   })
+
+  if (stage === `develop`) {
+    let isTypescriptDepAvailable
+    try {
+      isTypescriptDepAvailable = require.resolve(`typescript`)
+    } catch (e) {
+      reporter.warn(
+        `"typescript" is not installed. Builtin ESLint won't be working on typescript files.`
+      )
+    }
+
+    if (isTypescriptDepAvailable) {
+      const builtInEslintRule = getConfig().module.rules.find(rule => {
+        if (rule.enforce === `pre`) {
+          return rule.use.some(use => /eslint-loader/.test(use.loader))
+        }
+        return false
+      })
+
+      if (builtInEslintRule) {
+        const typescriptEslintRule = {
+          ...builtInEslintRule,
+          test: /\.tsx?$/,
+        }
+        actions.setWebpackConfig({
+          module: {
+            rules: [typescriptEslintRule],
+          },
+        })
+      }
+    }
+  }
 }
 
 exports.resolvableExtensions = resolvableExtensions