feat: support eslint check via process.env.ESLINT (#1819)

Close #1770

现在有个问题，配置生效了，但是打印的日志里**定位文件错误**，都是定在了 eslint-load.js。

.prettierignore

@@ -3,3 +3,8 @@
 **/bin/*.js
 **/website/*.js
 packages/umi-build-dev/src/plugins/commands/block/index.js
+packages/af-webpack/src/getConfig/index.js
+packages/af-webpack/src/getConfig/css.js
+packages/af-webpack/src/getConfig/eslint.js
+packages/af-webpack/src/getConfig/dev.js
+packages/af-webpack/src/getConfig/prod.js

packages/af-webpack/package.json

@@ -31,6 +31,13 @@
     "didyoumean": "1.2.1",
     "duplicate-package-checker-webpack-plugin": "3.0.0",
     "es5-imcompatible-versions": "^0.1.25",
+    "eslint": "5.12.0",
+    "eslint-config-umi": "1.3.0",
+    "eslint-loader": "2.1.1",
+    "eslint-plugin-flowtype": "2.50.3",
+    "eslint-plugin-import": "2.14.0",
+    "eslint-plugin-jsx-a11y": "6.1.2",
+    "eslint-plugin-react": "7.12.3",
     "file-loader": "2.0.0",
     "fork-ts-checker-webpack-plugin": "0.5.0",
     "friendly-errors-webpack-plugin": "1.7.0",
@@ -46,7 +53,7 @@
     "postcss": "7.0.8",
     "postcss-flexbugs-fixes": "4.1.0",
     "postcss-loader": "3.0.0",
-    "react-dev-utils": "6.1.1",
+    "react-dev-utils": "7.0.1",
     "react-error-overlay": "5.1.0",
     "requireindex": "1.2.0",
     "resolve": "1.8.1",

packages/af-webpack/src/getConfig/eslint.js

@@ -0,0 +1,26 @@
+import eslintFormatter from 'react-dev-utils/eslintFormatter';
+
+export default function(webpackConfig, opts) {
+  const eslintOptions = {
+    formatter: eslintFormatter,
+    baseConfig: {
+      extends: [require.resolve('eslint-config-umi')],
+    },
+    ignore: false,
+    eslintPath: require.resolve('eslint'),
+    useEslintrc: false,
+  };
+
+  webpackConfig.module
+    .rule('eslint')
+      .test(/\.(js|jsx)$/)
+      .include.add(opts.cwd)
+      .end()
+    .exclude
+      .add(/node_modules/)
+      .end()
+    .enforce('pre')
+    .use('eslint-loader')
+      .loader(require.resolve('eslint-loader'))
+      .options(eslintOptions);
+}

packages/af-webpack/src/getConfig/index.js

@@ -144,6 +144,11 @@ export default function(opts) {
     ];
   }
 
+  // module -> eslint
+  if (process.env.ESLINT && process.env.ESLINT !== 'none') {
+    require('./eslint').default(webpackConfig, opts);
+  }
+
   // Avoid "require is not defined" errors
   webpackConfig.module
     .rule('mjs-require')