Add custom eslint formatter (facebook#2138)

* Add custom eslint formatter

* Add formatter docs

* Update formatter docs

* Slightly tweak it

* Update README.md

Author: sidoshi

packages/react-dev-utils/README.md

@@ -110,6 +110,36 @@ clearConsole();
 console.log('Just cleared the screen!');
 ```
 
+#### `eslintFormatter(results: Object): string`
+
+This is our custom ESLint formatter that integrates well with Create React App console output.  
+You can use the default one instead if you prefer so.
+
+```js
+const eslintFormatter = require('react-dev-utils/eslintFormatter');
+
+// In your webpack config:
+// ...
+module: {
+   rules: [
+     {
+        test: /\.(js|jsx)$/,
+        include: paths.appSrc,
+        enforce: 'pre',
+        use: [
+          {
+            loader: 'eslint-loader',
+            options: {
+              // Pass the formatter:
+              formatter: eslintFormatter,
+            },
+          },
+        ],
+      }
+   ]
+}
+```
+
 #### `FileSizeReporter`
 
 ##### `measureFileSizesBeforeBuild(buildFolder: string): Promise<OpaqueFileSizes>`

packages/react-dev-utils/eslintFormatter.js

@@ -0,0 +1,71 @@
+'use strict';
+
+const chalk = require('chalk');
+const table = require('text-table');
+
+function isError(message) {
+  if (message.fatal || message.severity === 2) {
+    return true;
+  }
+  return false;
+}
+
+function formatter(results) {
+  let output = '\n';
+
+  let hasErrors = false;
+  let hasWarnings = false;
+
+  results.forEach(result => {
+    let messages = result.messages;
+    if (messages.length === 0) {
+      return;
+    }
+
+    let hasErrors = false;
+    messages = messages.map(message => {
+      let messageType;
+      if (isError(message)) {
+        messageType = 'error';
+        hasErrors = true;
+      } else {
+        messageType = 'warn';
+        hasWarnings = true;
+      }
+
+      let line = message.line || 0;
+      let column = message.column || 0;
+      let position = chalk.dim(`${line}:${column}`);
+      return [
+        '',
+        position,
+        messageType,
+        message.message.replace(/\.$/, ''),
+        chalk.dim(message.ruleId || ''),
+      ];
+    });
+
+    // if there are error messages, we want to show only errors
+    if (hasErrors) {
+      messages = messages.filter(m => m[2] === 'error');
+    }
+
+    // add color to messageTypes
+    messages.forEach(m => {
+      m[2] = m[2] === 'error' ? chalk.red(m[2]) : chalk.yellow(m[2]);
+    });
+
+    let outputTable = table(messages, {
+      align: ['l', 'l', 'l'],
+      stringLength(str) {
+        return chalk.stripColor(str).length;
+      },
+    });
+
+    output += `${outputTable}\n\n`;
+  });
+
+  return output;
+}
+
+module.exports = formatter;

packages/react-dev-utils/formatWebpackMessages.js

@@ -16,6 +16,7 @@
 // This is quite hacky and hopefully won't be needed when Webpack fixes this.
 // https://github.com/webpack/webpack/issues/2878
 
+var chalk = require('chalk');
 var friendlySyntaxErrorLabel = 'Syntax error:';
 
 function isLikelyASyntaxError(message) {
@@ -85,65 +86,8 @@ function formatMessage(message, isError) {
     );
   }
 
-  // TODO: Ideally we should write a custom ESLint formatter instead.
-
-  // If the second line already includes a filename, and it's a warning,
-  // this is likely coming from ESLint. Skip it because Webpack also prints it.
-  // Let's omit that in this case.
-  var BEGIN_ESLINT_FILENAME = String.fromCharCode(27) + '[4m';
-  // Also filter out ESLint summaries for each file
-  var BEGIN_ESLINT_WARNING_SUMMARY = String.fromCharCode(27) +
-    '[33m' +
-    String.fromCharCode(27) +
-    '[1m' +
-    String.fromCharCode(10006);
-  var BEGIN_ESLINT_ERROR_SUMMARY = String.fromCharCode(27) +
-    '[31m' +
-    String.fromCharCode(27) +
-    '[1m' +
-    String.fromCharCode(10006);
-  // ESLint puts separators like this between groups. We don't need them:
-  var ESLINT_EMPTY_SEPARATOR = String.fromCharCode(27) +
-    '[22m' +
-    String.fromCharCode(27) +
-    '[39m';
-  // Go!
-  lines = lines.filter(function(line) {
-    if (line === ESLINT_EMPTY_SEPARATOR) {
-      return false;
-    }
-    if (
-      line.indexOf(BEGIN_ESLINT_FILENAME) === 0 ||
-      line.indexOf(BEGIN_ESLINT_WARNING_SUMMARY) === 0 ||
-      line.indexOf(BEGIN_ESLINT_ERROR_SUMMARY) === 0
-    ) {
-      return false;
-    }
-    return true;
-  });
-
-  var ESLINT_WARNING_LABEL = String.fromCharCode(27) +
-    '[33m' +
-    'warning' +
-    String.fromCharCode(27) +
-    '[39m';
-  // If there were errors, omit any warnings.
-  if (isError) {
-    lines = lines.filter(function(line) {
-      return line.indexOf(ESLINT_WARNING_LABEL) === -1;
-    });
-  }
-
   // Prepend filename with an explanation.
-  lines[0] =
-    // Underline
-    String.fromCharCode(27) +
-    '[4m' +
-    // Filename
-    lines[0] +
-    // End underline
-    String.fromCharCode(27) +
-    '[24m' +
+  lines[0] = chalk.underline(lines[0]) +
     (isError ? ' contains errors.' : ' contains warnings.');
 
   // Reassemble the message.

packages/react-dev-utils/package.json

@@ -15,6 +15,7 @@
     "checkRequiredFiles.js",
     "clearConsole.js",
     "crashOverlay.js",
+    "eslintFormatter.js",
     "FileSizeReporter.js",
     "formatWebpackMessages.js",
     "getProcessForPort.js",

packages/react-scripts/config/webpack.config.dev.js

@@ -17,6 +17,7 @@ const HtmlWebpackPlugin = require('html-webpack-plugin');
 const CaseSensitivePathsPlugin = require('case-sensitive-paths-webpack-plugin');
 const InterpolateHtmlPlugin = require('react-dev-utils/InterpolateHtmlPlugin');
 const WatchMissingNodeModulesPlugin = require('react-dev-utils/WatchMissingNodeModulesPlugin');
+const eslintFormatter = require('react-dev-utils/eslintFormatter');
 const getClientEnvironment = require('./env');
 const paths = require('./paths');
 
@@ -120,16 +121,16 @@ module.exports = {
         enforce: 'pre',
         use: [
           {
-            // @remove-on-eject-begin
-            // Point ESLint to our predefined config.
             options: {
+              formatter: eslintFormatter,
+              // @remove-on-eject-begin
               baseConfig: {
                 extends: ['react-app'],
               },
               ignore: false,
               useEslintrc: false,
+              // @remove-on-eject-end
             },
-            // @remove-on-eject-end
             loader: 'eslint-loader',
           },
         ],

packages/react-scripts/config/webpack.config.prod.js

@@ -17,6 +17,7 @@ const HtmlWebpackPlugin = require('html-webpack-plugin');
 const ExtractTextPlugin = require('extract-text-webpack-plugin');
 const ManifestPlugin = require('webpack-manifest-plugin');
 const InterpolateHtmlPlugin = require('react-dev-utils/InterpolateHtmlPlugin');
+const eslintFormatter = require('react-dev-utils/eslintFormatter');
 const paths = require('./paths');
 const getClientEnvironment = require('./env');
 
@@ -117,17 +118,18 @@ module.exports = {
         enforce: 'pre',
         use: [
           {
-            // @remove-on-eject-begin
-            // Point ESLint to our predefined config.
             options: {
+              formatter: eslintFormatter,
+              // @remove-on-eject-begin
               // TODO: consider separate config for production,
               // e.g. to enable no-console and no-debugger only in production.
               baseConfig: {
                 extends: ['react-app'],
               },
+              ignore: false,
               useEslintrc: false,
+              // @remove-on-eject-end
             },
-            // @remove-on-eject-end
             loader: 'eslint-loader',
           },
         ],

packages/react-scripts/scripts/utils/createWebpackCompiler.js

@@ -100,17 +100,17 @@ module.exports = function createWebpackCompiler(config, onReadyCallback) {
         console.log(message);
         console.log();
       });
+
       // Teach some ESLint tricks.
-      console.log('You may use special comments to disable some warnings.');
       console.log(
-        'Use ' +
-          chalk.yellow('// eslint-disable-next-line') +
-          ' to ignore the next line.'
+        'Search the ' +
+          chalk.dim('keywords') +
+          ' from the right column to learn more.'
       );
       console.log(
-        'Use ' +
-          chalk.yellow('/* eslint-disable */') +
-          ' to ignore all warnings in a file.'
+        'To ignore, add ' +
+          chalk.yellow('// eslint-disable-next-line') +
+          ' to the line before.'
       );
     }
   });