Create an Eslint reporter (#6921)

README.md

@@ -98,6 +98,16 @@ If you want to run all tests and exit, type:
 yarn test-once
 ```
 
+### Eslint
+
+As you run tests you will see a report of Eslint errors at the end of the test output:
+
+    yarn test
+
+If you would like to run tests without Eslint checks, set an environment variable:
+
+    NO_ESLINT=1 yarn test
+
 ### Flow
 
 There is limited support for using [Flow](https://flowtype.org/) to validate the intention of our program.

jest.config.js

@@ -21,6 +21,7 @@ module.exports = {
     '<rootDir>/tests/jest-reporters/fingers-crossed.js',
     '<rootDir>/tests/jest-reporters/summary.js',
     '<rootDir>/tests/jest-reporters/flow-check.js',
+    '<rootDir>/tests/jest-reporters/eslint-check.js',
   ],
   setupTestFrameworkScriptFile: '<rootDir>/tests/setup.js',
   testPathIgnorePatterns: [

package.json

@@ -176,7 +176,8 @@
         "NODE_ICU_DATA": "./node_modules/full-icu",
         "NODE_PATH": "./:./src",
         "NODE_ENV": "test",
-        "NO_FLOW": "1"
+        "NO_FLOW": "1",
+        "NO_ESLINT": "1"
       }
     },
     "webpack-dev-server": {

tests/jest-reporters/eslint-check.js

@@ -0,0 +1,58 @@
+/* eslint-disable no-console */
+const { CLIEngine } = require('eslint');
+
+const { getChangedFiles } = require('./utils');
+
+const NO_ESLINT_ENV_VAR = 'NO_ESLINT';
+
+class EslintCheckReporter {
+  constructor() {
+    this.eslint = new CLIEngine();
+    this.eslintOutput = null;
+  }
+
+  isDisabled() {
+    return process.env[NO_ESLINT_ENV_VAR] === '1';
+  }
+
+  async onRunStart() {
+    if (this.isDisabled()) {
+      return;
+    }
+
+    const files = await getChangedFiles();
+
+    if (!files) {
+      throw new Error(`Failed to retrieve files in the eslint check reporter.`);
+    }
+
+    const report = this.eslint.executeOnFiles(files);
+
+    if (report.errorCount === 0 && report.warningCount === 0) {
+      // All good.
+      this.eslintOutput = null;
+    } else {
+      this.eslintOutput = CLIEngine.getFormatter()(report.results);
+    }
+  }
+
+  getLastError() {
+    if (this.isDisabled()) {
+      return undefined;
+    }
+
+    console.log('');
+    if (this.eslintOutput) {
+      console.log(this.eslintOutput);
+      console.log(
+        `Set ${NO_ESLINT_ENV_VAR}=1 in the environment to disable eslint checks`,
+      );
+      return new Error('eslint errors');
+    }
+    console.log('Eslint: no errors 💄 ✨');
+
+    return undefined;
+  }
+}
+
+module.exports = EslintCheckReporter;

tests/jest-reporters/utils.js

@@ -0,0 +1,45 @@
+const util = require('util');
+const exec = util.promisify(require('child_process').exec);
+
+const filterFileNamesFromGitStatusOutput = (output) => {
+  const files = output
+    .split('\n')
+    .map((line) => line.trim())
+    // Make sure we ignore deleted files.
+    .filter((line) => !line.startsWith('D'))
+    .map((line) => {
+      // Return the new name of a renamed file.
+      if (line.startsWith('RM')) {
+        return line.substring(line.indexOf('->'));
+      }
+
+      return line;
+    })
+    .map((line) => line.split(' '))
+    // .flatMap()
+    .reduce((chunks, chunk) => chunks.concat(chunk), [])
+    // We assume no filename can be smaller than 3 to filter the short format
+    // statuses: https://git-scm.com/docs/git-status#_short_format.
+    .filter((chunk) => chunk.length > 3)
+    // Allow directories OR JS/JSX files
+    .filter((filename) => /(\/|\.jsx?)$/.test(filename));
+
+  return files;
+};
+
+const getChangedFiles = async () => {
+  // We use the Porcelain Format Version 1,
+  // See: https://git-scm.com/docs/git-status#_porcelain_format_version_1
+  const { stdout, stderr } = await exec('git status --porcelain=1');
+
+  if (stderr) {
+    return null;
+  }
+
+  return filterFileNamesFromGitStatusOutput(stdout);
+};
+
+module.exports = {
+  filterFileNamesFromGitStatusOutput,
+  getChangedFiles,
+};

tests/unit/jest-reporters/test_utils.js

@@ -0,0 +1,56 @@
+import { filterFileNamesFromGitStatusOutput } from 'tests/jest-reporters/utils';
+
+describe(__filename, () => {
+  describe('_filterFileNamesFromGitStatusOutput', () => {
+    const _filterFileNamesFromGitStatusOutput = (lines = []) => {
+      return filterFileNamesFromGitStatusOutput(lines.join('\n'));
+    };
+
+    it('does not return deleted files', () => {
+      const files = _filterFileNamesFromGitStatusOutput([
+        'D  src/core/browserWindow.js',
+        ' D  src/core/browserWindow.js',
+      ]);
+
+      expect(files).toHaveLength(0);
+    });
+
+    it('only returned the new filename of a renamed file', () => {
+      const files = _filterFileNamesFromGitStatusOutput([
+        'RM src/amo/sagas/categories.js -> src/core/sagas/categories.js',
+      ]);
+
+      expect(files).toEqual(['src/core/sagas/categories.js']);
+    });
+
+    it('returns the filenames without the git statuses', () => {
+      const files = _filterFileNamesFromGitStatusOutput([
+        'M  jest.config.js',
+        'A  tests/jest-reporters/eslint-check.js',
+        'AM tests/jest-reporters/utils.js',
+        '?? tests/unit/jest-reporters/',
+      ]);
+
+      expect(files).toEqual([
+        'jest.config.js',
+        'tests/jest-reporters/eslint-check.js',
+        'tests/jest-reporters/utils.js',
+        'tests/unit/jest-reporters/',
+      ]);
+    });
+
+    it('only returns JavaScript files', () => {
+      const files = _filterFileNamesFromGitStatusOutput([
+        'M  README.md',
+        'M  package.json',
+        'M  src/test.jsx',
+        ' M tests/unit/jest-reporters/test_utils.js',
+      ]);
+
+      expect(files).toEqual([
+        'src/test.jsx',
+        'tests/unit/jest-reporters/test_utils.js',
+      ]);
+    });
+  });
+});