[New] Support "detect" option for React version setting

.gitignore

@@ -15,6 +15,7 @@ logs
 reports
 build
 node_modules
+!tests/**/node_modules
 npm-debug.log
 sftp-config.json
 

lib/util/version.js

@@ -4,15 +4,35 @@
  */
 'use strict';
 
+const resolve = require('resolve');
 const log = require('./log');
 
 let warnedForMissingVersion = false;
 
+function detectReactVersion() {
+  try {
+    const reactPath = resolve.sync('react', {basedir: process.cwd()});
+    const react = require(reactPath);
+    return react.version;
+  } catch (e) {
+    if (e.code === 'MODULE_NOT_FOUND') {
+      log('Warning: React version was set to "detect" in eslint-plugin-react settings, ' +
+        'but the "react" package is not installed. Assuming latest React version for linting.');
+      return '999.999.999';
+    }
+    throw e;
+  }
+}
+
 function getReactVersionFromContext(context) {
   let confVer = '999.999.999';
   // .eslintrc shared settings (http://eslint.org/docs/user-guide/configuring#adding-shared-settings)
   if (context.settings.react && context.settings.react.version) {
-    confVer = context.settings.react.version;
+    let settingsVersion = context.settings.react.version;
+    if (settingsVersion === 'detect') {
+      settingsVersion = detectReactVersion();
+    }
+    confVer = settingsVersion;
   } else if (!warnedForMissingVersion) {
     log('Warning: React version not specified in eslint-plugin-react settings. ' +
       'See https://github.com/yannickcr/eslint-plugin-react#configuration.');

package.json

@@ -9,7 +9,7 @@
     "lint": "eslint ./",
     "pretest": "npm run lint",
     "test": "npm run unit-test",
-    "unit-test": "istanbul cover --dir reports/coverage node_modules/mocha/bin/_mocha tests/**/*.js"
+    "unit-test": "istanbul cover --dir reports/coverage node_modules/mocha/bin/_mocha tests/lib/**/*.js tests/util/**/*.js tests/index.js"
   },
   "files": [
     "LICENSE",
@@ -29,7 +29,8 @@
     "has": "^1.0.3",
     "jsx-ast-utils": "^2.0.1",
     "object.fromentries": "^2.0.0",
-    "prop-types": "^15.6.2"
+    "prop-types": "^15.6.2",
+    "resolve": "^1.8.1"
   },
   "devDependencies": {
     "babel-eslint": "^8.2.5",

tests/util/version.js

@@ -0,0 +1,34 @@
+/* eslint-env mocha */
+'use strict';
+
+const path = require('path');
+const assert = require('assert');
+const versionUtil = require('../../lib/util/version');
+
+describe('Version', () => {
+  const base = path.resolve(__dirname, '..', 'fixtures', 'version');
+  let cwd;
+
+  beforeEach(() => {
+    cwd = process.cwd();
+    process.chdir(base);
+  });
+
+  afterEach(() => {
+    process.chdir(cwd);
+  });
+
+  describe('Detect version', () => {
+    const context = {settings: {react: {version: 'detect'}}};
+
+    it('matches detected version', () => {
+      process.chdir('detect-version');
+      assert.equal(versionUtil.testReactVersion(context, '1.2.3'), true);
+      assert.equal(versionUtil.testReactVersion(context, '1.2.4'), false);
+    });
+
+    it('assumes latest version if react is not installed', () => {
+      assert.equal(versionUtil.testReactVersion(context, '999.999.999'), true);
+    });
+  });
+});