Cache detected React version

lib/util/version.js

@@ -14,19 +14,31 @@ function resetWarningFlag() {
   warnedForMissingVersion = false;
 }
 
+let cachedDetectedReactVersion;
+
+function resetDetectedVersion() {
+  cachedDetectedReactVersion = undefined;
+}
+
 function detectReactVersion() {
+  if (cachedDetectedReactVersion) {
+    return cachedDetectedReactVersion;
+  }
+
   try {
     const reactPath = resolve.sync('react', {basedir: process.cwd()});
     const react = require(reactPath); // eslint-disable-line global-require, import/no-dynamic-require
-    return react.version;
+    cachedDetectedReactVersion = react.version;
+    return cachedDetectedReactVersion;
   } catch (e) {
     if (e.code === 'MODULE_NOT_FOUND') {
       if (!warnedForMissingVersion) {
         error('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.');
         warnedForMissingVersion = true;
       }
-      return '999.999.999';
+      cachedDetectedReactVersion = '999.999.999';
+      return cachedDetectedReactVersion;
     }
     throw e;
   }
@@ -116,5 +128,6 @@ function testFlowVersion(context, methodVer) {
 module.exports = {
   testReactVersion,
   testFlowVersion,
-  resetWarningFlag
+  resetWarningFlag,
+  resetDetectedVersion
 };

tests/util/version.js

@@ -16,6 +16,7 @@ describe('Version', () => {
     sinon.stub(console, 'error');
     expectedErrorArgs = [];
     versionUtil.resetWarningFlag();
+    versionUtil.resetDetectedVersion();
   });
 
   afterEach(() => {