Use watchAll fallback for non git/hq projects (jestjs#4419)

packages/jest-cli/src/cli/index.js

@@ -30,6 +30,7 @@ import {print as preRunMessagePrint} from '../pre_run_message';
 import runJest from '../run_jest';
 import Runtime from 'jest-runtime';
 import TestWatcher from '../test_watcher';
+import updateGlobalConfig from '../lib/update_global_config';
 import watch from '../watch';
 import yargs from 'yargs';
 import rimraf from 'rimraf';
@@ -297,6 +298,18 @@ const _run = async (
   // Queries to hg/git can take a while, so we need to start the process
   // as soon as possible, so by the time we need the result it's already there.
   const changedFilesPromise = getChangedFilesPromise(globalConfig, configs);
+
+  if (globalConfig.watch && !changedFilesPromise) {
+    console.log(
+      'The project folder is no git and no mercurial project. ' +
+        chalk.bold('Watching all files') +
+        ' instead...',
+    );
+    globalConfig = updateGlobalConfig(globalConfig, {
+      mode: 'watchAll',
+    });
+  }
+
   const {contexts, hasteMapInstances} = await buildContextsAndHasteMaps(
     configs,
     globalConfig,