Improve the error message when 2 projects resolve to the same config

CHANGELOG.md

@@ -14,6 +14,8 @@
   symlinked paths ([#5085](https://github.com/facebook/jest/pull/5085))
 * `[jest-editor-support]` Update `Settings` to use spawn in shell option
   ([#5658](https://github.com/facebook/jest/pull/5658))
+* `[jest-cli]` Improve the error message when 2 projects resolve to the same
+  config ([#5674](https://github.com/facebook/jest/pull/5674))
 
 ## 22.4.2
 

integration-tests/__tests__/multi_project_runner.test.js

@@ -12,6 +12,7 @@
 import runJest from '../runJest';
 import os from 'os';
 import path from 'path';
+import stripAnsi from 'strip-ansi';
 
 const {cleanup, extractSummary, writeFiles} = require('../Utils');
 const SkipOnWindows = require('../../scripts/SkipOnWindows');
@@ -303,12 +304,15 @@ test('resolves projects and their <rootDir> properly', () => {
     }),
   });
 
-  ({stderr} = runJest(DIR));
+  ({stderr} = stripAnsi(runJest(DIR)));
   expect(stderr).toMatch(
-    /One or more specified projects share the same config file/,
+    /Whoops! Two projects resolved to the same config path/,
   );
+  expect(stderr).toMatch(`${path.join(DIR, 'package.json')}`);
+  expect(stderr).toMatch(/Project 1|2: dir1/);
+  expect(stderr).toMatch(/Project 1|2: dir2/);
 
-  // praject with a directory/file that does not exist
+  // project with a directory/file that does not exist
   writeFiles(DIR, {
     'package.json': JSON.stringify({
       jest: {

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

@@ -173,27 +173,30 @@ const printVersionAndExit = outputStream => {
   exit(0);
 };
 
-const ensureNoDuplicateConfigs = (parsedConfigs, projects) => {
-  const configPathSet = new Set();
-
-  for (const {configPath} of parsedConfigs) {
-    if (configPathSet.has(configPath)) {
-      let message =
-        'One or more specified projects share the same config file\n';
-
-      parsedConfigs.forEach(({configPath}, index) => {
-        message =
-          message +
-          '\nProject: "' +
-          projects[index] +
-          '"\nConfig: "' +
-          String(configPath) +
-          '"';
-      });
+const ensureNoDuplicateConfigs = (parsedConfigs, projects, rootConfigPath) => {
+  const configPathMap = new Map();
+
+  for (const config of parsedConfigs) {
+    const {configPath} = config;
+    if (configPathMap.has(configPath)) {
+      const message = `Whoops! Two projects resolved to the same config path: ${chalk.bold(
+        String(configPath),
+      )}:
+
+  Project 1: ${chalk.bold(projects[parsedConfigs.findIndex(x => x === config)])}
+  Project 2: ${chalk.bold(
+    projects[parsedConfigs.findIndex(x => x === configPathMap.get(configPath))],
+  )}
+
+This usually means that your ${chalk.bold(
+        '"projects"',
+      )} config includes a directory that doesn't have any configuration recognizable by Jest. Please fix it.
+`;
+
       throw new Error(message);
     }
     if (configPath !== null) {
-      configPathSet.add(configPath);
+      configPathMap.set(configPath, config);
     }
   }
 };
@@ -259,7 +262,7 @@ const getConfigs = (
       })
       .map(root => readConfig(argv, root, true, configPath));
 
-    ensureNoDuplicateConfigs(parsedConfigs, projects);
+    ensureNoDuplicateConfigs(parsedConfigs, projects, configPath);
     configs = parsedConfigs.map(({projectConfig}) => projectConfig);
     if (!hasDeprecationWarnings) {
       hasDeprecationWarnings = parsedConfigs.some(