fix: getRootDir behaviour for single directory causing wrong project root

packages/core/utils/src/getRootDir.js

@@ -4,6 +4,8 @@ import type {FilePath} from '@parcel/types';
 import {isGlob} from './glob';
 import path from 'path';
 
+// Returns the common root of the given paths.
+// If there is no common root, returns the current working directory.
 export default function getRootDir(files: Array<FilePath>): FilePath {
   let cur = null;
 
@@ -27,10 +29,16 @@ export default function getRootDir(files: Array<FilePath>): FilePath {
       }
 
       cur.dir = i > 1 ? curParts.slice(0, i).join(path.sep) : cur.root;
+      cur.name = '';
+      cur.base = '';
     }
   }
 
-  return cur ? cur.dir : process.cwd();
+  if (!cur) {
+    return process.cwd();
+  }
+
+  return path.join(cur.dir, cur.name);
 }
 
 // Transforms a path like `packages/*/src/index.js` to the root of the glob, `packages/`

packages/core/utils/test/getRootDir.test.js

@@ -0,0 +1,19 @@
+import assert from 'assert';
+import getRootDir from '../src/getRootDir';
+import path from 'path';
+
+describe('getRootDir', () => {
+  it('Should return the common parts if provided a file list', () => {
+    const rootPath = process.cwd();
+    const fileList = [
+      path.join(rootPath, 'foo', 'bar'),
+      path.join(rootPath, 'foo', 'bar', 'baz', 'qux'),
+      path.join(rootPath, 'foo.js'),
+    ];
+    assert.equal(getRootDir(fileList), rootPath);
+  });
+  it('Should return the passsed path if its a directory', () => {
+    const rootPath = process.cwd();
+    assert.equal(getRootDir([rootPath]), rootPath);
+  });
+});