Fix PhutilUnitTest issue with symlinks that point into a libphutil library

Summary: Currently, if you change a symlink outside a libphutil library and the link target is something inside a libphutil library, we may enter an inifite loop in the "do { ... } while(...)" later. Just bail if the loop won't resolve.

Test Plan: Ran arc unit, Airtime reported the issue resolved by a similar fix.

Reviewers: cpiro, btrahan

Reviewed By: cpiro

CC: aran

Differential Revision: https://secure.phabricator.com/D2318

src/unit/engine/phutil/PhutilUnitTestEngine.php

@@ -57,6 +57,14 @@ final class PhutilUnitTestEngine extends ArcanistBaseUnitTestEngine {
         continue;
       }
 
+      if (!Filesystem::isDescendant($path, $library_root)) {
+        // We have encountered some kind of symlink maze -- for instance, $path
+        // is some symlink living outside the library that links into some file
+        // inside the library. Just ignore these cases, since the affected file
+        // does not actually lie within the library.
+        continue;
+      }
+
       $library_path = Filesystem::readablePath($path, $library_root);
       do {
         // Add the module and all parent modules as affected modules, which