SwiftBuildSupport: move WorkingDirectory class to the module so that it

is reusable

Swift SVN r24268

utils/SwiftBuildSupport.py

@@ -175,3 +175,20 @@ def get_all_preset_names(preset_file_names):
     config = _load_preset_files_impl(preset_file_names)
     return [ name[len(_PRESET_PREFIX):] for name in config.sections()
              if name.startswith(_PRESET_PREFIX) ]
+
+
+# A context manager for changing the current working directory.
+#
+#     with WorkingDirectory('/tmp'):
+#         ... do work in /tmp...
+class WorkingDirectory(object):
+    def __init__(self, new_cwd):
+        self.new_cwd = new_cwd
+
+    def __enter__(self):
+        self.old_cwd = os.getcwd()
+        os.chdir(self.new_cwd)
+
+    def __exit__(self, type, value, traceback):
+        os.chdir(self.old_cwd)
+