Allow wrapping exceptions in CreateFailed (#148)

* Allow wrapping exceptions in `CreateFailed`

* Make sure `ReadZipFS` and `ReadTarFS` raise CreateFailed

* Show error message of wrapped exception in `CreateFailed`

Author: althonos

fs/errors.py

@@ -11,6 +11,8 @@
 from __future__ import unicode_literals
 from __future__ import print_function
 
+import functools
+
 import six
 from six import text_type
 
@@ -90,8 +92,24 @@ class CreateFailed(FSError):
     """Filesystem could not be created.
     """
 
-    default_message = "unable to create filesystem"
-
+    default_message = "unable to create filesystem, {details}"
+
+    @classmethod
+    def catch_all(cls, func):
+        @functools.wraps(func)
+        def new_func(*args, **kwargs):
+            try:
+                return func(*args, **kwargs)
+            except cls:
+                raise
+            except Exception as e:
+                raise cls(exc=e)
+        return new_func
+
+    def __init__(self, msg=None, exc=None):
+        self._msg = msg or self.default_message
+        self.details = '' if exc is None else text_type(exc)
+        self.exc = exc
 
 class PathError(FSError):
     """Base exception for errors to do with a path string.

fs/osfs.py

@@ -88,13 +88,12 @@ def __init__(self,
                     os.makedirs(_root_path, mode=create_mode)
             except OSError as error:
                 raise errors.CreateFailed(
-                    'unable to create {} ({})'.format(root_path, error)
+                    'unable to create {} ({})'.format(root_path, error),
+                    error,
                 )
         else:
             if not os.path.isdir(_root_path):
-                raise errors.CreateFailed(
-                    'root path does not exist'
-                )
+                raise errors.CreateFailed('root path does not exist')
 
         _meta = self._meta = {
             'case_insensitive': os.path.normcase('Aa') != 'aa',

fs/tarfs.py

@@ -204,6 +204,7 @@ class ReadTarFS(FS):
         tarfile.LNKTYPE: ResourceType.symlink,
     }
 
+    @errors.CreateFailed.catch_all
     def __init__(self, file, encoding='utf-8'):
         super(ReadTarFS, self).__init__()
         self._file = file

fs/zipfs.py

@@ -241,6 +241,7 @@ class ReadZipFS(FS):
         'virtual': False,
     }
 
+    @errors.CreateFailed.catch_all
     def __init__(self, file, encoding='utf-8'):
         super(ReadZipFS, self).__init__()
         self._file = file

tests/test_errors.py

@@ -5,6 +5,7 @@
 from six import text_type
 
 from fs import errors
+from fs.errors import CreateFailed
 
 
 class TestErrors(unittest.TestCase):
@@ -24,3 +25,22 @@ def test_unsupported(self):
             text_type(err),
             "not supported"
         )
+
+
+class TestCreateFailed(unittest.TestCase):
+
+    def test_catch_all(self):
+
+        errors = (ZeroDivisionError, ValueError, CreateFailed)
+
+        @CreateFailed.catch_all
+        def test(x):
+            raise errors[x]
+
+        for index, exc in enumerate(errors):
+            try:
+                test(index)
+            except Exception as e:
+                self.assertIsInstance(e, CreateFailed)
+                if e.exc is not None:
+                    self.assertNotIsInstance(e.exc, CreateFailed)