Change File and Directory trait descriptions to take into account the…

… 'exists' flag (#1440)

traits/tests/test_directory.py

@@ -19,6 +19,8 @@
 class ExampleModel(HasTraits):
     path = Directory(exists=True)
 
+    new_path = Directory(exists=False)
+
 
 class ExistsBaseDirectory(HasTraits):
     path = BaseDirectory(value=pathlib.Path(gettempdir()), exists=True)
@@ -122,3 +124,16 @@ def test_simple_accepts_any_pathlib(self):
         foo.path = pathlib.Path("!!!")
 
         self.assertIsInstance(foo.path, str)
+
+    def test_info_text(self):
+        example_model = ExampleModel()
+        with self.assertRaises(TraitError) as exc_cm:
+            example_model.path = 47
+        self.assertIn("a string or os.PathLike object", str(exc_cm.exception))
+        self.assertIn(
+            "referring to an existing directory", str(exc_cm.exception))
+
+        with self.assertRaises(TraitError) as exc_cm:
+            example_model.new_path = 47
+        self.assertIn("a string or os.PathLike object", str(exc_cm.exception))
+        self.assertNotIn("exist", str(exc_cm.exception))

traits/tests/test_file.py

@@ -19,6 +19,8 @@
 class ExampleModel(HasTraits):
     file_name = File(exists=True)
 
+    new_file_name = File(exists=False)
+
 
 class FastExampleModel(HasTraits):
     file_name = File()
@@ -66,6 +68,18 @@ def test_fast(self):
         example_model = FastExampleModel(file_name=__file__)
         example_model.path = "."
 
+    def test_info_text(self):
+        example_model = ExampleModel()
+        with self.assertRaises(TraitError) as exc_cm:
+            example_model.file_name = 47
+        self.assertIn("a string or os.PathLike object", str(exc_cm.exception))
+        self.assertIn("referring to an existing file", str(exc_cm.exception))
+
+        with self.assertRaises(TraitError) as exc_cm:
+            example_model.new_file_name = 47
+        self.assertIn("a string or os.PathLike object", str(exc_cm.exception))
+        self.assertNotIn("exist", str(exc_cm.exception))
+
 
 class TestCreateEditor(unittest.TestCase):
 

traits/trait_types.py

@@ -1360,9 +1360,6 @@ class BaseFile(BaseStr):
         not.
     """
 
-    #: A description of the type of value this trait accepts:
-    info_text = "a filename or object implementing the os.PathLike interface"
-
     def __init__(
         self,
         value="",
@@ -1400,6 +1397,13 @@ def validate(self, object, name, value):
 
         self.error(object, name, value)
 
+    def info(self):
+        """ Return a description of the type of value this trait accepts. """
+        description = "a string or os.PathLike object"
+        if self.exists:
+            description += " referring to an existing file"
+        return description
+
     def create_editor(self):
         from traitsui.editors.file_editor import FileEditor
 
@@ -1498,10 +1502,6 @@ class BaseDirectory(BaseStr):
         not.
     """
 
-    #: A description of the type of value this trait accepts:
-    info_text = ("a directory name or an object implementing "
-                 "the os.PathLike interface")
-
     def __init__(
         self, value="", auto_set=False, entries=0, exists=False, **metadata
     ):
@@ -1531,6 +1531,13 @@ def validate(self, object, name, value):
 
         self.error(object, name, value)
 
+    def info(self):
+        """ Return a description of the type of value this trait accepts. """
+        description = "a string or os.PathLike object"
+        if self.exists:
+            description += " referring to an existing directory"
+        return description
+
     def create_editor(self):
         from traitsui.editors.directory_editor import DirectoryEditor