Inform if no custom dir when requesting to edit

Add checks to inform the user and do nothing if they request to edit
custom examples but no directory has been set.

eg/util.py

@@ -25,11 +25,36 @@
 ALIAS_FILE_NAME = 'aliases.json'
 
 
+def _inform_cannot_edit_no_custom_dir():
+    """
+    Inform the user that a custom dir has not be specified, and thus an edit
+    cannot be performed.
+    """
+    msg = """
+    You've requested to edit custom examples for a command, but no custom
+    directory has been found. The value must be set and the directory must
+    exist.
+
+    Custom examples are shown before the default examples and are under your
+    control. You must specify where to save them before editing them. This can
+    be done at the command line (with the `-c` or `--custom-dir` flags) or via
+    the `custom-dir` option in your egrc. A minimal egrc might look like:
+
+    [eg-config]
+    custom-dir = ~/.eg/
+    """
+    print(msg)
+
+
 def edit_custom_examples(program, config):
     """
     Edit custom examples for the given program, creating the file if it does
     not exist.
     """
+    if (not config.custom_dir) or (not os.path.exists(config.custom_dir)):
+        _inform_cannot_edit_no_custom_dir()
+        return
+
     # resolve aliases
     resolved_program = get_resolved_program(program, config)
     custom_file_path = get_file_path_for_program(

test/util_test.py

@@ -260,8 +260,9 @@ def test_handle_program_no_entries():
 
 def test_handle_program_finds_paths_and_calls_open_pager_no_alias():
     """
-    If there are entries for the program, handle_program needs to get the paths,
-    get the contents, format the contents, and page the resulting string.
+    If there are entries for the program, handle_program needs to get the
+    paths, get the contents, format the contents, and page the resulting
+    string.
     """
     program = 'mv'
 
@@ -378,8 +379,9 @@ def return_correct_path(*args, **kwargs):
 
 def test_handle_program_finds_paths_and_calls_open_pager_with_alias():
     """
-    If there are entries for the program, handle_program needs to get the paths,
-    get the contents, format the contents, and page the resulting string.
+    If there are entries for the program, handle_program needs to get the
+    paths, get the contents, format the contents, and page the resulting
+    string.
     """
     alias_for_program = 'link'
     resolved_program = 'ln'
@@ -853,8 +855,8 @@ def _helper_assert_formatted_contents(
     formatted_result
 ):
     """
-    Helper method to assist in asserting things about the get_formatted_contents
-    method.
+    Helper method to assist in asserting things about the
+    get_formatted_contents method.
 
     starting_contents: the starting string that we are working with
     use_color: True if we should use color
@@ -1276,13 +1278,17 @@ def test_can_parse_alias_file():
     assert_equal(alias_dict['link'], 'ln')
 
 
+@patch('os.path.exists')
+@patch('eg.util._inform_cannot_edit_no_custom_dir')
 @patch('eg.util.get_resolved_program')
 @patch('eg.util.get_file_path_for_program')
 @patch('subprocess.call')
-def test_edit_custom_examples_correct(
+def test_edit_custom_examples_correct_with_custom_dir(
     mock_call,
     mock_get_path,
     mock_get_program,
+    mock_inform,
+    mock_exists,
 ):
     """
     We should resolve aliases, get the custom file path, and call subprocess.
@@ -1294,9 +1300,47 @@ def test_edit_custom_examples_correct(
 
     mock_get_program.return_value = resolved_program
     mock_get_path.return_value = path
+    mock_exists.return_value = True
 
     util.edit_custom_examples(program, config)
 
     mock_get_program.assert_called_once_with(program, config)
     mock_get_path.assert_called_once_with(resolved_program, config.custom_dir)
     mock_call.assert_called_once_with([config.editor_cmd, path])
+    assert_equal(mock_inform.call_count, 0)
+
+
+@patch('os.path.exists')
+@patch('eg.util._inform_cannot_edit_no_custom_dir')
+@patch('eg.util.get_resolved_program')
+@patch('eg.util.get_file_path_for_program')
+@patch('subprocess.call')
+def test_edit_custom_examples_informs_if_no_custom_dir(
+    mock_call,
+    mock_get_path,
+    mock_get_program,
+    mock_inform,
+    mock_exists,
+):
+    """
+    We should inform the user if they are trying to edit with no custom dir.
+
+    This should be true if it is not set and if the path does not exist.
+    """
+    program = 'awk'
+
+    # First with no custom dir set.
+    config = _create_config(editor_cmd='vi -e')
+    mock_exists.return_value = True
+    util.edit_custom_examples(program, config)
+    assert_equal(mock_inform.call_count, 1)
+
+    # And now with it set but a nonexistent path.
+    config = _create_config(custom_dir='/path/to/custom', editor_cmd='vi -e')
+    mock_exists.return_value = False
+    util.edit_custom_examples(program, config)
+    assert_equal(mock_inform.call_count, 2)
+
+    assert_equal(mock_call.call_count, 0)
+    assert_equal(mock_get_path.call_count, 0)
+    assert_equal(mock_get_program.call_count, 0)