Make consistent the expectation around non-existent fragments directo…

…ry (#557)

* Add some documentation explaining the current behavior around the fragments directory.

* Reflect expectation that a non-existent directory is honored and treated like an empty directory. Closes #538.

* Add news fragment.

docs/cli.rst

@@ -24,6 +24,13 @@ The following options can be passed to all of the commands that explained below:
 Build the combined news file from news fragments.
 ``build`` is also assumed if no command is passed.
 
+If there are no news fragments (including an empty fragments directory or a
+non-existent directory), a notice of "no significant changes" will be added to
+the news file.
+
+By default, the processed news fragments are removed using ``git``, which will
+also remove the fragments directory if now empty.
+
 .. option:: --draft
 
    Only render news fragments to standard output.
@@ -67,6 +74,8 @@ Create a news fragment in the directory that ``towncrier`` is configured to look
 
 ``towncrier create`` will enforce that the passed type (e.g. ``bugfix``) is valid.
 
+If the fragments directory does not exist, it will be created.
+
 If the filename exists already, ``towncrier create`` will add (and then increment) a number after the fragment type until it finds a filename that does not exist yet.
 In the above example, it will generate ``123.bugfix.1.rst`` if ``123.bugfix.rst`` already exists.
 

src/towncrier/_builder.py

@@ -6,15 +6,12 @@
 
 import os
 import textwrap
-import traceback
 
 from collections import defaultdict
 from typing import Any, DefaultDict, Iterable, Iterator, Mapping, Sequence
 
 from jinja2 import Template
 
-from ._settings import ConfigError
-
 
 def strip_if_integer_string(s: str) -> str:
     try:
@@ -102,11 +99,8 @@ def find_fragments(
 
         try:
             files = os.listdir(section_dir)
-        except FileNotFoundError as e:
-            message = "Failed to list the news fragment files.\n{}".format(
-                "".join(traceback.format_exception_only(type(e), e)),
-            )
-            raise ConfigError(message)
+        except FileNotFoundError:
+            files = []
 
         file_content = {}
 

src/towncrier/newsfragments/538.bugfix

@@ -0,0 +1 @@
+``build`` now treats a missing fragments directory the same as an empty one, consistent with other operations.

src/towncrier/test/test_build.py

@@ -182,8 +182,8 @@ def test_no_newsfragment_directory(self, runner):
 
         result = runner.invoke(_main, ["--draft", "--date", "01-01-2001"])
 
-        self.assertEqual(1, result.exit_code, result.output)
-        self.assertIn("Failed to list the news fragment files.\n", result.output)
+        self.assertEqual(0, result.exit_code)
+        self.assertIn("No significant changes.\n", result.output)
 
     def test_no_newsfragments_draft(self):
         """