Clarify directory and filename wildcards in extraction mappings

babel/util.py

@@ -149,6 +149,11 @@ def pathmatch(pattern: str, filename: str) -> bool:
      * also supports a convenience pattern ("**") to match files at any
        directory level.
 
+    ``*`` matches one or more characters other than the path separator, not
+    an empty string. ``**/`` matches zero or more directory levels, whereas
+    ``**`` without a trailing slash also consumes one or more filename
+    characters. Use ``**/`` before a pattern for a specific filename prefix.
+
     Examples:
 
     >>> pathmatch('**.py', 'bar.py')

docs/messages.rst

@@ -140,12 +140,24 @@ Genshi markup templates and text templates:
     extract_messages = $._, jQuery._
 
 The extended glob patterns used in this configuration are similar to the glob
-patterns provided by most shells. A single asterisk (``*``) is a wildcard for
-any number of characters (except for the pathname component separator "/"),
-while a question mark (``?``) only matches a single character. In addition,
-two subsequent asterisk characters (``**``) can be used to make the wildcard
-match any directory level, so the pattern ``**.txt`` matches any file with the
-extension ``.txt`` in any directory.
+patterns provided by most shells, with the following differences:
+
+* A single asterisk (``*``) matches one or more characters within a pathname
+  component, but never the separator ``/``. Unlike shell globs, it does not
+  match an empty string.
+* A question mark (``?``) matches exactly one character other than ``/``.
+* ``**/`` matches zero or more directory levels. Use it before a filename
+  pattern to match that pattern both in the base directory and in subdirectories.
+* ``**`` without a trailing slash also matches one or more characters of the
+  filename. For example, ``**.txt`` matches ``notes.txt`` and
+  ``docs/notes.txt``.
+
+To ignore files whose names start with ``._``, have at least one character
+after that prefix, and end with ``.py``, use ``[ignore: **/._*.py]`` before
+the Python extraction rule. This matches
+``._module.py`` and ``pkg/._module.py``. In contrast, ``**._*.py`` requires
+at least one filename character before ``._``, so it does not match either
+of those paths.
 
 Babel supports two configuration file formats: INI and TOML.
 

tests/test_util.py

@@ -45,6 +45,28 @@ def test_pathmatch():
     assert not util.pathmatch('./foo/**.py', 'blah/foo/bar/baz.py')
 
 
+@pytest.mark.parametrize(('pattern', 'filename', 'expected'), [
+    ('*.txt', 'notes.txt', True),
+    ('*.txt', '.txt', False),
+    ('*.txt', 'docs/notes.txt', False),
+    ('?.txt', 'a.txt', True),
+    ('?.txt', '.txt', False),
+    ('?.txt', '/.txt', False),
+    ('**.txt', 'notes.txt', True),
+    ('**.txt', 'docs/notes.txt', True),
+    ('**.txt', '.txt', False),
+    ('**/._*.py', '._module.py', True),
+    ('**/._*.py', 'pkg/._module.py', True),
+    ('**/._*.py', 'pkg/sub/._module.py', True),
+    ('**/._*.py', 'pkg/module.py', False),
+    ('**._*.py', '._module.py', False),
+    ('**._*.py', 'pkg/._module.py', False),
+    ('**._*.py', 'pkg/prefix._module.py', True),
+])
+def test_pathmatch_documented_wildcards(pattern, filename, expected):
+    assert util.pathmatch(pattern, filename) is expected
+
+
 def test_fixed_zone_negative_offset():
     assert util.FixedOffsetTimezone(-60).zone == 'Etc/GMT-60'