utils: Change normalize_paths() contract

The `normalize_paths()` utility was doing too much — parsing
unstructured configuration path data and dispatching the scrubbed paths
to be normalized.

Towards moving the parsing of unstructured configuration path data
closer towards were configuration occurs, have the utility accept only
structured input for normalizing paths.

docs/source/internal/utils.rst

@@ -45,9 +45,9 @@ path if the string has a ``/`` in it. It also removes trailing ``/``\ s.
 
 .. autofunction:: flake8.utils.normalize_paths
 
-This function utilizes :func:`~flake8.utils.parse_comma_separated_list` and
-:func:`~flake8.utils.normalize_path` to normalize its input to a list of
-strings that should be paths.
+This function utilizes :func:`~flake8.utils.normalize_path` to normalize a
+sequence of paths.  See :func:`~flake8.utils.normalize_path` for what defines a
+normalized path.
 
 .. autofunction:: flake8.utils.stdin_get_value
 

src/flake8/utils.py

@@ -160,8 +160,8 @@ def parse_files_to_codes_mapping(value_):  # noqa: C901
 
 
 def normalize_paths(paths, parent=os.curdir):
-    # type: (Union[Sequence[str], str], str) -> List[str]
-    """Parse a comma-separated list of paths.
+    # type: (Sequence[str], str) -> List[str]
+    """Normalize a list of paths relative to a parent directory.
 
     :returns:
         The normalized paths.
@@ -169,9 +169,7 @@ def normalize_paths(paths, parent=os.curdir):
         [str]
     """
     assert isinstance(paths, list), paths  # nosec (for bandit)
-    return [
-        normalize_path(p, parent) for p in parse_comma_separated_list(paths)
-    ]
+    return [normalize_path(p, parent) for p in paths]
 
 
 def normalize_path(path, parent=os.curdir):

tests/unit/test_utils.py

@@ -127,14 +127,13 @@ def test_normalize_path(value, expected):
 
 
 @pytest.mark.parametrize("value,expected", [
-    ("flake8,pep8,pyflakes,mccabe", ["flake8", "pep8", "pyflakes", "mccabe"]),
-    ("flake8,\n\tpep8,\n  pyflakes,\n\n    mccabe",
+    (["flake8", "pep8", "pyflakes", "mccabe"],
         ["flake8", "pep8", "pyflakes", "mccabe"]),
-    ("../flake8,../pep8,../pyflakes,../mccabe",
+    (["../flake8", "../pep8", "../pyflakes", "../mccabe"],
         [os.path.abspath("../" + p) for p in RELATIVE_PATHS]),
 ])
 def test_normalize_paths(value, expected):
-    """Verify we normalize comma-separated paths provided to the tool."""
+    """Verify we normalizes a sequence of paths provided to the tool."""
     assert utils.normalize_paths(value) == expected