Raise ParseError on fstring docstrings as they are not valid docstrings

src/pydocstyle/checker.py

@@ -26,10 +26,8 @@
 from .utils import (
     common_prefix_length,
     is_blank,
-    is_fstring,
     log,
     pairwise,
-    safe_literal_eval,
     strip_non_alphanumeric,
 )
 from .wordlists import IMPERATIVE_BLACKLIST, IMPERATIVE_VERBS, stem
@@ -46,6 +44,27 @@ def decorator(f):
     return decorator
 
 
+FSTRING_REGEX = re(r'^([rR]?)[fF]')
+
+
+def is_fstring(docstring):
+    """Return True if docstring is an f-string."""
+    return FSTRING_REGEX.match(str(docstring))
+
+
+def safe_literal_eval(string):
+    """Safely evaluate a literal even if it is an fstring."""
+    try:
+        return ast.literal_eval(string)
+    except ValueError as error:
+        # If the docstring is a fstring, it is
+        # not considered a valid docstring. See
+        # https://bugs.python.org/issue28739
+        raise ParseError(
+            info="f-strings are not valid as docstrings."
+        ) from error
+
+
 class ConventionChecker:
     """Checker for PEP 257, NumPy and Google conventions.
 

src/pydocstyle/parser.py

@@ -30,8 +30,12 @@
 class ParseError(Exception):
     """An error parsing contents of a Python file."""
 
+    def __init__(self, info=""):
+        """Initialize the error with a more specific message."""
+        self.info = info
+
     def __str__(self):
-        return "Cannot parse file."
+        return f"Cannot parse file. {self.info}".strip()
 
 
 class UnexpectedTokenError(ParseError):

src/pydocstyle/utils.py

@@ -1,5 +1,4 @@
 """General shared utilities."""
-import ast
 import logging
 import re
 from itertools import tee, zip_longest
@@ -47,24 +46,3 @@ def common_prefix_length(a: str, b: str) -> int:
 def strip_non_alphanumeric(string: str) -> str:
     """Strip string from any non-alphanumeric characters."""
     return NON_ALPHANUMERIC_STRIP_RE.sub('', string)
-
-
-FSTRING_REGEX = re.compile(r'^([rR]?)[fF]')
-
-
-def is_fstring(docstring):
-    """Return True if docstring is an f-string."""
-    return FSTRING_REGEX.match(str(docstring))
-
-
-def safe_literal_eval(string):
-    """Safely evaluate a literal even if it is an fstring."""
-    try:
-        return ast.literal_eval(string)
-    except ValueError:
-        # In case we hit a value error due to an fstring
-        # we do a literal eval by subtituting the fstring
-        # with a normal string.
-        # We keep the first captured group if any. This includes
-        # the raw identifiers (r/R) and replace f/F with a blank.
-        return ast.literal_eval(FSTRING_REGEX.sub(r"\1", string))

src/tests/test_cases/fstrings.py

@@ -50,8 +50,3 @@ def fstring_with_other_errors(arg=1, missing_arg=2):
 @D303
 def fstring_with_blank_doc_string():
     f"""  """
-
-
-@expect("D103: Missing docstring in public function")
-def fstring_with_ignores():  # noqa: D303
-    f"""  """

src/tests/test_integration.py

@@ -571,6 +571,21 @@ def foo():
     assert code == 0
 
 
+def test_fstring_excluded(env):
+    """Test excluding D303 fstring error."""
+    with env.open('example.py', 'wt') as example:
+        example.write(textwrap.dedent("""\
+            def foo():  # noqa: D303
+                f'''Test'''
+        """))
+
+    env.write_config(add_ignore="D100")
+    out, err, code = env.invoke()
+    assert code == 1
+    assert out == ""
+    assert "f-strings are not valid as docstrings." in err
+
+
 def test_empty_select_with_added_error(env):
     """Test excluding all errors but one."""
     with env.open('example.py', 'wt') as example: