Make the missing docstring check more robust

Author: sambhav

src/pydocstyle/checker.py

@@ -186,8 +186,13 @@ def checks(self):
             for this_check in vars(type(self)).values()
             if hasattr(this_check, '_check_for')
         ]
+        # This returns the checks in the order they are
+        # listed in the file (since py3.6) if their priority is the same
         return sorted(all, key=lambda this_check: not this_check._terminal)
 
+    # Note - this needs to be listed before other checks
+    # as f string evalutaion may cause malformed AST Nodes.
+    # So we need to run this check first and terminate early.
     @check_for(Definition, terminal=True)
     def check_docstring_fstring(self, definition, docstring):
         """D303: Docstrings may not be f-strings.
@@ -213,14 +218,11 @@ def check_docstring_missing(self, definition, docstring):
               with a single underscore.
 
         """
-        if _is_fstring(docstring):
-            return  # checked above in check_docstring_fstring
-
         if (
             not docstring
             and definition.is_public
             or docstring
-            and is_blank(ast.literal_eval(docstring))
+            and is_blank(docstring, literal_eval=True)
         ):
             codes = {
                 Module: violations.D100,

src/pydocstyle/utils.py

@@ -13,8 +13,15 @@
 NON_ALPHANUMERIC_STRIP_RE = re.compile(r'[\W_]+')
 
 
-def is_blank(string: str) -> bool:
+def is_blank(string: str, literal_eval: bool = False) -> bool:
     """Return True iff the string contains only whitespaces."""
+    if literal_eval:
+        try:
+            string = ast.literal_eval(string)
+        except ValueError:
+            # This happens in case of an fstring
+            # in which case let's return false
+            return False
     return not string.strip()
 
 

src/tests/test_cases/fstrings.py

@@ -45,3 +45,8 @@ def fstring_with_other_errors(arg=1, missing_arg=2):
     This should not raise any other errors since fstrings
     are a terminal check.
     """
+
+
+@D303
+def fstring_with_blank_doc_string():
+    f"""  """