Address review nits

Co-authored-by: Bénédikt Tran <[email protected]>

Author: stephenfin

sphinx/ext/coverage.py

@@ -344,7 +344,7 @@ def build_py_coverage(self) -> None:
 
     def _write_py_statistics(self, op: TextIO) -> None:
         """ Outputs the table of ``op``."""
-        all_modules = set(self.py_documented.keys()).union(set(self.py_undocumented.keys()))
+        all_modules = frozenset(self.py_documented.keys() | self.py_undocumented.keys())
         all_objects: set[str] = set()
         all_documented_objects: set[str] = set()
         for module in all_modules:
@@ -363,7 +363,7 @@ def _write_py_statistics(self, op: TextIO) -> None:
 
             table.append([module, '%.2f%%' % value, '%d' % len(self.py_undocumented[module])])
 
-        if len(all_objects):
+        if all_objects:
             table.append([
                 'TOTAL',
                 f'{100 * len(all_documented_objects) / len(all_objects):.2f}%',

tests/roots/test-ext-coverage/grog/coverage_missing.py

@@ -5,4 +5,3 @@ class Missing:
 
     def missing_a(self):
         """An undocumented method."""
-        pass