gh-158780: Collect header defects without repeated copying

Author: GriffinCanCode

Lib/email/_header_value_parser.py

@@ -152,7 +152,10 @@ def value(self):
 
     @property
     def all_defects(self):
-        return sum((x.all_defects for x in self), self.defects)
+        if not self:
+            return self.defects
+        return self.defects + [
+            defect for token in self for defect in token.all_defects]
 
     def startswith_fws(self):
         return self[0].startswith_fws()

Lib/test/test_email/test__header_value_parser.py

@@ -7,6 +7,23 @@
 
 class TestTokens(TestEmailBase):
 
+    # TokenList
+
+    def test_all_defects_empty(self):
+        token = parser.TokenList()
+        self.assertIs(token.all_defects, token.defects)
+        token.defects.append(errors.InvalidHeaderDefect())
+        self.assertIs(token.all_defects, token.defects)
+
+    def test_all_defects(self):
+        leaf = parser.ValueTerminal('text\x00', 'utext')
+        leaf.defects.append(errors.NonPrintableDefect('\x00'))
+        token = parser.TokenList([parser.TokenList([leaf]), leaf])
+        token.defects.append(errors.InvalidHeaderDefect())
+        self.assertEqual(token.all_defects, token.defects + leaf.defects * 2)
+        self.assertEqual(len(token.defects), 1)
+        self.assertEqual(len(leaf.defects), 1)
+
     # EWWhiteSpaceTerminal
 
     def test_EWWhiteSpaceTerminal(self):