gh-111159: Fix SyntaxError doctests for non-builtin exception classes (#111541)

Lib/doctest.py

@@ -1399,10 +1399,14 @@ class DocTestRunner:
                     # we don't care about the carets / suggestions / etc
                     # We only care about the error message and notes.
                     # They start with `SyntaxError:` (or any other class name)
+                    exception_line_prefixes = (
+                        f"{exception[0].__qualname__}:",
+                        f"{exception[0].__module__}.{exception[0].__qualname__}:",
+                    )
                     exc_msg_index = next(
                         index
                         for index, line in enumerate(formatted_ex)
-                        if line.startswith(f"{exception[0].__name__}:")
+                        if line.startswith(exception_line_prefixes)
                     )
                     formatted_ex = formatted_ex[exc_msg_index:]
 

Lib/test/test_doctest.py

@@ -3310,6 +3310,24 @@ def test_syntax_error_with_note(cls, multiline=False):
     raise exc
 
 
+def test_syntax_error_subclass_from_stdlib():
+    """
+    `ParseError` is a subclass of `SyntaxError`, but it is not a builtin:
+
+    >>> test_syntax_error_subclass_from_stdlib()
+    Traceback (most recent call last):
+      ...
+    xml.etree.ElementTree.ParseError: error
+    error
+    Note
+    Line
+    """
+    from xml.etree.ElementTree import ParseError
+    exc = ParseError("error\nerror")
+    exc.add_note('Note\nLine')
+    raise exc
+
+
 def test_syntax_error_with_incorrect_expected_note():
     """
     >>> def f(x):

Misc/NEWS.d/next/Library/2023-11-04-10-24-25.gh-issue-111541.x0RBI1.rst

@@ -0,0 +1 @@
+Fix :mod:`doctest` for :exc:`SyntaxError` not-builtin subclasses.