gh-115392: Fix doctest reporting incorrect line numbers for decorated functions

Lib/doctest.py

@@ -1140,6 +1140,8 @@ def _find_lineno(self, obj, source_lines):
             obj = obj.fget
         if inspect.isfunction(obj) and getattr(obj, '__doc__', None):
             # We don't use `docstring` var here, because `obj` can be changed.
+            while hasattr(obj, "__wrapped__"):
+                obj = obj.__wrapped__
             obj = obj.__code__
         if inspect.istraceback(obj): obj = obj.tb_frame
         if inspect.isframe(obj): obj = obj.f_code

Lib/test/test_doctest/_support.py

@@ -0,0 +1,10 @@
+# This module is used in `doctest_lineno.py`.
+import functools
+
+
+def decorator(f):
+    @functools.wraps(f)
+    def inner():
+        return f()
+
+    return inner

Lib/test/test_doctest/doctest_lineno.py

@@ -67,3 +67,12 @@ def property_with_doctest(self):
 
 # https://github.com/python/cpython/issues/99433
 str_wrapper = object().__str__
+
+
+# https://github.com/python/cpython/issues/115392
+from test.test_doctest._support import decorator
+
+@decorator
+@decorator
+def func_with_docstring_wrapped():
+    """Some unrelated info."""

Lib/test/test_doctest/test_doctest.py

@@ -685,6 +685,7 @@ def basics(): r"""
      None  test.test_doctest.doctest_lineno.MethodWrapper.method_without_docstring
        61  test.test_doctest.doctest_lineno.MethodWrapper.property_with_doctest
         4  test.test_doctest.doctest_lineno.func_with_docstring
+       77  test.test_doctest.doctest_lineno.func_with_docstring_wrapped
        12  test.test_doctest.doctest_lineno.func_with_doctest
      None  test.test_doctest.doctest_lineno.func_without_docstring
 

Misc/NEWS.d/next/Library/2024-02-13-18-27-03.gh-issue-115392.gle5tp.rst

@@ -0,0 +1,2 @@
+Fix a bug in :mod:`doctest` where incorrect line numbers would be
+reported for decorated functions.