docs: note #1210 in the changelog

Author: nedbat

CHANGES.rst

@@ -25,7 +25,12 @@ Unreleased
 - Changed an internal detail of how tomli is imported, so that tomli can use
   coverage.py for their own test suite (`issue 1228`_).
 
+- Defend against an obscure possibility under code obfuscation, where a
+  function can have an argument called "self", but no local named "self"
+  (`pull request 1210`_).  Thanks, Ben Carlsson.
+
 .. _issue 1228: https://github.com/nedbat/coveragepy/issues/1228
+.. _pull request 1210: https://github.com/nedbat/coveragepy/pull/1210
 
 
 .. _changes_60:

CONTRIBUTORS.txt

@@ -20,6 +20,7 @@ Arcadiy Ivanov
 Aron Griffis
 Artem Dayneko
 Arthur Deygin
+Ben Carlsson
 Ben Finney
 Bernát Gábor
 Bill Hart

tests/test_context.py

@@ -278,6 +278,8 @@ class test_something:               # pylint: disable=unused-variable
             assert get_qualname() is None
 
     def test_bug_1210(self):
+        # Under pyarmor (an obfuscator), a function can have a "self" argument,
+        # but then not have a "self" local.
         co = mock.Mock(co_name="a_co_name", co_argcount=1, co_varnames=["self"])
-        frame = mock.Mock(f_code = co, f_locals={})
+        frame = mock.Mock(f_code=co, f_locals={})
         assert qualname_from_frame(frame) == "unittest.mock.a_co_name"