bpo 39114 broke 3.9, but maybe it's their bug

Author: nedbat

appveyor.yml

@@ -90,14 +90,14 @@ environment:
     - JOB: "3.9 32-bit"
       TOXENV: "py39"
       PYTHON: "C:\\Python39"
-      PYTHON_VERSION: "3.9.0a1"
+      PYTHON_VERSION: "3.9.0a2"
       PYTHON_ARCH: "32"
       COVERAGE_NO_PYTRACER: "1"
 
     - JOB: "3.9 64-bit"
       TOXENV: "py39"
       PYTHON: "C:\\Python39-x64"
-      PYTHON_VERSION: "3.9.0a1"
+      PYTHON_VERSION: "3.9.0a2"
       PYTHON_ARCH: "64"
 
     # Meta coverage

coverage/env.py

@@ -81,6 +81,10 @@ class PYBEHAVIOR(object):
     # Python 3.9a1 made sys.argv[0] and other reported files absolute paths.
     report_absolute_files = (PYVERSION >= (3, 9))
 
+    # Python 3.9a2 changed how return/finally was traced, but it could be
+    # temporary.
+    bug39114 = (PYVERSION >= (3, 9, 0, 'alpha', 2))
+
 # Coverage.py specifics.
 
 # Are we using the C-implemented trace function?

tests/coveragetest.py

@@ -15,6 +15,7 @@
 import sys
 import types
 
+import pytest
 from unittest_mixins import (
     EnvironmentAwareMixin, StdStreamCapturingMixin, TempDirMixin,
     DelayedAssertionMixin,
@@ -99,6 +100,10 @@ def setUp(self):
         self.last_command_output = None
         self.last_module_name = None
 
+    def xfail(self, msg):
+        """Mark this test as an expected failure."""
+        pytest.xfail(msg)
+
     def clean_local_file_imports(self):
         """Clean up the results of calls to `import_local_file`.
 

tests/test_arcs.py

@@ -630,6 +630,8 @@ def test_finally_in_loop(self):
 
 
     def test_break_through_finally(self):
+        if env.PYBEHAVIOR.bug39114:
+            self.xfail("https://bugs.python.org/issue39114")
         if env.PYBEHAVIOR.finally_jumps_back:
             arcz = ".1 12 23 34 3D 45 56 67 68 7A 7D 8A A3 A7 BC CD D."
         else:
@@ -654,6 +656,8 @@ def test_break_through_finally(self):
         )
 
     def test_continue_through_finally(self):
+        if env.PYBEHAVIOR.bug39114:
+            self.xfail("https://bugs.python.org/issue39114")
         if env.PYBEHAVIOR.finally_jumps_back:
             arcz = ".1 12 23 34 3D 45 56 67 68 73 7A 8A A3 A7 BC CD D."
         else:
@@ -691,6 +695,8 @@ def test_finally_in_loop_bug_92(self):
         )
 
     def test_bug_212(self):
+        if env.PYBEHAVIOR.bug39114:
+            self.xfail("https://bugs.python.org/issue39114")
         # "except Exception as e" is crucial here.
         # Bug 212 said that the "if exc" line was incorrectly marked as only
         # partially covered.
@@ -813,6 +819,8 @@ def test_multiple_except_clauses(self):
         )
 
     def test_return_finally(self):
+        if env.PYBEHAVIOR.bug39114:
+            self.xfail("https://bugs.python.org/issue39114")
         if env.PYBEHAVIOR.finally_jumps_back:
             arcz = ".1 12 29 9A AB BC C-1   -23 34 45 5-2 57 75 38 8-2"
         else:
@@ -835,6 +843,8 @@ def check_token(data):
         )
 
     def test_except_jump_finally(self):
+        if env.PYBEHAVIOR.bug39114:
+            self.xfail("https://bugs.python.org/issue39114")
         if env.PYBEHAVIOR.finally_jumps_back:
             arcz = (
                 ".1 1Q QR RS ST TU U. "
@@ -889,6 +899,8 @@ def func(x):
         )
 
     def test_else_jump_finally(self):
+        if env.PYBEHAVIOR.bug39114:
+            self.xfail("https://bugs.python.org/issue39114")
         if env.PYBEHAVIOR.finally_jumps_back:
             arcz = (
                 ".1 1S ST TU UV VW W. "
@@ -1511,6 +1523,8 @@ async def print_sum(x, y):                      # 8
         self.assertEqual(self.stdout(), "Compute 1 + 2 ...\n1 + 2 = 3\n")
 
     def test_async_for(self):
+        if env.PYBEHAVIOR.bug39114:
+            self.xfail("https://bugs.python.org/issue39114")
         self.check_coverage("""\
             import asyncio