Branch condition covered but labeled as uncovered

[aa-stevo]

Bug Description
The following code says a branch condition is never false when it is.

To Reproduce
Python code to reproduce the issue (parsers.py):

import unittest

def parse_sms(text):
    data = {}
    for i, split in enumerate(text.split(",")):
        if i == 0:
            data["name"] = split.title()
            print(len(data['name'].split()) == 1)
            if len(data['name'].split()) == 1:
                return None
            continue
    return data

class TestParsers(unittest.TestCase):
    def test_parse_sms(self):
        messages = [
            "John Doe, Jane",
            "Jane, John Doe",
        ]
        for message in messages:
            parse_sms(message)

Command to reproduce the issue:

python -m coverage erase
python -m coverage run --branch -m unittest parsers.py
python -m coverage html

I expected line 9 to be both True and False, but the coverage report says it is never False. The print statement on line 8 prints both False and True.

Relevant details:

$ python --version
Python 3.9.13
$ python -m coverage --version
Coverage.py, version 7.0.3 with C extension
$ python -m coverage debug sys
-- sys -------------------------------------------------------
               coverage_version: 7.0.3
                coverage_module: C:\Users\...\AppData\Local\Packages\PythonSoftwareFoundation.Python.3.9_qbz5n2kfra8p0\LocalCache\local-packages\Python39\site-packages\coverage\__init__.py
                         tracer: -none-
                        CTracer: available
           plugins.file_tracers: -none-
            plugins.configurers: -none-
      plugins.context_switchers: -none-
              configs_attempted: .coveragerc
                                 setup.cfg
                                 tox.ini
                                 pyproject.toml
                   configs_read: -none-
                    config_file: None
                config_contents: -none-
                      data_file: -none-
                         python: 3.9.13 (tags/v3.9.13:6de2ca5, May 17 2022, 16:36:42) [MSC v.1929 64 bit (AMD64)]
                       platform: Windows-10-10.0.19042-SP0
                 implementation: CPython
                     executable: C:\Users\...\AppData\Local\Microsoft\WindowsApps\PythonSoftwareFoundation.Python.3.9_qbz5n2kfra8p0\python.exe
                   def_encoding: utf-8
                    fs_encoding: utf-8
                            pid: 6636
                            cwd: ...
                           path: ...
                    environment: HOME = C:\Users\...
                                 PYTHONPATH = ...
                                 PYTHONUSERBASE = C:\Users\...\AppData\Local\Packages\PythonSoftwareFoundation.Python.3.9_qbz5n2kfra8p0\LocalCache\local-packages
                                 TEMP = C:\Users\...\AppData\Local\Temp
                                 TMP = C:\Users\...\AppData\Local\Temp
                   command_line: C:\Users\...\AppData\Local\Packages\PythonSoftwareFoundation.Python.3.9_qbz5n2kfra8p0\LocalCache\local-packages\Python39\site-packages\coverage\__main__.py debug sys
         sqlite3_sqlite_version: 3.37.2
             sqlite3_temp_store: 0
        sqlite3_compile_options: ATOMIC_INTRINSICS=0, COMPILER=msvc-1929, DEFAULT_AUTOVACUUM,
                                 DEFAULT_CACHE_SIZE=-2000, DEFAULT_FILE_FORMAT=4,
                                 DEFAULT_JOURNAL_SIZE_LIMIT=-1, DEFAULT_MMAP_SIZE=0, DEFAULT_PAGE_SIZE=4096,
                                 DEFAULT_PCACHE_INITSZ=20, DEFAULT_RECURSIVE_TRIGGERS,
                                 DEFAULT_SECTOR_SIZE=4096, DEFAULT_SYNCHRONOUS=2,
                                 DEFAULT_WAL_AUTOCHECKPOINT=1000, DEFAULT_WAL_SYNCHRONOUS=2,
                                 DEFAULT_WORKER_THREADS=0, ENABLE_FTS3, ENABLE_FTS4, ENABLE_FTS5,
                                 ENABLE_JSON1, MALLOC_SOFT_LIMIT=1024, MAX_ATTACHED=10, MAX_COLUMN=2000,
                                 MAX_COMPOUND_SELECT=500, MAX_DEFAULT_PAGE_SIZE=8192, MAX_EXPR_DEPTH=1000,
                                 MAX_FUNCTION_ARG=127, MAX_LENGTH=1000000000, MAX_LIKE_PATTERN_LENGTH=50000,
                                 MAX_MMAP_SIZE=0x7fff0000, MAX_PAGE_COUNT=1073741823, MAX_PAGE_SIZE=65536,
                                 MAX_SQL_LENGTH=1000000000, MAX_TRIGGER_DEPTH=1000,
                                 MAX_VARIABLE_NUMBER=32766, MAX_VDBE_OP=250000000, MAX_WORKER_THREADS=8,
                                 MUTEX_W32, SYSTEM_MALLOC, TEMP_STORE=1, THREADSAFE=1

[kevin-brown]

This issue does not occur on Python 3.11, but using your example I was able to reproduce it on Python 3.8 using Coveragepy 3.0.3.

Additionally, this issue still occurs in the latest stable release using Python 3.8 so I'm going to try to pick this up for the PyCon 2023 sprints.

[nedbat]

I believe this is a duplicate of #198.