Add support for Python 3.10 in tests and CI (#550)

It also fixes some line numbers in formatted exceptions that changed in
Python 3.10 due to https://bugs.python.org/issue42246 and
https://bugs.python.org/issue43933.

.github/workflows/tests.yml

@@ -19,12 +19,13 @@ jobs:
           - '3.7'
           - '3.8'
           - '3.9'
+          - '3.10'
           - 'pypy-3.8'
         include:
           - os: windows-latest
-            python-version: '3.9'
+            python-version: '3.10'
           - os: macos-latest
-            python-version: '3.9'
+            python-version: '3.10'
     steps:
       - uses: actions/checkout@v2
       - name: Set up Python ${{ matrix.python-version }}

setup.py

@@ -44,6 +44,7 @@
         "Programming Language :: Python :: 3.7",
         "Programming Language :: Python :: 3.8",
         "Programming Language :: Python :: 3.9",
+        "Programming Language :: Python :: 3.10",
         "Programming Language :: Python :: 3 :: Only",
         "Programming Language :: Python :: Implementation :: PyPy",
         "Programming Language :: Python :: Implementation :: CPython",

tests/exceptions/output/others/handler_formatting_with_context_manager.txt

@@ -1,4 +1,4 @@
-__main__ handler_formatting_with_context_manager.py a 17
+__main__ handler_formatting_with_context_manager.py a 16
 Traceback (most recent call last):
   File "tests/exceptions/source/others/handler_formatting_with_context_manager.py", line 17, in a
     1 / 0

tests/exceptions/output/others/message_formatting_with_context_manager.txt

@@ -1,4 +1,4 @@
-__main__ message_formatting_with_context_manager.py a 13
+__main__ message_formatting_with_context_manager.py a 10
 Traceback (most recent call last):
   File "tests/exceptions/source/others/message_formatting_with_context_manager.py", line 13, in a
     1 / 0

tests/test_exceptions_formatting.py

@@ -44,6 +44,16 @@ def fix_filepath(match):
         elif "IndentationError" in exception:
             exception = re.sub(r"\n *\^ *\n", "\n", exception)
 
+    if sys.version_info < (3, 10, 0):
+        for module, line_before, line_after in [
+            ("handler_formatting_with_context_manager.py", 17, 16),
+            ("message_formatting_with_context_manager.py", 13, 10),
+        ]:
+            if module not in exception:
+                continue
+            expression = r"^(__main__ %s a) %d\n" % (module, line_before)
+            exception = re.sub(expression, r"\1 %d\n" % line_after, exception)
+
     exception = re.sub(
         r'"[^"]*/somelib/__init__.py"', '"/usr/lib/python/somelib/__init__.py"', exception
     )

tox.ini

@@ -1,6 +1,6 @@
 [tox]
 skip_missing_interpreters = True
-envlist = py{35,36,37,38,39,py3}
+envlist = py{35,36,37,38,39,310,py3}
 
 [testenv]
 setenv = PYTHONPATH = {toxinidir}