Drop Python 3.6 support (#2210)

* Remove Python 3.6 IPython hack in CI script
* Remove exc_key compatibility hack in MultiError
* Remove KI test that is no longer required
* Update a number of comments referring to Python 3.6
* Stop checking for warn_on_full_buffer (this is always available now)
* Stop installing contextvars since we dropped 3.6 support
* Remove TCP_NOTSENT_LOWAT definitions (they always exist in Python 3.7+)
* Remove obsolete check for GenericMeta
* Remove check for ssl.OP_NO_TLSv1_3 (this flag was introduced in Python 3.7 so it's always there now)

Co-authored-by: Quentin Pradet <quentin.pradet@gmail.com>

.github/workflows/ci.yml

@@ -14,7 +14,7 @@ jobs:
     strategy:
       fail-fast: false
       matrix:
-        python: ['3.6', '3.7', '3.8', '3.9', '3.10']
+        python: ['3.7', '3.8', '3.9', '3.10']
         arch: ['x86', 'x64']
         lsp: ['']
         lsp_extract_file: ['']
@@ -51,7 +51,7 @@ jobs:
           # This avoids the need to update for each new alpha, beta, release candidate,
           # and then finally an actual release version.  actions/setup-python doesn't
           # support this for PyPy presently so we get no help there.
-          # 
+          #
           # CPython -> 3.9.0-alpha - 3.9.X
           # PyPy    -> pypy-3.7
           python-version: ${{ fromJSON(format('["{0}", "{1}"]', format('{0}.0-alpha - {0}.X', matrix.python), matrix.python))[startsWith(matrix.python, 'pypy')] }}
@@ -72,7 +72,7 @@ jobs:
     strategy:
       fail-fast: false
       matrix:
-        python: ['pypy-3.6', 'pypy-3.7', 'pypy-3.8', '3.6', '3.7', '3.8', '3.9', '3.10', '3.8-dev', '3.9-dev', '3.10-dev']
+        python: ['pypy-3.7', 'pypy-3.8', '3.7', '3.8', '3.9', '3.10', '3.8-dev', '3.9-dev', '3.10-dev']
         check_formatting: ['0']
         pypy_nightly_branch: ['']
         extra_name: ['']
@@ -114,7 +114,7 @@ jobs:
     strategy:
       fail-fast: false
       matrix:
-        python: ['3.6', '3.7', '3.8', '3.9', '3.10']
+        python: ['3.7', '3.8', '3.9', '3.10']
         include:
           - python: '3.8'  # <- not actually used
             arch: 'x64'

README.rst

@@ -9,14 +9,14 @@
 .. image:: https://img.shields.io/badge/docs-read%20now-blue.svg
    :target: https://trio.readthedocs.io
    :alt: Documentation
-   
+
 .. image:: https://img.shields.io/pypi/v/trio.svg
    :target: https://pypi.org/project/trio
    :alt: Latest PyPi version
 
 .. image:: https://img.shields.io/conda/vn/conda-forge/trio.svg
    :target: https://anaconda.org/conda-forge/trio
-   :alt: Latest conda-forge version   
+   :alt: Latest conda-forge version
 
 .. image:: https://codecov.io/gh/python-trio/trio/branch/master/graph/badge.svg
    :target: https://codecov.io/gh/python-trio/trio
@@ -92,7 +92,7 @@ demonstration of implementing the "Happy Eyeballs" algorithm in an
 older library versus Trio.
 
 **Cool, but will it work on my system?** Probably! As long as you have
-some kind of Python 3.6-or-better (CPython or the latest PyPy3 are
+some kind of Python 3.7-or-better (CPython or the latest PyPy3 are
 both fine), and are using Linux, macOS, Windows, or FreeBSD, then Trio
 will work. Other environments might work too, but those
 are the ones we test on. And all of our dependencies are pure Python,

ci.sh

@@ -72,14 +72,6 @@ python -m pip --version
 python setup.py sdist --formats=zip
 python -m pip install dist/*.zip
 
-if python -c 'import sys; sys.exit(sys.version_info >= (3, 7))'; then
-    # Python < 3.7, select last ipython with 3.6 support
-    # macOS requires the suffix for --in-place or you get an undefined label error
-    sed -i'.bak' 's/ipython==[^ ]*/ipython==7.16.1/' test-requirements.txt
-    sed -i'.bak' 's/traitlets==[^ ]*/traitlets==4.3.3/' test-requirements.txt
-    git diff test-requirements.txt
-fi
-
 if [ "$CHECK_FORMATTING" = "1" ]; then
     python -m pip install -r test-requirements.txt
     source check.sh

docs/source/index.rst

@@ -45,7 +45,7 @@ Vital statistics:
 
 * Supported environments: We test on
 
-  - Python: 3.6+ (CPython and PyPy)
+  - Python: 3.7+ (CPython and PyPy)
   - Windows, macOS, Linux (glibc and musl), FreeBSD
 
   Other environments might also work; give it a try and see.

docs/source/reference-io.rst

@@ -237,8 +237,7 @@ other constants and functions in the :mod:`ssl` module.
 
 .. warning:: Avoid instantiating :class:`ssl.SSLContext` directly.
    A newly constructed :class:`~ssl.SSLContext` has less secure
-   defaults than one returned by :func:`ssl.create_default_context`,
-   dramatically so before Python 3.6.
+   defaults than one returned by :func:`ssl.create_default_context`.
 
 Instead of using :meth:`ssl.SSLContext.wrap_socket`, you
 create a :class:`SSLStream`:
@@ -722,7 +721,7 @@ subprocess`` in order to access constants such as ``PIPE`` or
 
 Currently, Trio always uses unbuffered byte streams for communicating
 with a process, so it does not support the ``encoding``, ``errors``,
-``universal_newlines`` (alias ``text`` in 3.7+), and ``bufsize``
+``universal_newlines`` (alias ``text``), and ``bufsize``
 options.
 
 

docs/source/tutorial.rst

@@ -34,9 +34,6 @@ Tutorial
          print(response)
    and then again with /delay/10
 
-   (note that asks needs cpython 3.6 though. maybe just for one async
-   generator?)
-
    value of async/await: show you where the cancellation exceptions
    can happen -- see pillar re: explicit cancel points
 
@@ -94,7 +91,7 @@ Okay, ready? Let's get started.
 Before you begin
 ----------------
 
-1. Make sure you're using Python 3.6 or newer.
+1. Make sure you're using Python 3.7 or newer.
 
 2. ``python3 -m pip install --upgrade trio`` (or on Windows, maybe
    ``py -3 -m pip install --upgrade trio`` – `details

pyproject.toml

@@ -1,5 +1,5 @@
 [tool.black]
-target-version = ['py36']
+target-version = ['py37']
 
 
 [tool.towncrier]

setup.py

@@ -44,7 +44,7 @@
 Vital statistics:
 
 * Supported environments: Linux, macOS, or Windows running some kind of Python
-  3.6-or-better (either CPython or PyPy3 is fine). \\*BSD and illumos likely
+  3.7-or-better (either CPython or PyPy3 is fine). \\*BSD and illumos likely
   work too, but are not tested.
 
 * Install: ``python3 -m pip install -U trio`` (or on Windows, maybe
@@ -89,12 +89,11 @@
         # cffi 1.14 fixes memory leak inside ffi.getwinerror()
         # cffi is required on Windows, except on PyPy where it is built-in
         "cffi>=1.14; os_name == 'nt' and implementation_name != 'pypy'",
-        "contextvars>=2.1; python_version < '3.7'",
     ],
     # This means, just install *everything* you see under trio/, even if it
     # doesn't look like a source file, so long as it appears in MANIFEST.in:
     include_package_data=True,
-    python_requires=">=3.6",
+    python_requires=">=3.7",
     keywords=["async", "io", "networking", "trio"],
     classifiers=[
         "Development Status :: 3 - Alpha",
@@ -108,10 +107,11 @@
         "Programming Language :: Python :: Implementation :: CPython",
         "Programming Language :: Python :: Implementation :: PyPy",
         "Programming Language :: Python :: 3 :: Only",
-        "Programming Language :: Python :: 3.6",
         "Programming Language :: Python :: 3.7",
         "Programming Language :: Python :: 3.8",
         "Programming Language :: Python :: 3.9",
+        "Programming Language :: Python :: 3.10",
+        "Programming Language :: Python :: 3.11",
         "Topic :: System :: Networking",
         "Framework :: Trio",
     ],

test-requirements.in

@@ -22,15 +22,9 @@ typing-extensions; implementation_name == "cpython"
 
 # Trio's own dependencies
 cffi; os_name == "nt"
-contextvars; python_version < "3.7"
 attrs >= 19.2.0
 sortedcontainers
 async_generator >= 1.9
 idna
 outcome
 sniffio
-
-# Required by contextvars, but harmless to install everywhere.
-# dependabot drops the contextvars dependency because it runs
-# on 3.7.
-immutables >= 0.6

trio/_core/_entry_queue.py

@@ -15,8 +15,8 @@ class EntryQueue:
     # not signal-safe. deque is implemented in C, so each operation is atomic
     # WRT threads (and this is guaranteed in the docs), AND each operation is
     # atomic WRT signal delivery (signal handlers can run on either side, but
-    # not *during* a deque operation). dict makes similar guarantees - and on
-    # CPython 3.6 and PyPy, it's even ordered!
+    # not *during* a deque operation). dict makes similar guarantees - and
+    # it's even ordered!
     queue = attr.ib(factory=deque)
     idempotent_queue = attr.ib(factory=dict)
 

trio/_core/_multierror.py

@@ -5,13 +5,6 @@
 
 import attr
 
-# python traceback.TracebackException < 3.6.4 does not support unhashable exceptions
-# see https://github.com/python/cpython/pull/4014 for details
-if sys.version_info < (3, 6, 4):
-    exc_key = lambda exc: exc
-else:
-    exc_key = id
-
 ################################################################
 # MultiError
 ################################################################
@@ -419,7 +412,7 @@ def traceback_exception_init(
     if isinstance(exc_value, MultiError):
         embedded = []
         for exc in exc_value.exceptions:
-            if exc_key(exc) not in _seen:
+            if id(exc) not in _seen:
                 embedded.append(
                     traceback.TracebackException.from_exception(
                         exc,

trio/_core/_run.py

@@ -1,18 +1,12 @@
-# coding: utf-8
-
 import functools
 import itertools
-import logging
-import os
 import random
 import select
 import sys
 import threading
 from collections import deque
-import collections.abc
 from contextlib import contextmanager
 import warnings
-import weakref
 import enum
 
 from contextvars import copy_context
@@ -47,7 +41,6 @@
 from ._thread_cache import start_thread_soon
 from ._instrumentation import Instruments
 from .. import _core
-from .._deprecate import warn_deprecated
 from .._util import Final, NoPublicConstructor, coroutine_or_error
 
 DEADLINE_HEAP_MIN_PRUNE_THRESHOLD = 1000
@@ -70,13 +63,8 @@ def _public(fn):
 _r = random.Random()
 
 
-# On 3.7+, Context.run() is implemented in C and doesn't show up in
-# tracebacks. On 3.6, we use the contextvars backport, which is
-# currently implemented in Python and adds 1 frame to tracebacks. So this
-# function is a super-overkill version of "0 if sys.version_info >= (3, 7)
-# else 1". But if Context.run ever changes, we'll be ready!
-#
-# This can all be removed once we drop support for 3.6.
+# On CPython, Context.run() is implemented in C and doesn't show up in
+# tracebacks. On PyPy, it is implemented in Python and adds 1 frame to tracebacks.
 def _count_context_run_tb_frames():
     def function_with_unique_name_xyzzy():
         1 / 0
@@ -2172,7 +2160,7 @@ def unrolled_run(runner, async_fn, args, host_uses_signal_set_wakeup_fd=False):
                 try:
                     # We used to unwrap the Outcome object here and send/throw
                     # its contents in directly, but it turns out that .throw()
-                    # is buggy, at least on CPython 3.6:
+                    # is buggy, at least before CPython 3.9:
                     #   https://bugs.python.org/issue29587
                     #   https://bugs.python.org/issue29590
                     # So now we send in the Outcome object and unwrap it on the

trio/_core/_wakeup_socketpair.py

@@ -1,30 +1,11 @@
 import socket
-import sys
 import signal
 import warnings
 
 from .. import _core
 from .._util import is_main_thread
 
 
-def _has_warn_on_full_buffer():
-    if sys.version_info < (3, 7):
-        return False
-
-    if "__pypy__" not in sys.builtin_module_names:
-        # CPython has warn_on_full_buffer. Don't need to inspect.
-        # Also, CPython doesn't support inspecting built-in functions.
-        return True
-
-    import inspect
-
-    args_spec = inspect.getfullargspec(signal.set_wakeup_fd)
-    return "warn_on_full_buffer" in args_spec.kwonlyargs
-
-
-HAVE_WARN_ON_FULL_BUFFER = _has_warn_on_full_buffer()
-
-
 class WakeupSocketpair:
     def __init__(self):
         self.wakeup_sock, self.write_sock = socket.socketpair()
@@ -38,13 +19,8 @@ def __init__(self):
         #   Windows 10: 525347
         # Windows you're weird. (And on Windows setting SNDBUF to 0 makes send
         # blocking, even on non-blocking sockets, so don't do that.)
-        #
-        # But, if we're on an old Python and can't control the signal module's
-        # warn-on-full-buffer behavior, then we need to leave things alone, so
-        # the signal module won't spam the console with spurious warnings.
-        if HAVE_WARN_ON_FULL_BUFFER:
-            self.wakeup_sock.setsockopt(socket.SOL_SOCKET, socket.SO_RCVBUF, 1)
-            self.write_sock.setsockopt(socket.SOL_SOCKET, socket.SO_SNDBUF, 1)
+        self.wakeup_sock.setsockopt(socket.SOL_SOCKET, socket.SO_RCVBUF, 1)
+        self.write_sock.setsockopt(socket.SOL_SOCKET, socket.SO_SNDBUF, 1)
         # On Windows this is a TCP socket so this might matter. On other
         # platforms this fails b/c AF_UNIX sockets aren't actually TCP.
         try:
@@ -75,10 +51,7 @@ def wakeup_on_signals(self):
         if not is_main_thread():
             return
         fd = self.write_sock.fileno()
-        if HAVE_WARN_ON_FULL_BUFFER:
-            self.old_wakeup_fd = signal.set_wakeup_fd(fd, warn_on_full_buffer=False)
-        else:
-            self.old_wakeup_fd = signal.set_wakeup_fd(fd)
+        self.old_wakeup_fd = signal.set_wakeup_fd(fd, warn_on_full_buffer=False)
         if self.old_wakeup_fd != -1:
             warnings.warn(
                 RuntimeWarning(

trio/_core/tests/test_guest_mode.py

@@ -504,7 +504,7 @@ async def trio_main(in_host):
 
 @pytest.mark.skipif(buggy_pypy_asyncgens, reason="PyPy 7.2 is buggy")
 @pytest.mark.xfail(
-    sys.implementation.name == "pypy" and sys.version_info >= (3, 7),
+    sys.implementation.name == "pypy",
     reason="async generator issue under investigation",
 )
 @restore_unraisablehook()