3.11 regression: tracing with-statement on exit from block

[nedbat]

BPO	45709
Nosy	@nedbat, @markshannon, @pablogsal
PRs	bpo-45709: Fix tracing when exception is handled. #29638

^{Note: these values reflect the state of the issue at the time it was migrated and might not reflect the current state.}

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GitHub fields:

assignee = 'https://github.com/markshannon'
closed_at = <Date 2021-11-21.15:24:51.922>
created_at = <Date 2021-11-04.10:08:51.497>
labels = ['interpreter-core', 'type-bug', '3.11']
title = '3.11 regression: tracing with-statement on exit from block'
updated_at = <Date 2021-11-21.15:24:51.921>
user = 'https://github.com/nedbat'

bugs.python.org fields:

activity = <Date 2021-11-21.15:24:51.921>
actor = 'pablogsal'
assignee = 'Mark.Shannon'
closed = True
closed_date = <Date 2021-11-21.15:24:51.922>
closer = 'pablogsal'
components = ['Interpreter Core']
creation = <Date 2021-11-04.10:08:51.497>
creator = 'nedbat'
dependencies = []
files = []
hgrepos = []
issue_num = 45709
keywords = ['3.11regression']
message_count = 7.0
messages = ['405668', '405669', '405673', '406581', '406590', '406683', '406708']
nosy_count = 3.0
nosy_names = ['nedbat', 'Mark.Shannon', 'pablogsal']
pr_nums = ['29638']
priority = 'normal'
resolution = 'fixed'
stage = 'resolved'
status = 'closed'
superseder = None
type = 'behavior'
url = 'https://bugs.python.org/issue45709'
versions = ['Python 3.11']

[nedbat]

Python 3.11 seems to have reverted a behavior that was new in 3.10.0b1: exiting a with-statement re-visits the with line on the way out.

--- %< bug2.py ----------------------

import linecache, sys

def trace(frame, event, arg):
    # The weird globals here is to avoid a NameError on shutdown...
    if frame.f_code.co_filename == globals().get("__file__"):
        lineno = frame.f_lineno
        print("{} {}: {}".format(event[:4], lineno, linecache.getline(__file__, lineno).rstrip()))
    return trace

print(sys.version)
sys.settrace(trace)

import contextlib

def f():
    with contextlib.nullcontext():
        1/0

f()

---

Running with 3.10 shows re-visiting the with:

    $ python3.10 bug2.py
    3.10.0 (default, Oct  4 2021, 17:22:29) [Clang 12.0.0 (clang-1200.0.32.29)]
    call 15: def f():
    line 16:     with contextlib.nullcontext():
    line 17:         1/0
    exce 17:         1/0
    line 16:     with contextlib.nullcontext():
    retu 17:         1/0
    Traceback (most recent call last):
      File "/System/Volumes/Data/root/src/foo/bug1270/bug2.py", line 19, in <module>
        f()
      File "/System/Volumes/Data/root/src/foo/bug1270/bug2.py", line 17, in f
        1/0
    ZeroDivisionError: division by zero

3.11 does not:

    $ python3.11 bug2.py
    3.11.0a1 (default, Oct  6 2021, 07:21:05) [Clang 12.0.0 (clang-1200.0.32.29)]
    call 15: def f():
    line 16:     with contextlib.nullcontext():
    line 17:         1/0
    exce 17:         1/0
    retu 17:         1/0
    Traceback (most recent call last):
      File "/System/Volumes/Data/root/src/foo/bug1270/bug2.py", line 19, in <module>
        f()
        ^^^
      File "/System/Volumes/Data/root/src/foo/bug1270/bug2.py", line 17, in f
        1/0
        ~^~
    ZeroDivisionError: division by zero

Versions before 3.10 also do not visit the with statement:

    $ python3.9 bug2.py
    3.9.7 (default, Sep  7 2021, 22:16:49)
    [Clang 12.0.0 (clang-1200.0.32.29)]
    call 15: def f():
    line 16:     with contextlib.nullcontext():
    line 17:         1/0
    exce 17:         1/0
    line 17:         1/0
    retu 17:         1/0
    Traceback (most recent call last):
      File "/System/Volumes/Data/root/src/foo/bug1270/bug2.py", line 19, in <module>
        f()
      File "/System/Volumes/Data/root/src/foo/bug1270/bug2.py", line 17, in f
        1/0
    ZeroDivisionError: division by zero

Is this a bug in 3.11, or an intentional return to previous behavior?

(BTW: there is no 3.11regression keyword available)

[nedbat]

BTW, this is the coverage.py issue: nedbat/coveragepy#1270

[markshannon]

Probably an oversight when converting to zero-overhead exceptions.

[markshannon]

Sorry about the delay in fixing this.

[markshannon]

New changeset 337cb48 by Mark Shannon in branch 'main':
bpo-45709: Fix tracing when exception is handled. (GH-29638)
337cb48

[pablogsal]

Mark, os something left to do here?

[nedbat]

I can confirm that this fixes the problem.