[New-bugs-announce] [issue30113] Add profile test case for trace_dispatch_return assertion

[Louie Lu]

New submission from Louie Lu:

This is a sub-problem of #9285, in #9285, we aim to provide cProfile and profile a context manager, this will need to add code like this:

    def __enter__(self):
        self.set_cmd('')
        sys.setprofile(self.dispatcher)
        return self

Unfortunately, when setting up profiler via `sys.setprofile`, it will immediately work on next line `return self`, which cause the assertion inside `trace_dispatch_return` claim this is a "Bad return".

Technically, `profile.Profile` can not go return upper than it's frame inside the frame stack. This behavior can be observed by this code:

    def fib(n):
        if n > 2:
            return fib(n - 1) + fib(n - 2)
        return n

    def foo():
        pr = profile.Profile()
        # Profile was set in the `foo` frame, it can't get more upper than this
        # that means, we can't return to global frame when this profile is set
        sys.setprofile(pr.dispatcher)
        fib(5)
        # We didn't stop the profile here via sys.setprofile(None)
        # So it will return 0xDEADBEAF to global frame and cause a bad return
        return 0xDEADBEAF

    foo()

Here this issue will provide the test of this behavior, then will make some modify in #9285 to prevent this situation when using profile as a context manager.

----------
components: Library (Lib)
messages: 291957
nosy: louielu, ncoghlan
priority: normal
severity: normal
status: open
title: Add profile test case for trace_dispatch_return assertion
type: enhancement
versions: Python 3.7

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Python tracker <report at bugs.python.org>
<http://bugs.python.org/issue30113>
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