Add support for Python 3.11.

Review Request #12498 — Created Aug. 3, 2022 and submitted

Information

kgb
master

Reviewers

kgb

Python 3.11 introduced some internal changes to how functions with
closures and exceptions worked. This led to segfaults when calling our
forwarding functions, as our closure state didn't match what Python
internally expected; and failures representing stack traces, because
internal cached state was never rebuilt.

There's a lot more knowledge internally now in Python 3.11 when it comes
to closures. If a FunctionType and CodeType isn't set up properly,
that internal Python state crashes. The state that matters can't
actually be set by us after defining the function, so it needs to be
properly prepared up-front.

We conditionally do this now by generating the forwarding function code
string in such a way where the forwarding function is inside of another
function. The outer function provides all the variables the inner
function needs in its scope, and the inner forwarding function
references them just enough to satisfy Python.

The generated outer function is then called, returning the inner
forwarding function, which is properly set up for Python 3.11's closer
semantics.

Exception behavior has also changed. Python 3.11 has improved exception
support, and to facilitate this, the CodeType now keeps track of state
that helps map exceptions to lines, as well as marking ranges of lines
and columns to bytecode. The former is just another argument that goes
into CodeType, but the latter is more internal (accessible, but not
modifiable, by code_type.co_positions()) It seems we can't correctly
set it when setting up the CodeType.

We now use code_type.replace(...) on the forwarding function's
__code__, instead of constructing a CodeType(). This has been
available since Python 3.8, but we've never used it. It's historically
been equivalent to constructing a CodeType() with a function's
defaults, allowing the caller to selectively replace only what's needed.
It now seems to properly rebuild some state needed to ensure the cde
positions all map correctly.

Given the increased complexity in building the forwarding function and
the CodeType, these blocks of logic have been moved into new utility
methods.

With these fixes, all unit tests (including a couple new ones) pass on
Python 3.11. This is now listed in our documentation and in our
packaging metadata.

Unit tests pass on Python 2.7 through 3.11.

Performed complete runs of the Review Board and Djblets test suites
using Python 2.7, 3.6, 3.10, and 3.11.

Summary ID
Add support for Python 3.11.
Python 3.11 introduced some internal changes to how functions with closures and exceptions worked. This led to segfaults when calling our forwarding functions, as our closure state didn't match what Python internally expected; and failures representing stack traces, because internal cached state was never rebuilt. There's a lot more knowledge internally now in Python 3.11 when it comes to closures. If a `FunctionType` and `CodeType` isn't set up properly, that internal Python state crashes. The state that matters can't actually be set by us after defining the function, so it needs to be properly prepared up-front. We conditionally do this now by generating the forwarding function code string in such a way where the forwarding function is inside of another function. The outer function provides all the variables the inner function needs in its scope, and the inner forwarding function references them just enough to satisfy Python. The generated outer function is then called, returning the inner forwarding function, which is properly set up for Python 3.11's closer semantics. Exception behavior has also changed. Python 3.11 has improved exception support, and to facilitate this, the `CodeType` now keeps track of state that helps map exceptions to lines, as well as marking ranges of lines and columns to bytecode. The former is just another argument that goes into `CodeType`, but the latter is more internal (accessible, but not modifiable, by `code_type.co_positions()`) It seems we can't correctly set it when setting up the `CodeType`. We now use `code_type.replace(...)` on the forwarding function's `__code__`, instead of constructing a `CodeType()`. This has been available since Python 3.8, but we've never used it. It's historically been equivalent to constructing a `CodeType()` with a function's defaults, allowing the caller to selectively replace only what's needed. It now seems to properly rebuild some state needed to ensure the cde positions all map correctly. Given the increased complexity in building the forwarding function and the `CodeType`, these blocks of logic have been moved into new utility methods. With these fixes, all unit tests (including a couple new ones) pass on Python 3.11. This is now listed in our documentation and in our packaging metadata.
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Description From Last Updated

too many blank lines (2) Column: 9 Error code: E303

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local variable 'ctx' is assigned to but never used Column: 37 Error code: F841

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local variable 'ctx' is assigned to but never used Column: 37 Error code: F841

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local variable 'c' is assigned to but never used Column: 25 Error code: F841

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local variable 'b' is assigned to but never used Column: 21 Error code: F841

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chipx86
chipx86
david
  1. Ship It!
  2. 
      
chipx86
Review request changed
Status:
Completed
Change Summary:
Pushed to master (57947cc)