Fix #5713: Emit used-before-assignment instead of undefined-variable when accessing unused type annotations

[jacobtylerwalls]

Type of Changes

	Type
✓	🔨 Refactoring

Description

This one is somewhat pedantic, sorry! I simply noticed that we could attempt to raise more targeted messages so that undefined-variable corresponds generally with NameError and used-before-assignment corresponds generally with UnboundLocalError. The only use of the message affected by this PR is new in 2.12, so hopefully not breaking too many existing disables. But I suppose that should be balanced against people suppressing undefined-variable that would be glad to get used-before-assignment coming through now.

See example shell session drawn from existing unit tests adjusted in this PR:

In [1]: G: int
   ...: 
   ...: 
   ...: def a():
   ...:     global G
   ...:     print(G)
   ...: 
   ...: 
   ...: def bound_value():
   ...:     variable: int
   ...:     print(variable)
   ...: 
   ...: 
   ...: def decorator_returning_incorrect_function():
   ...:     """A decorator that returns a wrapper function with decoupled typing"""
   ...: 
   ...:     def wrapper_with_type_and_no_value():
   ...:         # This emits NameError, so undefined-variable is okay
   ...:         # even though the traceback refers to
   ...:         print(var)  # [undefined-variable]
   ...: 
   ...:     var: int
   ...:     return wrapper_with_type_and_no_value

In [2]: a()
---------------------------------------------------------------------------
NameError                                 Traceback (most recent call last)
Input In [2], in <module>
----> 1 a()

Input In [1], in a()
      4 def a():
      5     global G
----> 6     print(G)

NameError: name 'G' is not defined

In [3]: bound_value()
---------------------------------------------------------------------------
UnboundLocalError                         Traceback (most recent call last)
Input In [3], in <module>
----> 1 bound_value()

Input In [1], in bound_value()
      9 def bound_value():
     10     variable: int
---> 11     print(variable)

UnboundLocalError: local variable 'variable' referenced before assignment

In [4]: decorator_returning_incorrect_function()()
---------------------------------------------------------------------------
NameError                                 Traceback (most recent call last)
Input In [4], in <module>
----> 1 decorator_returning_incorrect_function()()

Input In [1], in decorator_returning_incorrect_function.<locals>.wrapper_with_type_and_no_value()
     17 def wrapper_with_type_and_no_value():
     18     # This emits NameError, so undefined-variable is okay
     19     # even though the traceback refers to "used before assignment"
---> 20     print(var)

NameError: free variable 'var' referenced before assignment in enclosing scope

Closes #5713

[coveralls]

Pull Request Test Coverage Report for Build 1746877150

• 3 of 3 (100.0%) changed or added relevant lines in 1 file are covered.
• No unchanged relevant lines lost coverage.
• Overall coverage increased (+0.0008%) to 93.844%

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Totals
Change from base Build 1741985260:	0.0008%
Covered Lines:	14712
Relevant Lines:	15677

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💛 - Coveralls

[Pierre-Sassoulas]

It's a nice consistency refactor, thank you 👍 I think we can do it as the number of false positives for those two message is probably low and of disable of those message even lower.

[Pierre-Sassoulas]

👌

[DanielNoord]

Thanks @jacobtylerwalls for looking into this. I think this makes sense (even though somewhat breaking)!

[DanielNoord]

This fails on main as well. I think it is related to the fail of #5711. Perhaps @jacobtylerwalls can take a look at them together and do a follow-up PR?

[jacobtylerwalls]

@DanielNoord actually this failure looks "random" -->

>               _winapi.TerminateProcess(int(self._handle), TERMINATE)
E               PermissionError: [WinError 5] Access is denied

Note the test suite passed on all other runners. 🤔

[Pierre-Sassoulas]

this failure looks "random"

I came to the same conclusion when looking at it (I'm notified if what I merge fail on main).