[conformance] Error if an imported name marked as Final is re-assigned

[fangyi-zhou]

Summary

This diff implements a new feature to error when an imported Final name is re-assigned.
This requirement stems from the spec section:

https://typing.python.org/en/latest/spec/qualifiers.html#importing-final-variables

If a module declares a Final variable and another module imports that variable in an import statement by name or wildcard, the imported symbol inherits the Final type qualifier. Any attempt to assign a different value to this symbol should be flagged as an error by a type checker

Implementation notes:

• Add a new field is_final for each Export, to indicate whether the name is final
• Extend export lookup to check for finality, similar to special exports are handled
• Raise an error if an imported final value is assigned to.

Test Plan

New test case.
Reran conformance test suite and observed 2 fewer errors.

[meta-codesync]

@migeed-z has imported this pull request. If you are a Meta employee, you can view this in D93045597.

[github-actions]

Diff from mypy_primer, showing the effect of this PR on open source code:

urllib3 (https://github.com/urllib3/urllib3)
+ ERROR src/urllib3/util/ssl_.py:125:9-36: Cannot assign to `HAS_NEVER_CHECK_COMMON_NAME` because it is imported as final [bad-assignment]
+ ::error file=src/urllib3/util/ssl_.py,line=125,col=9,endLine=125,endColumn=36,title=Pyrefly bad-assignment::Cannot assign to `HAS_NEVER_CHECK_COMMON_NAME` because it is imported as final

trio (https://github.com/python-trio/trio)
+ ERROR src/trio/_tests/test_highlevel_socket.py:11:33-34: Cannot assign to `TYPE_CHECKING` because it is imported as final [bad-assignment]
+ ::error file=src/trio/_tests/test_highlevel_socket.py,line=11,col=33,endLine=11,endColumn=34,title=Pyrefly bad-assignment::Cannot assign to `TYPE_CHECKING` because it is imported as final

zulip (https://github.com/zulip/zulip)
+ ERROR zproject/settings.py:41:34-35: Cannot assign to `TYPE_CHECKING` because it is imported as final [bad-assignment]
+ ::error file=zproject/settings.py,line=41,col=34,endLine=41,endColumn=35,title=Pyrefly bad-assignment::Cannot assign to `TYPE_CHECKING` because it is imported as final

ibis (https://github.com/ibis-project/ibis)
+ ERROR ibis/expr/datatypes/__init__.py:4:38-39: Cannot assign to `TYPE_CHECKING` because it is imported as final [bad-assignment]
+ ERROR ibis/expr/types/__init__.py:6:36-37: Cannot assign to `TYPE_CHECKING` because it is imported as final [bad-assignment]
+ ERROR ibis/expr/types/__init__.py:8:34-35: Cannot assign to `TYPE_CHECKING` because it is imported as final [bad-assignment]
+ ERROR ibis/expr/types/__init__.py:9:37-38: Cannot assign to `TYPE_CHECKING` because it is imported as final [bad-assignment]
+ ERROR ibis/expr/types/__init__.py:10:40-41: Cannot assign to `TYPE_CHECKING` because it is imported as final [bad-assignment]
+ ERROR ibis/expr/types/__init__.py:12:34-35: Cannot assign to `TYPE_CHECKING` because it is imported as final [bad-assignment]
+ ERROR ibis/expr/types/__init__.py:13:37-38: Cannot assign to `TYPE_CHECKING` because it is imported as final [bad-assignment]
+ ERROR ibis/expr/types/__init__.py:14:34-35: Cannot assign to `TYPE_CHECKING` because it is imported as final [bad-assignment]
+ ERROR ibis/expr/types/__init__.py:15:37-38: Cannot assign to `TYPE_CHECKING` because it is imported as final [bad-assignment]
+ ERROR ibis/expr/types/__init__.py:16:39-40: Cannot assign to `TYPE_CHECKING` because it is imported as final [bad-assignment]
+ ERROR ibis/expr/types/__init__.py:17:35-36: Cannot assign to `TYPE_CHECKING` because it is imported as final [bad-assignment]
+ ERROR ibis/expr/types/__init__.py:18:37-38: Cannot assign to `TYPE_CHECKING` because it is imported as final [bad-assignment]
+ ERROR ibis/expr/types/__init__.py:19:37-38: Cannot assign to `TYPE_CHECKING` because it is imported as final [bad-assignment]
+ ERROR ibis/expr/types/__init__.py:20:38-39: Cannot assign to `TYPE_CHECKING` because it is imported as final [bad-assignment]
+ ::error file=ibis/expr/datatypes/__init__.py,line=4,col=38,endLine=4,endColumn=39,title=Pyrefly bad-assignment::Cannot assign to `TYPE_CHECKING` because it is imported as final
+ ::error file=ibis/expr/types/__init__.py,line=6,col=36,endLine=6,endColumn=37,title=Pyrefly bad-assignment::Cannot assign to `TYPE_CHECKING` because it is imported as final
+ ::error file=ibis/expr/types/__init__.py,line=8,col=34,endLine=8,endColumn=35,title=Pyrefly bad-assignment::Cannot assign to `TYPE_CHECKING` because it is imported as final
+ ::error file=ibis/expr/types/__init__.py,line=9,col=37,endLine=9,endColumn=38,title=Pyrefly bad-assignment::Cannot assign to `TYPE_CHECKING` because it is imported as final
+ ::error file=ibis/expr/types/__init__.py,line=10,col=40,endLine=10,endColumn=41,title=Pyrefly bad-assignment::Cannot assign to `TYPE_CHECKING` because it is imported as final
+ ::error file=ibis/expr/types/__init__.py,line=12,col=34,endLine=12,endColumn=35,title=Pyrefly bad-assignment::Cannot assign to `TYPE_CHECKING` because it is imported as final
+ ::error file=ibis/expr/types/__init__.py,line=13,col=37,endLine=13,endColumn=38,title=Pyrefly bad-assignment::Cannot assign to `TYPE_CHECKING` because it is imported as final
+ ::error file=ibis/expr/types/__init__.py,line=14,col=34,endLine=14,endColumn=35,title=Pyrefly bad-assignment::Cannot assign to `TYPE_CHECKING` because it is imported as final
+ ::error file=ibis/expr/types/__init__.py,line=15,col=37,endLine=15,endColumn=38,title=Pyrefly bad-assignment::Cannot assign to `TYPE_CHECKING` because it is imported as final
+ ::error file=ibis/expr/types/__init__.py,line=16,col=39,endLine=16,endColumn=40,title=Pyrefly bad-assignment::Cannot assign to `TYPE_CHECKING` because it is imported as final
+ ::error file=ibis/expr/types/__init__.py,line=17,col=35,endLine=17,endColumn=36,title=Pyrefly bad-assignment::Cannot assign to `TYPE_CHECKING` because it is imported as final
+ ::error file=ibis/expr/types/__init__.py,line=18,col=37,endLine=18,endColumn=38,title=Pyrefly bad-assignment::Cannot assign to `TYPE_CHECKING` because it is imported as final
+ ::error file=ibis/expr/types/__init__.py,line=19,col=37,endLine=19,endColumn=38,title=Pyrefly bad-assignment::Cannot assign to `TYPE_CHECKING` because it is imported as final
+ ::error file=ibis/expr/types/__init__.py,line=20,col=38,endLine=20,endColumn=39,title=Pyrefly bad-assignment::Cannot assign to `TYPE_CHECKING` because it is imported as final

[fangyi-zhou]

Checked mypy-primer issues, most of them are of form of re-importing a Final value twice (potentially once via * import, once via direct import)

[stroxler]

Review automatically exported from Phabricator review in Meta.

[meta-codesync]

@migeed-z merged this pull request in a6d9bc1.