gh-160948: Fix annotationlib.ForwardRef.evaluate() ignoring explicit globals/locals for closure-cell references - #160952

Summary

ForwardRef.evaluate() had an early return for references holding a single closure cell (__cell__ is a CellType) that ran before any namespace handling. As a result, an explicitly passed locals was silently ignored for such references, while every other path in the same method gives it precedence: for references holding a dict of cells, the cells are merged into the locals with setdefault, so explicit locals win over the captured scope.

As discussed in gh-160948, the cell holds a nonlocal binding, so it correctly takes precedence over globals (on the dict-of-cells path, the nonlocals sit between the locals and the globals). Only the locals precedence was wrong, and that is all this PR changes.

Fix

In Lib/annotationlib.py (ForwardRef.evaluate):

• The single-cell shortcut now only applies when neither globals nor locals was passed, preserving the existing fast path and behaviour for the common no-argument call.
• In the plain-identifier resolution branch, the cell value is consulted after locals and before globals, mirroring the dict-of-cells path. An empty cell (ValueError) falls through exactly as before.

No other paths are changed: the dict-of-cells and __extra_names__ handling, type-parameter injection, and the non-identifier eval path are untouched.

Tests

Two regression tests in Lib/test/test_annotationlib.py (TestForwardRefClass):

• test_evaluate_cell_with_explicit_namespaces — an explicitly passed locals wins over the cell, in both VALUE and FORWARDREF formats; globals does not; the cell remains the fallback when the name is absent from locals.
• test_evaluate_empty_cell_with_explicit_namespaces — an emptied cell still raises NameError with no arguments, explicit namespaces are consulted, and a refilled cell resumes its place between locals and globals.

Both tests fail on the unmodified code and pass with this change.

Results (local build of main @ 83fe630):

• test_annotationlib: SUCCESS.
• test_typing: SUCCESS.

Fixes gh-160948.

Disclosure: this change was drafted with AI assistance and reviewed by the author, who takes responsibility for it.