Preserve saved globals when copying DelayEvaluator

[Hashim1999164]

PR Type

[x] Bug fix
[ ] New feature
[ ] Core Runtime change (higher bar; see CONTRIBUTING.md)
[ ] Docs / tooling
[ ] Refactoring

Summary

Attribute and item access on DelayEvaluator copy the object and previously dropped the caller globals captured by config_expr. Custom functions then raised NameError after any chained access.

Issue

Fixes #3345

Reproduction

Runtime: local

Commands to run:

PYTHONPATH=. pytest test/unit/test_delay_evaluator.py

Where evidence shows up: unit test output

Before (error / log snippet)

After copy or attribute access, DelayEvaluator._globals became None, so eval of config_expr("my_func()") lost my_func and raised NameError.

After (evidence that fix works)

test_copy_preserves_saved_globals PASSED
test_deepcopy_preserves_saved_globals PASSED
test_getattr_preserves_saved_globals PASSED
test_getitem_preserves_saved_globals PASSED

Root Cause

copy and deepcopy constructed DelayEvaluator(self._config_expr) without saved_globals. getattr and getitem call copy, so chaining dropped the globals config_expr had stored.

Why This Fix Is Correct

Pass saved_globals=self._globals into both copy paths so the reference is kept, matching the previous comment that globals stay as a reference. Scope is limited to those two methods plus unit tests.

Failure Modes Considered

1. Deep copy still keeps globals by reference (intentional; same object identity as before for globals).
2. Evaluators created without saved_globals still copy None correctly.

Tests

[x] Unit tests added/updated
[ ] Reproduction script provided (required for Core Runtime)
[ ] CI passes
[ ] If tests are impractical: explain why below and provide manual evidence above

Non Goals

No change to eval semantics beyond preserving the globals reference across copy.

AI Tool Usage

[ ] No AI tools were used in this contribution
[x] AI tools were used (describe below)

Cursor assisted with locating the bug from the issue report, applying the saved_globals pass through, and adding unit tests. All code was reviewed and the unit tests were run locally.

[greptile-apps]

Greptile Summary

This PR preserves the caller globals captured by config_expr when a DelayEvaluator is copied, including copies created during delayed attribute and item access.

• Passes the existing globals mapping through both shallow and deep-copy operations.
• Adds unit coverage for shallow copy, deep copy, attribute access, and item access.
• The tests verify internal state preservation but do not exercise the user-visible evaluation path.

Confidence Score: 4/5

The PR appears safe to merge, with only a non-blocking gap in the regression tests’ coverage of actual delayed evaluation.

The implementation preserves the intended globals reference through every changed copy path, but the new tests would not detect a later failure in expression construction or evaluation because they only inspect private fields.

Files Needing Attention: test/unit/test_delay_evaluator.py

Important Files Changed

Filename	Overview
metaflow/user_configs/config_parameters.py	Correctly retains the saved globals reference across shallow and deep copies, matching the intended delayed-evaluation semantics.
test/unit/test_delay_evaluator.py	Covers all affected copy entry points, but asserts private state instead of reproducing successful delayed expression evaluation.

_{Reviews (1): Last reviewed commit: "Preserve saved globals when copying Dela..." | Re-trigger Greptile}

[greptile-apps]

Chained evaluation remains untested

These regression tests only inspect _globals and _access, so they do not exercise the __call__ evaluation path where the reported NameError occurred. Evaluating a chained expression and asserting its result would ensure future changes cannot preserve these private fields while breaking expression construction or namespace handling.

Note: If this suggestion doesn't match your team's coding style, reply to this and let me know. I'll remember it for next time!