Protect variables in inner scopes.

[prozacchiwawa]

This would have prevented compilation so it doesn't need to be feature gated.

---

Note

Medium Risk
Medium risk because it changes common-subexpression elimination placement logic in the optimizer, which can subtly affect generated programs and correctness when assign/let bindings are involved.

Overview
Fixes a CSE optimizer bug where a common subexpression could be lifted outside the scope of variables it depends on (notably when one occurrence is inside an assign binding expression).

The CSE pass now computes a ceiling based on which binding names the subexpression uses, restricts detect_common_cse_root accordingly (skipping the optimization when no safe common root exists), and adds a regression test program (cse-complex-2.clsp) plus a new classic test that compiles and executes it to ensure the result remains correct.

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Cursor Bugbot has reviewed your changes and found 1 potential issue.

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Ceiling check bypassed when BodyOf found first

Medium Severity

In detect_common_cse_root, the BodyOf check at line 443 returns immediately without verifying the ceiling constraint. Since the loop iterates in reverse (deepest to shallowest), if target_path ends with BodyOf (or encounters one before hitting a non-BodyOf element where the ceiling check fires), the function returns that position even if it's above the ceiling. The ceiling check on lines 447–451 only executes for non-BodyOf elements, so it never gets a chance to reject a BodyOf that violates the ceiling constraint.

 

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