fix(wren): case-insensitive CTE name shadowing in CTERewriter

[goldmedal]

Summary

• Fix duplicate CTE generation when a user-defined CTE name differs only in case from an MDL model name (e.g. WITH Orders AS (...) vs model orders)
• _collect_user_cte_names() now lowercases names to match sqlglot's normalize_identifiers behavior
• Add test_user_cte_shadows_model_case_insensitive reproducing the exact scenario from feat(wren): CTE-based SQL planning with per-model expansion #1479 (comment)

Addresses #1479 (comment)

Test plan

• New test test_user_cte_shadows_model_case_insensitive passes
• All 17 existing CTE rewriter unit tests pass
• CI passes

🤖 Generated with Claude Code

Summary by CodeRabbit

• Bug Fixes
  • Fixed case-insensitive handling of CTE names to prevent duplicate generation when user-defined CTEs differ in case from model names.

[coderabbitai]

No actionable comments were generated in the recent review. 🎉

ℹ️ Recent review info

⚙️ Run configuration

Configuration used: defaults

Review profile: CHILL

Plan: Pro

Run ID: cf3f3d86-7607-477a-a679-1612cf4a0beb

📥 Commits

Reviewing files that changed from the base of the PR and between 6a78c12 and fdefa12.

📒 Files selected for processing (2)

• wren/src/wren/mdl/cte_rewriter.py
• wren/tests/unit/test_cte_rewriter.py

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📝 Walkthrough

Walkthrough

A case normalization fix for CTE (Common Table Expression) name comparison in the MDL rewriter. The _collect_user_cte_names function now converts collected CTE names to lowercase before comparison with model table names, preventing duplicate CTE generation when names differ only in case. A corresponding test case validates this behavior.

Changes

Cohort / File(s)	Summary
CTE Name Normalization wren/src/wren/mdl/cte_rewriter.py	Modified _collect_user_cte_names to normalize user-defined CTE names to lowercase via .lower() before insertion into the returned set, ensuring case-insensitive comparison against model table names.
Test Coverage wren/tests/unit/test_cte_rewriter.py	Added unit test test_user_cte_shadows_model_case_insensitive that verifies duplicate CTE generation is prevented when a user CTE name differs only in case from a model name (e.g., Orders vs orders).

Estimated code review effort

🎯 2 (Simple) | ⏱️ ~10 minutes

Suggested labels

core, python

Suggested reviewers

• douenergy

Poem

🐰 A rabbit hops through CTE trees,
Where Orders and orders once disagreed,
With .lower() cast, the shadows align,
No duplicate CTEs cause design,
Case-insensitive logic now pristine! ✨

🚥 Pre-merge checks | ✅ 3

✅ Passed checks (3 passed)

Check name	Status	Explanation
Description Check	✅ Passed	Check skipped - CodeRabbit’s high-level summary is enabled.
Title check	✅ Passed	The title clearly and specifically describes the main change: fixing case-insensitive CTE name shadowing in the CTERewriter, which directly matches the core modification to normalize CTE names to lowercase and the test case validating this behavior.
Docstring Coverage	✅ Passed	Docstring coverage is 100.00% which is sufficient. The required threshold is 80.00%.

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✨ Finishing Touches

🧪 Generate unit tests (beta)

• Create PR with unit tests

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