Fix KeyError in crossgen2_comparison.py for omitted_from_diff_dir lookups

[Copilot]

Description

Crossgen2-comparison outerloop tests intermittently fail with KeyError (e.g. KeyError: 'System.DirectoryServices') when an assembly is present in the base output but missing from the diff output.

Root cause: When generating XML results for assemblies in omitted_from_diff_dir (assemblies in base but not in diff), line 922 looked them up in diff_results_by_name — the dictionary that by definition does not contain them:

# Before (bug): looks up in the wrong dictionary
for assembly_name in omitted_from_diff_dir:
    base_result = diff_results_by_name[assembly_name]

# After (fix): looks up in the correct dictionary
for assembly_name in omitted_from_diff_dir:
    base_result = base_results_by_name[assembly_name]

The adjacent omitted_from_base_dir loop correctly uses diff_results_by_name; this was a copy-paste error in the opposite direction.

---

📍 Connect Copilot coding agent with Jira, Azure Boards or Linear to delegate work to Copilot in one click without leaving your project management tool.

[Copilot]

Pull request overview

Fixes an intermittent KeyError in the crossgen2 comparison outerloop script when generating XML results for assemblies that are present in the base output but missing from the diff output.

Changes:

• Correct dictionary lookup for omitted_from_diff_dir entries by using base_results_by_name instead of diff_results_by_name.

[github-actions]

🤖 Copilot Code Review — PR #126175

Note

This review was generated by GitHub Copilot.

Holistic Assessment

Motivation: The PR fixes a clear KeyError bug in crossgen2_comparison.py. The omitted_from_diff_dir set contains assembly names that exist in base but not in diff, so looking them up in diff_results_by_name would always raise a KeyError. The bug is real and verifiable from the code alone.

Approach: The fix is minimal and correct — switching the lookup to base_results_by_name and adding sorted() for deterministic output, matching the pattern used by the adjacent loops (lines 899 and 943).

Summary: ✅ LGTM. This is a straightforward, correct bug fix with no risk of collateral damage.

---

Detailed Findings

✅ Correctness — Dictionary lookup fix is correct

The core fix changes diff_results_by_name[assembly_name] → base_results_by_name[assembly_name] on line 922. This is correct because:

• omitted_from_diff_dir = base_assemblies - diff_assemblies (line 850) — these assemblies exist in base_assemblies only.
• base_results_by_name is keyed by assembly names from base_results (line 862), so these names are guaranteed to be present.
• The old code used diff_results_by_name, which by definition does not contain these assembly names, causing a KeyError whenever omitted_from_diff_dir is non-empty.

I verified the analogous omitted_from_base_dir loop at line 899 correctly uses diff_results_by_name[assembly_name] — no similar bug there.

✅ Consistency — sorted() matches adjacent loops

Adding sorted() to the omitted_from_diff_dir iteration matches the existing pattern in the omitted_from_base_dir loop (line 899) and the both_assemblies loop (line 943, 867). This ensures deterministic XML output ordering.

Generated by Code Review for issue #126175 · ◷