find-regression-risk

Detects potential regression risks in a PR by cross-referencing removed lines against lines added by recent labeled bug-fix PRs.

How It Works

Purely mechanical — no AI/LLM. Five-step algorithm:

1. PR diff — collects lines REMOVED by the PR under review.
2. Git history — git log --follow --since=6mo finds recent PRs that touched the same files.
3. Label filter — keeps PRs (or their linked issues) labeled i/regression, t/bug, p/0, or p/1.
4. Fix diff — fetches each fix PR's diff and collects lines it ADDED to the same file.
5. Compare — whitespace-insensitive string equality:
   • 🔴 REVERT — removed line matches a line a fix PR added (highest risk).
   • 🟡 OVERLAP — same file modified, but no exact line revert.
   • 🟢 CLEAN — no bug-fix PRs touch the same files.

Standalone Invocation

# Analyze a specific PR (auto-detects files)
pwsh -NoProfile -Command '& ./.github/scripts/Find-RegressionRisks.ps1 -PRNumber 33908 -OutputDir /tmp/out'

# Analyze specific files only
pwsh -NoProfile -Command '& ./.github/scripts/Find-RegressionRisks.ps1 -PRNumber 33908 -OutputDir /tmp/out -FilePaths @("src/Core/src/Platform/Android/MauiWindowInsetListener.cs")'

Parameters

Outputs

When -OutputDir is specified:

• result.txt — single token: CLEAN, OVERLAP, or REVERT
• risks.json — structured findings for downstream agents
• content.md — markdown summary for the PR comment
• inline-findings.json — (only with -WriteInlineFindings) inline annotations

Integration

The script runs as STEP 4 in Review-PR.ps1 (Regression Cross-Reference, after UI test detection and before the Gate step). Its content.md is assembled into the AI summary review by post-ai-summary-comment.ps1.

When REVERT risks are detected, the regression tests from the reverted fix PRs are executed:

• UI tests → BuildAndRunHostApp.ps1 -Platform <plat> -TestFilter <filter>
• Device tests → Run-DeviceTests.ps1 -Project <proj> -Platform <plat> -TestFilter <filter>
• Unit/XAML tests → dotnet test <project> --filter <filter>

The expert reviewer agent (maui-expert-reviewer.md, dimension #6) reads risks.json to check for REVERT entries.

Known Limitations

• Inline findings: The -WriteInlineFindings flag emits deletion-side (LEFT) annotations, but post-inline-review.ps1 currently only posts RIGHT-side comments. LEFT-side findings are silently dropped. This is documented as future work.
• Whitespace-only changes: By design, an indent-only change to a fix line won't trigger a REVERT (the normalization collapses whitespace). This avoids false positives from reformatting.
• pwsh -File array parameters: When invoking standalone from bash, use pwsh -Command '& ./script.ps1 -FilePaths @(...)' syntax. pwsh -File doesn't evaluate @() expressions.

Tests

pwsh -NoProfile -File .github/scripts/tests/Test-FindRegressionRisks.ps1