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:

PR diff — collects lines REMOVED by the PR under review.
Git history — git log --follow --since=6mo finds recent PRs that touched the same files.
Label filter — keeps PRs (or their linked issues) labeled i/regression, t/bug, p/0, or p/1.
Fix diff — fetches each fix PR's diff and collects lines it ADDED to the same file.
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

Parameter	Required	Default	Description
`-PRNumber`	Yes	—	PR number to analyze
`-Repo`	No	`dotnet/maui`	Repository in `owner/name` form
`-FilePaths`	No	auto-detect	Implementation files to check
`-MonthsBack`	No	`6`	History window for git log
`-MaxRecentPRsPerFile`	No	`20`	Rate-limit guard per file
`-BaseBranch`	No	`main`	Base branch for `git log` scope
`-OutputDir`	No	—	Directory for output files
`-WriteInlineFindings`	No	off	Emit `inline-findings.json`
`-DiffFile`	No	live PR diff	Frozen diff of the current PR; historical fix diffs are fetched normally
`-ChangedPathsFile`	No	live auto-detection	Frozen JSON array of changed file paths
`-StrictEvidence`	No	off	Fail on unavailable history/API evidence instead of reporting no match

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.

The standalone /review expert-review gh-aw collector supplies its frozen diff, changed paths and pinned base with -StrictEvidence. Collection failures become explicit evidence gaps, not CLEAN results. It inspects regression-test source but does not execute any of those tests.

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