Make the overlay changed files always include the diff

[alexet]

This includes the PR diff in the overlay changes so that any "overlay informed analysis" runs in a detailed way on those files..

This requires writing pr-diff-range.json in init and reading inside analyse.

A minor change is that for an empty PR diff, a dummy entry is not written to pr-diff-range.json. analyse still adds it to the generated pack, but it isn't used by `upload``.

I am assuming that mixing and matching init and analyse from different action versions is not supported.

Risk assessment

• High risk: Changes are not fully under feature flags, have limited visibility and/or cannot be tested outside of production.

Which use cases does this change impact?

This affects all cases where diff-informed may apply:

• Advanced setup - Impacts users who have custom workflows.
• Default setup - Impacts users who use default setup.
• Code Scanning - Impacts Code Scanning (i.e. analysis-kinds: code-scanning).
• GHES - Impacts GitHub Enterprise Server.

How did/will you validate this change?

• Test repository - This change will be tested on a test repository before merging. (TODO: Do this)
• Unit tests - I have run the existing unit tests but they don'#t cover much here.
• End-to-end tests -

If something goes wrong after this change is released, what are the mitigation and rollback strategies?

• Rollback - Rollback is the primary strategy as feature flagging this change is tricky.
• Feature flags - In an emergency (or if this only affects a few repos) we can switch off diff-informed.

How will you know if something goes wrong after this change is released?

• Telemetry - I rely on existing telemetry or have made changes to the telemetry.
  • Dashboards - I will watch the diff informed dashboard to check it still is positive.

Merge / deployment checklist

• Confirm this change is backwards compatible with existing workflows.
• Consider adding a changelog entry for this change.
• Confirm the readme and docs have been updated if necessary.

[Copilot]

Pull Request Overview

This PR integrates diff-informed analysis into overlay mode by computing PR diff ranges during init and including changed files from the diff in overlay analysis. This ensures that overlay analysis always processes files with at least one edited range, improving the coverage of diff-informed analysis.

Key changes:

• Moves diff range computation from analyze to init step to enable early persistence and reuse
• Augments overlay changed files with files from PR diff ranges
• Refactors diff-informed analysis logic to use precomputed ranges instead of computing them during analyze

Reviewed Changes

Copilot reviewed 18 out of 19 changed files in this pull request and generated 2 comments.

Show a summary per file

File	Description
src/overlay-database-utils.ts	Enhanced to accept PR diff changed files and include them in overlay analysis
src/init-action.ts	Added early computation and persistence of diff ranges with new helper function
src/diff-informed-analysis-utils.ts	Moved diff computation logic from analyze.ts and added export functions
src/analyze.ts	Refactored to use precomputed diff ranges instead of computing them inline
src/codeql.ts	Updated interface to accept PR diff changed files parameter

Comments suppressed due to low confidence (1)

src/diff-informed-analysis-utils.ts:1

• The replaceAll method may not be available in older Node.js versions. Consider using replace with a global regex for better compatibility: .replace(new RegExp('\\' + path.sep, 'g'), '/')

import * as fs from "fs";

[Copilot]

The slice operation on changedFiles array could be inefficient for large arrays. Consider tracking the added files separately to avoid the slice operation on potentially large arrays.

[Copilot]

Creating a Set from mapped array could be optimized by using a for loop to avoid creating an intermediate array, especially for large numbers of ranges.

Suggested change

	const distinctFiles = new Set(ranges.map((r) => r.path));
	const distinctFiles = new Set<string>();
	for (const r of ranges) {
	distinctFiles.add(r.path);
	}