Support diff-informed queries under Default Setup

[cklin]

This PR extends the diff-informed queries functionality to also work under the Default Setup.

Merge / deployment checklist

• Confirm this change is backwards compatible with existing workflows.
• Confirm the readme has been updated if necessary.
• Confirm the changelog has been updated if necessary.

[Copilot]

Pull Request Overview

This PR extends the diff-informed queries functionality to work under the Default Setup by introducing a new branch interface and updating diff-related functions.

• Introduces a new interface (PullRequestBranches) and helper function (getPullRequestBranches) to consistently extract branch information.
• Refactors several functions in both the src and lib directories to use the new branch structure.
• Simplifies diff-informed query setup in analyze-action files by removing redundant pull_request checks.

Reviewed Changes

Copilot reviewed 6 out of 6 changed files in this pull request and generated no comments.

File	Description
src/analyze.ts	Updated to use PullRequestBranches; refactored diff range retrieval.
lib/analyze.js	Updated to use PullRequestBranches; refactored diff range retrieval.
src/analyze-action.ts	Removed direct pull_request usage, now relying on unified branch info.
lib/analyze-action.js	Removed direct pull_request usage, now relying on unified branch info.

Comments suppressed due to low confidence (2)

src/analyze.ts:257

• Ensure that the new branch handling logic in getPullRequestBranches is adequately tested for both scenarios: when the pull_request context is available and when falling back to the CODE_SCANNING_REF and CODE_SCANNING_BASE_BRANCH environment variables.

interface PullRequestBranches {

lib/analyze.js:162

• Ensure that the new getPullRequestBranches implementation covers both the pull_request context and the Default Setup environment variable fallback case in the unit tests.

function getPullRequestBranches() {

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[NlightNFotis]

Some minor comments, thank you for your work here.

[NlightNFotis]

Can we get a (debug?) log message here that the environment variables weren't set in the else branch?

I'm thinking this might make it easier to identify where it goes wrong in the future, for either ourselves or an end user.

What are your thoughts on this one?

[cklin]

I added two info log statements:

• One to indicate that we are not performing diff-informed analysis because we are not analyzing a PR
• One to indicate that we are analyzing a PR, and what refs are being used for diff range calculation

[NlightNFotis]

Thank you for this refactoring. I always appreciate bundling information into its own semantic bundle.

Would it be possible to get some documentation above the interface as to what it's supposed to signify? I think it's clear from the context, but it might make future mantainer's life better.

I think some of that documentation could be sourced from the previous @param documentation in the getPullRequestEditedDiffRanges function.

[cklin]

I thought about it and decided that additional documentation would not have provided much value.

The interface is basically what the definition says: a record for storing the base and head branches of a pull request. Repeating the same thing in English does not seem to be all that useful.

Previous @param documentation for getPullRequestEditedDiffRanges() contains some useful information, and I have already incorporated them into code comments in getPullRequestBranches(). That documentation does not quite fit at the PullRequestBranches level, because the pull_request context is now only one of two possible sources for obtaining branch information. (When we set the head branch using CODE_SCANNING_REF, we are relying on the Default Setup workflow to set the environment variable correctly, without requiring the variable to use a head ref.)

All that is explained in getPullRequestBranches(), next to the code that creates PullRequestBranches values. I think that is a better place for that explanation because it is easier to keep the code comments up-to-date if the code needs to be changed in the future.