fix(bitbucket-datacenter): detect changes on merged PR push

[zakisk]

📝 Description of the Change

When a pull request is merged in Bitbucket Data Center, the resulting push event contains a merge commit that reports no file changes. This caused on-path-change and on-cel-expression filters to silently skip PipelineRuns because the changed files list was always empty.

The fix detects merge commits (commits with multiple parents) during payload parsing and uses the Bitbucket /changes API with since/until params to diff the previous HEAD against the current HEAD, retrieving the actual files modified by the merged PR.

Key changes:

• Parse merge commits in push payloads to capture previousHeadCommit
• Add getMergeCommitChanges using /changes API with proper pagination
• Add DiffStats/Pagination types for the /changes API response
• Update TearDown to skip deletion of already-merged PRs
• Allow CreatePR to target a custom base branch for merge test scenarios
• Add E2E test for on-path-change annotation surviving a PR merge push
• Add unit tests for getMergeCommitChanges and merge commit GetFiles path

🔗 Linked GitHub Issue

Fixes #

JIRA

https://redhat.atlassian.net/browse/SRVKP-9638

🧪 Testing Strategy

• Unit tests
• Integration tests
• End-to-end tests
• Manual testing
• Not Applicable

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✅ Submitter Checklist

• 📝 My commit messages are clear, informative, and follow the project's How to write a git commit message guide. The Gitlint linter ensures in CI it's properly validated
• ✨ I have ensured my commit message prefix (e.g., fix:, feat:) matches the "Type of Change" I selected above.
• ♽ I have run make test and make lint locally to check for and fix any
  issues. For an efficient workflow, I have considered installing
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  automate these checks.
• 📖 I have added or updated documentation for any user-facing changes.
• 🧪 I have added sufficient unit tests for my code changes.
• 🎁 I have added end-to-end tests where feasible. See README for more details.
• 🔎 I have addressed any CI test flakiness or provided a clear reason to bypass it.
• If adding a provider feature, I have filled in the following and updated the provider documentation:
  • GitHub App
  • GitHub Webhook
  • Gitea/Forgejo
  • GitLab
  • Bitbucket Cloud
  • Bitbucket Data Center

[gemini-code-assist]

Code Review

This pull request introduces support for accurately detecting file changes in Bitbucket Data Center push events involving merge commits. It implements a new getMergeCommitChanges method using the Bitbucket /changes API and updates the payload parsing logic to identify merge commits via parent counts. Feedback suggests improving the robustness of the API request by using url.Values for safer parameter escaping, refining the merge commit detection condition to be less restrictive, and enhancing error reporting for API failures.

[codecov-commenter]

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Codecov Report

❌ Patch coverage is 87.83784% with 9 lines in your changes missing coverage. Please review.
✅ Project coverage is 59.39%. Comparing base (c615efb) to head (e20f740).
⚠️ Report is 2 commits behind head on main.

Files with missing lines	Patch %	Lines
pkg/provider/bitbucketdatacenter/diff_api.go	90.62%	4 Missing and 2 partials ⚠️
pkg/provider/bitbucketdatacenter/parse_payload.go	0.00%	2 Missing and 1 partial ⚠️
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Additional details and impacted files

@@            Coverage Diff             @@
##             main    #2719      +/-   ##
==========================================
+ Coverage   59.25%   59.39%   +0.13%     
==========================================
  Files         208      209       +1     
  Lines       20573    20663      +90     
==========================================
+ Hits        12191    12272      +81     
- Misses       7610     7616       +6     
- Partials      772      775       +3     

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[zakisk]

/gemini review

[gemini-code-assist]

Code Review

This pull request enables accurate file change detection for Bitbucket Data Center when a pull request is merged. It implements a custom API client to retrieve changes between the previous HEAD and the merge commit, addressing limitations in the underlying scm library. The implementation includes merge commit detection during payload parsing and updated E2E tests for validation. Feedback recommends using the internal client wrapper to maintain API usage metrics, refining HTTP error handling, and improving the robustness of the commit matching logic.

[theakshaypant]

Minor comments on the changes

[theakshaypant]

Some of these structs are duplicated in pkg/provider/bitbucketdatacenter/test/test_types.go, can we avoid this duplication?

[zakisk]

thanks for pointing, didn't pay attention. removed types from test_types.go