Add delete branch after merge

[solababs]

Why

After a branch is merged, it typically has no further use but remains in the branch list until manually deleted. There is no way to automatically clean it up today.

This PR wires up the delete_branch_after_merge config setting (added in Phase 1) to the actual merge paths — both direct BranchMerge and proposed change merge — so that the Infrahub branch is automatically deleted after a successful merge when the setting is enabled.

What changed

• backend/infrahub/core/branch/tasks.py — after a successful BranchMerge, if delete_branch_after_merge=True and the branch is not the default branch and there is no associated proposed change, submits the BRANCH_DELETE workflow.
• backend/infrahub/proposed_change/tasks.py — after a proposed change is merged, if delete_branch_after_merge=True, checks that no other open proposed changes exist for the source branch before submitting BRANCH_DELETE.
• backend/tests/functional/branch/test_branch_delete_after_merge.py — 4 functional tests covering: config-enabled standard merge triggers delete, config-disabled standard merge does not, proposed change merge triggers delete, and a skipped test for the multi-PC guard (multiple PCs on the same branch are not currently allowed).

The default value of delete_branch_after_merge remains False, so existing deployments are unaffected.

Suggested review order

1. backend/infrahub/core/branch/tasks.py — merge_branch change
2. backend/infrahub/proposed_change/tasks.py — merge_proposed_change change
3. backend/tests/functional/branch/test_branch_delete_after_merge.py — functional tests

How to review

• In proposed_change/tasks.py: confirm the open-PC guard logic is correct — we query for open PCs on the source branch before deciding to delete. Worth checking whether the PC being merged is already in a non-open state at this point and would be excluded from the query.
• The proposed_change_id is None guard in branch/tasks.py prevents a double-delete when a proposed change merge internally calls merge_branch.

How to test

uv run pytest backend/tests/functional/branch/test_branch_delete_after_merge.py -v

Manual flow:

1. Set delete_branch_after_merge = true in infrahub.toml, restart service.
2. Create a branch, make a change, merge via BranchMerge GraphQL mutation — branch should no longer appear in the branch list.
3. Repeat by merging a proposed change — same result.
4. Confirm with delete_branch_after_merge = false (default) — branch is retained after merge.

Impact & rollout

• Backward compatibility: No breaking changes. delete_branch_after_merge defaults to false; existing behaviour is unchanged.
• Config/env changes: Behaviour is controlled by delete_branch_after_merge in MainSettings (introduced in Phase 1).
• Deployment notes: Safe to deploy. Feature is opt-in via config.

Checklist

• Tests added/updated
• Changelog entry added (uv run towncrier create ...)
• External docs updated (if user-facing or ops-facing change)
• Internal .md docs updated (internal knowledge and AI code tools knowledge)

[coderabbitai]

Important

Review skipped

Auto reviews are disabled on base/target branches other than the default branch.

🗂️ Base branches to auto review (4)

• main
• stable
• develop
• release-.*

Please check the settings in the CodeRabbit UI or the .coderabbit.yaml file in this repository. To trigger a single review, invoke the @coderabbitai review command.

⚙️ Run configuration

Configuration used: Organization UI

Review profile: CHILL

Plan: Pro

Run ID: 0237c32f-0459-4f33-91df-105a1191155d

You can disable this status message by setting the reviews.review_status to false in the CodeRabbit configuration file.

Use the checkbox below for a quick retry:

• 🔍 Trigger review

📝 Coding Plan

• Generate coding plan for human review comments

---

Thanks for using CodeRabbit! It's free for OSS, and your support helps us grow. If you like it, consider giving us a shout-out.

❤️ Share

• X
• Mastodon
• Reddit
• LinkedIn

_{Comment @coderabbitai help to get the list of available commands and usage tips.}

[codspeed-hq]

Merging this PR will improve performance by 38.81%

⚠️ Different runtime environments detected

Some benchmarks with significant performance changes were compared across different runtime environments,
which may affect the accuracy of the results.

Open the report in CodSpeed to investigate

⚡ 12 improved benchmarks

Performance Changes

	Benchmark	BASE	HEAD	Efficiency
⚡	test_nodemanager_querypeers	1.5 ms	1.2 ms	+21.8%
⚡	test_schemabranch_process	1,040.4 ms	795.5 ms	+30.78%
⚡	test_get_schema	327.3 ms	251.7 ms	+30.03%
⚡	test_graphql_generate_schema	516.1 ms	371.8 ms	+38.81%
⚡	test_query_rel_many	693.2 ms	523.6 ms	+32.38%
⚡	test_query_rel_one	662 ms	501.1 ms	+32.1%
⚡	test_get_menu	246 ms	188.3 ms	+30.62%
⚡	test_query_one_model	464.1 ms	353.5 ms	+31.29%
⚡	test_base_schema_duplicate_CoreProposedChange	2.1 ms	1.7 ms	+23.66%
⚡	test_load_node_to_db_node_schema	67.1 ms	52.2 ms	+28.57%
⚡	test_schemabranch_duplicate	7.2 ms	5.5 ms	+31.28%
⚡	test_relationshipmanager_getpeer	157.4 µs	131 µs	+20.2%

---

_{Comparing sb-13032026-delete-infrahub-branch-after-merge-ifc-2336 (3462605) with sb-13032026-add-config-settings-ifc-2336 (b07039d)}

[ajtmccarty]

why does the proposed_change_id need to be None here?

[ajtmccarty]

I'm guessing that the logic here is to prevent breaking open proposed changes, but any open PCs will be unmergeable once this PC finishes merging
maybe the right thing to do in this case is to set any open PCs on this branch to closed and then allow deleting it