Add tests for active-repositories feature

[erikd]

This PR only contains tests, which were generated by Claude code, and then manually reviewed. Unfortunately I have not worked much on Cabal so my manual review may not be up-to-scratch.

This PR was submitted in preparation for taking over the work in #8997 and getting it merged. One of the things mentioned in that PR was that need for tests for the active-repositories feature.

Include the following checklist in your PR:

• Patches conform to the coding conventions.
• Is this a PR that fixes CI? If so, it will need to be backported to older cabal release branches (ask maintainers for directions).

[erikd]

I asked Claude to give me an idea of the test coverage. Its response:

The top commit (6898e42) captures the IndexUtils/ActiveRepos.hs and the index-combining
tests we added to IndexUtils.hs.

So the breakdown for what this commit actually adds vs the total feature:

Layer	Coverage
Layer 1	~80%
Layer 2	~65%
Layer 3	~58%
Layer 4	~30%
Layer 5	~0%

Where:

• Layer 1 — pure logic (ActiveRepos.hs)
• Layer 2 — project config parsing (pre-existing tests only, nothing new in this PR)
• Layer 3 — index combining (IndexUtils.hs) (all 14 combining tests are in this PR)
• Layer 4 — freeze file (filterSkippedActiveRepos unit tests in this PR)
• Layer 5 — solver/planning wiring

[andreabedini]

I left a couple of comments but otherwise LGTM.

Not a deal breaker but any chance you can add a simple test for this edge case behaviour?

-- Note: currently if 'ActiveRepoRest' is provided more than once,
-- rest-repositories will be multiple times in the output.

[andreabedini]

A changelog file is missing, here is a suggestion:

---
synopsis: Add unit tests for active-repositories feature
packages: [cabal-install]
prs: 11684
---

Add unit tests for the `active-repositories` cabal configuration field:

- `organizeByRepos`: ordering and strategy assignment with `:rest`, named repos, and error cases
- `filterSkippedActiveRepos`: filtering of skipped entries in the absence of `:rest`
- `CombineStrategy` index-combining logic (Skip/Merge/Override)
- Parse/pretty roundtrip for `ActiveRepos` (QuickCheck)

[andreasabel]

I am afraid I do not even know what the active-repositories feature is, so I cannot judge this PR.
However, when it comes to tests: the more, the merrier!

[erikd]

The documentation for this feature is at: https://cabal.readthedocs.io/en/latest/cabal-project-description-file.html#cfg-field-active-repositories

[angerman]

The applyStrategy refactor is much more readable imo, great!

Thank you @erikd for working on this!

[angerman]

@Mergifyio queue

[mergify]

Merge Queue Status

• ✅ Entered queue — 2026-04-20 06:53 UTC · Rule: default
• ✅ Checks skipped · PR is already up-to-date
• ✅ Merged — 2026-04-20 07:03 UTC · at da8b314563feb15a3df7bc1baeef4b7aa08f7578 · merge

This pull request spent 10 minutes 33 seconds in the queue, including 1 second running CI.

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