werkator/docs/prs/2026-10-05-PR#125-artifact-prune-split.md

PR#125: Artifact Store Pruning Split into Its Steps

WARNING: This document describes only the change applied in this PR. It may already be outdated once the next PR is merged. Historic PR-documentation is not maintained along with new PRs — treat it as a snapshot, not as current documentation.

The Problem

FileArtifactStore.prune is above the Kotlin target of 15, measured by the nightly mutation build of 2026-10-05:

Method	Mutation-CRAP	Complexity	Mutation score
FileArtifactStore.prune	23.50	7	0.30

Most of its complexity and most of its 23 mutants were not its own. lock.write and use are inline functions, so their code is compiled into prune:

• lock.write gives back every read hold before it takes the write lock, and takes them again afterwards, for a caller that upgrades from the read lock; a prune never holds it, so those loops never run and no test can tell their mutants apart;
• use carries the closing of the stream with its exception handling.

The few mutants that were its own — the journal line and its condition — no test looked at.

Non-Goals

• No change in behaviour: the same directories are deleted under the same lock, with the same journal line.
• No change to persist, which takes the read lock as before.

The Scenarios

Feature: pruning removes what no result keeps, and says so

Scenario#125.01: prune says in the journal what it removed, and is silent when nothing goes

So that the journal tells which artifacts went, without a line for every poll that removed nothing.

• Given an artifact directory with nested reports that no kept result references
• When the store is pruned
• Then the directory is deleted with everything in it, and its key is returned
  • and the journal says pruned 1 artifact dir(s): [<key>]
• When the store is pruned again
• Then nothing is returned and the journal says nothing
• When the store never persisted anything
• Then a prune removes nothing and creates no branches directory

Verified by

• FileArtifactStoreUnitTest prune says in the journal what it removed, and is silent when nothing goes (Scenario#125.01), prune of a store that never persisted anything removes nothing and creates nothing (Scenario#125.01), and the earlier prune tests, including concurrent persists and a prune do not interfere

The Solution

prune takes the write lock itself, lock() and unlock() in finally, and hands the work to pruneUnreferenced. pruneUnreferenced lists the directory completely through childrenOf, then deletes what no kept key names, then writes the journal line. Listing first and deleting afterwards also stops deleting entries out of a directory stream that is still being read.

A local PIT run of FileArtifactStore afterwards:

Method	Mutation-CRAP	Complexity	Mutation score
FileArtifactStore.prune	1.04	1	0.67
FileArtifactStore.pruneUnreferenced	5.05	5	0.88
FileArtifactStore.childrenOf	1.30	1	0.33

The highest score left in the class is copyArtifactDirs at 5.93. The project maximum is now UiFormats.repoStatusLine at 16.03, so the gate goes down from 24 to 17.

Additional Changes

• maxMutationCrap in build.gradle.kts lowered from 24 to 17.
• Version 1.37.6 with its entry in releases.html.

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