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ci: nvx-rs mutants' summarize miscounts the shards when one artifact downloads

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Assessment

Difficulty
3/5
Estimated time
1-2 days
Newbie friendliness
76/100
Issue type
Bug
Clarity
Clearly specified
Activity status
Active
Tech stack
github-actions, rust, shell, yaml
Domain
ci-cd, devops

Research direction

Start with .github/workflows/nvx-rs-mutants.yml, especially the shard upload and summarize steps around lines 175–254, and review the linked actions/download-artifact behavior described in the issue. Check how shard indices and outcomes.json are handled when one artifact is downloaded or a shard uploads nothing. Done when summarize fails if either of two shards uploads nothing and succeeds with shards: 1, merging that shard’s outcomes.

Written by the indexing model from the issue text.

Description

Related: #726, for which 431cae05 added the workflow. Needs: nothing.

Goal. The summarize job of nvx-rs mutants passes only when every shard reported its outcomes, and then merges them all, whatever the number of shards.

Today (dev d1946233):

  • summarize counts directories. It downloads the shards' artifacts with actions/download-artifact@v8, with pattern: nvx-rs-mutants-shard-*-<run ID> and path: shards (#L195-L199). It then takes each directory shards/*/ for a shard, merges their caught.txt, missed.txt, timeout.txt and unviable.txt (#L211-L225), and fails unless it counted SHARDS of them (#L251-L254).
  • A lone artifact lands in shards/ itself. download-artifact gives each artifact a directory of its own only when several match, and extracts a lone one into path (download-artifact.ts#L185-L195, at the commit that @v8 resolved to). A shard's artifact, cargo-mutants' mutants.out, holds two directories, diff/ and log/.
  • So, with one artifact, summarize counts 2 shards, however many reported. It finds no outcome list in diff/ or log/, and uploads empty lists as nvx-rs-mutants-<run ID>. With 2 shards, as every push that changes the workflow runs (#L85-L88), the count check passes. With shards: 1, it always fails; none of the 18 dispatches so far used one shard.
  • A shard that fails early uploads nothing. Its upload needs outcomes.json (#L175-L184), and summarize runs whatever the shards' results (#L186-L189).
  • The summarize job dates from 431cae05. b2572d40 and 10035afd last changed the workflow, in its descriptions only.

Evidence: run 40441338923, a push of 4a8b5341.

  • Attempt 1: shard 1 failed in "Install Rust and cargo-mutants" (failed to download from https://index.crates.io/config.json, a connection timeout), and uploaded nothing. summarize logged Found 1 artifact(s) and Starting download of artifact to: /home/runner/work/nvx/nvx/shards, passed, and uploaded 484 bytes of empty lists. Shard 0's artifact lists 14 caught mutants and 1 unviable one.
  • Attempt 2 reran shard 1, and summarize merged both shards: 24 caught, 0 missed, 6 unviable.

Scope (one PR), for example:

  • Give each shard a directory that doesn't depend on the number of artifacts: for example, upload each shard's outcomes under a directory named for its index, and download them with merge-multiple: true, so that every shard lands in shards/<index>/.
  • Check each expected shard by its index, and count the shards by their outcomes.json, not by directories.
  • Fail summarize when a shard job didn't succeed (needs.mutants.result), besides counting.

Done when: summarize fails when one of two shards uploads nothing, and passes a dispatch with shards: 1, with that shard's outcomes merged.

Dominant language
Rust
Stars
758
Forks
48
Avg merge
18h 37m
Merged PRs (30d)
398

Getting set up

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First steps

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  3. Fork the repository and make your change on a branch.
  4. Open a pull request that references the issue number.

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