@systemfsoftware/stryker-plugins

Stop Effect Schema declarations from dragging your Stryker score below 100%.

A brand description, a _tag, a title — mutate any of them and the source changes but the behaviour does not, so no test can ever kill the mutant. Those unkillable mutants sit in your report forever, indistinguishable from real coverage gaps. This Stryker Ignore plugin removes them, so the score that remains is behaviour.

Install

pnpm add -D @systemfsoftware/stryker-plugins

In stryker.config.json:

{
  "plugins": [
    "@systemfsoftware/stryker-js-vitest-runner",
    "@systemfsoftware/stryker-js-typescript-checker",
    "@systemfsoftware/stryker-plugins"
  ],
  "ignorers": ["effect-schema-declarations"]
}

Mutants it recognizes are reported as Ignored, each carrying the reason it was safe to skip.

[!NOTE] @systemfsoftware/stryker-js-plugin-api is a peer dependency — your Stryker install provides it. effect is a direct dependency (the plugin decodes AST nodes with Schema).

What it ignores

| Declaration | Example | | --------------------------------------------------------- | ----------------------------------------------------------------- | | Brand descriptions | Symbol.for('UserId') | | TaggedClass / TaggedError tags | S.TaggedClass<A>()('Placed', {…}) | | The field schemas of those declarations | the {…} above | | optionalWith defaults | S.optionalWith(S.Number, { default: () => 0 }) | | Documentation annotations | identifier, description, title, documentation, examples | | An annotations({…}) object that is only documentation | S.annotations({ title: 'Amount' }) |

Where the line is

Every ignore is proven redundant, never merely assumed — anything a test could observe keeps its mutants.

arbitrary, pretty, equivalence, message, jsonSchema and parseIssueTitle are not documentation: each changes what the schema does, so a survivor there is a test gap to close. That is why the two annotations rules differ — a title is ignored wherever it appears, but the enclosing object is ignored only when every entry documents, since emptying an object holding an arbitrary would silently change what your property tests generate.

Contributing

Development setup and workflow: AGENTS.md.

License

Apache 2.0