Module mutation 

Mutation testing for Rust (unit mutation --language rust, #201) — the rung above coverage. A test that runs a line still passes if you delete its assertions; a surviving mutant proves it. This module wraps cargo-mutants: it runs the engine, reads its outcomes.json, and reports the surviving mutants the suite failed to catch.

The gate is binary, not a percentage (equivalent mutants make a fixed score unreachable, and a score isn’t comparable across engines) and on by default: any un-exempted surviving mutant is a finding. This module stays a pure measurement — measure_rust returns the survivors and unexplained_survivors is the pure core over a parsed report; the CLI layer turns a non-empty result into the failure.

Diff-scoping (--base) is delegated to cargo-mutants’ own --in-diff: the <base>...HEAD diff is written out and passed through, so only mutants on changed lines are tested (“no unexplained surviving mutant on the lines you touched”).

Structs

CosmicRayLine

One line of cosmic-ray dump output: a [work_item, result] pair. The result is absent (null) for an un-executed work item.

CrMutation

One mutation, pared to the location + operator the rule reads. cosmic-ray also carries occurrence, end_pos, operator_args; those are ignored.

CrResult

A work item’s result; only the test outcome is read (survived / killed / incompetent).

CrWorkItem

A cosmic-ray work item, pared to its one mutation’s location. (cosmic-ray models a list of mutations per item, but the operators here produce one apiece.)

LineCol

A line/column position; only the line is read.

MutantInfo

The mutant a scenario describes, pared to the location + description the report needs. cargo-mutants also carries function, genre, package, replacement; those are ignored.

MutantOutcome

One scenario’s outcome. summary is cargo-mutants’ result word — Success for the unmutated baseline, CaughtMutant / MissedMutant (and Timeout / Unviable) for each mutant.

MutantsReport

A cargo-mutants outcomes.json export, pared to what the rule reads. Unmodeled fields (total_mutants, caught, timings, …) are ignored.

Span

A source span; only the start line is read.

StrykerFile

One file’s mutants in a Stryker report.

StrykerLocation

A mutant’s source location; only the start line is read (reusing LineCol, whose extra column field Stryker also provides and serde ignores).

StrykerMutant

One mutant, pared to the location + status + description the rule needs. Stryker also carries id, coveredBy, static, testsCompleted, …; those are ignored.

StrykerReport

A Stryker mutation.json report (the mutation-testing-elements schema), pared to the fields the rule reads. Unmodeled keys (schemaVersion, thresholds, source, testFiles, projectRoot, config, …) are ignored.

Survivor

A surviving mutant — a mutation the unit suite ran but failed to catch.

Enums

Scenario

The scenario a result came from: the unmutated baseline, or one mutant. Matches cargo-mutants’ externally-tagged JSON ("Baseline" vs {"Mutant": {…}}).

Functions

evaluate

The shared evaluation core both engines feed: drop the survivors lifted by a mutation exemption (a file-path match), leaving the rule’s findings. Each engine produces the raw survivor list its own way (unexplained_survivors from a cargo-mutants report, stryker_survivors from a Stryker report); this applies the reason-required exemptions identically across languages.

measure_python

Run cosmic-ray over the Python project at root and return its un-exempted survivors — the Python arm of the mutation rule (#203), parity with measure_rust and measure_typescript.

measure_rust

Run cargo-mutants over the crate at root and return its un-exempted survivors.

measure_typescript

Run Stryker over the TypeScript project at root and return its un-exempted survivors — the TS arm of the mutation rule (#202), parity with measure_rust.

parse_cosmic_ray_dump

Parse cosmic-ray dump output (JSON Lines) into the surviving mutants — the raw list before exemptions.

parse_mutants_report

Parse a cargo-mutants outcomes.json export.

parse_stryker_report

Parse a Stryker mutation.json report.

stryker_survivors

The surviving mutants in a Stryker report — the raw list before exemptions.

unexplained_survivors

The surviving mutants not lifted by a mutation exemption — the rule’s findings.