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Rust edition

Events

mutastic run --format=jsonl writes one JSON object per line: the mutastic.events/v1 stream. It’s the format the Java edition writes, described by one JSON Schema for both editions, so a tool, a CI step or a coding agent’s plugin reads either edition the same way.

Each event has schema (mutastic.events/v1), edition (rust, where the Java edition writes java), and reason, which says which event it is:

reasonWhen
run-startedFirst, once the build is done
mutant-finishedFor each mutant
run-finishedLast: the totals, the score and the verdict
next-itemFrom mutastic next: each item shown, its lead mutant as mutant-finished has it, with ids and rank. See Working through misses
next-finishedLast, from mutastic next: how many lines and mutants are queued, shown, and waiting on a person

This is the pricing fixture’s whole stream:

Terminal window
{"schema":"mutastic.events/v1","edition":"rust","reason":"run-started","project":"pricing","rule":"add or change tests only; never change production code to make a mutant go away: tell the person","decline":"if a mutant's case can't happen in practice, or the change is one no caller can see, don't contrive a test: propose ignoring it, for a person to accept, as the kind it is (equivalent, unreachable, telemetry, deprecated or accepted-risk), with the reason in two sentences: the one case where it differs, and why that can't happen","profile":{"name":"mutastic","optLevel":"0","overflowChecks":true,"debugAssertions":true},"unsafe":"skip"}
{"schema":"mutastic.events/v1","edition":"rust","reason":"mutant-finished","id":"mc9e13290","fingerprint":"c9e13290e7d1ce44","status":"Killed","operator":"mutastic/return-value","docs":"https://docs.mutastic.io/rust/operators/returns/#return-value","location":{"file":"src/lib.rs","line":29,"column":9,"class":"Pricing","method":"discount"},"mutation":{"replacement":"1","description":"returns `1` instead","applied":{"level":"source","text":"0 -> 1"}},"coveredBy":["tests::small_orders_pay_full_price"],"caughtBy":"tests::small_orders_pay_full_price","caughtWith":"panic","inputs":{"total":[50]},"testsRun":1,"durationMs":1}
{"schema":"mutastic.events/v1","edition":"rust","reason":"mutant-finished","id":"mb2f8ae57","fingerprint":"b2f8ae57ca6c48cb","status":"Survived","operator":"mutastic/boundary","docs":"https://docs.mutastic.io/rust/operators/conditions/#boundary","location":{"file":"src/lib.rs","line":26,"column":18,"class":"Pricing","method":"discount"},"mutation":{"original":">=","replacement":">","description":"`>=` becomes `>`","applied":{"level":"source","text":"total >= 100 -> (total) > (100)"}},"coveredBy":["tests::small_orders_pay_full_price","pricing::big_orders_get_ten_percent_off"],"inputs":{"total":[50,250]},"testsRun":2,"durationMs":4,"doneWhen":"mutastic verify mb2f8ae57 fixtures/pricing passes","reproduce":"mutastic run --only=mb2f8ae57 fixtures/pricing","ignore":"mutastic ignore mb2f8ae57 --reason=\"<why>\" fixtures/pricing","propose":"mutastic ignore mb2f8ae57 --propose --as=<equivalent|unreachable|…> --reason=\"Differs only when <case>. That can't happen because <why>.\" fixtures/pricing","suggestedTest":{"testClass":"tests","name":"discount_at_the_total_edge","code":"#[test]\nfn discount_at_the_total_edge() {\n    assert_eq!(Pricing::new().discount(100), 10); // today 10 · with this mutant 0\n}","call":"Pricing::new().discount(100)","today":"10","withMutant":"0"},"suggestion":{"call":"Pricing::new().discount(100)","parameters":["total"],"arguments":[100],"receiver":[{"type":"Pricing","arguments":[]}],"today":"10","withMutant":"0"},"rendered":"missed mb2f8ae57: no test checks `discount()` at `total == 100`\n   at src/lib.rs:26\n   - if total >= 100 {\n   + if total > 100 {\n   covered by: tests::small_orders_pay_full_price, pricing::big_orders_get_ten_percent_off; all still pass with the change\n   evidence: every test calls `discount()` away from the boundary\n   evidence: inputs seen: 50, 250 (none is 100)\n   fix: test `discount()` with `total = 100` and assert the result\n   test to add in mod tests:\n     #[test]\n     fn discount_at_the_total_edge() {\n         assert_eq!(Pricing::new().discount(100), 10); // today 10 · with this mutant 0\n     }\n     // check today's value is the one you intend: the test pins what the code does now\n   done when: mutastic verify mb2f8ae57 fixtures/pricing passes\n   reproduce: mutastic run --only=mb2f8ae57 fixtures/pricing\n   or propose: mutastic ignore mb2f8ae57 --propose --as=<equivalent|unreachable|…> --reason=\"Differs only when <case>. That can't happen because <why>.\" fixtures/pricing\n"}
{"schema":"mutastic.events/v1","edition":"rust","reason":"mutant-finished","id":"md56e8c39","fingerprint":"d56e8c3934d92f41","status":"Killed","operator":"mutastic/remove-conditional","docs":"https://docs.mutastic.io/rust/operators/conditions/#remove-conditional","location":{"file":"src/lib.rs","line":26,"column":12,"class":"Pricing","method":"discount"},"mutation":{"replacement":"true","description":"`total >= 100` is always true","applied":{"level":"source","text":"total >= 100 -> true"}},"coveredBy":["tests::small_orders_pay_full_price","pricing::big_orders_get_ten_percent_off"],"caughtBy":"tests::small_orders_pay_full_price","caughtWith":"panic","inputs":{"total":[50,250]},"testsRun":1,"durationMs":2}
{"schema":"mutastic.events/v1","edition":"rust","reason":"mutant-finished","id":"m1636f6d5","fingerprint":"1636f6d59be655d5","status":"Killed","operator":"mutastic/remove-conditional","docs":"https://docs.mutastic.io/rust/operators/conditions/#remove-conditional","location":{"file":"src/lib.rs","line":26,"column":12,"class":"Pricing","method":"discount"},"mutation":{"replacement":"false","description":"`total >= 100` is always false","applied":{"level":"source","text":"total >= 100 -> false"}},"coveredBy":["tests::small_orders_pay_full_price","pricing::big_orders_get_ten_percent_off"],"caughtBy":"pricing::big_orders_get_ten_percent_off","caughtWith":"panic","inputs":{"total":[50,250]},"testsRun":2,"durationMs":4}
{"schema":"mutastic.events/v1","edition":"rust","reason":"mutant-finished","id":"m6d05659f","fingerprint":"6d05659f42679c6c","status":"Killed","operator":"mutastic/return-value","docs":"https://docs.mutastic.io/rust/operators/returns/#return-value","location":{"file":"src/lib.rs","line":27,"column":20,"class":"Pricing","method":"discount"},"mutation":{"replacement":"0","description":"returns `0` instead","applied":{"level":"source","text":"total / 10 -> 0"}},"coveredBy":["pricing::big_orders_get_ten_percent_off"],"caughtBy":"pricing::big_orders_get_ten_percent_off","caughtWith":"panic","inputs":{"total":[250]},"testsRun":1,"durationMs":2}
{"schema":"mutastic.events/v1","edition":"rust","reason":"mutant-finished","id":"m95f96847","fingerprint":"95f96847248b0509","status":"Killed","operator":"mutastic/math","docs":"https://docs.mutastic.io/rust/operators/arithmetic/#math","location":{"file":"src/lib.rs","line":27,"column":26,"class":"Pricing","method":"discount"},"mutation":{"original":"/","replacement":"*","description":"`/` becomes `*`","applied":{"level":"source","text":"total / 10 -> (total) * (10)"}},"coveredBy":["pricing::big_orders_get_ten_percent_off"],"caughtBy":"pricing::big_orders_get_ten_percent_off","caughtWith":"panic","inputs":{"total":[250]},"testsRun":1,"durationMs":2}
{"schema":"mutastic.events/v1","edition":"rust","reason":"mutant-finished","id":"m383e0002","fingerprint":"383e0002195614c2","status":"Killed","operator":"mutastic/return-value","docs":"https://docs.mutastic.io/rust/operators/returns/#return-value","location":{"file":"src/lib.rs","line":37,"column":9,"class":"Pricing","method":"shipping"},"mutation":{"replacement":"1","description":"returns `1` instead","applied":{"level":"source","text":"0 -> 1"}},"coveredBy":["tests::shipping_is_free_from_the_threshold"],"caughtBy":"tests::shipping_is_free_from_the_threshold","caughtWith":"panic","inputs":{"total":[39,40]},"testsRun":1,"durationMs":2}
{"schema":"mutastic.events/v1","edition":"rust","reason":"mutant-finished","id":"m7d92063c","fingerprint":"7d92063c80e7deae","status":"Killed","operator":"mutastic/boundary","docs":"https://docs.mutastic.io/rust/operators/conditions/#boundary","location":{"file":"src/lib.rs","line":34,"column":18,"class":"Pricing","method":"shipping"},"mutation":{"original":"<","replacement":"<=","description":"`<` becomes `<=`","applied":{"level":"source","text":"total < self.free_shipping_from -> (total) <= (self.free_shipping_from)"}},"coveredBy":["tests::shipping_is_free_from_the_threshold"],"caughtBy":"tests::shipping_is_free_from_the_threshold","caughtWith":"panic","inputs":{"total":[39,40]},"testsRun":1,"durationMs":2}
{"schema":"mutastic.events/v1","edition":"rust","reason":"mutant-finished","id":"m3be6b420","fingerprint":"3be6b420676ea8f8","status":"Killed","operator":"mutastic/remove-conditional","docs":"https://docs.mutastic.io/rust/operators/conditions/#remove-conditional","location":{"file":"src/lib.rs","line":34,"column":12,"class":"Pricing","method":"shipping"},"mutation":{"replacement":"true","description":"`total < self.free_shipping_from` is always true","applied":{"level":"source","text":"total < self.free_shipping_from -> true"}},"coveredBy":["tests::shipping_is_free_from_the_threshold"],"caughtBy":"tests::shipping_is_free_from_the_threshold","caughtWith":"panic","inputs":{"total":[39,40]},"testsRun":1,"durationMs":2}
{"schema":"mutastic.events/v1","edition":"rust","reason":"mutant-finished","id":"m89be540d","fingerprint":"89be540de2153650","status":"Killed","operator":"mutastic/remove-conditional","docs":"https://docs.mutastic.io/rust/operators/conditions/#remove-conditional","location":{"file":"src/lib.rs","line":34,"column":12,"class":"Pricing","method":"shipping"},"mutation":{"replacement":"false","description":"`total < self.free_shipping_from` is always false","applied":{"level":"source","text":"total < self.free_shipping_from -> false"}},"coveredBy":["tests::shipping_is_free_from_the_threshold"],"caughtBy":"tests::shipping_is_free_from_the_threshold","caughtWith":"panic","inputs":{"total":[39,40]},"testsRun":1,"durationMs":2}
{"schema":"mutastic.events/v1","edition":"rust","reason":"mutant-finished","id":"mbddcd9c4","fingerprint":"bddcd9c42b757c41","status":"Killed","operator":"mutastic/return-value","docs":"https://docs.mutastic.io/rust/operators/returns/#return-value","location":{"file":"src/lib.rs","line":35,"column":20,"class":"Pricing","method":"shipping"},"mutation":{"replacement":"0","description":"returns `0` instead","applied":{"level":"source","text":"5 -> 0"}},"coveredBy":["tests::shipping_is_free_from_the_threshold"],"caughtBy":"tests::shipping_is_free_from_the_threshold","caughtWith":"panic","inputs":{"total":[39,40]},"testsRun":1,"durationMs":2}
{"schema":"mutastic.events/v1","edition":"rust","reason":"run-finished","toolchain":{"name":"rustc","version":"1.99.1"},"mutants":11,"killed":10,"survived":1,"timeout":0,"noCoverage":0,"ignored":0,"runtimeError":0,"notMutated":{"unsafe":0,"cfg":0},"score":90.9,"threshold":80,"passed":true,"coveredScore":90.9,"tests":3,"workers":4,"workersStarted":4,"coverageMs":4,"flaky":[],"flakyEvidence":[],"likelyFlaky":[],"unrelatedCatches":[],"reports":["target/mutastic/mutation.json","target/mutastic/mutation.html"],"staleIgnores":[],"build":{"rounds":2,"unviable":0,"setupMs":49},"durationMs":85}

Read what you know and let the rest pass: ignore a field you don’t know, and an event whose reason you don’t know, and treat a status you don’t know as neither caught nor missed. Any release may add a field, an event or a value.

What the Rust edition adds

Section titled “What the Rust edition adds”

Every field the schema requires is there, with the schema’s meaning. A few say what only Rust has; the schema names each as the Rust edition’s, and a reader written for the Java edition passes over them.

EventFieldMeans
every eventeditionrust. The schema asks the Java edition’s own field, run-finished’s jdk, only of events whose edition is java
run-startedprofileHow mutastic’s build was made: name, optLevel, overflowChecks, debugAssertions, as Cargo reports them. See Profiles
run-startedunsafeskip, enclosing or all: how unsafe code was treated
mutant-finishedstatus: "RuntimeError"Crashed where a crash proves nothing; out of the score. See Unsafe code
mutant-finishednearUnsafeWhy the mutant is near unsafe code: called from unsafe code, in a module with unsafe code, and, with --unsafe, in a function with an unsafe block or inside unsafe code
mutant-finishedcaughtWithHow the test failed: panic, panic: attempt to subtract with overflow for a panic the language raised, or crash: SIGABRT when the process died and no test is named
mutant-finishedlocation.columnThe column of the change, from 1
run-finishedtoolchain{"name": "rustc", "version": …}, the compiler that built the tests, where the Java edition also writes jdk
run-finishedruntimeErrorHow many crashed where a crash proves nothing
run-finishednotMutated.unsafeHow many mutants were left out in or around unsafe code
run-finishednotMutated.cfgHow many mutants were left out because their code is under a cfg this build doesn’t have. See Troubleshooting
run-finishedbuildrounds, the builds it took, unviable, the mutants withdrawn, and setupMs, how long reading the package and building it took, before the coverage pass

A run split across CI jobs writes what the Java edition’s does, so --from-shards can put the whole run together from the shares’ events: run-started’s share says which share a run is (number, of, the mutastic version and a hash of the code, every Rust file and Cargo manifest in the workspace); a missed mutant with a suggested test carries the call it was found by, whole, in suggestion; and run-finished says how many workers ran side by side and how long the coverage pass took, coverageMs. workersStarted is the same as workers, as a Rust worker is a thread, never stopped and started again. See One run across CI jobs.

Some fields keep the Java edition’s names where Rust has other words. In location, class is the item that holds the function (pricing::Pricing, or the module for a free function), and method is the function’s name. In mutation, applied is the change as the engine makes it, and at what level: the Java edition’s is bytecode, to the instruction (IF_ICMPLT -> IF_ICMPLE); the Rust edition’s is source, the whole changed code before and after (total >= 100 -> true), which no other field gives for every kind of change. A later engine may add a level, so accept one you don’t know and read its text as opaque.

What stays the same

Section titled “What stays the same”

Before 1.0.0 the schema may change; from 1.0.0 it only gains. Within v1, a field keeps its name and its type, a field every event has stays in every event, and anything new is optional, so a reader that takes what it knows keeps working, release after release. A change that would break a reader comes only with a major release, as mutastic.events/v2. The words in some fields (rendered, rule, decline, a mutation’s description, and the commands offered with a missed mutant) are for people and agents to read, and can change from one release to the next; the field stays. Schemas and stability says exactly what counts as breaking.

Not there yet

Section titled “Not there yet”

flaky names each test that failed, then passed when run again, and flakyEvidence says what it reaches that varies, as the Java edition’s do. A Rust test fails with a panic, not a chain of exceptions, so each one’s failure is empty and outside is false. The lists the Java edition fills that the Rust edition doesn’t yet (likelyFlaky, unrelatedCatches) are there and empty.