Add cargo_mutants_version field to outcomes.json (#562)

Author: Copilot

NEWS.md

@@ -10,6 +10,8 @@
 
 - New: `start_time` and `end_time` fields in `outcomes.json`.
 
+- New: `cargo_mutants_version` field in `outcomes.json`.
+
 - Changed: Functions with attributes whose path ends with `test` are now skipped, not just those with the plain `#[test]` attribute. This means functions with `#[tokio::test]`, `#[sqlx::test]`, and similar testing framework attributes are automatically excluded from mutation testing.
 
 - Changed: The bitwise assignment operators `&=` and `|=` are no longer mutated to `^=`. In code that accumulates bits into a bitmap starting from zero (e.g., `bitmap |= new_bits`), `|=` and `^=` produce the same result, making such mutations uninformative.

book/src/mutants-out.md

@@ -18,7 +18,7 @@ The output directory contains:
   This file is completely written before testing begins.
 
 * An `outcomes.json` file describing the results of all tests,
-  and summary counts of each outcome.
+  summary counts of each outcome, and the cargo-mutants version.
 
 * A `diff/` directory, containing a diff file for each mutation, relative to the unmutated baseline.
   `mutants.json` includes for each mutant the name of the diff file.

src/outcome.rs

@@ -67,6 +67,7 @@ pub struct LabOutcome {
     pub success: usize,
     pub start_time: Timestamp,
     pub end_time: Option<Timestamp>,
+    pub cargo_mutants_version: String,
 }
 
 impl LabOutcome {
@@ -81,6 +82,7 @@ impl LabOutcome {
             success: 0,
             start_time,
             end_time: None,
+            cargo_mutants_version: crate::VERSION.to_string(),
         }
     }
 

tests/main.rs

@@ -241,6 +241,15 @@ fn small_well_tested_tree_is_clean() {
     let end_time: Timestamp = end_time.as_str().unwrap().parse().unwrap();
     assert!(end_time >= start_time);
     assert!(end_time <= Timestamp::now());
+
+    // Verify cargo_mutants_version field exists
+    let version = outcomes["cargo_mutants_version"]
+        .as_str()
+        .expect("cargo_mutants_version should be present and be a string");
+    assert!(
+        version.contains('.'),
+        "cargo_mutants_version should look like a version"
+    );
 }
 
 #[test]

tests/util/mod.rs

@@ -159,5 +159,6 @@ pub fn outcome_json_counts(tmp_src_dir: &TempDir) -> serde_json::Value {
     outcomes_object.remove("outcomes").unwrap();
     outcomes_object.remove("end_time").unwrap();
     outcomes_object.remove("start_time").unwrap();
+    outcomes_object.remove("cargo_mutants_version").unwrap();
     outcomes
 }