Support --list --json --diff

Keys within --list --json elements are now sorted.

NEWS.md

@@ -23,6 +23,9 @@
 - Mutate `(A, B, C, ...)` into the product of all replacements for
   `a, b, c, ...`
 
+- The combination of options `--list --diff --json` is now supported, and emits
+  a `diff` key in the JSON.
+
 ## 23.9.0
 
 - Fixed a bug causing an assertion failure when cargo-mutants was run from a

book/src/list.md

@@ -8,4 +8,3 @@
 (The same format is written to `mutants.out/mutants.json` when running tests.)
 
 `--check`: Run `cargo check` on all generated mutants to find out which ones are viable, but don't actually run the tests. (This is primarily useful when debugging cargo-mutants.)
-

src/list.rs

@@ -5,7 +5,6 @@
 use std::fmt;
 use std::io;
 
-use anyhow::bail;
 use camino::Utf8Path;
 use serde_json::{json, Value};
 
@@ -36,11 +35,17 @@ pub(crate) fn list_mutants<W: fmt::Write>(
 ) -> Result<()> {
     let discovered = walk_tree(tool, source_tree_root, options)?;
     if options.emit_json {
-        if options.emit_diffs {
-            // TODO: Include diffs in json.
-            bail!("--list --diff --json is not (yet) supported");
+        let mut list: Vec<serde_json::Value> = Vec::new();
+        for mutant in discovered.mutants {
+            let mut obj = serde_json::to_value(&mutant)?;
+            if options.emit_diffs {
+                obj.as_object_mut()
+                    .unwrap()
+                    .insert("diff".to_owned(), json!(mutant.diff()));
+            }
+            list.push(obj);
         }
-        out.write_str(&serde_json::to_string_pretty(&discovered.mutants)?)?;
+        out.write_str(&serde_json::to_string_pretty(&list)?)?;
     } else {
         for mutant in &discovered.mutants {
             if options.colors {

tests/cli/main.rs

@@ -147,15 +147,28 @@ fn uses_cargo_env_var_to_run_cargo_so_invalid_value_fails() {
 }
 
 #[test]
-fn list_diff_json_not_yet_supported() {
-    run()
-        .args(["mutants", "--list", "--json", "--diff"])
+fn list_diff_json_contains_diffs() {
+    let cmd = run()
+        .args([
+            "mutants",
+            "--list",
+            "--json",
+            "--diff",
+            "-d",
+            "testdata/tree/factorial",
+        ])
         .assert()
-        .code(1)
-        .stderr(predicates::str::contains(
-            "Error: --list --diff --json is not (yet) supported\n",
-        ))
-        .stdout("");
+        .success(); // needed for lifetime
+    let out = cmd.get_output();
+    assert_eq!(String::from_utf8_lossy(&out.stderr), "");
+    println!("{}", String::from_utf8_lossy(&out.stdout));
+    let out_json = serde_json::from_slice::<serde_json::Value>(&out.stdout).unwrap();
+    let mutants_json = out_json.as_array().expect("json output is array");
+    assert_eq!(mutants_json.len(), 3);
+    assert!(mutants_json.iter().all(|e| e.as_object().unwrap()["diff"]
+        .as_str()
+        .unwrap()
+        .contains("--- src/bin/factorial.rs")));
 }
 
 /// Return paths to all testdata trees, in order, excluding leftover git