--output creates the containing directory

NEWS.md

@@ -4,6 +4,8 @@
 
 - New: `missed.txt`, `caught.txt`, `timeout.txt` and `unviable.txt` files are written in to the output directory to make results easier to review later.
 
+- New: `--output` creates the containing directory if it does not exist.
+
 - Internal: Switched from Argh to Clap for command-line parsing. There may be some small changes in CLI behavior and help formatting.
 
 ## 1.0.0

src/output.rs

@@ -101,12 +101,18 @@ pub struct OutputDir {
 impl OutputDir {
     /// Create a new `mutants.out` output directory, within the given directory.
     ///
+    /// If `in_dir` does not exist, it's created too, so that users can name a new directory
+    /// with `--output`.
+    ///
     /// If the directory already exists, it's rotated to `mutants.out.old`. If that directory
     /// exists, it's deleted.
     ///
     /// If the directory already exists and `lock.json` exists and is locked, this waits for
     /// the lock to be released. The returned `OutputDir` holds a lock for its lifetime.
     pub fn new(in_dir: &Utf8Path) -> Result<OutputDir> {
+        if !in_dir.exists() {
+            fs::create_dir(&in_dir).context("create output parent directory {in_dir:?}")?;
+        }
         let output_dir = in_dir.join(OUTDIR_NAME);
         if output_dir.exists() {
             LockFile::acquire_lock(output_dir.as_ref())?;

tests/cli.rs

@@ -757,17 +757,21 @@ fn small_well_tested_mutants_with_cargo_arg_release() {
 }
 
 #[test]
+/// The `--output` directory creates the named directory if necessary, and then
+/// creates `mutants.out` within it. `mutants.out` is not created in the
+/// source directory in this case.
 fn output_option() {
     let tmp_src_dir = copy_of_testdata("factorial");
     let output_tmpdir = TempDir::new().unwrap();
+    let output_parent = output_tmpdir.path().join("output_parent");
     assert!(
         !tmp_src_dir.path().join("mutants.out").exists(),
         "mutants.out should not be in a clean copy of the test data"
     );
     run_assert_cmd()
         .arg("mutants")
         .arg("--output")
-        .arg(&output_tmpdir.path())
+        .arg(&output_parent)
         .args(["--check", "--no-times"])
         .arg("-d")
         .arg(&tmp_src_dir.path())
@@ -777,28 +781,19 @@ fn output_option() {
         !tmp_src_dir.path().join("mutants.out").exists(),
         "mutants.out should not be in the source directory after --output was given"
     );
-    assert!(
-        output_tmpdir.path().join("mutants.out").exists(),
-        "mutants.out is in --output directory"
-    );
-    assert!(
-        output_tmpdir
-            .path()
-            .join("mutants.out/mutants.json")
-            .is_file(),
-        "mutants.out/mutants.json is in --output directory"
-    );
-    assert!(
-        output_tmpdir
-            .path()
-            .join("mutants.out/outcomes.json")
-            .is_file(),
-        "mutants.out/outcomes.json is in --output directory"
-    );
-    assert!(
-        output_tmpdir.path().join("mutants.out/debug.log").is_file(),
-        "mutants.out/debug.log is in --output directory"
-    );
+    let mutants_out = output_parent.join("mutants.out");
+    assert!(mutants_out.exists(), "mutants.out is in --output directory");
+    for name in [
+        "mutants.json",
+        "debug.log",
+        "outcomes.json",
+        "missed.txt",
+        "caught.txt",
+        "timeout.txt",
+        "unviable.txt",
+    ] {
+        assert!(mutants_out.join(name).is_file(), "{name} is in mutants.out",);
+    }
 }
 
 #[test]