Support --target-dir

NEWS.md

@@ -2,6 +2,7 @@
 
 ## Unreleased
 
+- New: `--target-dir` sets the Cargo target directory for check, build, and test commands ([#407](https://github.com/sourcefrog/cargo-mutants/issues/407)).
 - New: `#[mutants::exclude_re("pattern")]` attribute to exclude specific mutations by regex, without disabling all mutations on the function. The attribute can be placed on functions, `impl` blocks, `trait` blocks, modules, files, and on expressions that can carry an attribute (such as `match`, struct literals, call expressions, method calls, and unary expressions). Multiple patterns can be applied. Also supported within `cfg_attr`. Requires the [mutants](https://crates.io/crates/mutants) crate version `0.0.5` or later.
 - Fixed: `#[mutants::skip]` (and `#[cfg_attr(..., mutants::skip)]`) is now honoured when placed on `const` and `static` items, including associated constants in `impl` and `trait` blocks. Previously the attribute was silently ignored on these items and operator mutants inside the initializer expression were still generated ([#508](https://github.com/sourcefrog/cargo-mutants/issues/508)).
 

book/src/cargo-args.md

@@ -27,6 +27,20 @@ no_default_features = true
 
 When both command line and config options are specified, the command line flags take precedence for boolean options (`all_features` and `no_default_features`), while features from both sources are combined.
 
+## Target directory
+
+Use `--target-dir` to set the Cargo target directory for every check, build, and test invocation:
+
+```shell
+cargo mutants --target-dir target/mutants
+```
+
+The path is passed to Cargo unchanged. The equivalent configuration-file form is:
+
+```toml
+additional_cargo_args = ["--target-dir=target/mutants"]
+```
+
 ## Arguments to all `cargo` commands
 
 To pass more arguments to every Cargo invocation, use `--cargo-arg`, or the `additional_cargo_args` configuration key.

src/cargo.rs

@@ -135,6 +135,9 @@ fn cargo_argv(packages: &PackageSelection, phase: Phase, options: &Options) -> V
             }
         }
     }
+    if let Some(target_dir) = &options.target_dir {
+        cargo_args.push(format!("--target-dir={target_dir}"));
+    }
     cargo_args.push("--verbose".to_string());
     match packages {
         PackageSelection::All => {
@@ -365,6 +368,41 @@ mod test {
         );
     }
 
+    #[test]
+    fn target_dir_is_passed_to_all_cargo_commands() {
+        let options = Options::from_arg_strs(["mutants", "--target-dir", "target/mutants"]);
+
+        assert_eq!(
+            cargo_argv(&PackageSelection::All, Phase::Check, &options)[1..],
+            [
+                "check",
+                "--tests",
+                "--target-dir=target/mutants",
+                "--verbose",
+                "--workspace",
+            ]
+        );
+        assert_eq!(
+            cargo_argv(&PackageSelection::All, Phase::Build, &options)[1..],
+            [
+                "test",
+                "--no-run",
+                "--target-dir=target/mutants",
+                "--verbose",
+                "--workspace",
+            ]
+        );
+        assert_eq!(
+            cargo_argv(&PackageSelection::All, Phase::Test, &options)[1..],
+            [
+                "test",
+                "--target-dir=target/mutants",
+                "--verbose",
+                "--workspace",
+            ]
+        );
+    }
+
     #[test]
     fn nextest_gets_special_cargo_profile_option() {
         let args = Args::try_parse_from(

src/main.rs

@@ -148,6 +148,10 @@ pub struct Args {
     #[arg(long, help_heading = "Build")]
     profile: Option<String>,
 
+    /// Directory for all generated Cargo artifacts.
+    #[arg(long, help_heading = "Build", value_name = "DIRECTORY")]
+    target_dir: Option<Utf8PathBuf>,
+
     // Config ============================================================
     /// Read configuration from this file instead of .cargo/mutants.toml.
     #[arg(

src/options.rs

@@ -122,6 +122,9 @@ pub struct Options {
     /// Cargo profile.
     pub profile: Option<String>,
 
+    /// Directory for Cargo build artifacts.
+    pub target_dir: Option<Utf8PathBuf>,
+
     /// Additional arguments for every cargo invocation.
     pub additional_cargo_args: Vec<String>,
 
@@ -384,6 +387,7 @@ impl Options {
             test_package,
             test_timeout: args.timeout.map(Duration::from_secs_f64),
             test_timeout_multiplier: args.timeout_multiplier.or(config.timeout_multiplier),
+            target_dir: args.target_dir.clone(),
         };
         if let Some(jobs) = options.jobs
             && jobs > 8