build(rust): vendor rnix parser crate

third_party/crates/rowan-0.16.1/tests/tidy.rs

@@ -0,0 +1,46 @@
+use std::{
+    env,
+    path::{Path, PathBuf},
+    process::{Command, Stdio},
+};
+
+fn project_root() -> PathBuf {
+    PathBuf::from(
+        env::var("CARGO_MANIFEST_DIR").unwrap_or_else(|_| env!("CARGO_MANIFEST_DIR").to_owned()),
+    )
+}
+
+fn run(cmd: &str, dir: impl AsRef<Path>) -> Result<(), ()> {
+    let mut args: Vec<_> = cmd.split_whitespace().collect();
+    let bin = args.remove(0);
+    println!("> {}", cmd);
+    let output = Command::new(bin)
+        .args(args)
+        .current_dir(dir)
+        .stdin(Stdio::null())
+        .stdout(Stdio::piped())
+        .stderr(Stdio::inherit())
+        .output()
+        .map_err(drop)?;
+    if output.status.success() {
+        Ok(())
+    } else {
+        let stdout = String::from_utf8(output.stdout).map_err(drop)?;
+        print!("{}", stdout);
+        Err(())
+    }
+}
+
+#[test]
+fn check_code_formatting() {
+    let dir = project_root();
+    if run("rustfmt +stable --version", &dir).is_err() {
+        panic!(
+            "failed to run rustfmt from toolchain 'stable'; \
+             please run `rustup component add rustfmt --toolchain stable` to install it.",
+        );
+    }
+    if run("cargo +stable fmt -- --check", &dir).is_err() {
+        panic!("code is not properly formatted; please format the code by running `cargo fmt`")
+    }
+}