Changed signature of cargo::metadata according to review comment.

clippy_lints/src/utils/cargo.rs

@@ -65,10 +65,10 @@ impl From<json::DecoderError> for Error {
     }
 }
 
-pub fn metadata(manifest_path_arg: &Option<String>) -> Result<Metadata, Error> {
+pub fn metadata(manifest_path_arg: Option<&str>) -> Result<Metadata, Error> {
     let mut cmd = Command::new("cargo");
     cmd.arg("metadata").arg("--no-deps");
-    if let Some(ref mani) = *manifest_path_arg {
+    if let Some(mani) = manifest_path_arg {
         cmd.arg(mani);
     }
     let output = cmd.output()?;

src/main.rs

@@ -140,7 +140,7 @@ pub fn main() {
         // this arm is executed on the initial call to `cargo clippy`
         let manifest_path_arg = std::env::args().skip(2).find(|val| val.starts_with("--manifest-path="));
 
-        let mut metadata = cargo::metadata(&manifest_path_arg).expect("could not obtain cargo metadata");
+        let mut metadata = cargo::metadata(manifest_path_arg.as_ref().map(AsRef::as_ref)).expect("could not obtain cargo metadata");
         assert_eq!(metadata.version, 1);
 
         let manifest_path = manifest_path_arg.map(|arg| PathBuf::from(Path::new(&arg["--manifest-path=".len()..])));

tests/versioncheck.rs

@@ -3,9 +3,9 @@ use clippy_lints::utils::cargo;
 
 #[test]
 fn check_that_clippy_lints_has_the_same_version_as_clippy() {
-    let clippy_meta = cargo::metadata(&None).expect("could not obtain cargo metadata");
+    let clippy_meta = cargo::metadata(None).expect("could not obtain cargo metadata");
     std::env::set_current_dir(std::env::current_dir().unwrap().join("clippy_lints")).unwrap();
-    let clippy_lints_meta = cargo::metadata(&None).expect("could not obtain cargo metadata");
+    let clippy_lints_meta = cargo::metadata(None).expect("could not obtain cargo metadata");
     assert_eq!(clippy_lints_meta.packages[0].version, clippy_meta.packages[0].version);
     for package in &clippy_meta.packages[0].dependencies {
         if package.name == "clippy_lints" {