fix some clippy warnings

crates/cargo-test-support/src/lib.rs

@@ -1511,7 +1511,7 @@ fn find_json_mismatch_r<'a>(
             l.values()
                 .zip(r.values())
                 .filter_map(|(l, r)| find_json_mismatch_r(l, r))
-                .nth(0)
+                .next()
         }
         (&Null, &Null) => None,
         // Magic string literal `"{...}"` acts as wildcard for any sub-JSON.

src/cargo/core/compiler/mod.rs

@@ -937,7 +937,7 @@ fn build_deps_args<'a, 'cfg>(
         cmd.arg("-Z").arg("unstable-options");
     }
 
-    return Ok(());
+    Ok(())
 }
 
 /// Generates a list of `--extern` arguments.

src/cargo/core/resolver/encode.rs

@@ -349,7 +349,7 @@ impl EncodableResolve {
         // To help fix this issue we special case here. If our lockfile only has
         // one trailing newline, not two, *and* it only has one package, then
         // this is actually the v2 format.
-        if original.ends_with("\n")
+        if original.ends_with('\n')
             && !original.ends_with("\n\n")
             && version == ResolveVersion::V1
             && g.iter().count() == 1

src/cargo/ops/cargo_compile.rs

@@ -449,7 +449,7 @@ pub fn compile_ws<'a>(
             // the target is a binary. Binary crates get their private items
             // documented by default.
             if rustdoc_document_private_items || unit.target.is_bin() {
-                let mut args = extra_args.take().unwrap_or(vec![]);
+                let mut args = extra_args.take().unwrap_or_else(|| vec![]);
                 args.push("--document-private-items".into());
                 extra_args = Some(args);
             }

src/cargo/ops/cargo_new.rs

@@ -181,7 +181,7 @@ fn check_name(name: &str, opts: &NewOptions) -> CargoResult<()> {
         )
     }
 
-    if let Some(ref c) = name.chars().nth(0) {
+    if let Some(ref c) = name.chars().next() {
         if c.is_digit(10) {
             anyhow::bail!(
                 "Package names starting with a digit cannot be used as a crate name{}",

src/cargo/ops/common_for_install_and_uninstall.rs

@@ -552,7 +552,7 @@ where
             // version range, otherwise parse it as a specific version
             let first = v
                 .chars()
-                .nth(0)
+                .next()
                 .ok_or_else(|| format_err!("no version provided for the `--vers` flag"))?;
 
             let is_req = "<>=^~".contains(first) || v.contains('*');

src/cargo/util/config/mod.rs

@@ -823,7 +823,7 @@ impl Config {
             let mut seen = HashSet::new();
             let tmp_table = self
                 .load_includes(tmp_table, &mut seen)
-                .chain_err(|| format!("failed to load --config include"))?;
+                .chain_err(|| "failed to load --config include".to_string())?;
             loaded_args
                 .merge(tmp_table, true)
                 .chain_err(|| format!("failed to merge --config argument `{}`", arg))?;
@@ -1526,7 +1526,7 @@ pub fn save_credentials(cfg: &Config, token: String, registry: Option<String>) -
             .insert("registry".into(), map.into());
     }
 
-    if let Some(_) = registry {
+    if registry.is_some() {
         if let Some(table) = toml.as_table_mut().unwrap().remove("registries") {
             let v = CV::from_toml(Definition::Path(file.path().to_path_buf()), table)?;
             value.merge(v, false)?;

src/cargo/util/cpu.rs

@@ -72,7 +72,7 @@ mod imp {
         let nice = next.nice - prev.nice;
         let system = next.system - prev.system;
         let idle = next.idle - prev.idle;
-        let iowait = next.iowait.checked_sub(prev.iowait).unwrap_or(0);
+        let iowait = next.iowait.saturating_sub(prev.iowait);
         let irq = next.irq - prev.irq;
         let softirq = next.softirq - prev.softirq;
         let steal = next.steal - prev.steal;

src/cargo/util/toml/mod.rs

@@ -635,11 +635,11 @@ impl TomlProfile {
         }
 
         if let Some(v) = &profile.inherits {
-            self.inherits = Some(v.clone());
+            self.inherits = Some(*v);
         }
 
         if let Some(v) = &profile.dir_name {
-            self.dir_name = Some(v.clone());
+            self.dir_name = Some(*v);
         }
     }
 }

tests/testsuite/build.rs

@@ -2258,7 +2258,7 @@ fn credentials_is_unreadable() {
     let stat = fs::metadata(credentials.as_path()).unwrap();
     let mut perms = stat.permissions();
     perms.set_mode(0o000);
-    fs::set_permissions(credentials, perms.clone()).unwrap();
+    fs::set_permissions(credentials, perms).unwrap();
 
     p.cargo("build").run();
 }