Fix clippy warnings

src/uucore/c_types.rs

@@ -109,7 +109,7 @@ extern {
     pub fn getgroupcount(name: *const c_char, gid: gid_t) -> int32_t;
 }
 
-pub fn get_pw_from_args(free: &Vec<String>) -> Option<c_passwd> {
+pub fn get_pw_from_args(free: &[String]) -> Option<c_passwd> {
     if free.len() == 1 {
         let username = &free[0][..];
 
@@ -219,7 +219,7 @@ pub fn group(possible_pw: Option<c_passwd>, nflag: bool) {
         Err(errno) =>
             crash!(1, "failed to get group list (errno={})", errno),
         Ok(groups) => {
-            for &g in groups.iter() {
+            for &g in &groups {
                 if nflag {
                     let group = unsafe { getgrgid(g) };
                     if !group.is_null() {

src/uucore/fs.rs

@@ -82,7 +82,7 @@ pub fn canonicalize<P: AsRef<Path>>(original: P, can_mode: CanonicalizeMode) ->
     }
 
     // Resolve the symlinks where possible
-    if parts.len() > 0 {
+    if !parts.is_empty() {
         for part in parts[..parts.len()-1].iter() {
             result.push(part);
 

src/uucore/parse_time.rs

@@ -10,7 +10,7 @@
 pub fn from_str(string: &str) -> Result<f64, String> {
     let len = string.len();
     if len == 0 {
-        return Err("empty string".to_string())
+        return Err("empty string".to_owned())
     }
     let slice = &string[..len - 1];
     let (numstr, times) = match string.chars().next_back().unwrap() {

src/uucore/signals.rs

@@ -141,7 +141,7 @@ pub fn signal_by_name_or_value(signal_name_or_value: &str) -> Option<usize> {
     if signal_name_or_value == "0" {
         return Some(0);
     }
-    for signal in ALL_SIGNALS.iter() {
+    for signal in &ALL_SIGNALS {
         let long_name = format!("SIG{}", signal.name);
         if signal.name == signal_name_or_value  || (signal_name_or_value == signal.value.to_string()) || (long_name == signal_name_or_value) {
             return Some(signal.value);