a few clippy fixes

crates/cfg/src/lib.rs

@@ -113,6 +113,10 @@ impl CfgDiff {
     pub fn len(&self) -> usize {
         self.enable.len() + self.disable.len()
     }
+
+    pub fn is_empty(&self) -> bool {
+        self.len() == 0
+    }
 }
 
 impl fmt::Display for CfgDiff {

crates/flycheck/src/lib.rs

@@ -297,7 +297,7 @@ impl CargoActor {
                 read_at_least_one_message = true;
 
                 // Try to deserialize a message from Cargo or Rustc.
-                let mut deserializer = serde_json::Deserializer::from_str(&line);
+                let mut deserializer = serde_json::Deserializer::from_str(line);
                 deserializer.disable_recursion_limit();
                 if let Ok(message) = JsonMessage::deserialize(&mut deserializer) {
                     match message {

crates/ide/src/goto_declaration.rs

@@ -57,7 +57,7 @@ mod tests {
             .unwrap()
             .expect("no declaration or definition found")
             .info;
-        if navs.len() == 0 {
+        if navs.is_empty() {
             panic!("unresolved reference")
         }
 

crates/ide/src/syntax_highlighting/highlight.rs

@@ -741,7 +741,7 @@ fn parents_match(mut node: NodeOrToken<SyntaxNode, SyntaxToken>, mut kinds: &[Sy
     }
 
     // Only true if we matched all expected kinds
-    kinds.len() == 0
+    kinds.is_empty()
 }
 
 #[inline]

crates/syntax/test_data/parser/fuzz-failures/0000.rs

@@ -101,7 +101,7 @@ pub /*(meh)*/ fn replace_range(mut text: String, range: TextRange, replace_with:
 }
 
 fn is_balanced(tokens: &[Token]) -> bool {
-    if tokens.len() == 0
+    if tokens.is_empty()
        || tokens.first().unwrap().kind != L_CURLY
        || tokens.last().unwrap().kind != R_CURLY {
         return false
@@ -153,7 +153,7 @@ pub /*(meh)*/ fn replace_range(mut text: String, range: TextRange, replace_with:
 }
 
 fn is_balanced(tokens: &[Token]) -> bool {
-    if tokens.len() == 0
+    if tokens.is_empty()
        || tokens.first().unwrap().kind != L_CURLY
        || tokens.last().unwrap().kind != R_CURLY {
         return false