diff --git a/src/comment.rs b/src/comment.rs
index eb9e96f2509f..31b6f25bf086 100644
--- a/src/comment.rs
+++ b/src/comment.rs
@@ -328,7 +328,7 @@ fn rewrite_comment_inner(
         while let Some(line) = iter.next() {
             result.push_str(line);
             result.push_str(match iter.peek() {
-                Some(ref next_line) if next_line.is_empty() => comment_line_separator.trim_right(),
+                Some(next_line) if next_line.is_empty() => comment_line_separator.trim_right(),
                 Some(..) => &comment_line_separator,
                 None => "",
             });
diff --git a/src/lib.rs b/src/lib.rs
index 817188925cdb..1dd122133746 100644
--- a/src/lib.rs
+++ b/src/lib.rs
@@ -165,7 +165,7 @@ pub fn warning_count(&self) -> usize {
         self.file_error_map
             .iter()
             .map(|(_, errors)| errors.len())
-            .fold(0, |acc, x| acc + x)
+            .sum()
     }
 
     pub fn has_warnings(&self) -> bool {
diff --git a/src/macros.rs b/src/macros.rs
index 926c76dce7f0..b0080695449c 100644
--- a/src/macros.rs
+++ b/src/macros.rs
@@ -351,7 +351,7 @@ pub fn rewrite_macro_def(
 
     // Undo our replacement of macro variables.
     // FIXME: this could be *much* more efficient.
-    for (old, new) in substs.iter() {
+    for (old, new) in &substs {
         if old_body.find(new).is_some() {
             debug!(
                 "rewrite_macro_def: bailing matching variable: `{}` in `{}`",
@@ -368,7 +368,7 @@ pub fn rewrite_macro_def(
         ident,
         args_str,
         new_body,
-        indent.to_string(&context.config),
+        indent.to_string(context.config),
     );
 
     Some(result)
@@ -467,13 +467,10 @@ fn format_macro_args(toks: ThinTokenStream) -> Option<String> {
                 insert_space = next_space(&t);
             }
             TokenTree::Delimited(_, d) => {
-                let formatted = format_macro_args(d.tts)?;
-                match insert_space {
-                    SpaceState::Always => {
-                        result.push(' ');
-                    }
-                    _ => {}
+                if let SpaceState::Always = insert_space {
+                    result.push(' ');
                 }
+                let formatted = format_macro_args(d.tts)?;
                 match d.delim {
                     DelimToken::Paren => {
                         result.push_str(&format!("({})", formatted));
@@ -713,7 +710,7 @@ fn parse(&mut self) -> Option<Macro> {
     fn parse_branch(&mut self) -> Option<MacroBranch> {
         let (args_paren_kind, args) = match self.toks.next()? {
             TokenTree::Token(..) => return None,
-            TokenTree::Delimited(_, ref d) => (d.delim, d.tts.clone().into()),
+            TokenTree::Delimited(_, ref d) => (d.delim, d.tts.clone()),
         };
         match self.toks.next()? {
             TokenTree::Token(_, Token::FatArrow) => {}
diff --git a/tests/system.rs b/tests/system.rs
index 24a6b15e421a..06bfa1418d14 100644
--- a/tests/system.rs
+++ b/tests/system.rs
@@ -95,7 +95,7 @@ fn verify_config_test_names() {
                 let config_name = path.file_name().unwrap().to_str().unwrap();
 
                 // Make sure that config name is used in the files in the directory.
-                verify_config_used(&path, &config_name);
+                verify_config_used(&path, config_name);
             }
         }
     }
@@ -105,7 +105,7 @@ fn verify_config_test_names() {
 // println!) that is used by `rustfmt::rustfmt_diff::print_diff`. Writing
 // using only one or the other will cause the output order to differ when
 // `print_diff` selects the approach not used.
-fn write_message(msg: String) {
+fn write_message(msg: &str) {
     let mut writer = OutputWriter::new(Color::Auto);
     writer.writeln(&format!("{}", msg), None);
 }
@@ -359,8 +359,8 @@ pub enum IdempotentCheckError {
 }
 
 pub fn idempotent_check(filename: &PathBuf) -> Result<FormatReport, IdempotentCheckError> {
-    let sig_comments = read_significant_comments(&filename);
-    let config = read_config(&filename);
+    let sig_comments = read_significant_comments(filename);
+    let config = read_config(filename);
     let (error_summary, file_map, format_report) = format_file(filename, &config);
     if error_summary.has_parsing_errors() {
         return Err(IdempotentCheckError::Parse);
@@ -660,7 +660,7 @@ fn code_block_valid(&self) -> bool {
         assert!(self.code_block.is_some() && self.code_block_start.is_some());
 
         if self.config_name.is_none() {
-            write_message(format!(
+            write_message(&format!(
                 "No configuration name for {}:{}",
                 CONFIGURATIONS_FILE_NAME,
                 self.code_block_start.unwrap()
@@ -668,7 +668,7 @@ fn code_block_valid(&self) -> bool {
             return false;
         }
         if self.config_value.is_none() {
-            write_message(format!(
+            write_message(&format!(
                 "No configuration value for {}:{}",
                 CONFIGURATIONS_FILE_NAME,
                 self.code_block_start.unwrap()
@@ -680,7 +680,7 @@ fn code_block_valid(&self) -> bool {
 
     fn has_parsing_errors(&self, error_summary: Summary) -> bool {
         if error_summary.has_parsing_errors() {
-            write_message(format!(
+            write_message(&format!(
                 "\u{261d}\u{1f3fd} Cannot format {}:{}",
                 CONFIGURATIONS_FILE_NAME,
                 self.code_block_start.unwrap()
@@ -703,7 +703,7 @@ fn print_diff(&self, compare: Vec<Mismatch>) {
         });
     }
 
-    fn formatted_has_diff(&self, file_map: FileMap) -> bool {
+    fn formatted_has_diff(&self, file_map: &FileMap) -> bool {
         let &(ref _file_name, ref text) = file_map.first().unwrap();
         let compare = make_diff(self.code_block.as_ref().unwrap(), text, DIFF_CONTEXT_SIZE);
         if !compare.is_empty() {
@@ -729,7 +729,7 @@ fn formatted_is_idempotent(&self) -> bool {
         let (error_summary, file_map, _report) =
             format_input::<io::Stdout>(input, &config, None).unwrap();
 
-        !self.has_parsing_errors(error_summary) && !self.formatted_has_diff(file_map)
+        !self.has_parsing_errors(error_summary) && !self.formatted_has_diff(&file_map)
     }
 
     // Extract a code block from the iterator. Behavior:
@@ -746,7 +746,7 @@ fn extract<I: Iterator<Item = String>>(
         prev: Option<&ConfigCodeBlock>,
     ) -> Option<ConfigCodeBlock> {
         let mut code_block = ConfigCodeBlock::new();
-        code_block.config_name = prev.map_or(None, |cb| cb.config_name.clone());
+        code_block.config_name = prev.and_then(|cb| cb.config_name.clone());
 
         loop {
             match ConfigurationSection::get_section(file) {