style(clippy): quickly fix up clippy lints

src/eyreish/error.rs

@@ -280,7 +280,7 @@ impl Report {
     /// The root cause is the last error in the iterator produced by
     /// [`chain()`](Report::chain).
     pub fn root_cause(&self) -> &(dyn StdError + 'static) {
-        self.chain().last().unwrap()
+        self.chain().next_back().unwrap()
     }
 
     /// Returns true if `E` is the type held by this error object.

src/handler.rs

@@ -424,7 +424,7 @@ impl HighlighterOption {
         highlighter: Option<MietteHighlighter>,
         supports_color: bool,
     ) -> HighlighterOption {
-        if color == Some(false) || (color == None && !supports_color) {
+        if color == Some(false) || (color.is_none() && !supports_color) {
             return HighlighterOption::Disable;
         }
         highlighter
@@ -433,6 +433,9 @@ impl HighlighterOption {
     }
 }
 
+// NOTE: This is manually implemented so that it's clearer what's going on with
+// the conditional compilation — clippy isn't picking up the `cfg` stuff here
+#[allow(clippy::derivable_impls)]
 impl Default for HighlighterOption {
     fn default() -> Self {
         cfg_if! {

src/highlighters/syntect.rs

@@ -96,12 +96,12 @@ impl SyntectHighlighter {
             }
         }
         // finally, attempt to guess syntax based on first line
-        return self.syntax_set.find_syntax_by_first_line(
+        self.syntax_set.find_syntax_by_first_line(
             std::str::from_utf8(contents.data())
                 .ok()?
                 .split('\n')
                 .next()?,
-        );
+        )
     }
 }
 
@@ -115,7 +115,7 @@ pub(crate) struct SyntectHighlighterState<'h> {
     use_bg_color: bool,
 }
 
-impl<'h> HighlighterState for SyntectHighlighterState<'h> {
+impl HighlighterState for SyntectHighlighterState<'_> {
     fn highlight_line<'s>(&mut self, line: &'s str) -> Vec<Styled<&'s str>> {
         if let Ok(ops) = self.parse_state.parse_line(line, self.syntax_set) {
             let use_bg_color = self.use_bg_color;