rust: clippy pass

This removes some justified warnings and one hard error that, while technically
not a bug, was an ugly oversight on my part.

Differential Revision: https://phab.mercurial-scm.org/D9094

rust/hg-core/src/dirstate/dirstate_tree/iter.rs

@@ -160,7 +160,7 b" impl<'a> FsIter<'a> {"
         let meta = self.root_dir.join(filename_as_path).symlink_metadata();
         match meta {
             Ok(ref m) if m.file_type().is_symlink() => true,
-            _ => return false,
+            _ => false,
         }
     }
 }
@@ -182,7 +182,7 b" impl<'a> Iterator for FsIter<'a> {"
 
     fn next(&mut self) -> Option<Self::Item> {
         // If any paths have already been `Dispatch`-ed, return them
-        while let Some(res) = self.shortcuts.pop_front() {
+        if let Some(res) = self.shortcuts.pop_front() {
             return Some(res);
         }
 
@@ -250,7 +250,7 b" fn add_children_to_visit<'a>("
 ) {
     to_visit.extend(dir.children.iter().map(|(path, child)| {
         let full_path = join_path(&base_path, &path);
-        (Cow::from(full_path), child)
+        (full_path, child)
     }));
 }
 

rust/hg-core/src/dirstate/dirstate_tree/node.rs

@@ -91,9 +91,9 b' impl Node {'
 
         match &mut self.kind {
             NodeKind::Directory(directory) => {
-                return Node::insert_in_directory(
+                Node::insert_in_directory(
                     directory, new_entry, head, tail,
-                );
+                )
             }
             NodeKind::File(_) => {
                 unreachable!("The file case has already been handled")
@@ -227,7 +227,7 b' impl Node {'
                             d.children.remove(head);
                         }
                         res.cleanup =
-                            d.children.len() == 0 && d.was_file.is_none();
+                            d.children.is_empty() && d.was_file.is_none();
                         res
                     } else {
                         empty_result
@@ -241,7 +241,7 b' impl Node {'
                             if cleanup {
                                 d.children.remove(head);
                             }
-                            if d.children.len() == 0 && d.was_file.is_none() {
+                            if d.children.is_empty() && d.was_file.is_none() {
                                 f.was_directory = None;
                             }
 
@@ -288,7 +288,7 b' impl Node {'
                     }
 
                     RemoveResult {
-                        cleanup: cleanup,
+                        cleanup,
                         old_entry: Some(entry),
                     }
                 }