Remove some unnecessary clones.

I found these by grepping for `&[a-z_\.]*\.clone()`, i.e. expressions
like `&a.b.clone()`, which are sometimes unnecessary clones, and also
looking at clones nearby to cases like that.

Author: nnethercote

compiler/rustc_ast_pretty/src/pprust/state.rs

@@ -799,7 +799,7 @@ pub trait PrintState<'a>: std::ops::Deref<Target = pp::Printer> + std::ops::Dere
             has_bang,
             Some(*ident),
             macro_def.body.delim,
-            &macro_def.body.tokens.clone(),
+            &macro_def.body.tokens,
             true,
             sp,
         );
@@ -1469,7 +1469,7 @@ impl<'a> State<'a> {
             true,
             None,
             m.args.delim,
-            &m.args.tokens.clone(),
+            &m.args.tokens,
             true,
             m.span(),
         );

compiler/rustc_trait_selection/src/traits/query/type_op/ascribe_user_type.rs

@@ -117,8 +117,7 @@ fn relate_mir_and_user_args<'tcx>(
             CRATE_DEF_ID,
             ObligationCauseCode::AscribeUserTypeProvePredicate(predicate_span),
         );
-        let instantiated_predicate =
-            ocx.normalize(&cause.clone(), param_env, instantiated_predicate);
+        let instantiated_predicate = ocx.normalize(&cause, param_env, instantiated_predicate);
 
         ocx.register_obligation(Obligation::new(tcx, cause, param_env, instantiated_predicate));
     }

library/alloc/src/collections/btree/set.rs

@@ -139,7 +139,7 @@ pub struct Iter<'a, T: 'a> {
 #[stable(feature = "collection_debug", since = "1.17.0")]
 impl<T: fmt::Debug> fmt::Debug for Iter<'_, T> {
     fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
-        f.debug_tuple("Iter").field(&self.iter.clone()).finish()
+        f.debug_tuple("Iter").field(&self.iter).finish()
     }
 }
 

src/bootstrap/src/core/build_steps/setup.rs

@@ -683,7 +683,7 @@ impl Step for Editor {
         match EditorKind::prompt_user() {
             Ok(editor_kind) => {
                 if let Some(editor_kind) = editor_kind {
-                    while !t!(create_editor_settings_maybe(config, editor_kind.clone())) {}
+                    while !t!(create_editor_settings_maybe(config, &editor_kind)) {}
                 } else {
                     println!("Ok, skipping editor setup!");
                 }
@@ -695,7 +695,7 @@ impl Step for Editor {
 
 /// Create the recommended editor LSP config file for rustc development, or just print it
 /// If this method should be re-called, it returns `false`.
-fn create_editor_settings_maybe(config: &Config, editor: EditorKind) -> io::Result<bool> {
+fn create_editor_settings_maybe(config: &Config, editor: &EditorKind) -> io::Result<bool> {
     let hashes = editor.hashes();
     let (current_hash, historical_hashes) = hashes.split_last().unwrap();
     let settings_path = editor.settings_path(config);
@@ -752,7 +752,7 @@ fn create_editor_settings_maybe(config: &Config, editor: EditorKind) -> io::Resu
             // exists but user modified, back it up
             Some(false) => {
                 // exists and is not current version or outdated, so back it up
-                let backup = settings_path.clone().with_extension(editor.backup_extension());
+                let backup = settings_path.with_extension(editor.backup_extension());
                 eprintln!(
                     "WARNING: copying `{}` to `{}`",
                     settings_path.file_name().unwrap().to_str().unwrap(),