Rollup merge of #111492 - calebcartwright:by-ref-tokentree-1, r=compiler-errors

use by ref TokenTree iterator to avoid a few clones

Just a handful of swaps from the by-value cursor to by-ref cursor so as to avoid some unnecessary clones.

I've been doing some analysis on internal cleanup opportunities within rustfmt and as part of that yak-shave I found myself perusing broader token stream and tree usage (which we use within rustfmt). As reflected in some inline comments on the cursor structs (not part of this diff), there's probably many other such cases throughout the code, but figured I'd start small with these while I had the time. May take a look at the other sites in the future

Author: matthiaskrgr

compiler/rustc_builtin_macros/src/concat_idents.rs

@@ -19,7 +19,7 @@ pub fn expand_concat_idents<'cx>(
     }
 
     let mut res_str = String::new();
-    for (i, e) in tts.into_trees().enumerate() {
+    for (i, e) in tts.trees().enumerate() {
         if i & 1 == 1 {
             match e {
                 TokenTree::Token(Token { kind: token::Comma, .. }, _) => {}

compiler/rustc_builtin_macros/src/trace_macros.rs

@@ -8,7 +8,7 @@ pub fn expand_trace_macros(
     sp: Span,
     tt: TokenStream,
 ) -> Box<dyn base::MacResult + 'static> {
-    let mut cursor = tt.into_trees();
+    let mut cursor = tt.trees();
     let mut err = false;
     let value = match &cursor.next() {
         Some(TokenTree::Token(token, _)) if token.is_keyword(kw::True) => true,

compiler/rustc_lint/src/builtin.rs

@@ -1882,8 +1882,8 @@ declare_lint_pass!(
 struct UnderMacro(bool);
 
 impl KeywordIdents {
-    fn check_tokens(&mut self, cx: &EarlyContext<'_>, tokens: TokenStream) {
-        for tt in tokens.into_trees() {
+    fn check_tokens(&mut self, cx: &EarlyContext<'_>, tokens: &TokenStream) {
+        for tt in tokens.trees() {
             match tt {
                 // Only report non-raw idents.
                 TokenTree::Token(token, _) => {
@@ -1944,10 +1944,10 @@ impl KeywordIdents {
 
 impl EarlyLintPass for KeywordIdents {
     fn check_mac_def(&mut self, cx: &EarlyContext<'_>, mac_def: &ast::MacroDef) {
-        self.check_tokens(cx, mac_def.body.tokens.clone());
+        self.check_tokens(cx, &mac_def.body.tokens);
     }
     fn check_mac(&mut self, cx: &EarlyContext<'_>, mac: &ast::MacCall) {
-        self.check_tokens(cx, mac.args.tokens.clone());
+        self.check_tokens(cx, &mac.args.tokens);
     }
     fn check_ident(&mut self, cx: &EarlyContext<'_>, ident: Ident) {
         self.check_ident_token(cx, UnderMacro(false), ident);