use CursorRef more, to not to clone Trees

compiler/rustc_ast/src/attr/mod.rs

@@ -552,7 +552,7 @@ impl MetaItemKind {
     ) -> Option<MetaItemKind> {
         match tokens.next() {
             Some(TokenTree::Delimited(_, Delimiter::Invisible, inner_tokens)) => {
-                MetaItemKind::name_value_from_tokens(&mut inner_tokens.trees())
+                MetaItemKind::name_value_from_tokens(&mut inner_tokens.into_trees())
             }
             Some(TokenTree::Token(token)) => {
                 Lit::from_token(&token).ok().map(MetaItemKind::NameValue)

compiler/rustc_ast/src/tokenstream.rs

@@ -442,8 +442,8 @@ impl TokenStream {
         }
     }
 
-    pub fn trees(&self) -> Cursor {
+    pub fn trees(&self) -> CursorRef<'_> {
-        self.clone().into_trees()
+        CursorRef::new(self)
     }
 
     pub fn into_trees(self) -> Cursor {
@@ -538,12 +538,21 @@ pub struct CursorRef<'t> {
 }
 
 impl<'t> CursorRef<'t> {
+    fn new(stream: &'t TokenStream) -> Self {
+        CursorRef { stream, index: 0 }
+    }
+
+    #[inline]
     fn next_with_spacing(&mut self) -> Option<&'t TreeAndSpacing> {
         self.stream.0.get(self.index).map(|tree| {
             self.index += 1;
             tree
         })
     }
+
+    pub fn look_ahead(&self, n: usize) -> Option<&TokenTree> {
+        self.stream.0[self.index..].get(n).map(|(tree, _)| tree)
+    }
 }
 
 impl<'t> Iterator for CursorRef<'t> {

compiler/rustc_ast_pretty/src/pprust/state.rs

@@ -550,9 +550,9 @@ pub trait PrintState<'a>: std::ops::Deref<Target = pp::Printer> + std::ops::Dere
     fn print_tts(&mut self, tts: &TokenStream, convert_dollar_crate: bool) {
         let mut iter = tts.trees().peekable();
         while let Some(tt) = iter.next() {
-            self.print_tt(&tt, convert_dollar_crate);
+            self.print_tt(tt, convert_dollar_crate);
             if let Some(next) = iter.peek() {
-                if tt_prepend_space(next, &tt) {
+                if tt_prepend_space(next, tt) {
                     self.space();
                 }
             }

compiler/rustc_expand/src/config.rs

@@ -400,7 +400,7 @@ impl<'a> StripUnconfigured<'a> {
 
         // Use the `#` in `#[cfg_attr(pred, attr)]` as the `#` token
         // for `attr` when we expand it to `#[attr]`
-        let mut orig_trees = orig_tokens.trees();
+        let mut orig_trees = orig_tokens.into_trees();
         let TokenTree::Token(pound_token @ Token { kind: TokenKind::Pound, .. }) = orig_trees.next().unwrap() else {
             panic!("Bad tokens for attribute {:?}", attr);
         };

compiler/rustc_expand/src/mbe/metavar_expr.rs

@@ -1,5 +1,5 @@
 use rustc_ast::token::{self, Delimiter};
-use rustc_ast::tokenstream::{Cursor, TokenStream, TokenTree};
+use rustc_ast::tokenstream::{CursorRef, TokenStream, TokenTree};
 use rustc_ast::{LitIntType, LitKind};
 use rustc_ast_pretty::pprust;
 use rustc_errors::{Applicability, PResult};
@@ -71,12 +71,14 @@ impl MetaVarExpr {
 }
 
 // Checks if there are any remaining tokens. For example, `${ignore(ident ... a b c ...)}`
-fn check_trailing_token<'sess>(iter: &mut Cursor, sess: &'sess ParseSess) -> PResult<'sess, ()> {
+fn check_trailing_token<'sess>(
+    iter: &mut CursorRef<'_>,
+    sess: &'sess ParseSess,
+) -> PResult<'sess, ()> {
     if let Some(tt) = iter.next() {
-        let mut diag = sess.span_diagnostic.struct_span_err(
+        let mut diag = sess
-            tt.span(),
+            .span_diagnostic
-            &format!("unexpected token: {}", pprust::tt_to_string(&tt)),
+            .struct_span_err(tt.span(), &format!("unexpected token: {}", pprust::tt_to_string(tt)));
-        );
         diag.span_note(tt.span(), "meta-variable expression must not have trailing tokens");
         Err(diag)
     } else {
@@ -86,7 +88,7 @@ fn check_trailing_token<'sess>(iter: &mut Cursor, sess: &'sess ParseSess) -> PRe
 
 /// Parse a meta-variable `count` expression: `count(ident[, depth])`
 fn parse_count<'sess>(
-    iter: &mut Cursor,
+    iter: &mut CursorRef<'_>,
     sess: &'sess ParseSess,
     span: Span,
 ) -> PResult<'sess, MetaVarExpr> {
@@ -97,7 +99,7 @@ fn parse_count<'sess>(
 
 /// Parses the depth used by index(depth) and length(depth).
 fn parse_depth<'sess>(
-    iter: &mut Cursor,
+    iter: &mut CursorRef<'_>,
     sess: &'sess ParseSess,
     span: Span,
 ) -> PResult<'sess, usize> {
@@ -110,7 +112,7 @@ fn parse_depth<'sess>(
             "meta-variable expression depth must be a literal"
         ));
     };
-    if let Ok(lit_kind) = LitKind::from_lit_token(lit)
+    if let Ok(lit_kind) = LitKind::from_lit_token(*lit)
         && let LitKind::Int(n_u128, LitIntType::Unsuffixed) = lit_kind
         && let Ok(n_usize) = usize::try_from(n_u128)
     {
@@ -124,7 +126,7 @@ fn parse_depth<'sess>(
 
 /// Parses an generic ident
 fn parse_ident<'sess>(
-    iter: &mut Cursor,
+    iter: &mut CursorRef<'_>,
     sess: &'sess ParseSess,
     span: Span,
 ) -> PResult<'sess, Ident> {
@@ -132,7 +134,7 @@ fn parse_ident<'sess>(
         if let Some((elem, false)) = token.ident() {
             return Ok(elem);
         }
-        let token_str = pprust::token_to_string(&token);
+        let token_str = pprust::token_to_string(token);
         let mut err = sess.span_diagnostic.struct_span_err(
             span,
             &format!("expected identifier, found `{}`", &token_str)
@@ -150,7 +152,7 @@ fn parse_ident<'sess>(
 
 /// Tries to move the iterator forward returning `true` if there is a comma. If not, then the
 /// iterator is not modified and the result is `false`.
-fn try_eat_comma(iter: &mut Cursor) -> bool {
+fn try_eat_comma(iter: &mut CursorRef<'_>) -> bool {
     if let Some(TokenTree::Token(token::Token { kind: token::Comma, .. })) = iter.look_ahead(0) {
         let _ = iter.next();
         return true;

compiler/rustc_expand/src/mbe/quoted.rs

@@ -48,7 +48,7 @@ pub(super) fn parse(
 
     // For each token tree in `input`, parse the token into a `self::TokenTree`, consuming
     // additional trees if need be.
-    let mut trees = input.trees();
+    let mut trees = input.into_trees();
     while let Some(tree) = trees.next() {
         // Given the parsed tree, if there is a metavar and we are expecting matchers, actually
         // parse out the matcher (i.e., in `$id:ident` this would parse the `:` and `ident`).

compiler/rustc_expand/src/parse/tests.rs

@@ -61,7 +61,7 @@ fn bad_path_expr_1() {
 fn string_to_tts_macro() {
     create_default_session_globals_then(|| {
         let tts: Vec<_> =
-            string_to_stream("macro_rules! zip (($a)=>($a))".to_string()).trees().collect();
+            string_to_stream("macro_rules! zip (($a)=>($a))".to_string()).into_trees().collect();
         let tts: &[TokenTree] = &tts[..];
 
         match tts {
@@ -293,7 +293,7 @@ fn ttdelim_span() {
         .unwrap();
 
         let tts: Vec<_> = match expr.kind {
-            ast::ExprKind::MacCall(ref mac) => mac.args.inner_tokens().trees().collect(),
+            ast::ExprKind::MacCall(ref mac) => mac.args.inner_tokens().into_trees().collect(),
             _ => panic!("not a macro"),
         };
 

compiler/rustc_expand/src/proc_macro_server.rs

@@ -484,7 +484,7 @@ impl server::TokenStream for Rustc<'_, '_> {
         tree.to_internal()
     }
     fn into_iter(&mut self, stream: Self::TokenStream) -> Self::TokenStreamIter {
-        TokenStreamIter { cursor: stream.trees(), stack: vec![] }
+        TokenStreamIter { cursor: stream.into_trees(), stack: vec![] }
     }
 }
 

compiler/rustc_expand/src/tokenstream/tests.rs

@@ -35,7 +35,7 @@ fn test_concat() {
 fn test_to_from_bijection() {
     create_default_session_globals_then(|| {
         let test_start = string_to_ts("foo::bar(baz)");
-        let test_end = test_start.trees().collect();
+        let test_end = test_start.trees().cloned().collect();
         assert_eq!(test_start, test_end)
     })
 }

compiler/rustc_session/src/utils.rs

@@ -108,7 +108,7 @@ impl<'a> FlattenNonterminals<'a> {
         fn can_skip(stream: &TokenStream) -> bool {
             stream.trees().all(|tree| match tree {
                 TokenTree::Token(token) => !matches!(token.kind, token::Interpolated(_)),
-                TokenTree::Delimited(_, _, inner) => can_skip(&inner),
+                TokenTree::Delimited(_, _, inner) => can_skip(inner),
             })
         }