parser: Cleanup LazyTokenStream and avoid some clones

compiler/rustc_ast/src/tokenstream.rs

@@ -22,7 +22,7 @@ use rustc_serialize::{Decodable, Decoder, Encodable, Encoder};
 use rustc_span::{Span, DUMMY_SP};
 use smallvec::{smallvec, SmallVec};
 
-use std::{iter, mem};
+use std::{fmt, iter, mem};
 
 /// When the main rust parser encounters a syntax-extension invocation, it
 /// parses the arguments to the invocation as a token-tree. This is a very
@@ -120,72 +120,51 @@ where
     }
 }
 
-// A cloneable callback which produces a `TokenStream`. Each clone
-// of this should produce the same `TokenStream`
-pub trait CreateTokenStream: sync::Send + sync::Sync + FnOnce() -> TokenStream {
-    // Workaround for the fact that `Clone` is not object-safe
-    fn clone_it(&self) -> Box<dyn CreateTokenStream>;
+pub trait CreateTokenStream: sync::Send + sync::Sync {
+    fn create_token_stream(&self) -> TokenStream;
 }
 
-impl<F: 'static + Clone + sync::Send + sync::Sync + FnOnce() -> TokenStream> CreateTokenStream
-    for F
-{
-    fn clone_it(&self) -> Box<dyn CreateTokenStream> {
-        Box::new(self.clone())
-    }
-}
-
-impl Clone for Box<dyn CreateTokenStream> {
-    fn clone(&self) -> Self {
-        let val: &(dyn CreateTokenStream) = &**self;
-        val.clone_it()
+impl CreateTokenStream for TokenStream {
+    fn create_token_stream(&self) -> TokenStream {
+        self.clone()
     }
 }
 
-/// A lazy version of `TokenStream`, which may defer creation
+/// A lazy version of `TokenStream`, which defers creation
 /// of an actual `TokenStream` until it is needed.
-pub type LazyTokenStream = Lrc<LazyTokenStreamInner>;
-
+/// `Box` is here only to reduce the structure size.
 #[derive(Clone)]
-pub enum LazyTokenStreamInner {
-    Lazy(Box<dyn CreateTokenStream>),
-    Ready(TokenStream),
-}
+pub struct LazyTokenStream(Lrc<Box<dyn CreateTokenStream>>);
 
-impl std::fmt::Debug for LazyTokenStreamInner {
-    fn fmt(&self, f: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
-        match self {
-            LazyTokenStreamInner::Lazy(..) => f.debug_struct("LazyTokenStream::Lazy").finish(),
-            LazyTokenStreamInner::Ready(..) => f.debug_struct("LazyTokenStream::Ready").finish(),
-        }
+impl LazyTokenStream {
+    pub fn new(inner: impl CreateTokenStream + 'static) -> LazyTokenStream {
+        LazyTokenStream(Lrc::new(Box::new(inner)))
+    }
+
+    pub fn create_token_stream(&self) -> TokenStream {
+        self.0.create_token_stream()
     }
 }
 
-impl LazyTokenStreamInner {
-    pub fn into_token_stream(&self) -> TokenStream {
-        match self {
-            // Note that we do not cache this. If this ever becomes a performance
-            // problem, we should investigate wrapping `LazyTokenStreamInner`
-            // in a lock
-            LazyTokenStreamInner::Lazy(cb) => (cb.clone())(),
-            LazyTokenStreamInner::Ready(stream) => stream.clone(),
-        }
+impl fmt::Debug for LazyTokenStream {
+    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
+        fmt::Debug::fmt("LazyTokenStream", f)
     }
 }
 
-impl<S: Encoder> Encodable<S> for LazyTokenStreamInner {
+impl<S: Encoder> Encodable<S> for LazyTokenStream {
     fn encode(&self, _s: &mut S) -> Result<(), S::Error> {
         panic!("Attempted to encode LazyTokenStream");
     }
 }
 
-impl<D: Decoder> Decodable<D> for LazyTokenStreamInner {
+impl<D: Decoder> Decodable<D> for LazyTokenStream {
     fn decode(_d: &mut D) -> Result<Self, D::Error> {
         panic!("Attempted to decode LazyTokenStream");
     }
 }
 
-impl<CTX> HashStable<CTX> for LazyTokenStreamInner {
+impl<CTX> HashStable<CTX> for LazyTokenStream {
     fn hash_stable(&self, _hcx: &mut CTX, _hasher: &mut StableHasher) {
         panic!("Attempted to compute stable hash for LazyTokenStream");
     }

compiler/rustc_expand/src/config.rs

@@ -4,12 +4,11 @@ use rustc_ast::attr::HasAttrs;
 use rustc_ast::mut_visit::*;
 use rustc_ast::ptr::P;
 use rustc_ast::token::{DelimToken, Token, TokenKind};
-use rustc_ast::tokenstream::{DelimSpan, LazyTokenStreamInner, Spacing, TokenStream, TokenTree};
+use rustc_ast::tokenstream::{DelimSpan, LazyTokenStream, Spacing, TokenStream, TokenTree};
 use rustc_ast::{self as ast, AttrItem, Attribute, MetaItem};
 use rustc_attr as attr;
 use rustc_data_structures::fx::FxHashMap;
 use rustc_data_structures::map_in_place::MapInPlace;
-use rustc_data_structures::sync::Lrc;
 use rustc_errors::{error_code, struct_span_err, Applicability, Handler};
 use rustc_feature::{Feature, Features, State as FeatureState};
 use rustc_feature::{
@@ -303,7 +302,7 @@ impl<'a> StripUnconfigured<'a> {
 
                 // Use the `#` in `#[cfg_attr(pred, attr)]` as the `#` token
                 // for `attr` when we expand it to `#[attr]`
-                let pound_token = orig_tokens.into_token_stream().trees().next().unwrap();
+                let pound_token = orig_tokens.create_token_stream().trees().next().unwrap();
                 if !matches!(pound_token, TokenTree::Token(Token { kind: TokenKind::Pound, .. })) {
                     panic!("Bad tokens for attribute {:?}", attr);
                 }
@@ -313,16 +312,16 @@ impl<'a> StripUnconfigured<'a> {
                     DelimSpan::from_single(pound_token.span()),
                     DelimToken::Bracket,
                     item.tokens
-                        .clone()
+                        .as_ref()
                         .unwrap_or_else(|| panic!("Missing tokens for {:?}", item))
-                        .into_token_stream(),
+                        .create_token_stream(),
                 );
 
                 let mut attr = attr::mk_attr_from_item(attr.style, item, span);
-                attr.tokens = Some(Lrc::new(LazyTokenStreamInner::Ready(TokenStream::new(vec![
+                attr.tokens = Some(LazyTokenStream::new(TokenStream::new(vec![
                     (pound_token, Spacing::Alone),
                     (bracket_group, Spacing::Alone),
-                ]))));
+                ])));
                 self.process_cfg_attr(attr)
             })
             .collect()

compiler/rustc_parse/src/lib.rs

@@ -249,29 +249,30 @@ pub fn nt_to_tokenstream(nt: &Nonterminal, sess: &ParseSess, span: Span) -> Toke
     // came from. Here we attempt to extract these lossless token streams
     // before we fall back to the stringification.
 
-    let convert_tokens = |tokens: Option<LazyTokenStream>| tokens.map(|t| t.into_token_stream());
+    let convert_tokens =
+        |tokens: &Option<LazyTokenStream>| tokens.as_ref().map(|t| t.create_token_stream());
 
     let tokens = match *nt {
         Nonterminal::NtItem(ref item) => prepend_attrs(&item.attrs, item.tokens.as_ref()),
-        Nonterminal::NtBlock(ref block) => convert_tokens(block.tokens.clone()),
+        Nonterminal::NtBlock(ref block) => convert_tokens(&block.tokens),
         Nonterminal::NtStmt(ref stmt) => {
             // FIXME: We currently only collect tokens for `:stmt`
             // matchers in `macro_rules!` macros. When we start collecting
             // tokens for attributes on statements, we will need to prepend
             // attributes here
-            convert_tokens(stmt.tokens.clone())
+            convert_tokens(&stmt.tokens)
         }
-        Nonterminal::NtPat(ref pat) => convert_tokens(pat.tokens.clone()),
-        Nonterminal::NtTy(ref ty) => convert_tokens(ty.tokens.clone()),
+        Nonterminal::NtPat(ref pat) => convert_tokens(&pat.tokens),
+        Nonterminal::NtTy(ref ty) => convert_tokens(&ty.tokens),
         Nonterminal::NtIdent(ident, is_raw) => {
             Some(tokenstream::TokenTree::token(token::Ident(ident.name, is_raw), ident.span).into())
         }
         Nonterminal::NtLifetime(ident) => {
             Some(tokenstream::TokenTree::token(token::Lifetime(ident.name), ident.span).into())
         }
-        Nonterminal::NtMeta(ref attr) => convert_tokens(attr.tokens.clone()),
-        Nonterminal::NtPath(ref path) => convert_tokens(path.tokens.clone()),
-        Nonterminal::NtVis(ref vis) => convert_tokens(vis.tokens.clone()),
+        Nonterminal::NtMeta(ref attr) => convert_tokens(&attr.tokens),
+        Nonterminal::NtPath(ref path) => convert_tokens(&path.tokens),
+        Nonterminal::NtVis(ref vis) => convert_tokens(&vis.tokens),
         Nonterminal::NtTT(ref tt) => Some(tt.clone().into()),
         Nonterminal::NtExpr(ref expr) | Nonterminal::NtLiteral(ref expr) => {
             if expr.tokens.is_none() {
@@ -604,7 +605,7 @@ fn prepend_attrs(
     attrs: &[ast::Attribute],
     tokens: Option<&tokenstream::LazyTokenStream>,
 ) -> Option<tokenstream::TokenStream> {
-    let tokens = tokens?.clone().into_token_stream();
+    let tokens = tokens?.create_token_stream();
     if attrs.is_empty() {
         return Some(tokens);
     }
@@ -617,9 +618,9 @@ fn prepend_attrs(
         );
         builder.push(
             attr.tokens
-                .clone()
+                .as_ref()
                 .unwrap_or_else(|| panic!("Attribute {:?} is missing tokens!", attr))
-                .into_token_stream(),
+                .create_token_stream(),
         );
     }
     builder.push(tokens);

compiler/rustc_parse/src/parser/mod.rs

@@ -16,8 +16,8 @@ pub use path::PathStyle;
 
 use rustc_ast::ptr::P;
 use rustc_ast::token::{self, DelimToken, Token, TokenKind};
-use rustc_ast::tokenstream::{self, DelimSpan, LazyTokenStream, LazyTokenStreamInner, Spacing};
-use rustc_ast::tokenstream::{TokenStream, TokenTree};
+use rustc_ast::tokenstream::{self, DelimSpan, LazyTokenStream, Spacing};
+use rustc_ast::tokenstream::{CreateTokenStream, TokenStream, TokenTree};
 use rustc_ast::DUMMY_NODE_ID;
 use rustc_ast::{self as ast, AnonConst, AttrStyle, AttrVec, Const, CrateSugar, Extern, Unsafe};
 use rustc_ast::{Async, Expr, ExprKind, MacArgs, MacDelimiter, Mutability, StrLit};
@@ -1199,15 +1199,12 @@ impl<'a> Parser<'a> {
         f: impl FnOnce(&mut Self) -> PResult<'a, R>,
     ) -> PResult<'a, (R, Option<LazyTokenStream>)> {
         let start_token = (self.token.clone(), self.token_spacing);
-        let mut cursor_snapshot = self.token_cursor.clone();
+        let cursor_snapshot = self.token_cursor.clone();
 
         let ret = f(self)?;
 
-        let new_calls = self.token_cursor.num_next_calls;
-        let num_calls = new_calls - cursor_snapshot.num_next_calls;
-        let desugar_doc_comments = self.desugar_doc_comments;
-
         // We didn't capture any tokens
+        let num_calls = self.token_cursor.num_next_calls - cursor_snapshot.num_next_calls;
         if num_calls == 0 {
             return Ok((ret, None));
         }
@@ -1220,27 +1217,41 @@ impl<'a> Parser<'a> {
         //
         // This also makes `Parser` very cheap to clone, since
         // there is no intermediate collection buffer to clone.
-        let lazy_cb = move || {
-            // The token produced by the final call to `next` or `next_desugared`
-            // was not actually consumed by the callback. The combination
-            // of chaining the initial token and using `take` produces the desired
-            // result - we produce an empty `TokenStream` if no calls were made,
-            // and omit the final token otherwise.
-            let tokens = std::iter::once(start_token)
-                .chain((0..num_calls).map(|_| {
-                    if desugar_doc_comments {
-                        cursor_snapshot.next_desugared()
-                    } else {
-                        cursor_snapshot.next()
-                    }
-                }))
-                .take(num_calls);
+        struct LazyTokenStreamImpl {
+            start_token: (Token, Spacing),
+            cursor_snapshot: TokenCursor,
+            num_calls: usize,
+            desugar_doc_comments: bool,
+        }
+        impl CreateTokenStream for LazyTokenStreamImpl {
+            fn create_token_stream(&self) -> TokenStream {
+                // The token produced by the final call to `next` or `next_desugared`
+                // was not actually consumed by the callback. The combination
+                // of chaining the initial token and using `take` produces the desired
+                // result - we produce an empty `TokenStream` if no calls were made,
+                // and omit the final token otherwise.
+                let mut cursor_snapshot = self.cursor_snapshot.clone();
+                let tokens = std::iter::once(self.start_token.clone())
+                    .chain((0..self.num_calls).map(|_| {
+                        if self.desugar_doc_comments {
+                            cursor_snapshot.next_desugared()
+                        } else {
+                            cursor_snapshot.next()
+                        }
+                    }))
+                    .take(self.num_calls);
 
-            make_token_stream(tokens)
-        };
-        let stream = LazyTokenStream::new(LazyTokenStreamInner::Lazy(Box::new(lazy_cb)));
+                make_token_stream(tokens)
+            }
+        }
 
-        Ok((ret, Some(stream)))
+        let lazy_impl = LazyTokenStreamImpl {
+            start_token,
+            cursor_snapshot,
+            num_calls,
+            desugar_doc_comments: self.desugar_doc_comments,
+        };
+        Ok((ret, Some(LazyTokenStream::new(lazy_impl))))
     }
 
     /// `::{` or `::*`