diff options
| -rw-r--r-- | compiler/rustc_ast/src/tokenstream.rs | 85 |
1 files changed, 32 insertions, 53 deletions
diff --git a/compiler/rustc_ast/src/tokenstream.rs b/compiler/rustc_ast/src/tokenstream.rs index 66b9e9c7eaf..37de90d64c7 100644 --- a/compiler/rustc_ast/src/tokenstream.rs +++ b/compiler/rustc_ast/src/tokenstream.rs @@ -523,46 +523,7 @@ impl TokenStreamBuilder { } pub fn push<T: Into<TokenStream>>(&mut self, stream: T) { - let mut stream = stream.into(); - - // If `self` is not empty and the last tree within the last stream is a - // token tree marked with `Joint`... - if let Some(TokenStream(ref mut last_stream_lrc)) = self.0.last_mut() - && let Some((TokenTree::Token(last_token), Spacing::Joint)) = last_stream_lrc.last() - // ...and `stream` is not empty and the first tree within it is - // a token tree... - && let TokenStream(ref mut stream_lrc) = stream - && let Some((TokenTree::Token(token), spacing)) = stream_lrc.first() - // ...and the two tokens can be glued together... - && let Some(glued_tok) = last_token.glue(&token) - { - // ...then do so, by overwriting the last token - // tree in `self` and removing the first token tree - // from `stream`. This requires using `make_mut()` - // on the last stream in `self` and on `stream`, - // and in practice this doesn't cause cloning 99.9% - // of the time. - - // Overwrite the last token tree with the merged - // token. - let last_vec_mut = Lrc::make_mut(last_stream_lrc); - *last_vec_mut.last_mut().unwrap() = (TokenTree::Token(glued_tok), *spacing); - - // Remove the first token tree from `stream`. (This - // is almost always the only tree in `stream`.) - let stream_vec_mut = Lrc::make_mut(stream_lrc); - stream_vec_mut.remove(0); - - // Don't push `stream` if it's empty -- that could - // block subsequent token gluing, by getting - // between two token trees that should be glued - // together. - if !stream.is_empty() { - self.0.push(stream); - } - return; - } - self.0.push(stream); + self.0.push(stream.into()); } pub fn build(self) -> TokenStream { @@ -571,9 +532,9 @@ impl TokenStreamBuilder { 0 => TokenStream::default(), 1 => streams.pop().unwrap(), _ => { - // We are going to extend the first stream in `streams` with - // the elements from the subsequent streams. This requires - // using `make_mut()` on the first stream, and in practice this + // We will extend the first stream in `streams` with the + // elements from the subsequent streams. This requires using + // `make_mut()` on the first stream, and in practice this // doesn't cause cloning 99.9% of the time. // // One very common use case is when `streams` has two elements, @@ -586,21 +547,39 @@ impl TokenStreamBuilder { // reallocations (#57735). let num_appends = streams.iter().skip(1).map(|ts| ts.len()).sum(); - // Get the first stream. If it's `None`, create an empty - // stream. + // Get the first stream, which will become the result stream. + // If it's `None`, create an empty stream. let mut iter = streams.drain(..); - let mut first_stream_lrc = iter.next().unwrap().0; + let mut res_stream_lrc = iter.next().unwrap().0; - // Append the elements to the first stream, after reserving - // space for them. - let first_vec_mut = Lrc::make_mut(&mut first_stream_lrc); - first_vec_mut.reserve(num_appends); + // Append the subsequent elements to the result stream, after + // reserving space for them. + let res_vec_mut = Lrc::make_mut(&mut res_stream_lrc); + res_vec_mut.reserve(num_appends); for stream in iter { - first_vec_mut.extend(stream.0.iter().cloned()); + let stream_iter = stream.0.iter().cloned(); + + // If (a) `res_mut_vec` is not empty and the last tree + // within it is a token tree marked with `Joint`, and (b) + // `stream` is not empty and the first tree within it is a + // token tree, and (c) the two tokens can be glued + // together... + if let Some((TokenTree::Token(last_tok), Spacing::Joint)) = res_vec_mut.last() + && let Some((TokenTree::Token(tok), spacing)) = stream.0.first() + && let Some(glued_tok) = last_tok.glue(&tok) + { + // ...then overwrite the last token tree in + // `res_vec_mut` with the glued token, and skip the + // first token tree from `stream`. + *res_vec_mut.last_mut().unwrap() = (TokenTree::Token(glued_tok), *spacing); + res_vec_mut.extend(stream_iter.skip(1)); + } else { + // Append all of `stream`. + res_vec_mut.extend(stream_iter); + } } - // Create the final `TokenStream`. - TokenStream(first_stream_lrc) + TokenStream(res_stream_lrc) } } } |