Split the stack in make_attr_token_stream.

It makes for shorter code, and fewer allocations.
rust-lang · bors · Jul 14, 2024 · Apr 14, 2024 · Apr 14, 2024 · Apr 14, 2024
commit a88c4d67d9ea8a9f450638f207be867fa984bfce
diff --git a/compiler/rustc_parse/src/parser/attr_wrapper.rs b/compiler/rustc_parse/src/parser/attr_wrapper.rs
@@ -376,18 376,19 @@ fn make_attr_token_stream(
  open_delim_sp: Option<(Delimiter, Span, Spacing)>,
  inner: Vec<AttrTokenTree>,
  }
- let mut stack = vec![FrameData { open_delim_sp: None, inner: vec![] }];
  // The stack always has at least one element. Storing it separately makes for shorter code.
  let mut stack_top = FrameData { open_delim_sp: None, inner: vec![] };
  let mut stack_rest = vec![];
  for (token, spacing) in iter {
  match token {
  FlatToken::Token(Token { kind: TokenKind::OpenDelim(delim), span }) => {
- stack
- .push(FrameData { open_delim_sp: Some((delim, span, spacing)), inner: vec![] });
  stack_rest.push(mem::replace(
  &mut stack_top,
  FrameData { open_delim_sp: Some((delim, span, spacing)), inner: vec![] },
  ));
  }
  FlatToken::Token(Token { kind: TokenKind::CloseDelim(delim), span }) => {
- let frame_data = stack
- .pop()
- .unwrap_or_else(|| panic!("Token stack was empty for token: {token:?}"));
-
  let frame_data = mem::replace(&mut stack_top, stack_rest.pop().unwrap());
  let (open_delim, open_sp, open_spacing) = frame_data.open_delim_sp.unwrap();
  assert_eq!(
  open_delim, delim,
@@ -397,43 398,33 @@ fn make_attr_token_stream(
  let dspacing = DelimSpacing::new(open_spacing, spacing);
  let stream = AttrTokenStream::new(frame_data.inner);
  let delimited = AttrTokenTree::Delimited(dspan, dspacing, delim, stream);
- stack
-  .last_mut()
-  .unwrap_or_else(|| panic!("Bottom token frame is missing for token: {token:?}"))
-  .inner
-  .push(delimited);
  stack_top.inner.push(delimited);
  }
  FlatToken::Token(token) => stack_top.inner.push(AttrTokenTree::Token(token, spacing)),
  FlatToken::AttrsTarget(target) => {
  stack_top.inner.push(AttrTokenTree::AttrsTarget(target))
  }
- FlatToken::Token(token) => stack
- .last_mut()
- .expect("Bottom token frame is missing!")
- .inner
- .push(AttrTokenTree::Token(token, spacing)),
- FlatToken::AttrsTarget(target) => stack
- .last_mut()
- .expect("Bottom token frame is missing!")
- .inner
- .push(AttrTokenTree::AttrsTarget(target)),
  FlatToken::Empty => {}
  }
  }
- let mut final_buf = stack.pop().expect("Missing final buf!");
 
  if break_last_token {
- let last_token = final_buf.inner.pop().unwrap();
  let last_token = stack_top.inner.pop().unwrap();
  if let AttrTokenTree::Token(last_token, spacing) = last_token {
  let unglued_first = last_token.kind.break_two_token_op().unwrap().0;
 
  // An 'unglued' token is always two ASCII characters
  let mut first_span = last_token.span.shrink_to_lo();
  first_span = first_span.with_hi(first_span.lo() rustc_span::BytePos(1));
 
- final_buf
  stack_top
  .inner
  .push(AttrTokenTree::Token(Token::new(unglued_first, first_span), spacing));
  } else {
  panic!("Unexpected last token {last_token:?}")
  }
  }
- AttrTokenStream::new(final_buf.inner)
  AttrTokenStream::new(stack_top.inner)
 }
 
 // Some types are used a lot. Make sure they don't unintentionally get bigger.