Pretty printer algorithm revamp step 2

compiler/rustc_ast_pretty/src/pp.rs

@@ -167,14 +167,9 @@ pub enum Token {
  Break(BreakToken),
  Begin(BeginToken),
  End,
- Eof,
 }
 
 impl Token {
- crate fn is_eof(&self) -> bool {
- matches!(self, Token::Eof)
- }
-
  pub fn is_hardbreak_tok(&self) -> bool {
  matches!(self, Token::Break(BreakToken { offset: 0, blank_space: SIZE_INFINITY }))
  }
@@ -187,7 +182,6 @@ impl fmt::Display for Token {
  Token::Break(_) => f.write_str("BREAK"),
  Token::Begin(_) => f.write_str("BEGIN"),
  Token::End => f.write_str("END"),
- Token::Eof => f.write_str("EOF"),
  }
  }
 }
@@ -212,10 +206,6 @@ pub struct Printer {
  margin: isize,
  /// Number of spaces left on line
  space: isize,
- /// Index of left side of input stream
- left: usize,
- /// Index of right side of input stream
- right: usize,
  /// Ring-buffer of tokens and calculated sizes
  buf: RingBuffer<BufEntry>,
  /// Running size of stream "...left"
@@ -233,6 +223,9 @@ pub struct Printer {
  print_stack: Vec<PrintStackElem>,
  /// Buffered indentation to avoid writing trailing whitespace
  pending_indentation: isize,
+ /// The token most recently popped from the left boundary of the
+ /// ring-buffer for printing
+ last_printed: Option<Token>,
 }
 
 #[derive(Clone)]
@@ -241,39 +234,34 @@ struct BufEntry {
  size: isize,
 }
 
-impl Default for BufEntry {
- fn default() -> Self {
- BufEntry { token: Token::Eof, size: 0 }
- }
-}
-
 impl Printer {
  pub fn new() -> Self {
  let linewidth = 78;
- let mut buf = RingBuffer::new();
- buf.advance_right();
  Printer {
  out: String::new(),
  margin: linewidth as isize,
  space: linewidth as isize,
- left: 0,
- right: 0,
- buf,
+ buf: RingBuffer::new(),
  left_total: 0,
  right_total: 0,
  scan_stack: VecDeque::new(),
  print_stack: Vec::new(),
  pending_indentation: 0,
+ last_printed: None,
  }
  }
 
- pub fn last_token(&self) -> Token {
- self.buf[self.right].token.clone()
+ pub fn last_token(&self) -> Option<&Token> {
+ self.last_token_still_buffered().or_else(|| self.last_printed.as_ref())
+ }
+
+ pub fn last_token_still_buffered(&self) -> Option<&Token> {
+ self.buf.last().map(|last| &last.token)
  }
 
  /// Be very careful with this!
- pub fn replace_last_token(&mut self, t: Token) {
- self.buf[self.right].token = t;
+ pub fn replace_last_token_still_buffered(&mut self, t: Token) {
+ self.buf.last_mut().unwrap().token = t;
  }
 
  fn scan_eof(&mut self) {
@@ -287,89 +275,63 @@ impl Printer {
  if self.scan_stack.is_empty() {
  self.left_total = 1;
  self.right_total = 1;
- self.right = self.left;
- self.buf.truncate(1);
- } else {
- self.advance_right();
+ self.buf.clear();
  }
- self.scan_push(BufEntry { token: Token::Begin(b), size: -self.right_total });
+ let right = self.buf.push(BufEntry { token: Token::Begin(b), size: -self.right_total });
+ self.scan_stack.push_front(right);
  }
 
  fn scan_end(&mut self) {
  if self.scan_stack.is_empty() {
  self.print_end();
  } else {
- self.advance_right();
- self.scan_push(BufEntry { token: Token::End, size: -1 });
+ let right = self.buf.push(BufEntry { token: Token::End, size: -1 });
+ self.scan_stack.push_front(right);
  }
  }
 
  fn scan_break(&mut self, b: BreakToken) {
  if self.scan_stack.is_empty() {
  self.left_total = 1;
  self.right_total = 1;
- self.right = self.left;
- self.buf.truncate(1);
+ self.buf.clear();
  } else {
- self.advance_right();
+ self.check_stack(0);
  }
- self.check_stack(0);
- self.scan_push(BufEntry { token: Token::Break(b), size: -self.right_total });
+ let right = self.buf.push(BufEntry { token: Token::Break(b), size: -self.right_total });
+ self.scan_stack.push_front(right);
  self.right_total += b.blank_space;
  }
 
  fn scan_string(&mut self, s: Cow<'static, str>) {
  if self.scan_stack.is_empty() {
- self.print_string(s);
+ self.print_string(&s);
  } else {
- self.advance_right();
  let len = s.len() as isize;
- self.buf[self.right] = BufEntry { token: Token::String(s), size: len };
+ self.buf.push(BufEntry { token: Token::String(s), size: len });
  self.right_total += len;
  self.check_stream();
  }
  }
 
  fn check_stream(&mut self) {
- if self.right_total - self.left_total > self.space {
- if Some(&self.left) == self.scan_stack.back() {
- let scanned = self.scan_pop_bottom();
- self.buf[scanned].size = SIZE_INFINITY;
+ while self.right_total - self.left_total > self.space {
+ if *self.scan_stack.back().unwrap() == self.buf.index_of_first() {
+ self.scan_stack.pop_back().unwrap();
+ self.buf.first_mut().unwrap().size = SIZE_INFINITY;
  }
  self.advance_left();
- if self.left != self.right {
- self.check_stream();
+ if self.buf.is_empty() {
+ break;
  }
  }
  }
 
- fn scan_push(&mut self, entry: BufEntry) {
- self.buf[self.right] = entry;
- self.scan_stack.push_front(self.right);
- }
-
- fn scan_pop(&mut self) -> usize {
- self.scan_stack.pop_front().unwrap()
- }
-
- fn scan_top(&self) -> usize {
- *self.scan_stack.front().unwrap()
- }
-
- fn scan_pop_bottom(&mut self) -> usize {
- self.scan_stack.pop_back().unwrap()
- }
-
- fn advance_right(&mut self) {
- self.right += 1;
- self.buf.advance_right();
- }
-
  fn advance_left(&mut self) {
- let mut left_size = self.buf[self.left].size;
+ let mut left_size = self.buf.first().unwrap().size;
 
  while left_size >= 0 {
- let left = self.buf[self.left].token.clone();
+ let left = self.buf.first().unwrap().token.clone();
 
  let len = match left {
  Token::Break(b) => b.blank_space,
@@ -385,39 +347,38 @@ impl Printer {
 
  self.left_total += len;
 
- if self.left == self.right {
+ self.buf.advance_left();
+ if self.buf.is_empty() {
  break;
  }
 
- self.buf.advance_left();
- self.left += 1;
-
- left_size = self.buf[self.left].size;
+ left_size = self.buf.first().unwrap().size;
  }
  }
 
- fn check_stack(&mut self, k: usize) {
- if !self.scan_stack.is_empty() {
- let x = self.scan_top();
- match self.buf[x].token {
+ fn check_stack(&mut self, mut k: usize) {
+ while let Some(&x) = self.scan_stack.front() {
+ let mut entry = &mut self.buf[x];
+ match entry.token {
  Token::Begin(_) => {
- if k > 0 {
- self.scan_pop();
- self.buf[x].size += self.right_total;
- self.check_stack(k - 1);
+ if k == 0 {
+ break;
  }
+ self.scan_stack.pop_front().unwrap();
+ entry.size += self.right_total;
+ k -= 1;
  }
  Token::End => {
  // paper says + not =, but that makes no sense.
- self.scan_pop();
- self.buf[x].size = 1;
- self.check_stack(k + 1);
+ self.scan_stack.pop_front().unwrap();
+ entry.size = 1;
+ k += 1;
  }
  _ => {
- self.scan_pop();
- self.buf[x].size += self.right_total;
- if k > 0 {
- self.check_stack(k);
+ self.scan_stack.pop_front().unwrap();
+ entry.size += self.right_total;
+ if k == 0 {
+ break;
  }
  }
  }
@@ -477,7 +438,7 @@ impl Printer {
  }
  }
 
- fn print_string(&mut self, s: Cow<'static, str>) {
+ fn print_string(&mut self, s: &str) {
  let len = s.len() as isize;
  // assert!(len <= space);
  self.space -= len;
@@ -491,21 +452,21 @@ impl Printer {
  self.out.reserve(self.pending_indentation as usize);
  self.out.extend(std::iter::repeat(' ').take(self.pending_indentation as usize));
  self.pending_indentation = 0;
- self.out.push_str(&s);
+ self.out.push_str(s);
  }
 
  fn print(&mut self, token: Token, l: isize) {
- match token {
- Token::Begin(b) => self.print_begin(b, l),
+ match &token {
+ Token::Begin(b) => self.print_begin(*b, l),
  Token::End => self.print_end(),
- Token::Break(b) => self.print_break(b, l),
+ Token::Break(b) => self.print_break(*b, l),
  Token::String(s) => {
  let len = s.len() as isize;
  assert_eq!(len, l);
  self.print_string(s);
  }
- Token::Eof => panic!(), // Eof should never get here.
  }
+ self.last_printed = Some(token);
  }
 
  // Convenience functions to talk to the printer.
@@ -560,7 +521,10 @@ impl Printer {
  }
 
  pub fn is_beginning_of_line(&self) -> bool {
- self.last_token().is_eof() || self.last_token().is_hardbreak_tok()
+ match self.last_token() {
+ Some(last_token) => last_token.is_hardbreak_tok(),
+ None => true,
+ }
  }
 
  pub fn hardbreak_tok_offset(off: isize) -> Token {

compiler/rustc_ast_pretty/src/pp/ring.rs

@@ -22,20 +22,43 @@ impl<T> RingBuffer<T> {
  RingBuffer { data: VecDeque::new(), offset: 0 }
  }
 
- pub fn advance_right(&mut self)
- where
- T: Default,
- {
- self.data.push_back(T::default());
+ pub fn is_empty(&self) -> bool {
+ self.data.is_empty()
+ }
+
+ pub fn push(&mut self, value: T) -> usize {
+ let index = self.offset + self.data.len();
+ self.data.push_back(value);
+ index
  }
 
  pub fn advance_left(&mut self) {
  self.data.pop_front().unwrap();
  self.offset += 1;
  }
 
- pub fn truncate(&mut self, len: usize) {
- self.data.truncate(len);
+ pub fn clear(&mut self) {
+ self.data.clear();
+ }
+
+ pub fn index_of_first(&self) -> usize {
+ self.offset
+ }
+
+ pub fn first(&self) -> Option<&T> {
+ self.data.front()
+ }
+
+ pub fn first_mut(&mut self) -> Option<&mut T> {
+ self.data.front_mut()
+ }
+
+ pub fn last(&self) -> Option<&T> {
+ self.data.back()
+ }
+
+ pub fn last_mut(&mut self) -> Option<&mut T> {
+ self.data.back_mut()
  }
 }
 

compiler/rustc_ast_pretty/src/pprust/state.rs

@@ -329,9 +329,9 @@ pub trait PrintState<'a>: std::ops::Deref<Target = pp::Printer> + std::ops::Dere
  CommentStyle::BlankLine => {
  // We need to do at least one, possibly two hardbreaks.
  let twice = match self.last_token() {
- pp::Token::String(s) => ";" == s,
- pp::Token::Begin(_) => true,
- pp::Token::End => true,
+ Some(pp::Token::String(s)) => ";" == s,
+ Some(pp::Token::Begin(_)) => true,
+ Some(pp::Token::End) => true,
  _ => false,
  };
  if twice {
@@ -687,11 +687,15 @@ pub trait PrintState<'a>: std::ops::Deref<Target = pp::Printer> + std::ops::Dere
  fn break_offset_if_not_bol(&mut self, n: usize, off: isize) {
  if !self.is_beginning_of_line() {
  self.break_offset(n, off)
- } else if off != 0 && self.last_token().is_hardbreak_tok() {
- // We do something pretty sketchy here: tuck the nonzero
- // offset-adjustment we were going to deposit along with the
- // break into the previous hardbreak.
- self.replace_last_token(pp::Printer::hardbreak_tok_offset(off));
+ } else if off != 0 {
+ if let Some(last_token) = self.last_token_still_buffered() {
+ if last_token.is_hardbreak_tok() {
+ // We do something pretty sketchy here: tuck the nonzero
+ // offset-adjustment we were going to deposit along with the
+ // break into the previous hardbreak.
+ self.replace_last_token_still_buffered(pp::Printer::hardbreak_tok_offset(off));
+ }
+ }
  }
  }