-// Copyright 2012 The Rust Project Developers. See the COPYRIGHT
-// file at the top-level directory of this distribution and at
-// http://rust-lang.org/COPYRIGHT.
-//
-// Licensed under the Apache License, Version 2.0 <LICENSE-APACHE or
-// http://www.apache.org/licenses/LICENSE-2.0> or the MIT license
-// <LICENSE-MIT or http://opensource.org/licenses/MIT>, at your
-// option. This file may not be copied, modified, or distributed
-// except according to those terms.
-
-//! This pretty-printer is a direct reimplementation of Philip Karlton's
-//! Mesa pretty-printer, as described in appendix A of
-//!
-//! STAN-CS-79-770: "Pretty Printing", by Derek C. Oppen.
-//! Stanford Department of Computer Science, 1979.
-//!
-//! The algorithm's aim is to break a stream into as few lines as possible
-//! while respecting the indentation-consistency requirements of the enclosing
-//! block, and avoiding breaking at silly places on block boundaries, for
-//! example, between "x" and ")" in "x)".
-//!
-//! I am implementing this algorithm because it comes with 20 pages of
-//! documentation explaining its theory, and because it addresses the set of
-//! concerns I've seen other pretty-printers fall down on. Weirdly. Even though
-//! it's 32 years old. What can I say?
-//!
-//! Despite some redundancies and quirks in the way it's implemented in that
-//! paper, I've opted to keep the implementation here as similar as I can,
-//! changing only what was blatantly wrong, a typo, or sufficiently
-//! non-idiomatic rust that it really stuck out.
-//!
-//! In particular you'll see a certain amount of churn related to INTEGER vs.
-//! CARDINAL in the Mesa implementation. Mesa apparently interconverts the two
-//! somewhat readily? In any case, I've used usize for indices-in-buffers and
-//! ints for character-sizes-and-indentation-offsets. This respects the need
-//! for ints to "go negative" while carrying a pending-calculation balance, and
-//! helps differentiate all the numbers flying around internally (slightly).
-//!
-//! I also inverted the indentation arithmetic used in the print stack, since
-//! the Mesa implementation (somewhat randomly) stores the offset on the print
-//! stack in terms of margin-col rather than col itself. I store col.
-//!
-//! I also implemented a small change in the String token, in that I store an
-//! explicit length for the string. For most tokens this is just the length of
-//! the accompanying string. But it's necessary to permit it to differ, for
-//! encoding things that are supposed to "go on their own line" -- certain
-//! classes of comment and blank-line -- where relying on adjacent
-//! hardbreak-like Break tokens with long blankness indication doesn't actually
-//! work. To see why, consider when there is a "thing that should be on its own
-//! line" between two long blocks, say functions. If you put a hardbreak after
-//! each function (or before each) and the breaking algorithm decides to break
-//! there anyways (because the functions themselves are long) you wind up with
-//! extra blank lines. If you don't put hardbreaks you can wind up with the
-//! "thing which should be on its own line" not getting its own line in the
-//! rare case of "really small functions" or such. This re-occurs with comments
-//! and explicit blank lines. So in those cases we use a string with a payload
-//! we want isolated to a line and an explicit length that's huge, surrounded
-//! by two zero-length breaks. The algorithm will try its best to fit it on a
-//! line (which it can't) and so naturally place the content on its own line to
-//! avoid combining it with other lines and making matters even worse.
-
-use std::io;
-use std::string;
-
-#[derive(Clone, Copy, PartialEq)]
-pub enum Breaks {
- Consistent,
- Inconsistent,
-}
-
-#[derive(Clone, Copy)]
-pub struct BreakToken {
- offset: isize,
- blank_space: isize
-}
-
-#[derive(Clone, Copy)]
-pub struct BeginToken {
- offset: isize,
- breaks: Breaks
-}
-
-#[derive(Clone)]
-pub enum Token {
- String(String, isize),
- Break(BreakToken),
- Begin(BeginToken),
- End,
- Eof,
-}
-
-impl Token {
- pub fn is_eof(&self) -> bool {
- match *self {
- Token::Eof => true,
- _ => false,
- }
- }
-
- pub fn is_hardbreak_tok(&self) -> bool {
- match *self {
- Token::Break(BreakToken {
- offset: 0,
- blank_space: bs
- }) if bs == SIZE_INFINITY =>
- true,
- _ =>
- false
- }
- }
-}
-
-pub fn tok_str(token: &Token) -> String {
- match *token {
- Token::String(ref s, len) => format!("STR({},{})", s, len),
- Token::Break(_) => "BREAK".to_string(),
- Token::Begin(_) => "BEGIN".to_string(),
- Token::End => "END".to_string(),
- Token::Eof => "EOF".to_string()
- }
-}
-
-pub fn buf_str(toks: &[Token],
- szs: &[isize],
- left: usize,
- right: usize,
- lim: usize)
- -> String {
- let n = toks.len();
- assert_eq!(n, szs.len());
- let mut i = left;
- let mut l = lim;
- let mut s = string::String::from("[");
- while i != right && l != 0 {
- l -= 1;
- if i != left {
- s.push_str(", ");
- }
- s.push_str(&format!("{}={}",
- szs[i],
- tok_str(&toks[i])));
- i += 1;
- i %= n;
- }
- s.push(']');
- s
-}
-
-#[derive(Copy, Clone)]
-pub enum PrintStackBreak {
- Fits,
- Broken(Breaks),
-}
-
-#[derive(Copy, Clone)]
-pub struct PrintStackElem {
- offset: isize,
- pbreak: PrintStackBreak
-}
-
-const SIZE_INFINITY: isize = 0xffff;
-
-pub fn mk_printer<'a>(out: Box<io::Write+'a>, linewidth: usize) -> Printer<'a> {
- // Yes 3, it makes the ring buffers big enough to never
- // fall behind.
- let n: usize = 3 * linewidth;
- debug!("mk_printer {}", linewidth);
- let token = vec![Token::Eof; n];
- let size = vec![0_isize; n];
- let scan_stack = vec![0_usize; n];
- Printer {
- out: out,
- buf_len: n,
- margin: linewidth as isize,
- space: linewidth as isize,
- left: 0,
- right: 0,
- token: token,
- size: size,
- left_total: 0,
- right_total: 0,
- scan_stack: scan_stack,
- scan_stack_empty: true,
- top: 0,
- bottom: 0,
- print_stack: Vec::new(),
- pending_indentation: 0
- }
-}
-
-
-/// In case you do not have the paper, here is an explanation of what's going
-/// on.
-///
-/// There is a stream of input tokens flowing through this printer.
-///
-/// The printer buffers up to 3N tokens inside itself, where N is linewidth.
-/// Yes, linewidth is chars and tokens are multi-char, but in the worst
-/// case every token worth buffering is 1 char long, so it's ok.
-///
-/// Tokens are String, Break, and Begin/End to delimit blocks.
-///
-/// Begin tokens can carry an offset, saying "how far to indent when you break
-/// inside here", as well as a flag indicating "consistent" or "inconsistent"
-/// breaking. Consistent breaking means that after the first break, no attempt
-/// will be made to flow subsequent breaks together onto lines. Inconsistent
-/// is the opposite. Inconsistent breaking example would be, say:
-///
-/// foo(hello, there, good, friends)
-///
-/// breaking inconsistently to become
-///
-/// foo(hello, there
-/// good, friends);
-///
-/// whereas a consistent breaking would yield:
-///
-/// foo(hello,
-/// there
-/// good,
-/// friends);
-///
-/// That is, in the consistent-break blocks we value vertical alignment
-/// more than the ability to cram stuff onto a line. But in all cases if it
-/// can make a block a one-liner, it'll do so.
-///
-/// Carrying on with high-level logic:
-///
-/// The buffered tokens go through a ring-buffer, 'tokens'. The 'left' and
-/// 'right' indices denote the active portion of the ring buffer as well as
-/// describing hypothetical points-in-the-infinite-stream at most 3N tokens
-/// apart (i.e. "not wrapped to ring-buffer boundaries"). The paper will switch
-/// between using 'left' and 'right' terms to denote the wrapped-to-ring-buffer
-/// and point-in-infinite-stream senses freely.
-///
-/// There is a parallel ring buffer, 'size', that holds the calculated size of
-/// each token. Why calculated? Because for Begin/End pairs, the "size"
-/// includes everything between the pair. That is, the "size" of Begin is
-/// actually the sum of the sizes of everything between Begin and the paired
-/// End that follows. Since that is arbitrarily far in the future, 'size' is
-/// being rewritten regularly while the printer runs; in fact most of the
-/// machinery is here to work out 'size' entries on the fly (and give up when
-/// they're so obviously over-long that "infinity" is a good enough
-/// approximation for purposes of line breaking).
-///
-/// The "input side" of the printer is managed as an abstract process called
-/// SCAN, which uses 'scan_stack', 'scan_stack_empty', 'top' and 'bottom', to
-/// manage calculating 'size'. SCAN is, in other words, the process of
-/// calculating 'size' entries.
-///
-/// The "output side" of the printer is managed by an abstract process called
-/// PRINT, which uses 'print_stack', 'margin' and 'space' to figure out what to
-/// do with each token/size pair it consumes as it goes. It's trying to consume
-/// the entire buffered window, but can't output anything until the size is >=
-/// 0 (sizes are set to negative while they're pending calculation).
-///
-/// So SCAN takes input and buffers tokens and pending calculations, while
-/// PRINT gobbles up completed calculations and tokens from the buffer. The
-/// theory is that the two can never get more than 3N tokens apart, because
-/// once there's "obviously" too much data to fit on a line, in a size
-/// calculation, SCAN will write "infinity" to the size and let PRINT consume
-/// it.
-///
-/// In this implementation (following the paper, again) the SCAN process is
-/// the method called 'pretty_print', and the 'PRINT' process is the method
-/// called 'print'.
-pub struct Printer<'a> {
- pub out: Box<io::Write+'a>,
- buf_len: usize,
- /// Width of lines we're constrained to
- 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 stream goes through
- token: Vec<Token> ,
- /// Ring-buffer of calculated sizes
- size: Vec<isize> ,
- /// Running size of stream "...left"
- left_total: isize,
- /// Running size of stream "...right"
- right_total: isize,
- /// Pseudo-stack, really a ring too. Holds the
- /// primary-ring-buffers index of the Begin that started the
- /// current block, possibly with the most recent Break after that
- /// Begin (if there is any) on top of it. Stuff is flushed off the
- /// bottom as it becomes irrelevant due to the primary ring-buffer
- /// advancing.
- scan_stack: Vec<usize> ,
- /// Top==bottom disambiguator
- scan_stack_empty: bool,
- /// Index of top of scan_stack
- top: usize,
- /// Index of bottom of scan_stack
- bottom: usize,
- /// Stack of blocks-in-progress being flushed by print
- print_stack: Vec<PrintStackElem> ,
- /// Buffered indentation to avoid writing trailing whitespace
- pending_indentation: isize,
-}
-
-impl<'a> Printer<'a> {
- pub fn last_token(&mut self) -> Token {
- self.token[self.right].clone()
- }
- // be very careful with this!
- pub fn replace_last_token(&mut self, t: Token) {
- self.token[self.right] = t;
- }
- pub fn pretty_print(&mut self, token: Token) -> io::Result<()> {
- debug!("pp Vec<{},{}>", self.left, self.right);
- match token {
- Token::Eof => {
- if !self.scan_stack_empty {
- self.check_stack(0);
- try!(self.advance_left());
- }
- self.indent(0);
- Ok(())
- }
- Token::Begin(b) => {
- if self.scan_stack_empty {
- self.left_total = 1;
- self.right_total = 1;
- self.left = 0;
- self.right = 0;
- } else { self.advance_right(); }
- debug!("pp Begin({})/buffer Vec<{},{}>",
- b.offset, self.left, self.right);
- self.token[self.right] = token;
- self.size[self.right] = -self.right_total;
- let right = self.right;
- self.scan_push(right);
- Ok(())
- }
- Token::End => {
- if self.scan_stack_empty {
- debug!("pp End/print Vec<{},{}>", self.left, self.right);
- self.print(token, 0)
- } else {
- debug!("pp End/buffer Vec<{},{}>", self.left, self.right);
- self.advance_right();
- self.token[self.right] = token;
- self.size[self.right] = -1;
- let right = self.right;
- self.scan_push(right);
- Ok(())
- }
- }
- Token::Break(b) => {
- if self.scan_stack_empty {
- self.left_total = 1;
- self.right_total = 1;
- self.left = 0;
- self.right = 0;
- } else { self.advance_right(); }
- debug!("pp Break({})/buffer Vec<{},{}>",
- b.offset, self.left, self.right);
- self.check_stack(0);
- let right = self.right;
- self.scan_push(right);
- self.token[self.right] = token;
- self.size[self.right] = -self.right_total;
- self.right_total += b.blank_space;
- Ok(())
- }
- Token::String(s, len) => {
- if self.scan_stack_empty {
- debug!("pp String('{}')/print Vec<{},{}>",
- s, self.left, self.right);
- self.print(Token::String(s, len), len)
- } else {
- debug!("pp String('{}')/buffer Vec<{},{}>",
- s, self.left, self.right);
- self.advance_right();
- self.token[self.right] = Token::String(s, len);
- self.size[self.right] = len;
- self.right_total += len;
- self.check_stream()
- }
- }
- }
- }
- pub fn check_stream(&mut self) -> io::Result<()> {
- debug!("check_stream Vec<{}, {}> with left_total={}, right_total={}",
- self.left, self.right, self.left_total, self.right_total);
- if self.right_total - self.left_total > self.space {
- debug!("scan window is {}, longer than space on line ({})",
- self.right_total - self.left_total, self.space);
- if !self.scan_stack_empty {
- if self.left == self.scan_stack[self.bottom] {
- debug!("setting {} to infinity and popping", self.left);
- let scanned = self.scan_pop_bottom();
- self.size[scanned] = SIZE_INFINITY;
- }
- }
- try!(self.advance_left());
- if self.left != self.right {
- try!(self.check_stream());
- }
- }
- Ok(())
- }
- pub fn scan_push(&mut self, x: usize) {
- debug!("scan_push {}", x);
- if self.scan_stack_empty {
- self.scan_stack_empty = false;
- } else {
- self.top += 1;
- self.top %= self.buf_len;
- assert!((self.top != self.bottom));
- }
- self.scan_stack[self.top] = x;
- }
- pub fn scan_pop(&mut self) -> usize {
- assert!((!self.scan_stack_empty));
- let x = self.scan_stack[self.top];
- if self.top == self.bottom {
- self.scan_stack_empty = true;
- } else {
- self.top += self.buf_len - 1; self.top %= self.buf_len;
- }
- return x;
- }
- pub fn scan_top(&mut self) -> usize {
- assert!((!self.scan_stack_empty));
- return self.scan_stack[self.top];
- }
- pub fn scan_pop_bottom(&mut self) -> usize {
- assert!((!self.scan_stack_empty));
- let x = self.scan_stack[self.bottom];
- if self.top == self.bottom {
- self.scan_stack_empty = true;
- } else {
- self.bottom += 1; self.bottom %= self.buf_len;
- }
- return x;
- }
- pub fn advance_right(&mut self) {
- self.right += 1;
- self.right %= self.buf_len;
- assert!((self.right != self.left));
- }
- pub fn advance_left(&mut self) -> io::Result<()> {
- debug!("advance_left Vec<{},{}>, sizeof({})={}", self.left, self.right,
- self.left, self.size[self.left]);
-
- let mut left_size = self.size[self.left];
-
- while left_size >= 0 {
- let left = self.token[self.left].clone();
-
- let len = match left {
- Token::Break(b) => b.blank_space,
- Token::String(_, len) => {
- assert_eq!(len, left_size);
- len
- }
- _ => 0
- };
-
- try!(self.print(left, left_size));
-
- self.left_total += len;
-
- if self.left == self.right {
- break;
- }
-
- self.left += 1;
- self.left %= self.buf_len;
-
- left_size = self.size[self.left];
- }
-
- Ok(())
- }
- pub fn check_stack(&mut self, k: isize) {
- if !self.scan_stack_empty {
- let x = self.scan_top();
- match self.token[x] {
- Token::Begin(_) => {
- if k > 0 {
- let popped = self.scan_pop();
- self.size[popped] = self.size[x] + self.right_total;
- self.check_stack(k - 1);
- }
- }
- Token::End => {
- // paper says + not =, but that makes no sense.
- let popped = self.scan_pop();
- self.size[popped] = 1;
- self.check_stack(k + 1);
- }
- _ => {
- let popped = self.scan_pop();
- self.size[popped] = self.size[x] + self.right_total;
- if k > 0 {
- self.check_stack(k);
- }
- }
- }
- }
- }
- pub fn print_newline(&mut self, amount: isize) -> io::Result<()> {
- debug!("NEWLINE {}", amount);
- let ret = write!(self.out, "\n");
- self.pending_indentation = 0;
- self.indent(amount);
- return ret;
- }
- pub fn indent(&mut self, amount: isize) {
- debug!("INDENT {}", amount);
- self.pending_indentation += amount;
- }
- pub fn get_top(&mut self) -> PrintStackElem {
- let print_stack = &mut self.print_stack;
- let n = print_stack.len();
- if n != 0 {
- (*print_stack)[n - 1]
- } else {
- PrintStackElem {
- offset: 0,
- pbreak: PrintStackBreak::Broken(Breaks::Inconsistent)
- }
- }
- }
- pub fn print_str(&mut self, s: &str) -> io::Result<()> {
- while self.pending_indentation > 0 {
- try!(write!(self.out, " "));
- self.pending_indentation -= 1;
- }
- write!(self.out, "{}", s)
- }
- pub fn print(&mut self, token: Token, l: isize) -> io::Result<()> {
- debug!("print {} {} (remaining line space={})", tok_str(&token), l,
- self.space);
- debug!("{}", buf_str(&self.token,
- &self.size,
- self.left,
- self.right,
- 6));
- match token {
- Token::Begin(b) => {
- if l > self.space {
- let col = self.margin - self.space + b.offset;
- debug!("print Begin -> push broken block at col {}", col);
- self.print_stack.push(PrintStackElem {
- offset: col,
- pbreak: PrintStackBreak::Broken(b.breaks)
- });
- } else {
- debug!("print Begin -> push fitting block");
- self.print_stack.push(PrintStackElem {
- offset: 0,
- pbreak: PrintStackBreak::Fits
- });
- }
- Ok(())
- }
- Token::End => {
- debug!("print End -> pop End");
- let print_stack = &mut self.print_stack;
- assert!((!print_stack.is_empty()));
- print_stack.pop().unwrap();
- Ok(())
- }
- Token::Break(b) => {
- let top = self.get_top();
- match top.pbreak {
- PrintStackBreak::Fits => {
- debug!("print Break({}) in fitting block", b.blank_space);
- self.space -= b.blank_space;
- self.indent(b.blank_space);
- Ok(())
- }
- PrintStackBreak::Broken(Breaks::Consistent) => {
- debug!("print Break({}+{}) in consistent block",
- top.offset, b.offset);
- let ret = self.print_newline(top.offset + b.offset);
- self.space = self.margin - (top.offset + b.offset);
- ret
- }
- PrintStackBreak::Broken(Breaks::Inconsistent) => {
- if l > self.space {
- debug!("print Break({}+{}) w/ newline in inconsistent",
- top.offset, b.offset);
- let ret = self.print_newline(top.offset + b.offset);
- self.space = self.margin - (top.offset + b.offset);
- ret
- } else {
- debug!("print Break({}) w/o newline in inconsistent",
- b.blank_space);
- self.indent(b.blank_space);
- self.space -= b.blank_space;
- Ok(())
- }
- }
- }
- }
- Token::String(s, len) => {
- debug!("print String({})", s);
- assert_eq!(l, len);
- // assert!(l <= space);
- self.space -= len;
- self.print_str(&s[..])
- }
- Token::Eof => {
- // Eof should never get here.
- panic!();
- }
- }
- }
-}
-
-// Convenience functions to talk to the printer.
-//
-// "raw box"
-pub fn rbox(p: &mut Printer, indent: usize, b: Breaks) -> io::Result<()> {
- p.pretty_print(Token::Begin(BeginToken {
- offset: indent as isize,
- breaks: b
- }))
-}
-
-pub fn ibox(p: &mut Printer, indent: usize) -> io::Result<()> {
- rbox(p, indent, Breaks::Inconsistent)
-}
-
-pub fn cbox(p: &mut Printer, indent: usize) -> io::Result<()> {
- rbox(p, indent, Breaks::Consistent)
-}
-
-pub fn break_offset(p: &mut Printer, n: usize, off: isize) -> io::Result<()> {
- p.pretty_print(Token::Break(BreakToken {
- offset: off,
- blank_space: n as isize
- }))
-}
-
-pub fn end(p: &mut Printer) -> io::Result<()> {
- p.pretty_print(Token::End)
-}
-
-pub fn eof(p: &mut Printer) -> io::Result<()> {
- p.pretty_print(Token::Eof)
-}
-
-pub fn word(p: &mut Printer, wrd: &str) -> io::Result<()> {
- p.pretty_print(Token::String(/* bad */ wrd.to_string(), wrd.len() as isize))
-}
-
-pub fn huge_word(p: &mut Printer, wrd: &str) -> io::Result<()> {
- p.pretty_print(Token::String(/* bad */ wrd.to_string(), SIZE_INFINITY))
-}
-
-pub fn zero_word(p: &mut Printer, wrd: &str) -> io::Result<()> {
- p.pretty_print(Token::String(/* bad */ wrd.to_string(), 0))
-}
-
-pub fn spaces(p: &mut Printer, n: usize) -> io::Result<()> {
- break_offset(p, n, 0)
-}
-
-pub fn zerobreak(p: &mut Printer) -> io::Result<()> {
- spaces(p, 0)
-}
-
-pub fn space(p: &mut Printer) -> io::Result<()> {
- spaces(p, 1)
-}
-
-pub fn hardbreak(p: &mut Printer) -> io::Result<()> {
- spaces(p, SIZE_INFINITY as usize)
-}
-
-pub fn hardbreak_tok_offset(off: isize) -> Token {
- Token::Break(BreakToken {offset: off, blank_space: SIZE_INFINITY})
-}
-
-pub fn hardbreak_tok() -> Token {
- hardbreak_tok_offset(0)
-}