Adding upstream version 1.64.0+dfsg1.upstream/1.64.0+dfsg1

Signed-off-by: Daniel Baumann <daniel.baumann@progress-linux.org>

1 files changed, 451 insertions, 0 deletions

diff --git a/compiler/rustc_ast_pretty/src/pp.rs b/compiler/rustc_ast_pretty/src/pp.rs
new file mode 100644
index 000000000..c93022308
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+++ b/compiler/rustc_ast_pretty/src/pp.rs
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+//! This pretty-printer is a direct reimplementation of Philip Karlton's
+//! Mesa pretty-printer, as described in the appendix to
+//! Derek C. Oppen, "Pretty Printing" (1979),
+//! Stanford Computer Science Department STAN-CS-79-770,
+//! <http://i.stanford.edu/pub/cstr/reports/cs/tr/79/770/CS-TR-79-770.pdf>.
+//!
+//! 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.
+//!
+//! # Explanation
+//!
+//! 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:
+//!
+//! ```ignore (illustrative)
+//! foo(hello, there, good, friends)
+//! ```
+//!
+//! breaking inconsistently to become
+//!
+//! ```ignore (illustrative)
+//! foo(hello, there,
+//!     good, friends);
+//! ```
+//!
+//! whereas a consistent breaking would yield:
+//!
+//! ```ignore (illustrative)
+//! 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`, 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
+//! methods called `Printer::scan_*`, and the 'PRINT' process is the
+//! method called `Printer::print`.
+
+mod convenience;
+mod ring;
+
+use ring::RingBuffer;
+use std::borrow::Cow;
+use std::cmp;
+use std::collections::VecDeque;
+use std::iter;
+
+/// How to break. Described in more detail in the module docs.
+#[derive(Clone, Copy, PartialEq)]
+pub enum Breaks {
+    Consistent,
+    Inconsistent,
+}
+
+#[derive(Clone, Copy, PartialEq)]
+enum IndentStyle {
+    /// Vertically aligned under whatever column this block begins at.
+    ///
+    ///     fn demo(arg1: usize,
+    ///             arg2: usize) {}
+    Visual,
+    /// Indented relative to the indentation level of the previous line.
+    ///
+    ///     fn demo(
+    ///         arg1: usize,
+    ///         arg2: usize,
+    ///     ) {}
+    Block { offset: isize },
+}
+
+#[derive(Clone, Copy, Default, PartialEq)]
+pub struct BreakToken {
+    offset: isize,
+    blank_space: isize,
+    pre_break: Option<char>,
+}
+
+#[derive(Clone, Copy, PartialEq)]
+pub struct BeginToken {
+    indent: IndentStyle,
+    breaks: Breaks,
+}
+
+#[derive(Clone, PartialEq)]
+pub enum Token {
+    // In practice a string token contains either a `&'static str` or a
+    // `String`. `Cow` is overkill for this because we never modify the data,
+    // but it's more convenient than rolling our own more specialized type.
+    String(Cow<'static, str>),
+    Break(BreakToken),
+    Begin(BeginToken),
+    End,
+}
+
+#[derive(Copy, Clone)]
+enum PrintFrame {
+    Fits,
+    Broken { indent: usize, breaks: Breaks },
+}
+
+const SIZE_INFINITY: isize = 0xffff;
+
+/// Target line width.
+const MARGIN: isize = 78;
+/// Every line is allowed at least this much space, even if highly indented.
+const MIN_SPACE: isize = 60;
+
+pub struct Printer {
+    out: String,
+    /// Number of spaces left on line
+    space: isize,
+    /// Ring-buffer of tokens and calculated sizes
+    buf: RingBuffer<BufEntry>,
+    /// 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: VecDeque<usize>,
+    /// Stack of blocks-in-progress being flushed by print
+    print_stack: Vec<PrintFrame>,
+    /// Level of indentation of current line
+    indent: usize,
+    /// 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)]
+struct BufEntry {
+    token: Token,
+    size: isize,
+}
+
+impl Printer {
+    pub fn new() -> Self {
+        Printer {
+            out: String::new(),
+            space: MARGIN,
+            buf: RingBuffer::new(),
+            left_total: 0,
+            right_total: 0,
+            scan_stack: VecDeque::new(),
+            print_stack: Vec::new(),
+            indent: 0,
+            pending_indentation: 0,
+            last_printed: None,
+        }
+    }
+
+    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_still_buffered(&mut self, token: Token) {
+        self.buf.last_mut().unwrap().token = token;
+    }
+
+    fn scan_eof(&mut self) {
+        if !self.scan_stack.is_empty() {
+            self.check_stack(0);
+            self.advance_left();
+        }
+    }
+
+    fn scan_begin(&mut self, token: BeginToken) {
+        if self.scan_stack.is_empty() {
+            self.left_total = 1;
+            self.right_total = 1;
+            self.buf.clear();
+        }
+        let right = self.buf.push(BufEntry { token: Token::Begin(token), size: -self.right_total });
+        self.scan_stack.push_back(right);
+    }
+
+    fn scan_end(&mut self) {
+        if self.scan_stack.is_empty() {
+            self.print_end();
+        } else {
+            let right = self.buf.push(BufEntry { token: Token::End, size: -1 });
+            self.scan_stack.push_back(right);
+        }
+    }
+
+    fn scan_break(&mut self, token: BreakToken) {
+        if self.scan_stack.is_empty() {
+            self.left_total = 1;
+            self.right_total = 1;
+            self.buf.clear();
+        } else {
+            self.check_stack(0);
+        }
+        let right = self.buf.push(BufEntry { token: Token::Break(token), size: -self.right_total });
+        self.scan_stack.push_back(right);
+        self.right_total += token.blank_space;
+    }
+
+    fn scan_string(&mut self, string: Cow<'static, str>) {
+        if self.scan_stack.is_empty() {
+            self.print_string(&string);
+        } else {
+            let len = string.len() as isize;
+            self.buf.push(BufEntry { token: Token::String(string), size: len });
+            self.right_total += len;
+            self.check_stream();
+        }
+    }
+
+    pub fn offset(&mut self, offset: isize) {
+        if let Some(BufEntry { token: Token::Break(token), .. }) = &mut self.buf.last_mut() {
+            token.offset += offset;
+        }
+    }
+
+    fn check_stream(&mut self) {
+        while self.right_total - self.left_total > self.space {
+            if *self.scan_stack.front().unwrap() == self.buf.index_of_first() {
+                self.scan_stack.pop_front().unwrap();
+                self.buf.first_mut().unwrap().size = SIZE_INFINITY;
+            }
+            self.advance_left();
+            if self.buf.is_empty() {
+                break;
+            }
+        }
+    }
+
+    fn advance_left(&mut self) {
+        while self.buf.first().unwrap().size >= 0 {
+            let left = self.buf.pop_first().unwrap();
+
+            match &left.token {
+                Token::String(string) => {
+                    self.left_total += string.len() as isize;
+                    self.print_string(string);
+                }
+                Token::Break(token) => {
+                    self.left_total += token.blank_space;
+                    self.print_break(*token, left.size);
+                }
+                Token::Begin(token) => self.print_begin(*token, left.size),
+                Token::End => self.print_end(),
+            }
+
+            self.last_printed = Some(left.token);
+
+            if self.buf.is_empty() {
+                break;
+            }
+        }
+    }
+
+    fn check_stack(&mut self, mut depth: usize) {
+        while let Some(&index) = self.scan_stack.back() {
+            let mut entry = &mut self.buf[index];
+            match entry.token {
+                Token::Begin(_) => {
+                    if depth == 0 {
+                        break;
+                    }
+                    self.scan_stack.pop_back().unwrap();
+                    entry.size += self.right_total;
+                    depth -= 1;
+                }
+                Token::End => {
+                    // paper says + not =, but that makes no sense.
+                    self.scan_stack.pop_back().unwrap();
+                    entry.size = 1;
+                    depth += 1;
+                }
+                _ => {
+                    self.scan_stack.pop_back().unwrap();
+                    entry.size += self.right_total;
+                    if depth == 0 {
+                        break;
+                    }
+                }
+            }
+        }
+    }
+
+    fn get_top(&self) -> PrintFrame {
+        *self
+            .print_stack
+            .last()
+            .unwrap_or(&PrintFrame::Broken { indent: 0, breaks: Breaks::Inconsistent })
+    }
+
+    fn print_begin(&mut self, token: BeginToken, size: isize) {
+        if size > self.space {
+            self.print_stack.push(PrintFrame::Broken { indent: self.indent, breaks: token.breaks });
+            self.indent = match token.indent {
+                IndentStyle::Block { offset } => {
+                    usize::try_from(self.indent as isize + offset).unwrap()
+                }
+                IndentStyle::Visual => (MARGIN - self.space) as usize,
+            };
+        } else {
+            self.print_stack.push(PrintFrame::Fits);
+        }
+    }
+
+    fn print_end(&mut self) {
+        if let PrintFrame::Broken { indent, .. } = self.print_stack.pop().unwrap() {
+            self.indent = indent;
+        }
+    }
+
+    fn print_break(&mut self, token: BreakToken, size: isize) {
+        let fits = match self.get_top() {
+            PrintFrame::Fits => true,
+            PrintFrame::Broken { breaks: Breaks::Consistent, .. } => false,
+            PrintFrame::Broken { breaks: Breaks::Inconsistent, .. } => size <= self.space,
+        };
+        if fits {
+            self.pending_indentation += token.blank_space;
+            self.space -= token.blank_space;
+        } else {
+            if let Some(pre_break) = token.pre_break {
+                self.out.push(pre_break);
+            }
+            self.out.push('\n');
+            let indent = self.indent as isize + token.offset;
+            self.pending_indentation = indent;
+            self.space = cmp::max(MARGIN - indent, MIN_SPACE);
+        }
+    }
+
+    fn print_string(&mut self, string: &str) {
+        // Write the pending indent. A more concise way of doing this would be:
+        //
+        //   write!(self.out, "{: >n$}", "", n = self.pending_indentation as usize)?;
+        //
+        // But that is significantly slower. This code is sufficiently hot, and indents can get
+        // sufficiently large, that the difference is significant on some workloads.
+        self.out.reserve(self.pending_indentation as usize);
+        self.out.extend(iter::repeat(' ').take(self.pending_indentation as usize));
+        self.pending_indentation = 0;
+
+        self.out.push_str(string);
+        self.space -= string.len() as isize;
+    }
+}