582 lines
21 KiB
Rust
582 lines
21 KiB
Rust
use io::WriterUtil;
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use dvec::DVec;
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/*
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* This pretty-printer is a direct reimplementation of Philip Karlton's
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* Mesa pretty-printer, as described in appendix A of
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*
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* STAN-CS-79-770: "Pretty Printing", by Derek C. Oppen.
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* Stanford Department of Computer Science, 1979.
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*
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* The algorithm's aim is to break a stream into as few lines as possible
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* while respecting the indentation-consistency requirements of the enclosing
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* block, and avoiding breaking at silly places on block boundaries, for
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* example, between "x" and ")" in "x)".
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*
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* I am implementing this algorithm because it comes with 20 pages of
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* documentation explaining its theory, and because it addresses the set of
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* concerns I've seen other pretty-printers fall down on. Weirdly. Even though
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* it's 32 years old and not written in Haskell. What can I say?
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*
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* Despite some redundancies and quirks in the way it's implemented in that
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* paper, I've opted to keep the implementation here as similar as I can,
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* changing only what was blatantly wrong, a typo, or sufficiently
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* non-idiomatic rust that it really stuck out.
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*
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* In particular you'll see a certain amount of churn related to INTEGER vs.
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* CARDINAL in the Mesa implementation. Mesa apparently interconverts the two
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* somewhat readily? In any case, I've used uint for indices-in-buffers and
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* ints for character-sizes-and-indentation-offsets. This respects the need
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* for ints to "go negative" while carrying a pending-calculation balance, and
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* helps differentiate all the numbers flying around internally (slightly).
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*
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* I also inverted the indentation arithmetic used in the print stack, since
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* the Mesa implementation (somewhat randomly) stores the offset on the print
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* stack in terms of margin-col rather than col itself. I store col.
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*
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* I also implemented a small change in the STRING token, in that I store an
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* explicit length for the string. For most tokens this is just the length of
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* the accompanying string. But it's necessary to permit it to differ, for
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* encoding things that are supposed to "go on their own line" -- certain
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* classes of comment and blank-line -- where relying on adjacent
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* hardbreak-like BREAK tokens with long blankness indication doesn't actually
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* work. To see why, consider when there is a "thing that should be on its own
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* line" between two long blocks, say functions. If you put a hardbreak after
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* each function (or before each) and the breaking algorithm decides to break
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* there anyways (because the functions themselves are long) you wind up with
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* extra blank lines. If you don't put hardbreaks you can wind up with the
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* "thing which should be on its own line" not getting its own line in the
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* rare case of "really small functions" or such. This re-occurs with comments
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* and explicit blank lines. So in those cases we use a string with a payload
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* we want isolated to a line and an explicit length that's huge, surrounded
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* by two zero-length breaks. The algorithm will try its best to fit it on a
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* line (which it can't) and so naturally place the content on its own line to
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* avoid combining it with other lines and making matters even worse.
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*/
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enum breaks { consistent, inconsistent, }
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#[cfg(stage0)]
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impl breaks : cmp::Eq {
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pure fn eq(&&other: breaks) -> bool {
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match (self, other) {
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(consistent, consistent) => true,
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(inconsistent, inconsistent) => true,
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(consistent, _) => false,
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(inconsistent, _) => false,
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}
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}
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pure fn ne(&&other: breaks) -> bool { !self.eq(other) }
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}
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#[cfg(stage1)]
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#[cfg(stage2)]
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impl breaks : cmp::Eq {
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pure fn eq(other: &breaks) -> bool {
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match (self, (*other)) {
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(consistent, consistent) => true,
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(inconsistent, inconsistent) => true,
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(consistent, _) => false,
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(inconsistent, _) => false,
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}
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}
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pure fn ne(other: &breaks) -> bool { !self.eq(other) }
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}
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type break_t = {offset: int, blank_space: int};
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type begin_t = {offset: int, breaks: breaks};
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enum token { STRING(@~str, int), BREAK(break_t), BEGIN(begin_t), END, EOF, }
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impl token {
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fn is_eof() -> bool {
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match self { EOF => true, _ => false }
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}
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fn is_hardbreak_tok() -> bool {
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match self {
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BREAK({offset: 0, blank_space: bs }) if bs == size_infinity =>
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true,
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_ =>
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false
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}
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}
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}
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fn tok_str(++t: token) -> ~str {
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match t {
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STRING(s, len) => return fmt!("STR(%s,%d)", *s, len),
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BREAK(_) => return ~"BREAK",
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BEGIN(_) => return ~"BEGIN",
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END => return ~"END",
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EOF => return ~"EOF"
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}
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}
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fn buf_str(toks: ~[mut token], szs: ~[mut int], left: uint, right: uint,
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lim: uint) -> ~str {
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let n = vec::len(toks);
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assert (n == vec::len(szs));
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let mut i = left;
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let mut L = lim;
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let mut s = ~"[";
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while i != right && L != 0u {
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L -= 1u;
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if i != left { s += ~", "; }
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s += fmt!("%d=%s", szs[i], tok_str(toks[i]));
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i += 1u;
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i %= n;
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}
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s += ~"]";
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return s;
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}
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enum print_stack_break { fits, broken(breaks), }
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type print_stack_elt = {offset: int, pbreak: print_stack_break};
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const size_infinity: int = 0xffff;
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fn mk_printer(out: io::Writer, linewidth: uint) -> printer {
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// Yes 3, it makes the ring buffers big enough to never
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// fall behind.
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let n: uint = 3 * linewidth;
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debug!("mk_printer %u", linewidth);
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let token: ~[mut token] = vec::to_mut(vec::from_elem(n, EOF));
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let size: ~[mut int] = vec::to_mut(vec::from_elem(n, 0));
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let scan_stack: ~[mut uint] = vec::to_mut(vec::from_elem(n, 0u));
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printer_(@{out: out,
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buf_len: n,
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mut margin: linewidth as int,
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mut space: linewidth as int,
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mut left: 0,
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mut right: 0,
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token: move token,
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size: move size,
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mut left_total: 0,
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mut right_total: 0,
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mut scan_stack: move scan_stack,
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mut scan_stack_empty: true,
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mut top: 0,
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mut bottom: 0,
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print_stack: DVec(),
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mut pending_indentation: 0,
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mut token_tree_last_was_ident: false})
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}
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/*
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* In case you do not have the paper, here is an explanation of what's going
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* on.
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*
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* There is a stream of input tokens flowing through this printer.
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*
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* The printer buffers up to 3N tokens inside itself, where N is linewidth.
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* Yes, linewidth is chars and tokens are multi-char, but in the worst
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* case every token worth buffering is 1 char long, so it's ok.
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*
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* Tokens are STRING, BREAK, and BEGIN/END to delimit blocks.
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*
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* BEGIN tokens can carry an offset, saying "how far to indent when you break
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* inside here", as well as a flag indicating "consistent" or "inconsistent"
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* breaking. Consistent breaking means that after the first break, no attempt
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* will be made to flow subsequent breaks together onto lines. Inconsistent
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* is the opposite. Inconsistent breaking example would be, say:
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*
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* foo(hello, there, good, friends)
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*
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* breaking inconsistently to become
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*
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* foo(hello, there
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* good, friends);
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*
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* whereas a consistent breaking would yield:
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*
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* foo(hello,
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* there
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* good,
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* friends);
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*
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* That is, in the consistent-break blocks we value vertical alignment
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* more than the ability to cram stuff onto a line. But in all cases if it
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* can make a block a one-liner, it'll do so.
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*
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* Carrying on with high-level logic:
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*
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* The buffered tokens go through a ring-buffer, 'tokens'. The 'left' and
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* 'right' indices denote the active portion of the ring buffer as well as
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* describing hypothetical points-in-the-infinite-stream at most 3N tokens
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* apart (i.e. "not wrapped to ring-buffer boundaries"). The paper will switch
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* between using 'left' and 'right' terms to denote the wrapepd-to-ring-buffer
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* and point-in-infinite-stream senses freely.
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*
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* There is a parallel ring buffer, 'size', that holds the calculated size of
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* each token. Why calculated? Because for BEGIN/END pairs, the "size"
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* includes everything betwen the pair. That is, the "size" of BEGIN is
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* actually the sum of the sizes of everything between BEGIN and the paired
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* END that follows. Since that is arbitrarily far in the future, 'size' is
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* being rewritten regularly while the printer runs; in fact most of the
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* machinery is here to work out 'size' entries on the fly (and give up when
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* they're so obviously over-long that "infinity" is a good enough
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* approximation for purposes of line breaking).
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*
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* The "input side" of the printer is managed as an abstract process called
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* SCAN, which uses 'scan_stack', 'scan_stack_empty', 'top' and 'bottom', to
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* manage calculating 'size'. SCAN is, in other words, the process of
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* calculating 'size' entries.
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*
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* The "output side" of the printer is managed by an abstract process called
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* PRINT, which uses 'print_stack', 'margin' and 'space' to figure out what to
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* do with each token/size pair it consumes as it goes. It's trying to consume
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* the entire buffered window, but can't output anything until the size is >=
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* 0 (sizes are set to negative while they're pending calculation).
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*
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* So SCAN takeks input and buffers tokens and pending calculations, while
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* PRINT gobbles up completed calculations and tokens from the buffer. The
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* theory is that the two can never get more than 3N tokens apart, because
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* once there's "obviously" too much data to fit on a line, in a size
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* calculation, SCAN will write "infinity" to the size and let PRINT consume
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* it.
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*
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* In this implementation (following the paper, again) the SCAN process is
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* the method called 'pretty_print', and the 'PRINT' process is the method
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* called 'print'.
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*/
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type printer_ = {
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out: io::Writer,
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buf_len: uint,
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mut margin: int, // width of lines we're constrained to
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mut space: int, // number of spaces left on line
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mut left: uint, // index of left side of input stream
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mut right: uint, // index of right side of input stream
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token: ~[mut token], // ring-buffr stream goes through
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size: ~[mut int], // ring-buffer of calculated sizes
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mut left_total: int, // running size of stream "...left"
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mut right_total: int, // running size of stream "...right"
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// pseudo-stack, really a ring too. Holds the
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// primary-ring-buffers index of the BEGIN that started the
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// current block, possibly with the most recent BREAK after that
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// BEGIN (if there is any) on top of it. Stuff is flushed off the
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// bottom as it becomes irrelevant due to the primary ring-buffer
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// advancing.
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mut scan_stack: ~[mut uint],
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mut scan_stack_empty: bool, // top==bottom disambiguator
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mut top: uint, // index of top of scan_stack
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mut bottom: uint, // index of bottom of scan_stack
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// stack of blocks-in-progress being flushed by print
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print_stack: DVec<print_stack_elt>,
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// buffered indentation to avoid writing trailing whitespace
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mut pending_indentation: int,
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mut token_tree_last_was_ident: bool
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};
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enum printer {
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printer_(@printer_)
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}
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impl printer {
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fn last_token() -> token { self.token[self.right] }
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// be very careful with this!
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fn replace_last_token(t: token) { self.token[self.right] = t; }
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fn pretty_print(t: token) {
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debug!("pp ~[%u,%u]", self.left, self.right);
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match t {
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EOF => {
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if !self.scan_stack_empty {
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self.check_stack(0);
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self.advance_left(self.token[self.left],
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self.size[self.left]);
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}
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self.indent(0);
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}
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BEGIN(b) => {
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if self.scan_stack_empty {
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self.left_total = 1;
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self.right_total = 1;
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self.left = 0u;
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self.right = 0u;
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} else { self.advance_right(); }
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debug!("pp BEGIN(%d)/buffer ~[%u,%u]",
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b.offset, self.left, self.right);
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self.token[self.right] = t;
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self.size[self.right] = -self.right_total;
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self.scan_push(self.right);
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}
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END => {
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if self.scan_stack_empty {
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debug!("pp END/print ~[%u,%u]", self.left, self.right);
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self.print(t, 0);
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} else {
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debug!("pp END/buffer ~[%u,%u]", self.left, self.right);
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self.advance_right();
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self.token[self.right] = t;
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self.size[self.right] = -1;
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self.scan_push(self.right);
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}
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}
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BREAK(b) => {
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if self.scan_stack_empty {
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self.left_total = 1;
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self.right_total = 1;
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self.left = 0u;
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self.right = 0u;
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} else { self.advance_right(); }
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debug!("pp BREAK(%d)/buffer ~[%u,%u]",
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b.offset, self.left, self.right);
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self.check_stack(0);
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self.scan_push(self.right);
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self.token[self.right] = t;
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self.size[self.right] = -self.right_total;
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self.right_total += b.blank_space;
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}
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STRING(s, len) => {
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if self.scan_stack_empty {
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debug!("pp STRING('%s')/print ~[%u,%u]",
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*s, self.left, self.right);
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self.print(t, len);
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} else {
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debug!("pp STRING('%s')/buffer ~[%u,%u]",
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*s, self.left, self.right);
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self.advance_right();
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self.token[self.right] = t;
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self.size[self.right] = len;
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self.right_total += len;
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self.check_stream();
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}
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}
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}
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}
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fn check_stream() {
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debug!("check_stream ~[%u, %u] with left_total=%d, right_total=%d",
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self.left, self.right, self.left_total, self.right_total);
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if self.right_total - self.left_total > self.space {
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debug!("scan window is %d, longer than space on line (%d)",
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self.right_total - self.left_total, self.space);
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if !self.scan_stack_empty {
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if self.left == self.scan_stack[self.bottom] {
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debug!("setting %u to infinity and popping", self.left);
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self.size[self.scan_pop_bottom()] = size_infinity;
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}
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}
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self.advance_left(self.token[self.left], self.size[self.left]);
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if self.left != self.right { self.check_stream(); }
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}
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}
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fn scan_push(x: uint) {
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debug!("scan_push %u", x);
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if self.scan_stack_empty {
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self.scan_stack_empty = false;
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} else {
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self.top += 1u;
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self.top %= self.buf_len;
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assert (self.top != self.bottom);
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}
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self.scan_stack[self.top] = x;
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}
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fn scan_pop() -> uint {
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assert (!self.scan_stack_empty);
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let x = self.scan_stack[self.top];
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if self.top == self.bottom {
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self.scan_stack_empty = true;
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} else { self.top += self.buf_len - 1u; self.top %= self.buf_len; }
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return x;
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}
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fn scan_top() -> uint {
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assert (!self.scan_stack_empty);
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return self.scan_stack[self.top];
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}
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fn scan_pop_bottom() -> uint {
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assert (!self.scan_stack_empty);
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let x = self.scan_stack[self.bottom];
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if self.top == self.bottom {
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self.scan_stack_empty = true;
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} else { self.bottom += 1u; self.bottom %= self.buf_len; }
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return x;
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}
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fn advance_right() {
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self.right += 1u;
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self.right %= self.buf_len;
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assert (self.right != self.left);
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}
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fn advance_left(++x: token, L: int) {
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debug!("advnce_left ~[%u,%u], sizeof(%u)=%d", self.left, self.right,
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self.left, L);
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if L >= 0 {
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self.print(x, L);
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match x {
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BREAK(b) => self.left_total += b.blank_space,
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STRING(_, len) => { assert (len == L); self.left_total += len; }
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_ => ()
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}
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if self.left != self.right {
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self.left += 1u;
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self.left %= self.buf_len;
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self.advance_left(self.token[self.left],
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self.size[self.left]);
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}
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}
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}
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fn check_stack(k: int) {
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if !self.scan_stack_empty {
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let x = self.scan_top();
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match copy self.token[x] {
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BEGIN(_) => {
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if k > 0 {
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self.size[self.scan_pop()] = self.size[x] +
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self.right_total;
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self.check_stack(k - 1);
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}
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}
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END => {
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// paper says + not =, but that makes no sense.
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self.size[self.scan_pop()] = 1;
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self.check_stack(k + 1);
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}
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_ => {
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self.size[self.scan_pop()] = self.size[x] + self.right_total;
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if k > 0 { self.check_stack(k); }
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}
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}
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}
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}
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fn print_newline(amount: int) {
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debug!("NEWLINE %d", amount);
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self.out.write_str(~"\n");
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self.pending_indentation = 0;
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self.indent(amount);
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}
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fn indent(amount: int) {
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debug!("INDENT %d", amount);
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self.pending_indentation += amount;
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}
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fn get_top() -> print_stack_elt {
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let n = self.print_stack.len();
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if n != 0u {
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self.print_stack[n - 1u]
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} else {
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{offset: 0, pbreak: broken(inconsistent)}
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}
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}
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fn print_str(s: ~str) {
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while self.pending_indentation > 0 {
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self.out.write_str(~" ");
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self.pending_indentation -= 1;
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}
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self.out.write_str(s);
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}
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fn print(x: token, L: int) {
|
|
debug!("print %s %d (remaining line space=%d)", tok_str(x), L,
|
|
self.space);
|
|
log(debug, buf_str(self.token, self.size, self.left, self.right, 6u));
|
|
match x {
|
|
BEGIN(b) => {
|
|
if L > self.space {
|
|
let col = self.margin - self.space + b.offset;
|
|
debug!("print BEGIN -> push broken block at col %d", col);
|
|
self.print_stack.push({offset: col,
|
|
pbreak: broken(b.breaks)});
|
|
} else {
|
|
debug!("print BEGIN -> push fitting block");
|
|
self.print_stack.push({offset: 0,
|
|
pbreak: fits});
|
|
}
|
|
}
|
|
END => {
|
|
debug!("print END -> pop END");
|
|
assert (self.print_stack.len() != 0u);
|
|
self.print_stack.pop();
|
|
}
|
|
BREAK(b) => {
|
|
let top = self.get_top();
|
|
match top.pbreak {
|
|
fits => {
|
|
debug!("print BREAK(%d) in fitting block", b.blank_space);
|
|
self.space -= b.blank_space;
|
|
self.indent(b.blank_space);
|
|
}
|
|
broken(consistent) => {
|
|
debug!("print BREAK(%d+%d) in consistent block",
|
|
top.offset, b.offset);
|
|
self.print_newline(top.offset + b.offset);
|
|
self.space = self.margin - (top.offset + b.offset);
|
|
}
|
|
broken(inconsistent) => {
|
|
if L > self.space {
|
|
debug!("print BREAK(%d+%d) w/ newline in inconsistent",
|
|
top.offset, b.offset);
|
|
self.print_newline(top.offset + b.offset);
|
|
self.space = self.margin - (top.offset + b.offset);
|
|
} else {
|
|
debug!("print BREAK(%d) w/o newline in inconsistent",
|
|
b.blank_space);
|
|
self.indent(b.blank_space);
|
|
self.space -= b.blank_space;
|
|
}
|
|
}
|
|
}
|
|
}
|
|
STRING(s, len) => {
|
|
debug!("print STRING(%s)", *s);
|
|
assert (L == len);
|
|
// assert L <= space;
|
|
self.space -= len;
|
|
self.print_str(*s);
|
|
}
|
|
EOF => {
|
|
// EOF should never get here.
|
|
fail;
|
|
}
|
|
}
|
|
}
|
|
}
|
|
|
|
// Convenience functions to talk to the printer.
|
|
fn box(p: printer, indent: uint, b: breaks) {
|
|
p.pretty_print(BEGIN({offset: indent as int, breaks: b}));
|
|
}
|
|
|
|
fn ibox(p: printer, indent: uint) { box(p, indent, inconsistent); }
|
|
|
|
fn cbox(p: printer, indent: uint) { box(p, indent, consistent); }
|
|
|
|
fn break_offset(p: printer, n: uint, off: int) {
|
|
p.pretty_print(BREAK({offset: off, blank_space: n as int}));
|
|
}
|
|
|
|
fn end(p: printer) { p.pretty_print(END); }
|
|
|
|
fn eof(p: printer) { p.pretty_print(EOF); }
|
|
|
|
fn word(p: printer, wrd: ~str) {
|
|
p.pretty_print(STRING(@wrd, str::len(wrd) as int));
|
|
}
|
|
|
|
fn huge_word(p: printer, wrd: ~str) {
|
|
p.pretty_print(STRING(@wrd, size_infinity));
|
|
}
|
|
|
|
fn zero_word(p: printer, wrd: ~str) { p.pretty_print(STRING(@wrd, 0)); }
|
|
|
|
fn spaces(p: printer, n: uint) { break_offset(p, n, 0); }
|
|
|
|
fn zerobreak(p: printer) { spaces(p, 0u); }
|
|
|
|
fn space(p: printer) { spaces(p, 1u); }
|
|
|
|
fn hardbreak(p: printer) { spaces(p, size_infinity as uint); }
|
|
|
|
fn hardbreak_tok_offset(off: int) -> token {
|
|
return BREAK({offset: off, blank_space: size_infinity});
|
|
}
|
|
|
|
fn hardbreak_tok() -> token { return hardbreak_tok_offset(0); }
|
|
|
|
|
|
//
|
|
// Local Variables:
|
|
// mode: rust
|
|
// fill-column: 78;
|
|
// indent-tabs-mode: nil
|
|
// c-basic-offset: 4
|
|
// buffer-file-coding-system: utf-8-unix
|
|
// End:
|
|
//
|