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/*!
This module provides a regular expression printer for `Hir`.
*/
use std::fmt;
use hir::{self, Hir, HirKind};
use hir::visitor::{self, Visitor};
use is_meta_character;
/// A builder for constructing a printer.
///
/// Note that since a printer doesn't have any configuration knobs, this type
/// remains unexported.
#[derive(Clone, Debug)]
struct PrinterBuilder {
_priv: (),
}
impl Default for PrinterBuilder {
fn default() -> PrinterBuilder {
PrinterBuilder::new()
}
}
impl PrinterBuilder {
fn new() -> PrinterBuilder {
PrinterBuilder {
_priv: (),
}
}
fn build(&self) -> Printer {
Printer {
_priv: (),
}
}
}
/// A printer for a regular expression's high-level intermediate
/// representation.
///
/// A printer converts a high-level intermediate representation (HIR) to a
/// regular expression pattern string. This particular printer uses constant
/// stack space and heap space proportional to the size of the HIR.
///
/// Since this printer is only using the HIR, the pattern it prints will likely
/// not resemble the original pattern at all. For example, a pattern like
/// `\pL` will have its entire class written out.
///
/// The purpose of this printer is to provide a means to mutate an HIR and then
/// build a regular expression from the result of that mutation. (A regex
/// library could provide a constructor from this HIR explicitly, but that
/// creates an unnecessary public coupling between the regex library and this
/// specific HIR representation.)
#[derive(Debug)]
pub struct Printer {
_priv: (),
}
impl Printer {
/// Create a new printer.
pub fn new() -> Printer {
PrinterBuilder::new().build()
}
/// Print the given `Ast` to the given writer. The writer must implement
/// `fmt::Write`. Typical implementations of `fmt::Write` that can be used
/// here are a `fmt::Formatter` (which is available in `fmt::Display`
/// implementations) or a `&mut String`.
pub fn print<W: fmt::Write>(&mut self, hir: &Hir, wtr: W) -> fmt::Result {
visitor::visit(hir, Writer { printer: self, wtr: wtr })
}
}
#[derive(Debug)]
struct Writer<'p, W> {
printer: &'p mut Printer,
wtr: W,
}
impl<'p, W: fmt::Write> Visitor for Writer<'p, W> {
type Output = ();
type Err = fmt::Error;
fn finish(self) -> fmt::Result {
Ok(())
}
fn visit_pre(&mut self, hir: &Hir) -> fmt::Result {
match *hir.kind() {
HirKind::Empty
| HirKind::Repetition(_)
| HirKind::Concat(_)
| HirKind::Alternation(_) => {}
HirKind::Literal(hir::Literal::Unicode(c)) => {
self.write_literal_char(c)?;
}
HirKind::Literal(hir::Literal::Byte(b)) => {
self.write_literal_byte(b)?;
}
HirKind::Class(hir::Class::Unicode(ref cls)) => {
self.wtr.write_str("[")?;
for range in cls.iter() {
if range.start() == range.end() {
self.write_literal_char(range.start())?;
} else {
self.write_literal_char(range.start())?;
self.wtr.write_str("-")?;
self.write_literal_char(range.end())?;
}
}
self.wtr.write_str("]")?;
}
HirKind::Class(hir::Class::Bytes(ref cls)) => {
self.wtr.write_str("(?-u:[")?;
for range in cls.iter() {
if range.start() == range.end() {
self.write_literal_class_byte(range.start())?;
} else {
self.write_literal_class_byte(range.start())?;
self.wtr.write_str("-")?;
self.write_literal_class_byte(range.end())?;
}
}
self.wtr.write_str("])")?;
}
HirKind::Anchor(hir::Anchor::StartLine) => {
self.wtr.write_str("(?m:^)")?;
}
HirKind::Anchor(hir::Anchor::EndLine) => {
self.wtr.write_str("(?m:$)")?;
}
HirKind::Anchor(hir::Anchor::StartText) => {
self.wtr.write_str(r"\A")?;
}
HirKind::Anchor(hir::Anchor::EndText) => {
self.wtr.write_str(r"\z")?;
}
HirKind::WordBoundary(hir::WordBoundary::Unicode) => {
self.wtr.write_str(r"\b")?;
}
HirKind::WordBoundary(hir::WordBoundary::UnicodeNegate) => {
self.wtr.write_str(r"\B")?;
}
HirKind::WordBoundary(hir::WordBoundary::Ascii) => {
self.wtr.write_str(r"(?-u:\b)")?;
}
HirKind::WordBoundary(hir::WordBoundary::AsciiNegate) => {
self.wtr.write_str(r"(?-u:\B)")?;
}
HirKind::Group(ref x) => {
match x.kind {
hir::GroupKind::CaptureIndex(_) => {
self.wtr.write_str("(")?;
}
hir::GroupKind::CaptureName { ref name, .. } => {
write!(self.wtr, "(?P<{}>", name)?;
}
hir::GroupKind::NonCapturing => {
self.wtr.write_str("(?:")?;
}
}
}
}
Ok(())
}
fn visit_post(&mut self, hir: &Hir) -> fmt::Result {
match *hir.kind() {
// Handled during visit_pre
HirKind::Empty
| HirKind::Literal(_)
| HirKind::Class(_)
| HirKind::Anchor(_)
| HirKind::WordBoundary(_)
| HirKind::Concat(_)
| HirKind::Alternation(_) => {}
HirKind::Repetition(ref x) => {
match x.kind {
hir::RepetitionKind::ZeroOrOne => {
self.wtr.write_str("?")?;
}
hir::RepetitionKind::ZeroOrMore => {
self.wtr.write_str("*")?;
}
hir::RepetitionKind::OneOrMore => {
self.wtr.write_str("+")?;
}
hir::RepetitionKind::Range(ref x) => {
match *x {
hir::RepetitionRange::Exactly(m) => {
write!(self.wtr, "{{{}}}", m)?;
}
hir::RepetitionRange::AtLeast(m) => {
write!(self.wtr, "{{{},}}", m)?;
}
hir::RepetitionRange::Bounded(m, n) => {
write!(self.wtr, "{{{},{}}}", m, n)?;
}
}
}
}
if !x.greedy {
self.wtr.write_str("?")?;
}
}
HirKind::Group(_) => {
self.wtr.write_str(")")?;
}
}
Ok(())
}
fn visit_alternation_in(&mut self) -> fmt::Result {
self.wtr.write_str("|")
}
}
impl<'p, W: fmt::Write> Writer<'p, W> {
fn write_literal_char(&mut self, c: char) -> fmt::Result {
if is_meta_character(c) {
self.wtr.write_str("\\")?;
}
self.wtr.write_char(c)
}
fn write_literal_byte(&mut self, b: u8) -> fmt::Result {
let c = b as char;
if c <= 0x7F as char && !c.is_control() && !c.is_whitespace() {
self.write_literal_char(c)
} else {
write!(self.wtr, "(?-u:\\x{:02X})", b)
}
}
fn write_literal_class_byte(&mut self, b: u8) -> fmt::Result {
let c = b as char;
if c <= 0x7F as char && !c.is_control() && !c.is_whitespace() {
self.write_literal_char(c)
} else {
write!(self.wtr, "\\x{:02X}", b)
}
}
}
#[cfg(test)]
mod tests {
use ParserBuilder;
use super::Printer;
fn roundtrip(given: &str, expected: &str) {
roundtrip_with(|b| b, given, expected);
}
fn roundtrip_bytes(given: &str, expected: &str) {
roundtrip_with(|b| b.allow_invalid_utf8(true), given, expected);
}
fn roundtrip_with<F>(mut f: F, given: &str, expected: &str)
where F: FnMut(&mut ParserBuilder) -> &mut ParserBuilder
{
let mut builder = ParserBuilder::new();
f(&mut builder);
let hir = builder.build().parse(given).unwrap();
let mut printer = Printer::new();
let mut dst = String::new();
printer.print(&hir, &mut dst).unwrap();
// Check that the result is actually valid.
builder.build().parse(&dst).unwrap();
assert_eq!(expected, dst);
}
#[test]
fn print_literal() {
roundtrip("a", "a");
roundtrip(r"\xff", "\u{FF}");
roundtrip_bytes(r"\xff", "\u{FF}");
roundtrip_bytes(r"(?-u)\xff", r"(?-u:\xFF)");
roundtrip("☃", "☃");
}
#[test]
fn print_class() {
roundtrip(r"[a]", r"[a]");
roundtrip(r"[a-z]", r"[a-z]");
roundtrip(r"[a-z--b-c--x-y]", r"[ad-wz]");
roundtrip(r"[^\x01-\u{10FFFF}]", "[\u{0}]");
roundtrip(r"[-]", r"[\-]");
roundtrip(r"[☃-⛄]", r"[☃-⛄]");
roundtrip(r"(?-u)[a]", r"(?-u:[a])");
roundtrip(r"(?-u)[a-z]", r"(?-u:[a-z])");
roundtrip_bytes(r"(?-u)[a-\xFF]", r"(?-u:[a-\xFF])");
// The following test that the printer escapes meta characters
// in character classes.
roundtrip(r"[\[]", r"[\[]");
roundtrip(r"[Z-_]", r"[Z-_]");
roundtrip(r"[Z-_--Z]", r"[\[-_]");
// The following test that the printer escapes meta characters
// in byte oriented character classes.
roundtrip_bytes(r"(?-u)[\[]", r"(?-u:[\[])");
roundtrip_bytes(r"(?-u)[Z-_]", r"(?-u:[Z-_])");
roundtrip_bytes(r"(?-u)[Z-_--Z]", r"(?-u:[\[-_])");
}
#[test]
fn print_anchor() {
roundtrip(r"^", r"\A");
roundtrip(r"$", r"\z");
roundtrip(r"(?m)^", r"(?m:^)");
roundtrip(r"(?m)$", r"(?m:$)");
}
#[test]
fn print_word_boundary() {
roundtrip(r"\b", r"\b");
roundtrip(r"\B", r"\B");
roundtrip(r"(?-u)\b", r"(?-u:\b)");
roundtrip_bytes(r"(?-u)\B", r"(?-u:\B)");
}
#[test]
fn print_repetition() {
roundtrip("a?", "a?");
roundtrip("a??", "a??");
roundtrip("(?U)a?", "a??");
roundtrip("a*", "a*");
roundtrip("a*?", "a*?");
roundtrip("(?U)a*", "a*?");
roundtrip("a+", "a+");
roundtrip("a+?", "a+?");
roundtrip("(?U)a+", "a+?");
roundtrip("a{1}", "a{1}");
roundtrip("a{1,}", "a{1,}");
roundtrip("a{1,5}", "a{1,5}");
roundtrip("a{1}?", "a{1}?");
roundtrip("a{1,}?", "a{1,}?");
roundtrip("a{1,5}?", "a{1,5}?");
roundtrip("(?U)a{1}", "a{1}?");
roundtrip("(?U)a{1,}", "a{1,}?");
roundtrip("(?U)a{1,5}", "a{1,5}?");
}
#[test]
fn print_group() {
roundtrip("()", "()");
roundtrip("(?P<foo>)", "(?P<foo>)");
roundtrip("(?:)", "(?:)");
roundtrip("(a)", "(a)");
roundtrip("(?P<foo>a)", "(?P<foo>a)");
roundtrip("(?:a)", "(?:a)");
roundtrip("((((a))))", "((((a))))");
}
#[test]
fn print_alternation() {
roundtrip("|", "|");
roundtrip("||", "||");
roundtrip("a|b", "a|b");
roundtrip("a|b|c", "a|b|c");
roundtrip("foo|bar|quux", "foo|bar|quux");
}
}