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use crate::{ast, hir, Error};
/// A convenience routine for parsing a regex using default options.
///
/// This is equivalent to `Parser::new().parse(pattern)`.
///
/// If you need to set non-default options, then use a [`ParserBuilder`].
///
/// This routine returns an [`Hir`](hir::Hir) value. Namely, it automatically
/// parses the pattern as an [`Ast`](ast::Ast) and then invokes the translator
/// to convert the `Ast` into an `Hir`. If you need access to the `Ast`, then
/// you should use a [`ast::parse::Parser`].
pub fn parse(pattern: &str) -> Result<hir::Hir, Error> {
Parser::new().parse(pattern)
}
/// A builder for a regular expression parser.
///
/// This builder permits modifying configuration options for the parser.
///
/// This type combines the builder options for both the [AST
/// `ParserBuilder`](ast::parse::ParserBuilder) and the [HIR
/// `TranslatorBuilder`](hir::translate::TranslatorBuilder).
#[derive(Clone, Debug, Default)]
pub struct ParserBuilder {
ast: ast::parse::ParserBuilder,
hir: hir::translate::TranslatorBuilder,
}
impl ParserBuilder {
/// Create a new parser builder with a default configuration.
pub fn new() -> ParserBuilder {
ParserBuilder::default()
}
/// Build a parser from this configuration with the given pattern.
pub fn build(&self) -> Parser {
Parser { ast: self.ast.build(), hir: self.hir.build() }
}
/// Set the nesting limit for this parser.
///
/// The nesting limit controls how deep the abstract syntax tree is allowed
/// to be. If the AST exceeds the given limit (e.g., with too many nested
/// groups), then an error is returned by the parser.
///
/// The purpose of this limit is to act as a heuristic to prevent stack
/// overflow for consumers that do structural induction on an `Ast` using
/// explicit recursion. While this crate never does this (instead using
/// constant stack space and moving the call stack to the heap), other
/// crates may.
///
/// This limit is not checked until the entire Ast is parsed. Therefore,
/// if callers want to put a limit on the amount of heap space used, then
/// they should impose a limit on the length, in bytes, of the concrete
/// pattern string. In particular, this is viable since this parser
/// implementation will limit itself to heap space proportional to the
/// length of the pattern string.
///
/// Note that a nest limit of `0` will return a nest limit error for most
/// patterns but not all. For example, a nest limit of `0` permits `a` but
/// not `ab`, since `ab` requires a concatenation, which results in a nest
/// depth of `1`. In general, a nest limit is not something that manifests
/// in an obvious way in the concrete syntax, therefore, it should not be
/// used in a granular way.
pub fn nest_limit(&mut self, limit: u32) -> &mut ParserBuilder {
self.ast.nest_limit(limit);
self
}
/// Whether to support octal syntax or not.
///
/// Octal syntax is a little-known way of uttering Unicode codepoints in
/// a regular expression. For example, `a`, `\x61`, `\u0061` and
/// `\141` are all equivalent regular expressions, where the last example
/// shows octal syntax.
///
/// While supporting octal syntax isn't in and of itself a problem, it does
/// make good error messages harder. That is, in PCRE based regex engines,
/// syntax like `\0` invokes a backreference, which is explicitly
/// unsupported in Rust's regex engine. However, many users expect it to
/// be supported. Therefore, when octal support is disabled, the error
/// message will explicitly mention that backreferences aren't supported.
///
/// Octal syntax is disabled by default.
pub fn octal(&mut self, yes: bool) -> &mut ParserBuilder {
self.ast.octal(yes);
self
}
/// When disabled, translation will permit the construction of a regular
/// expression that may match invalid UTF-8.
///
/// When enabled (the default), the translator is guaranteed to produce an
/// expression that, for non-empty matches, will only ever produce spans
/// that are entirely valid UTF-8 (otherwise, the translator will return an
/// error).
///
/// Perhaps surprisingly, when UTF-8 is enabled, an empty regex or even
/// a negated ASCII word boundary (uttered as `(?-u:\B)` in the concrete
/// syntax) will be allowed even though they can produce matches that split
/// a UTF-8 encoded codepoint. This only applies to zero-width or "empty"
/// matches, and it is expected that the regex engine itself must handle
/// these cases if necessary (perhaps by suppressing any zero-width matches
/// that split a codepoint).
pub fn utf8(&mut self, yes: bool) -> &mut ParserBuilder {
self.hir.utf8(yes);
self
}
/// Enable verbose mode in the regular expression.
///
/// When enabled, verbose mode permits insignificant whitespace in many
/// places in the regular expression, as well as comments. Comments are
/// started using `#` and continue until the end of the line.
///
/// By default, this is disabled. It may be selectively enabled in the
/// regular expression by using the `x` flag regardless of this setting.
pub fn ignore_whitespace(&mut self, yes: bool) -> &mut ParserBuilder {
self.ast.ignore_whitespace(yes);
self
}
/// Enable or disable the case insensitive flag by default.
///
/// By default this is disabled. It may alternatively be selectively
/// enabled in the regular expression itself via the `i` flag.
pub fn case_insensitive(&mut self, yes: bool) -> &mut ParserBuilder {
self.hir.case_insensitive(yes);
self
}
/// Enable or disable the multi-line matching flag by default.
///
/// By default this is disabled. It may alternatively be selectively
/// enabled in the regular expression itself via the `m` flag.
pub fn multi_line(&mut self, yes: bool) -> &mut ParserBuilder {
self.hir.multi_line(yes);
self
}
/// Enable or disable the "dot matches any character" flag by default.
///
/// By default this is disabled. It may alternatively be selectively
/// enabled in the regular expression itself via the `s` flag.
pub fn dot_matches_new_line(&mut self, yes: bool) -> &mut ParserBuilder {
self.hir.dot_matches_new_line(yes);
self
}
/// Enable or disable the CRLF mode flag by default.
///
/// By default this is disabled. It may alternatively be selectively
/// enabled in the regular expression itself via the `R` flag.
///
/// When CRLF mode is enabled, the following happens:
///
/// * Unless `dot_matches_new_line` is enabled, `.` will match any character
/// except for `\r` and `\n`.
/// * When `multi_line` mode is enabled, `^` and `$` will treat `\r\n`,
/// `\r` and `\n` as line terminators. And in particular, neither will
/// match between a `\r` and a `\n`.
pub fn crlf(&mut self, yes: bool) -> &mut ParserBuilder {
self.hir.crlf(yes);
self
}
/// Sets the line terminator for use with `(?u-s:.)` and `(?-us:.)`.
///
/// Namely, instead of `.` (by default) matching everything except for `\n`,
/// this will cause `.` to match everything except for the byte given.
///
/// If `.` is used in a context where Unicode mode is enabled and this byte
/// isn't ASCII, then an error will be returned. When Unicode mode is
/// disabled, then any byte is permitted, but will return an error if UTF-8
/// mode is enabled and it is a non-ASCII byte.
///
/// In short, any ASCII value for a line terminator is always okay. But a
/// non-ASCII byte might result in an error depending on whether Unicode
/// mode or UTF-8 mode are enabled.
///
/// Note that if `R` mode is enabled then it always takes precedence and
/// the line terminator will be treated as `\r` and `\n` simultaneously.
///
/// Note also that this *doesn't* impact the look-around assertions
/// `(?m:^)` and `(?m:$)`. That's usually controlled by additional
/// configuration in the regex engine itself.
pub fn line_terminator(&mut self, byte: u8) -> &mut ParserBuilder {
self.hir.line_terminator(byte);
self
}
/// Enable or disable the "swap greed" flag by default.
///
/// By default this is disabled. It may alternatively be selectively
/// enabled in the regular expression itself via the `U` flag.
pub fn swap_greed(&mut self, yes: bool) -> &mut ParserBuilder {
self.hir.swap_greed(yes);
self
}
/// Enable or disable the Unicode flag (`u`) by default.
///
/// By default this is **enabled**. It may alternatively be selectively
/// disabled in the regular expression itself via the `u` flag.
///
/// Note that unless `utf8` is disabled (it's enabled by default), a
/// regular expression will fail to parse if Unicode mode is disabled and a
/// sub-expression could possibly match invalid UTF-8.
pub fn unicode(&mut self, yes: bool) -> &mut ParserBuilder {
self.hir.unicode(yes);
self
}
}
/// A convenience parser for regular expressions.
///
/// This parser takes as input a regular expression pattern string (the
/// "concrete syntax") and returns a high-level intermediate representation
/// (the HIR) suitable for most types of analysis. In particular, this parser
/// hides the intermediate state of producing an AST (the "abstract syntax").
/// The AST is itself far more complex than the HIR, so this parser serves as a
/// convenience for never having to deal with it at all.
///
/// If callers have more fine grained use cases that need an AST, then please
/// see the [`ast::parse`] module.
///
/// A `Parser` can be configured in more detail via a [`ParserBuilder`].
#[derive(Clone, Debug)]
pub struct Parser {
ast: ast::parse::Parser,
hir: hir::translate::Translator,
}
impl Parser {
/// Create a new parser with a default configuration.
///
/// The parser can be run with `parse` method. The parse method returns
/// a high level intermediate representation of the given regular
/// expression.
///
/// To set configuration options on the parser, use [`ParserBuilder`].
pub fn new() -> Parser {
ParserBuilder::new().build()
}
/// Parse the regular expression into a high level intermediate
/// representation.
pub fn parse(&mut self, pattern: &str) -> Result<hir::Hir, Error> {
let ast = self.ast.parse(pattern)?;
let hir = self.hir.translate(pattern, &ast)?;
Ok(hir)
}
}