doc: remove incomplete sentence

[rust.git] / src / libregex / lib.rs

// Copyright 2014 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.
//
// ignore-lexer-test FIXME #15679

//! This crate provides a native implementation of regular expressions that is
//! heavily based on RE2 both in syntax and in implementation. Notably,
//! backreferences and arbitrary lookahead/lookbehind assertions are not
//! provided. In return, regular expression searching provided by this package
//! has excellent worst case performance. The specific syntax supported is
//! documented further down.
//!
//! This crate's documentation provides some simple examples, describes Unicode
//! support and exhaustively lists the supported syntax. For more specific
//! details on the API, please see the documentation for the `Regex` type.
//!
//! # First example: find a date
//!
//! General use of regular expressions in this package involves compiling an
//! expression and then using it to search, split or replace text. For example,
//! to confirm that some text resembles a date:
//!
//! ```rust
//! use regex::Regex;
//! let re = match Regex::new(r"^\d{4}-\d{2}-\d{2}$") {
//!     Ok(re) => re,
//!     Err(err) => panic!("{}", err),
//! };
//! assert_eq!(re.is_match("2014-01-01"), true);
//! ```
//!
//! Notice the use of the `^` and `$` anchors. In this crate, every expression
//! is executed with an implicit `.*?` at the beginning and end, which allows
//! it to match anywhere in the text. Anchors can be used to ensure that the
//! full text matches an expression.
//!
//! This example also demonstrates the utility of [raw
//! strings](../reference.html#character-and-string-literals) in Rust, which
//! are just like regular strings except they are prefixed with an `r` and do
//! not process any escape sequences. For example, `"\\d"` is the same
//! expression as `r"\d"`.
//!
//! # The `regex!` macro
//!
//! Rust's compile time meta-programming facilities provide a way to write a
//! `regex!` macro which compiles regular expressions *when your program
//! compiles*. Said differently, if you only use `regex!` to build regular
//! expressions in your program, then your program cannot compile with an
//! invalid regular expression. Moreover, the `regex!` macro compiles the
//! given expression to native Rust code, which makes it much faster for
//! searching text.
//!
//! Since `regex!` provides compiled regular expressions that are both safer
//! and faster to use, you should use them whenever possible. The only
//! requirement for using them is that you have a string literal corresponding
//! to your expression. Otherwise, it is indistinguishable from an expression
//! compiled at runtime with `Regex::new`.
//!
//! To use the `regex!` macro, you must enable the `phase` feature and import
//! the `regex_macros` crate as a syntax extension:
//!
//! ```rust
//! #![feature(phase)]
//! #[phase(plugin)]
//! extern crate regex_macros;
//! extern crate regex;
//!
//! fn main() {
//!     let re = regex!(r"^\d{4}-\d{2}-\d{2}$");
//!     assert_eq!(re.is_match("2014-01-01"), true);
//! }
//! ```
//!
//! There are a few things worth mentioning about using the `regex!` macro.
//! Firstly, the `regex!` macro *only* accepts string *literals*.
//! Secondly, the `regex` crate *must* be linked with the name `regex` since
//! the generated code depends on finding symbols in the `regex` crate.
//!
//! The only downside of using the `regex!` macro is that it can increase the
//! size of your program's binary since it generates specialized Rust code.
//! The extra size probably won't be significant for a small number of
//! expressions, but 100+ calls to `regex!` will probably result in a
//! noticeably bigger binary.
//!
//! # Example: iterating over capture groups
//!
//! This crate provides convenient iterators for matching an expression
//! repeatedly against a search string to find successive non-overlapping
//! matches. For example, to find all dates in a string and be able to access
//! them by their component pieces:
//!
//! ```rust
//! # #![feature(phase)]
//! # extern crate regex; #[phase(plugin)] extern crate regex_macros;
//! # fn main() {
//! let re = regex!(r"(\d{4})-(\d{2})-(\d{2})");
//! let text = "2012-03-14, 2013-01-01 and 2014-07-05";
//! for cap in re.captures_iter(text) {
//!     println!("Month: {} Day: {} Year: {}",
//!              cap.at(2).unwrap_or(""), cap.at(3).unwrap_or(""),
//!              cap.at(1).unwrap_or(""));
//! }
//! // Output:
//! // Month: 03 Day: 14 Year: 2012
//! // Month: 01 Day: 01 Year: 2013
//! // Month: 07 Day: 05 Year: 2014
//! # }
//! ```
//!
//! Notice that the year is in the capture group indexed at `1`. This is
//! because the *entire match* is stored in the capture group at index `0`.
//!
//! # Example: replacement with named capture groups
//!
//! Building on the previous example, perhaps we'd like to rearrange the date
//! formats. This can be done with text replacement. But to make the code
//! clearer, we can *name*  our capture groups and use those names as variables
//! in our replacement text:
//!
//! ```rust
//! # #![feature(phase)]
//! # extern crate regex; #[phase(plugin)] extern crate regex_macros;
//! # fn main() {
//! let re = regex!(r"(?P<y>\d{4})-(?P<m>\d{2})-(?P<d>\d{2})");
//! let before = "2012-03-14, 2013-01-01 and 2014-07-05";
//! let after = re.replace_all(before, "$m/$d/$y");
//! assert_eq!(after.as_slice(), "03/14/2012, 01/01/2013 and 07/05/2014");
//! # }
//! ```
//!
//! The `replace` methods are actually polymorphic in the replacement, which
//! provides more flexibility than is seen here. (See the documentation for
//! `Regex::replace` for more details.)
//!
//! # Pay for what you use
//!
//! With respect to searching text with a regular expression, there are three
//! questions that can be asked:
//!
//! 1. Does the text match this expression?
//! 2. If so, where does it match?
//! 3. Where are the submatches?
//!
//! Generally speaking, this crate could provide a function to answer only #3,
//! which would subsume #1 and #2 automatically. However, it can be
//! significantly more expensive to compute the location of submatches, so it's
//! best not to do it if you don't need to.
//!
//! Therefore, only use what you need. For example, don't use `find` if you
//! only need to test if an expression matches a string. (Use `is_match`
//! instead.)
//!
//! # Unicode
//!
//! This implementation executes regular expressions **only** on sequences of
//! Unicode code points while exposing match locations as byte indices into the
//! search string.
//!
//! Currently, only naive case folding is supported. Namely, when matching
//! case insensitively, the characters are first converted to their uppercase
//! forms and then compared.
//!
//! Regular expressions themselves are also **only** interpreted as a sequence
//! of Unicode code points. This means you can use Unicode characters
//! directly in your expression:
//!
//! ```rust
//! # #![feature(phase)]
//! # extern crate regex; #[phase(plugin)] extern crate regex_macros;
//! # fn main() {
//! let re = regex!(r"(?i)Δ+");
//! assert_eq!(re.find("ΔδΔ"), Some((0, 6)));
//! # }
//! ```
//!
//! Finally, Unicode general categories and scripts are available as character
//! classes. For example, you can match a sequence of numerals, Greek or
//! Cherokee letters:
//!
//! ```rust
//! # #![feature(phase)]
//! # extern crate regex; #[phase(plugin)] extern crate regex_macros;
//! # fn main() {
//! let re = regex!(r"[\pN\p{Greek}\p{Cherokee}]+");
//! assert_eq!(re.find("abcΔᎠβⅠᏴγδⅡxyz"), Some((3, 23)));
//! # }
//! ```
//!
//! # Syntax
//!
//! The syntax supported in this crate is almost in an exact correspondence
//! with the syntax supported by RE2.
//!
//! ## Matching one character
//!
//! <pre class="rust">
//! .           any character except new line (includes new line with s flag)
//! [xyz]       A character class matching either x, y or z.
//! [^xyz]      A character class matching any character except x, y and z.
//! [a-z]       A character class matching any character in range a-z.
//! \d          Perl character class ([0-9])
//! \D          Negated Perl character class ([^0-9])
//! [:alpha:]   ASCII character class ([A-Za-z])
//! [:^alpha:]  Negated ASCII character class ([^A-Za-z])
//! \pN         One letter name Unicode character class
//! \p{Greek}   Unicode character class (general category or script)
//! \PN         Negated one letter name Unicode character class
//! \P{Greek}   negated Unicode character class (general category or script)
//! </pre>
//!
//! Any named character class may appear inside a bracketed `[...]` character
//! class. For example, `[\p{Greek}\pN]` matches any Greek or numeral
//! character.
//!
//! ## Composites
//!
//! <pre class="rust">
//! xy    concatenation (x followed by y)
//! x|y   alternation (x or y, prefer x)
//! </pre>
//!
//! ## Repetitions
//!
//! <pre class="rust">
//! x*        zero or more of x (greedy)
//! x+        one or more of x (greedy)
//! x?        zero or one of x (greedy)
//! x*?       zero or more of x (ungreedy)
//! x+?       one or more of x (ungreedy)
//! x??       zero or one of x (ungreedy)
//! x{n,m}    at least n x and at most m x (greedy)
//! x{n,}     at least n x (greedy)
//! x{n}      exactly n x
//! x{n,m}?   at least n x and at most m x (ungreedy)
//! x{n,}?    at least n x (ungreedy)
//! x{n}?     exactly n x
//! </pre>
//!
//! ## Empty matches
//!
//! <pre class="rust">
//! ^     the beginning of text (or start-of-line with multi-line mode)
//! $     the end of text (or end-of-line with multi-line mode)
//! \A    only the beginning of text (even with multi-line mode enabled)
//! \z    only the end of text (even with multi-line mode enabled)
//! \b    a Unicode word boundary (\w on one side and \W, \A, or \z on other)
//! \B    not a Unicode word boundary
//! </pre>
//!
//! ## Grouping and flags
//!
//! <pre class="rust">
//! (exp)          numbered capture group (indexed by opening parenthesis)
//! (?P&lt;name&gt;exp)  named (also numbered) capture group (allowed chars: [_0-9a-zA-Z])
//! (?:exp)        non-capturing group
//! (?flags)       set flags within current group
//! (?flags:exp)   set flags for exp (non-capturing)
//! </pre>
//!
//! Flags are each a single character. For example, `(?x)` sets the flag `x`
//! and `(?-x)` clears the flag `x`. Multiple flags can be set or cleared at
//! the same time: `(?xy)` sets both the `x` and `y` flags and `(?x-y)` sets
//! the `x` flag and clears the `y` flag.
//!
//! All flags are by default disabled. They are:
//!
//! <pre class="rust">
//! i     case insensitive
//! m     multi-line mode: ^ and $ match begin/end of line
//! s     allow . to match \n
//! U     swap the meaning of x* and x*?
//! </pre>
//!
//! Here's an example that matches case insensitively for only part of the
//! expression:
//!
//! ```rust
//! # #![feature(phase)]
//! # extern crate regex; #[phase(plugin)] extern crate regex_macros;
//! # fn main() {
//! let re = regex!(r"(?i)a+(?-i)b+");
//! let cap = re.captures("AaAaAbbBBBb").unwrap();
//! assert_eq!(cap.at(0), Some("AaAaAbb"));
//! # }
//! ```
//!
//! Notice that the `a+` matches either `a` or `A`, but the `b+` only matches
//! `b`.
//!
//! ## Escape sequences
//!
//! <pre class="rust">
//! \*         literal *, works for any punctuation character: \.+*?()|[]{}^$
//! \a         bell (\x07)
//! \f         form feed (\x0C)
//! \t         horizontal tab
//! \n         new line
//! \r         carriage return
//! \v         vertical tab (\x0B)
//! \123       octal character code (up to three digits)
//! \x7F       hex character code (exactly two digits)
//! \x{10FFFF} any hex character code corresponding to a Unicode code point
//! </pre>
//!
//! ## Perl character classes (Unicode friendly)
//!
//! These classes are based on the definitions provided in
//! [UTS#18](http://www.unicode.org/reports/tr18/#Compatibility_Properties):
//!
//! <pre class="rust">
//! \d     digit (\p{Nd})
//! \D     not digit
//! \s     whitespace (\p{White_Space})
//! \S     not whitespace
//! \w     word character (\p{Alphabetic} + \p{M} + \d + \p{Pc} + \p{Join_Control})
//! \W     not word character
//! </pre>
//!
//! ## ASCII character classes
//!
//! <pre class="rust">
//! [:alnum:]    alphanumeric ([0-9A-Za-z])
//! [:alpha:]    alphabetic ([A-Za-z])
//! [:ascii:]    ASCII ([\x00-\x7F])
//! [:blank:]    blank ([\t ])
//! [:cntrl:]    control ([\x00-\x1F\x7F])
//! [:digit:]    digits ([0-9])
//! [:graph:]    graphical ([!-~])
//! [:lower:]    lower case ([a-z])
//! [:print:]    printable ([ -~])
//! [:punct:]    punctuation ([!-/:-@[-`{-~])
//! [:space:]    whitespace ([\t\n\v\f\r ])
//! [:upper:]    upper case ([A-Z])
//! [:word:]     word characters ([0-9A-Za-z_])
//! [:xdigit:]   hex digit ([0-9A-Fa-f])
//! </pre>
//!
//! # Untrusted input
//!
//! There are two factors to consider here: untrusted regular expressions and
//! untrusted search text.
//!
//! Currently, there are no counter-measures in place to prevent a malicious
//! user from writing an expression that may use a lot of resources. One such
//! example is to repeat counted repetitions: `((a{100}){100}){100}` will try
//! to repeat the `a` instruction `100^3` times. Essentially, this means it's
//! very easy for an attacker to exhaust your system's memory if they are
//! allowed to execute arbitrary regular expressions. A possible solution to
//! this is to impose a hard limit on the size of a compiled expression, but it
//! does not yet exist.
//!
//! The story is a bit better with untrusted search text, since this crate's
//! implementation provides `O(nm)` search where `n` is the number of
//! characters in the search text and `m` is the number of instructions in a
//! compiled expression.

#![crate_name = "regex"]
#![crate_type = "rlib"]
#![crate_type = "dylib"]
#![experimental = "use the crates.io `regex` library instead"]
#![doc(html_logo_url = "http://www.rust-lang.org/logos/rust-logo-128x128-blk-v2.png",
       html_favicon_url = "http://www.rust-lang.org/favicon.ico",
       html_root_url = "http://doc.rust-lang.org/nightly/",
       html_playground_url = "http://play.rust-lang.org/")]

#![allow(unknown_features)]
#![feature(macro_rules, phase, slicing_syntax, globs)]
#![feature(unboxed_closures)]
#![feature(associated_types)]
#![deny(missing_docs)]

#[cfg(test)]
extern crate "test" as stdtest;
#[cfg(test)]
extern crate rand;

// During tests, this links with the `regex` crate so that the `regex!` macro
// can be tested.
#[cfg(test)]
extern crate regex;

// Unicode tables for character classes are defined in libunicode
extern crate unicode;

pub use parse::Error;
pub use re::{Regex, Captures, SubCaptures, SubCapturesPos};
pub use re::{FindCaptures, FindMatches};
pub use re::{Replacer, NoExpand, RegexSplits, RegexSplitsN};
pub use re::{quote, is_match};

mod compile;
mod parse;
mod re;
mod vm;

#[cfg(test)]
mod test;

/// The `native` module exists to support the `regex!` macro. Do not use.
#[doc(hidden)]
pub mod native {
    // Exporting this stuff is bad form, but it's necessary for two reasons.
    // Firstly, the `regex!` syntax extension is in a different crate and
    // requires access to the representation of a regex (particularly the
    // instruction set) in order to compile to native Rust. This could be
    // mitigated if `regex!` was defined in the same crate, but this has
    // undesirable consequences (such as requiring a dependency on
    // `libsyntax`).
    //
    // Secondly, the code generated by `regex!` must *also* be able
    // to access various functions in this crate to reduce code duplication
    // and to provide a value with precisely the same `Regex` type in this
    // crate. This, AFAIK, is impossible to mitigate.
    //
    // On the bright side, `rustdoc` lets us hide this from the public API
    // documentation.
    pub use compile::{
        Program,
        OneChar, CharClass, Any, Save, Jump, Split,
        Match, EmptyBegin, EmptyEnd, EmptyWordBoundary,
    };
    pub use parse::{
        FLAG_EMPTY, FLAG_NOCASE, FLAG_MULTI, FLAG_DOTNL,
        FLAG_SWAP_GREED, FLAG_NEGATED,
    };
    pub use re::{Dynamic, ExDynamic, Native, ExNative};
    pub use vm::{
        MatchKind, Exists, Location, Submatches,
        StepState, StepMatchEarlyReturn, StepMatch, StepContinue,
        CharReader, find_prefix,
    };
}