1/*!
2This crate provides a robust regular expression parser.
3
4This crate defines two primary types:
5
6* [`Ast`](ast/enum.Ast.html) is the abstract syntax of a regular expression.
7 An abstract syntax corresponds to a *structured representation* of the
8 concrete syntax of a regular expression, where the concrete syntax is the
9 pattern string itself (e.g., `foo(bar)+`). Given some abstract syntax, it
10 can be converted back to the original concrete syntax (modulo some details,
11 like whitespace). To a first approximation, the abstract syntax is complex
12 and difficult to analyze.
13* [`Hir`](hir/struct.Hir.html) is the high-level intermediate representation
14 ("HIR" or "high-level IR" for short) of regular expression. It corresponds to
15 an intermediate state of a regular expression that sits between the abstract
16 syntax and the low level compiled opcodes that are eventually responsible for
17 executing a regular expression search. Given some high-level IR, it is not
18 possible to produce the original concrete syntax (although it is possible to
19 produce an equivalent concrete syntax, but it will likely scarcely resemble
20 the original pattern). To a first approximation, the high-level IR is simple
21 and easy to analyze.
22
23These two types come with conversion routines:
24
25* An [`ast::parse::Parser`](ast/parse/struct.Parser.html) converts concrete
26 syntax (a `&str`) to an [`Ast`](ast/enum.Ast.html).
27* A [`hir::translate::Translator`](hir/translate/struct.Translator.html)
28 converts an [`Ast`](ast/enum.Ast.html) to a [`Hir`](hir/struct.Hir.html).
29
30As a convenience, the above two conversion routines are combined into one via
31the top-level [`Parser`](struct.Parser.html) type. This `Parser` will first
32convert your pattern to an `Ast` and then convert the `Ast` to an `Hir`.
33
34
35# Example
36
37This example shows how to parse a pattern string into its HIR:
38
39```
40use regex_syntax::Parser;
41use regex_syntax::hir::{self, Hir};
42
43let hir = Parser::new().parse("a|b").unwrap();
44assert_eq!(hir, Hir::alternation(vec![
45 Hir::literal(hir::Literal::Unicode('a')),
46 Hir::literal(hir::Literal::Unicode('b')),
47]));
48```
49
50
51# Concrete syntax supported
52
53The concrete syntax is documented as part of the public API of the
54[`regex` crate](https://docs.rs/regex/%2A/regex/#syntax).
55
56
57# Input safety
58
59A key feature of this library is that it is safe to use with end user facing
60input. This plays a significant role in the internal implementation. In
61particular:
62
631. Parsers provide a `nest_limit` option that permits callers to control how
64 deeply nested a regular expression is allowed to be. This makes it possible
65 to do case analysis over an `Ast` or an `Hir` using recursion without
66 worrying about stack overflow.
672. Since relying on a particular stack size is brittle, this crate goes to
68 great lengths to ensure that all interactions with both the `Ast` and the
69 `Hir` do not use recursion. Namely, they use constant stack space and heap
70 space proportional to the size of the original pattern string (in bytes).
71 This includes the type's corresponding destructors. (One exception to this
72 is literal extraction, but this will eventually get fixed.)
73
74
75# Error reporting
76
77The `Display` implementations on all `Error` types exposed in this library
78provide nice human readable errors that are suitable for showing to end users
79in a monospace font.
80
81
82# Literal extraction
83
84This crate provides limited support for
85[literal extraction from `Hir` values](hir/literal/struct.Literals.html).
86Be warned that literal extraction currently uses recursion, and therefore,
87stack size proportional to the size of the `Hir`.
88
89The purpose of literal extraction is to speed up searches. That is, if you
90know a regular expression must match a prefix or suffix literal, then it is
91often quicker to search for instances of that literal, and then confirm or deny
92the match using the full regular expression engine. These optimizations are
93done automatically in the `regex` crate.
94
95
96# Crate features
97
98An important feature provided by this crate is its Unicode support. This
99includes things like case folding, boolean properties, general categories,
100scripts and Unicode-aware support for the Perl classes `\w`, `\s` and `\d`.
101However, a downside of this support is that it requires bundling several
102Unicode data tables that are substantial in size.
103
104A fair number of use cases do not require full Unicode support. For this
105reason, this crate exposes a number of features to control which Unicode
106data is available.
107
108If a regular expression attempts to use a Unicode feature that is not available
109because the corresponding crate feature was disabled, then translating that
110regular expression to an `Hir` will return an error. (It is still possible
111construct an `Ast` for such a regular expression, since Unicode data is not
112used until translation to an `Hir`.) Stated differently, enabling or disabling
113any of the features below can only add or subtract from the total set of valid
114regular expressions. Enabling or disabling a feature will never modify the
115match semantics of a regular expression.
116
117The following features are available:
118
119* **unicode** -
120 Enables all Unicode features. This feature is enabled by default, and will
121 always cover all Unicode features, even if more are added in the future.
122* **unicode-age** -
123 Provide the data for the
124 [Unicode `Age` property](https://www.unicode.org/reports/tr44/tr44-24.html#Character_Age).
125 This makes it possible to use classes like `\p{Age:6.0}` to refer to all
126 codepoints first introduced in Unicode 6.0
127* **unicode-bool** -
128 Provide the data for numerous Unicode boolean properties. The full list
129 is not included here, but contains properties like `Alphabetic`, `Emoji`,
130 `Lowercase`, `Math`, `Uppercase` and `White_Space`.
131* **unicode-case** -
132 Provide the data for case insensitive matching using
133 [Unicode's "simple loose matches" specification](https://www.unicode.org/reports/tr18/#Simple_Loose_Matches).
134* **unicode-gencat** -
135 Provide the data for
136 [Uncode general categories](https://www.unicode.org/reports/tr44/tr44-24.html#General_Category_Values).
137 This includes, but is not limited to, `Decimal_Number`, `Letter`,
138 `Math_Symbol`, `Number` and `Punctuation`.
139* **unicode-perl** -
140 Provide the data for supporting the Unicode-aware Perl character classes,
141 corresponding to `\w`, `\s` and `\d`. This is also necessary for using
142 Unicode-aware word boundary assertions. Note that if this feature is
143 disabled, the `\s` and `\d` character classes are still available if the
144 `unicode-bool` and `unicode-gencat` features are enabled, respectively.
145* **unicode-script** -
146 Provide the data for
147 [Unicode scripts and script extensions](https://www.unicode.org/reports/tr24/).
148 This includes, but is not limited to, `Arabic`, `Cyrillic`, `Hebrew`,
149 `Latin` and `Thai`.
150* **unicode-segment** -
151 Provide the data necessary to provide the properties used to implement the
152 [Unicode text segmentation algorithms](https://www.unicode.org/reports/tr29/).
153 This enables using classes like `\p{gcb=Extend}`, `\p{wb=Katakana}` and
154 `\p{sb=ATerm}`.
155*/
156
157#![deny(missing_docs)]
158#![warn(missing_debug_implementations)]
159#![forbid(unsafe_code)]
160
161pub use crate::error::{Error, Result};
162pub use crate::parser::{Parser, ParserBuilder};
163pub use crate::unicode::UnicodeWordError;
164
165pub mod ast;
166mod either;
167mod error;
168pub mod hir;
169mod parser;
170mod unicode;
171mod unicode_tables;
172pub mod utf8;
173
174/// Escapes all regular expression meta characters in `text`.
175///
176/// The string returned may be safely used as a literal in a regular
177/// expression.
178pub fn escape(text: &str) -> String {
179 let mut quoted: String = String::new();
180 escape_into(text, &mut quoted);
181 quoted
182}
183
184/// Escapes all meta characters in `text` and writes the result into `buf`.
185///
186/// This will append escape characters into the given buffer. The characters
187/// that are appended are safe to use as a literal in a regular expression.
188pub fn escape_into(text: &str, buf: &mut String) {
189 buf.reserve(additional:text.len());
190 for c: char in text.chars() {
191 if is_meta_character(c) {
192 buf.push(ch:'\\');
193 }
194 buf.push(ch:c);
195 }
196}
197
198/// Returns true if the given character has significance in a regex.
199///
200/// These are the only characters that are allowed to be escaped, with one
201/// exception: an ASCII space character may be escaped when extended mode (with
202/// the `x` flag) is enabled. In particular, `is_meta_character(' ')` returns
203/// `false`.
204///
205/// Note that the set of characters for which this function returns `true` or
206/// `false` is fixed and won't change in a semver compatible release.
207pub fn is_meta_character(c: char) -> bool {
208 match c {
209 '\\' | '.' | '+' | '*' | '?' | '(' | ')' | '|' | '[' | ']' | '{'
210 | '}' | '^' | '$' | '#' | '&' | '-' | '~' => true,
211 _ => false,
212 }
213}
214
215/// Returns true if and only if the given character is a Unicode word
216/// character.
217///
218/// A Unicode word character is defined by
219/// [UTS#18 Annex C](https://unicode.org/reports/tr18/#Compatibility_Properties).
220/// In particular, a character
221/// is considered a word character if it is in either of the `Alphabetic` or
222/// `Join_Control` properties, or is in one of the `Decimal_Number`, `Mark`
223/// or `Connector_Punctuation` general categories.
224///
225/// # Panics
226///
227/// If the `unicode-perl` feature is not enabled, then this function panics.
228/// For this reason, it is recommended that callers use
229/// [`try_is_word_character`](fn.try_is_word_character.html)
230/// instead.
231pub fn is_word_character(c: char) -> bool {
232 try_is_word_character(c).expect(msg:"unicode-perl feature must be enabled")
233}
234
235/// Returns true if and only if the given character is a Unicode word
236/// character.
237///
238/// A Unicode word character is defined by
239/// [UTS#18 Annex C](https://unicode.org/reports/tr18/#Compatibility_Properties).
240/// In particular, a character
241/// is considered a word character if it is in either of the `Alphabetic` or
242/// `Join_Control` properties, or is in one of the `Decimal_Number`, `Mark`
243/// or `Connector_Punctuation` general categories.
244///
245/// # Errors
246///
247/// If the `unicode-perl` feature is not enabled, then this function always
248/// returns an error.
249pub fn try_is_word_character(
250 c: char,
251) -> std::result::Result<bool, UnicodeWordError> {
252 unicode::is_word_character(c)
253}
254
255/// Returns true if and only if the given character is an ASCII word character.
256///
257/// An ASCII word character is defined by the following character class:
258/// `[_0-9a-zA-Z]'.
259pub fn is_word_byte(c: u8) -> bool {
260 match c {
261 b'_' | b'0'..=b'9' | b'a'..=b'z' | b'A'..=b'Z' => true,
262 _ => false,
263 }
264}
265
266#[cfg(test)]
267mod tests {
268 use super::*;
269
270 #[test]
271 fn escape_meta() {
272 assert_eq!(
273 escape(r"\.+*?()|[]{}^$#&-~"),
274 r"\\\.\+\*\?\(\)\|\[\]\{\}\^\$\#\&\-\~".to_string()
275 );
276 }
277
278 #[test]
279 fn word_byte() {
280 assert!(is_word_byte(b'a'));
281 assert!(!is_word_byte(b'-'));
282 }
283
284 #[test]
285 #[cfg(feature = "unicode-perl")]
286 fn word_char() {
287 assert!(is_word_character('a'), "ASCII");
288 assert!(is_word_character('à'), "Latin-1");
289 assert!(is_word_character('β'), "Greek");
290 assert!(is_word_character('\u{11011}'), "Brahmi (Unicode 6.0)");
291 assert!(is_word_character('\u{11611}'), "Modi (Unicode 7.0)");
292 assert!(is_word_character('\u{11711}'), "Ahom (Unicode 8.0)");
293 assert!(is_word_character('\u{17828}'), "Tangut (Unicode 9.0)");
294 assert!(is_word_character('\u{1B1B1}'), "Nushu (Unicode 10.0)");
295 assert!(is_word_character('\u{16E40}'), "Medefaidrin (Unicode 11.0)");
296 assert!(!is_word_character('-'));
297 assert!(!is_word_character('☃'));
298 }
299
300 #[test]
301 #[should_panic]
302 #[cfg(not(feature = "unicode-perl"))]
303 fn word_char_disabled_panic() {
304 assert!(is_word_character('a'));
305 }
306
307 #[test]
308 #[cfg(not(feature = "unicode-perl"))]
309 fn word_char_disabled_error() {
310 assert!(try_is_word_character('a').is_err());
311 }
312}
313