sdk/lib/core/regexp.dart

// Copyright (c) 2012, the Dart project authors.  Please see the AUTHORS file
// for details. All rights reserved. Use of this source code is governed by a
// BSD-style license that can be found in the LICENSE file.

part of dart.core;

/// A regular expression pattern.
///
/// Regular expressions are [Pattern]s, and can as such be used to match strings
/// or parts of strings.
///
/// Dart regular expressions have the same syntax and semantics as
/// JavaScript regular expressions. See
/// <https://ecma-international.org/ecma-262/9.0/#sec-regexp-regular-expression-objects>
/// for the specification of JavaScript regular expressions.
///
/// The [firstMatch] method is the main implementation method
/// that applies a regular expression to a string
/// and returns the first [RegExpMatch].
/// All other methods in [RegExp] can be build from that.
///
/// The following example finds the first match of a regular expression in
/// a string.
/// ```dart
/// RegExp exp = RegExp(r'(\w+)');
/// String str = 'Parse my string';
/// RegExpMatch? match = exp.firstMatch(str);
/// print(match![0]); // "Parse"
/// ```
/// Use [allMatches] to look for all matches of a regular expression in
/// a string.
///
/// The following example finds all matches of a regular expression in
/// a string.
/// ```dart
/// RegExp exp = RegExp(r'(\w+)');
/// String str = 'Parse my string';
/// Iterable<RegExpMatch> matches = exp.allMatches(str);
/// for (final m in matches) {
///   print(m[0]);
/// }
/// ```
/// The output of the example is:
/// ```
/// Parse
/// my
/// string
/// ```
///
/// Note the use of a _raw string_ (a string prefixed with `r`)
/// in the example above. Use a raw string to treat each character in a string
/// as a literal character.
abstract class RegExp implements Pattern {
  /// Constructs a regular expression.
  ///
  /// Throws a [FormatException] if [source] is not valid regular
  /// expression syntax.
  ///
  /// If `multiLine` is enabled, then `^` and `$` will match the beginning and
  /// end of a _line_, in addition to matching beginning and end of input,
  /// respectively.
  ///
  /// If `caseSensitive` is disabled, then case is ignored.
  ///
  /// If `unicode` is enabled, then the pattern is treated as a Unicode
  /// pattern as described by the ECMAScript standard.
  ///
  /// If `dotAll` is enabled, then the `.` pattern will match _all_ characters,
  /// including line terminators.
  ///
  /// Example:
  ///
  /// ```dart
  /// final wordPattern = RegExp(r'(\w+)');
  /// final digitPattern = RegExp(r'(\d+)');
  /// ```
  ///
  /// Notice the use of a _raw string_ in the first example, and a regular
  /// string in the second. Because of the many escapes, like `\d`, used in
  /// regular expressions, it is common to use a raw string here, unless string
  /// interpolation is required.
  external factory RegExp(String source,
      {bool multiLine = false,
      bool caseSensitive = true,
      @Since("2.4") bool unicode = false,
      @Since("2.4") bool dotAll = false});

  /// Creates regular expression syntax that matches [text].
  ///
  /// If [text] contains characters that are meaningful in regular expressions,
  /// the resulting regular expression will match those characters literally.
  /// If [text] contains no characters that have special meaning in a regular
  /// expression, it is returned unmodified.
  ///
  /// The characters that have special meaning in regular expressions are:
  /// `(`, `)`, `[`, `]`, `{`, `}`, `*`, `+`, `?`, `.`, `^`, `$`, `|` and `\`.
  ///
  /// This method is mainly used to create a pattern to be included in a
  /// larger regular expression. Since a [String] is itself a [Pattern]
  /// which matches itself, converting the string to a regular expression
  /// isn't needed in order to search for just that string.
  /// ```dart
  /// print(RegExp.escape('dash@example.com')); // dash@example\.com
  /// print(RegExp.escape('a+b')); // a\+b
  /// print(RegExp.escape('a*b')); // a\*b
  /// print(RegExp.escape('{a-b}')); // \{a-b\}
  /// print(RegExp.escape('a?')); // a\?
  /// ```
  external static String escape(String text);

  /// Finds the first match of the regular expression in the string [input].
  ///
  /// Returns `null` if there is no match.
  /// ```dart
  /// final string = '[00:13.37] This is a chat message.';
  /// final regExp = RegExp(r'c\w*');
  /// final match = regExp.firstMatch(string)!;
  /// print(match[0]); // chat
  /// ```
  RegExpMatch? firstMatch(String input);

  Iterable<RegExpMatch> allMatches(String input, [int start = 0]);

  /// Whether the regular expression has a match in the string [input].
  /// ```dart
  /// var string = 'Dash is a bird';
  /// var regExp = RegExp(r'(humming)?bird');
  /// var match = regExp.hasMatch(string); // true
  ///
  /// regExp = RegExp(r'dog');
  /// match = regExp.hasMatch(string); // false
  /// ```
  bool hasMatch(String input);

  /// The substring of the first match of this regular expression in [input].
  /// ```dart
  /// var string = 'Dash is a bird';
  /// var regExp = RegExp(r'(humming)?bird');
  /// var match = regExp.stringMatch(string); // Match
  ///
  /// regExp = RegExp(r'dog');
  /// match = regExp.stringMatch(string); // No match
  /// ```
  String? stringMatch(String input);

  /// The source regular expression string used to create this `RegExp`.
  /// ```dart
  /// final regExp = RegExp(r'\p{L}');
  /// print(regExp.pattern); // \p{L}
  /// ```
  String get pattern;

  /// Whether this regular expression matches multiple lines.
  ///
  /// If the regexp does match multiple lines, the "^" and "$" characters
  /// match the beginning and end of lines. If not, the characters match the
  /// beginning and end of the input.
  bool get isMultiLine;

  /// Whether this regular expression is case sensitive.
  ///
  /// If the regular expression is not case sensitive, it will match an input
  /// letter with a pattern letter even if the two letters are different case
  /// versions of the same letter.
  /// ```dart
  /// final str = 'Parse my string';
  /// var regExp = RegExp(r'STRING', caseSensitive: false);
  /// final hasMatch = regExp.hasMatch(str); // Has matches.
  /// print(regExp.isCaseSensitive); // false
  ///
  /// regExp = RegExp(r'STRING', caseSensitive: true);
  /// final hasCaseSensitiveMatch = regExp.hasMatch(str); // No matches.
  /// print(regExp.isCaseSensitive); // true
  /// ```
  bool get isCaseSensitive;

  /// Whether this regular expression is in Unicode mode.
  ///
  /// In Unicode mode, UTF-16 surrogate pairs in the original string will be
  /// treated as a single code point and will not match separately. Otherwise,
  /// the target string will be treated purely as a sequence of individual code
  /// units and surrogates will not be treated specially.
  ///
  /// In Unicode mode, the syntax of the RegExp pattern is more restricted, but
  /// some pattern features, like Unicode property escapes, are only available in
  /// this mode.
  /// ```dart
  /// var regExp = RegExp(r'^\p{L}$', unicode: true);
  /// print(regExp.hasMatch('a')); // true
  /// print(regExp.hasMatch('b')); // true
  /// print(regExp.hasMatch('?')); // false
  /// print(regExp.hasMatch(r'p{L}')); // false
  ///
  /// regExp = RegExp(r'^\p{L}$', unicode: false);
  /// print(regExp.hasMatch('a')); // false
  /// print(regExp.hasMatch('b')); // false
  /// print(regExp.hasMatch('?')); // false
  /// print(regExp.hasMatch(r'p{L}')); // true
  /// ```
  @Since("2.4")
  bool get isUnicode;

  /// Whether "." in this regular expression matches line terminators.
  ///
  /// When false, the "." character matches a single character, unless that
  /// character is a line terminator. When true, then the "." character will
  /// match any single character including line terminators.
  ///
  /// This feature is distinct from [isMultiLine], as they affect the behavior
  /// of different pattern characters, and so they can be used together or
  /// separately.
  @Since("2.4")
  bool get isDotAll;
}

/// A regular expression match.
///
/// Regular expression matches are [Match]es, but also include the ability
/// to retrieve the names for any named capture groups and to retrieve
/// matches for named capture groups by name instead of their index.
///
/// Example:
/// ```dart
/// const pattern =
///     r'^\[(?<Time>\s*((?<hour>\d+)):((?<minute>\d+))\.((?<second>\d+)))\]'
///     r'\s(?<Message>\s*(.*)$)';
///
/// final regExp = RegExp(
///   pattern,
///   multiLine: true,
/// );
///
/// const multilineText = '[00:13.37] This is a first message.\n'
///     '[01:15.57] This is a second message.\n';
///
/// RegExpMatch regExpMatch = regExp.firstMatch(multilineText)!;
/// print(regExpMatch.groupNames.join('-')); // hour-minute-second-Time-Message.
/// final time = regExpMatch.namedGroup('Time'); // 00:13.37
/// final hour = regExpMatch.namedGroup('hour'); // 00
/// final minute = regExpMatch.namedGroup('minute'); // 13
/// final second = regExpMatch.namedGroup('second'); // 37
/// final message =
///     regExpMatch.namedGroup('Message'); // This is a first message.
/// final date = regExpMatch.namedGroup('Date'); // Undefined `Date`, throws.
///
/// Iterable<RegExpMatch> matches = regExp.allMatches(multilineText);
/// for (final m in matches) {
///   print(m.namedGroup('Time'));
///   print(m.namedGroup('Message'));
///   // 00:13.37
///   // This is a first message.
///   // 01:15.57
///   // This is a second message.
/// }
/// ```
@Since("2.3")
abstract class RegExpMatch implements Match {
  /// The string matched by the group named [name].
  ///
  /// Returns the string matched by the capture group named [name], or
  /// `null` if no string was matched by that capture group as part of
  /// this match.
  ///
  /// The [name] must be the name of a named capture group in the regular
  /// expression creating this match (that is, the name must be in
  /// [groupNames]).
  String? namedGroup(String name);

  /// The names of the captured groups in the match.
  Iterable<String> get groupNames;
}