Mihaela Mihaljevic
951b808f02
Add the PureXML.Regex namespace: a recursive-descent parser for the XSD
regex grammar (literals, ., character classes with ranges and negation, the
\d \w \s family and negations, single-char escapes, grouping, alternation,
and the ?, *, +, {n}, {n,}, {n,m} quantifiers) compiled to a Thompson NFA.
matches(_:) is whole-string as xs:pattern requires, and runs linear in the
input with no backtracking blow-up. \p{...} category escapes are not yet
supported.
Closes #59
Closes #60
Closes #30
88 lines
3.2 KiB
Swift
88 lines
3.2 KiB
Swift
extension PureXML.Regex {
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/// An error compiling a regular expression.
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enum RegexError: Swift.Error, Equatable, Sendable, CustomStringConvertible {
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case empty
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case unbalanced
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case danglingQuantifier
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case badEscape(String)
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case badClass
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case badQuantifier
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case unsupported(String)
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var description: String {
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switch self {
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case .empty: "the pattern is empty"
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case .unbalanced: "unbalanced parentheses"
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case .danglingQuantifier: "a quantifier has nothing to repeat"
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case let .badEscape(detail): "invalid escape '\\\(detail)'"
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case .badClass: "malformed character class"
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case .badQuantifier: "malformed quantifier"
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case let .unsupported(detail): "unsupported construct: \(detail)"
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}
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}
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}
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/// A named character class (`\d`, `\w`, `\s`, `\i`, `\c`) or the `.` wildcard.
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enum NamedClass: Equatable, Sendable {
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case digit
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case word
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case space
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case nameStart
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case nameChar
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case anyButLineBreak
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func contains(_ scalar: Unicode.Scalar) -> Bool {
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switch self {
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case .digit: scalar.properties.numericType == .decimal
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case .space: scalar == " " || scalar == "\t" || scalar == "\n" || scalar == "\r"
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case .word: scalar.properties.isAlphabetic || scalar.properties.numericType == .decimal || scalar == "_"
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case .nameStart: PureXML.Parsing.XMLCharacter.isNameStart(scalar)
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case .nameChar: PureXML.Parsing.XMLCharacter.isNameChar(scalar)
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case .anyButLineBreak: scalar != "\n" && scalar != "\r"
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}
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}
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}
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/// A character class: ranges, named sub-classes, and an optional negation.
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struct CharClass: Equatable, Sendable {
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var negated = false
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var ranges: [ClosedRange<Unicode.Scalar>] = []
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var named: [NamedClass] = []
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var negatedNamed: [NamedClass] = []
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func matches(_ character: Character) -> Bool {
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guard character.unicodeScalars.count == 1, let scalar = character.unicodeScalars.first else {
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return false
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}
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let hit = ranges.contains { $0.contains(scalar) }
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|| named.contains { $0.contains(scalar) }
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|| negatedNamed.contains { !$0.contains(scalar) }
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return negated ? !hit : hit
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}
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static func single(_ scalar: Unicode.Scalar) -> CharClass {
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CharClass(ranges: [scalar ... scalar])
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}
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static func named(_ named: NamedClass) -> CharClass {
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CharClass(named: [named])
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}
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}
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/// The parsed regular-expression tree. Groups are non-capturing; `?`, `*`,
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/// `+`, and `{n,m}` all become ``repeated``.
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indirect enum Node: Equatable, Sendable {
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case empty
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case characters(CharClass)
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case concat([Node])
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case alternate([Node])
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case repeated(Node, min: Int, max: Int?)
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}
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}
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extension Unicode.Scalar: @retroactive Comparable {
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public static func < (lhs: Unicode.Scalar, rhs: Unicode.Scalar) -> Bool {
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lhs.value < rhs.value
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}
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}
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