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//===----------------------------------------------------------------------===//
//
// This source file is part of the Swift.org open source project
//
// Copyright (c) 2014 - 2023 Apple Inc. and the Swift project authors
// Licensed under Apache License v2.0 with Runtime Library Exception
//
// See https://swift.org/LICENSE.txt for license information
// See https://swift.org/CONTRIBUTORS.txt for the list of Swift project authors
//
//===----------------------------------------------------------------------===//
#if swift(>=6)
@_spi(RawSyntax) @_spi(BumpPtrAllocator) internal import SwiftSyntax
#else
@_spi(RawSyntax) @_spi(BumpPtrAllocator) import SwiftSyntax
#endif
extension Lexer {
/// A sequence of ``Lexer/Lexeme`` tokens starting from a ``Lexer/Cursor``
/// that points into an input buffer.
@_spi(Testing)
public struct LexemeSequence: IteratorProtocol, Sequence, CustomDebugStringConvertible {
fileprivate let sourceBufferStart: Lexer.Cursor
fileprivate var cursor: Lexer.Cursor
fileprivate var nextToken: Lexer.Lexeme
/// If the lexer has more than one state on its state stack, it will
/// allocate a new memory region in this allocator to represent the
/// additional states on its stack. This is more efficient than paying the
/// retain/release cost of an array.
///
/// The states will be freed when the lexer is finished, i.e. when this
/// ``LexemeSequence`` is deallocated.
///
/// The memory footprint of not freeing past lexer states is negligible. It's
/// usually less than 0.1% of the memory allocated by the syntax arena.
var lexerStateAllocator = BumpPtrAllocator(initialSlabSize: 256)
/// The offset of the trailing trivia end of `nextToken` relative to the source buffer’s start.
var offsetToNextTokenEnd: Int {
self.offsetToStart(self.nextToken) + self.nextToken.byteLength
}
/// See doc comments in ``LookaheadTracker``
///
/// This is an `UnsafeMutablePointer` for two reasons
/// - When `LexemeSequence` gets copied (e.g. when a ``Lookahead`` gets created), it should still reference the same ``LookaheadTracker`` so that any lookahead performed in the ``Lookahead`` also affects the original ``Parser``. It thus needs to be a reference type
/// - ``LookaheadTracker`` is not a class to avoid reference counting it. The ``Parser`` that creates the ``LexemeSequence`` will always outlive any ``Lookahead`` created for it.
let lookaheadTracker: UnsafeMutablePointer<LookaheadTracker>
fileprivate init(
sourceBufferStart: Lexer.Cursor,
cursor: Lexer.Cursor,
lookaheadTracker: UnsafeMutablePointer<LookaheadTracker>
) {
self.sourceBufferStart = sourceBufferStart
self.cursor = cursor
self.nextToken = self.cursor.nextToken(
sourceBufferStart: self.sourceBufferStart,
stateAllocator: lexerStateAllocator
)
self.lookaheadTracker = lookaheadTracker
}
@_spi(Testing)
public mutating func next() -> Lexer.Lexeme? {
return self.advance()
}
/// Record the offset of the end of `nextToken` as the furthest offset in ``LookaheadTracker``
private func recordNextTokenInLookaheadTracker() {
self.lookaheadTracker.pointee.recordFurthestOffset(self.offsetToNextTokenEnd)
}
mutating func advance() -> Lexer.Lexeme {
defer {
self.nextToken = self.cursor.nextToken(
sourceBufferStart: self.sourceBufferStart,
stateAllocator: lexerStateAllocator
)
}
self.recordNextTokenInLookaheadTracker()
return self.nextToken
}
/// Get the offset of the leading trivia start of `token` relative to `sourceBufferStart`.
func offsetToStart(_ token: Lexer.Lexeme) -> Int {
return self.sourceBufferStart.distance(to: token.cursor)
}
/// Advance the the cursor by `offset` and reset `currentToken`
///
/// - Important: This should only be used for incremental parsing.
mutating func advance(by offset: Int, currentToken: inout Lexer.Lexeme) {
self.cursor = currentToken.cursor
self.cursor.position = self.cursor.position.advanced(by: offset)
self.nextToken = self.cursor.nextToken(
sourceBufferStart: self.sourceBufferStart,
stateAllocator: lexerStateAllocator
)
currentToken = self.advance()
}
/// Reset the lexeme sequence to the state we were in when lexing `splitToken`
/// but after we consumed `consumedPrefix` bytes from `splitToken`.
/// - Warning: Do not add more usages of this function.
mutating func resetForSplit(splitToken: Lexeme, consumedPrefix: Int) -> Lexer.Lexeme {
self.cursor = splitToken.cursor
for _ in 0..<consumedPrefix {
_ = self.cursor.advance()
}
self.nextToken = self.cursor.nextToken(
sourceBufferStart: self.sourceBufferStart,
stateAllocator: lexerStateAllocator
)
return self.advance()
}
func peek() -> Lexer.Lexeme {
self.recordNextTokenInLookaheadTracker()
return self.nextToken
}
/// Force the lexer to perform a state transition, re-lexing `currentToken`
/// in the new state.
mutating func perform(stateTransition: StateTransition, currentToken: inout Lexeme) {
self.cursor = currentToken.cursor
self.cursor.perform(stateTransition: stateTransition, stateAllocator: self.lexerStateAllocator)
self.nextToken = self.cursor.nextToken(
sourceBufferStart: self.sourceBufferStart,
stateAllocator: self.lexerStateAllocator
)
currentToken = self.advance()
}
@_spi(Testing)
public var debugDescription: String {
let remainingText =
self.nextToken.debugDescription
+ String(syntaxText: SyntaxText(baseAddress: self.cursor.input.baseAddress, count: self.cursor.input.count))
if remainingText.count > 100 {
return remainingText.prefix(100) + "..."
} else {
return remainingText
}
}
}
@_spi(Testing)
public static func tokenize(
_ input: UnsafeBufferPointer<UInt8>,
from startIndex: Int = 0,
lookaheadTracker: UnsafeMutablePointer<LookaheadTracker>
) -> LexemeSequence {
precondition(input.isEmpty || startIndex < input.endIndex)
let startChar = startIndex == input.startIndex ? UInt8(ascii: "\0") : input[startIndex - 1]
let start = Cursor(input: input, previous: UInt8(ascii: "\0"))
let cursor = Cursor(input: UnsafeBufferPointer(rebasing: input[startIndex...]), previous: startChar)
return LexemeSequence(sourceBufferStart: start, cursor: cursor, lookaheadTracker: lookaheadTracker)
}
}
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