Fix compilation errors in Swift <5.8

Author: ahoppen

Sources/SwiftParser/StringLiterals.swift

@@ -48,7 +48,7 @@ fileprivate class StringLiteralExpressionIndentationChecker {
       // Only checking tokens on a newline
       return nil
     }
-    let hasSufficientIndentation = token.tokenView.leadingTrivia { leadingTrivia in
+    let hasSufficientIndentation = token.tokenView.leadingTrivia { leadingTrivia -> Bool in
       let indentationStartIndex = leadingTrivia.lastIndex(where: { $0 == UInt8(ascii: "\n") || $0 == UInt8(ascii: "\r") })?.advanced(by: 1) ?? leadingTrivia.startIndex
       return SyntaxText(rebasing: leadingTrivia[indentationStartIndex...]).hasPrefix(expectedIndentation)
     }

Sources/SwiftSyntax/Raw/RawSyntaxNodeProtocol.swift

@@ -64,6 +64,22 @@ extension RawSyntax: RawSyntaxNodeProtocol {
   }
 }
 
+#if swift(<5.8)
+// Cherry-pick this function from SE-0370
+extension Slice {
+  @inlinable
+  public func initialize<S>(
+    from source: S
+  ) -> (unwritten: S.Iterator, index: Index)
+  where S: Sequence, Base == UnsafeMutableBufferPointer<S.Element> {
+    let buffer = Base(rebasing: self)
+    let (iterator, index) = buffer.initialize(from: source)
+    let distance = buffer.distance(from: buffer.startIndex, to: index)
+    return (iterator, startIndex.advanced(by: distance))
+  }
+}
+#endif
+
 @_spi(RawSyntax)
 public struct RawTokenSyntax: RawSyntaxNodeProtocol {
   public typealias SyntaxType = TokenSyntax

Tests/SwiftParserTest/LexerTests.swift

@@ -15,7 +15,7 @@ import XCTest
 @_spi(RawSyntax) import SwiftParser
 
 fileprivate func lex(_ sourceBytes: [UInt8]) -> [Lexer.Lexeme] {
-  return sourceBytes.withUnsafeBufferPointer { buf in
+  return sourceBytes.withUnsafeBufferPointer { (buf) -> [Lexer.Lexeme] in
     var lexemes = [Lexer.Lexeme]()
     for token in Lexer.tokenize(buf, from: 0) {
       lexemes.append(token)