Introduce the concept of snapshotting content

Author: mattmassicotte

Sources/SwiftTreeSitter/Parser.swift

@@ -97,6 +97,7 @@ extension Parser {
 
 extension Parser {
     public typealias ReadBlock = (Int, Point) -> Data?
+	public typealias DataSnapshotProvider = @Sendable (Int, Point) -> Data?
 
     public func parse(_ string: String) -> MutableTree? {
         guard let data = string.data(using: encoding) else { return nil }
@@ -144,15 +145,18 @@ extension Parser {
 		parse(tree: tree?.tree, string: string, limit: limit, chunkSize: chunkSize)
 	}
 
-    public static func readFunction(for string: String, limit: Int? = nil, chunkSize: Int = 2048) -> Parser.ReadBlock {
-        let usableLimit = limit ?? string.utf16.count
-        let encoding = String.nativeUTF16Encoding
-
-        return { (start, _) -> Data? in
-            return string.data(at: start,
-                               limit: usableLimit,
-                               using: encoding,
-                               chunkSize: chunkSize)
-        }
-    }
+	/// Form a function that captures an immutable view into the data of a `String`.
+	public static func readFunction(for string: String, limit: Int? = nil, chunkSize: Int = 2048) -> Parser.DataSnapshotProvider {
+		let usableLimit = limit ?? string.utf16.count
+		let encoding = String.nativeUTF16Encoding
+		
+		return { (start, _) -> Data? in
+			return string.data(
+				at: start,
+				limit: usableLimit,
+				using: encoding,
+				chunkSize: chunkSize
+			)
+		}
+	}
 }

Sources/SwiftTreeSitter/Predicate.swift

@@ -79,6 +79,7 @@ public enum Predicate: Hashable, Sendable {
 
 extension Predicate {
 	public typealias TextProvider = (NSRange, Range<Point>) -> String?
+	public typealias TextSnapshotProvider = @Sendable (NSRange, Range<Point>) -> String?
 	public typealias GroupMembershipProvider = (String, NSRange, Range<Point>) -> Bool
 
 	public struct Context {

Sources/SwiftTreeSitter/String+TextProvider.swift

@@ -14,7 +14,11 @@ extension String {
 	}
 
 	public var predicateTextProvider: Predicate.TextProvider {
-		return { (nsRange, _) in
+		predicateTextSnapshotProvider
+	}
+	
+	public var predicateTextSnapshotProvider: Predicate.TextSnapshotProvider {
+		{ (nsRange, _) in
 			guard let range = Range<String.Index>(nsRange, in: self) else {
 				return nil
 			}

Sources/SwiftTreeSitterLayer/LanguageLayer.swift

@@ -35,6 +35,36 @@ public final class LanguageLayer {
 			)
 		}
 	}
+	
+	public struct ContentSnapshot: Sendable {
+		public let readHandler: Parser.DataSnapshotProvider
+		public let textProvider: SwiftTreeSitter.Predicate.TextSnapshotProvider
+		
+		public init(
+			readHandler: @escaping @Sendable (Int, Point) -> Data?,
+			textProvider: @escaping @Sendable (NSRange, Range<Point>) -> String?
+		) {
+			self.readHandler = readHandler
+			self.textProvider = textProvider
+		}
+		
+		public init(string: String, limit: Int) {
+			let read = Parser.readFunction(for: string, limit: limit)
+
+			self.init(
+				readHandler: read,
+				textProvider: string.predicateTextSnapshotProvider
+			)
+		}
+		
+		public init(string: String) {
+			self.init(string: string, limit: string.utf16.count)
+		}
+
+		public var content: LanguageLayer.Content {
+			.init(readHandler: readHandler, textProvider: textProvider)
+		}
+	}
 
 	public struct Configuration {
 		public let languageProvider: LanguageProvider