Add test to try to expose #24 bug

Sources/SwiftTreeSitter/Input.swift

@@ -46,28 +46,34 @@ final class Input {
     }
 }
 
-private func readFunction(payload: UnsafeMutableRawPointer?, byteIndex: UInt32, position: TSPoint, bytesRead: UnsafeMutablePointer<UInt32>?) -> UnsafePointer<Int8>? {
-    // get our self reference
-    let wrapper: Input = Unmanaged.fromOpaque(payload!).takeUnretainedValue()
+private func readFunction(
+	payload: UnsafeMutableRawPointer?,
+	byteIndex: UInt32,
+	position: TSPoint,
+	bytesRead: UnsafeMutablePointer<UInt32>?
+) -> UnsafePointer<Int8>? {
+	// get our self reference
+	let wrapper: Input = Unmanaged.fromOpaque(payload!).takeUnretainedValue()
 
-    // call our Swift-friendly reader block, or early out if there's no data to copy.
-    guard let data = wrapper.readBlock(Int(byteIndex), Point(internalPoint: position)),
-          data.count > 0
-    else
-    {
-      bytesRead?.pointee = 0
-      return nil
-    }
+	// call our Swift-friendly reader block, or early out if there's no data to copy.
+	guard
+		let data = wrapper.readBlock(Int(byteIndex), Point(internalPoint: position)),
+		data.count > 0
+	else
+	{
+		bytesRead?.pointee = 0
+		return nil
+	}
 
-    // copy the data into an internally-managed buffer with a lifetime of wrapper
-	  let buffer = Input.Buffer.allocate(capacity: data.count)
-    let copiedLength = data.copyBytes(to: buffer)
-    precondition(copiedLength == data.count)
+	// copy the data into an internally-managed buffer with a lifetime of wrapper
+	let buffer = Input.Buffer.allocate(capacity: data.count)
+	let copiedLength = data.copyBytes(to: buffer)
+	precondition(copiedLength == data.count)
 
-    wrapper.buffer = buffer
+	wrapper.buffer = buffer
 
-    // return to the caller
-    bytesRead?.pointee = UInt32(buffer.count)
+	// return to the caller
+	bytesRead?.pointee = UInt32(buffer.count)
 
-    return wrapper.bufferPointer
+	return wrapper.bufferPointer
 }

Tests/SwiftTreeSitterTests/ParserTests.swift

@@ -140,3 +140,17 @@ func main😃😃() {
 	}
 #endif
 }
+
+extension ParserTests {
+	// Attempt to expose the bug introduced by https://github.com/ChimeHQ/SwiftTreeSitter/pull/24
+	func testReadEmptyData() throws {
+		let language = Language(language: tree_sitter_swift())
+
+		let parser = Parser()
+		try parser.setLanguage(language)
+
+		let _ = parser.parse(tree: Tree?.none, readBlock: { _, _ in
+			return nil
+		})
+	}
+}