Following code crashes (sigsegv in lldb-rpc-server) when run as swift 6, but runs correctly when run as swift 5 (from "Metal by tutorials"): import PlaygroundSupport import MetalKit print("start") guard let device = MTLCreateSystemDefaultDevice() else { fatalError("GPU is not supported") } let frame = CGRect(x: 0, y: 0, width: 600, height: 600) let view = MTKView(frame: frame, device: device) view.clearColor = MTLClearColor(red: 1, green: 1, blue: 0.8, alpha: 1) let allocator = MTKMeshBufferAllocator(device: device) let mdlMesh = MDLMesh(sphereWithExtent: [0.75,0.75,0.75], segments: [100, 100], inwardNormals: false, geometryType: .triangles, allocator: allocator) let mesh = try MTKMesh(mesh: mdlMesh, device: device) guard let commandQueue = device.makeCommandQueue() else { fatalError("Could not create a command queue") } let shader = """ #include <metal_stdlib> using namespace metal; struct VertexIn { float4 position [[attribute(0)]]; }; vertex float4 vertex_main(const VertexIn vertex_in [[stage_in]]) { return vertex_in.position; } fragment float4 fragment_main() { return float4(1, 0, 0, 1); } """ print("A") let library = try device.makeLibrary(source: shader, options: nil) let vertexFunction = library.makeFunction(name: "vertex_main") let fragmentFunction = library.makeFunction(name: "fragment_main") let pipelineDescriptor = MTLRenderPipelineDescriptor() pipelineDescriptor.colorAttachments[0].pixelFormat = .bgra8Unorm pipelineDescriptor.vertexFunction = vertexFunction pipelineDescriptor.fragmentFunction = fragmentFunction print("X") pipelineDescriptor.vertexDescriptor = MTKMetalVertexDescriptorFromModelIO(mesh.vertexDescriptor) let pipelineState = try device.makeRenderPipelineState(descriptor: pipelineDescriptor) guard let commandBuffer = commandQueue.makeCommandBuffer(), let renderPassDescriptor = view.currentRenderPassDescriptor, let renderEncoder = commandBuffer.makeRenderCommandEncoder(descriptor: renderPassDescriptor) else { fatalError() } renderEncoder.setRenderPipelineState(pipelineState) renderEncoder.setVertexBuffer(mesh.vertexBuffers[0].buffer, offset: 0, index: 0) guard let submesh = mesh.submeshes.first else { fatalError() } renderEncoder.drawIndexedPrimitives(type: .triangle, indexCount: submesh.indexCount, indexType: submesh.indexType, indexBuffer: submesh.indexBuffer.buffer, indexBufferOffset: 0) renderEncoder.endEncoding() guard let drawable = view.currentDrawable else { fatalError() } commandBuffer.present(drawable) commandBuffer.commit() print("test") PlaygroundPage.current.liveView = view Crash report: https://gist.githubusercontent.com/tumdum/8aa53bc806619c0d21c93a55fae07937/raw/370b00c07b08fff8856f9fc678de9888faa8d06e/crash.log I'm on macOS 15.1.1 (24B2091) + Xcode 16.2 (16C5032a)