Swift Charts - Heat Map compilation issue

heatmap_issue.swift

import SwiftUI
import Charts

struct ContentView: View {
    @State private var grid = Grid(numRows: 10, numCols: 10)

    var body: some View {
        if #available(iOS 16.0, *) {
            VStack {
                Spacer()
                Chart(grid.points) { point in
                    RectangleMark(
                        xStart: PlottableValue.value("xStart", point.x),
                        xEnd: PlottableValue.value("xEnd", point.x + 1),
                        yStart: PlottableValue.value("yStart", point.y),
                        yEnd: PlottableValue.value("yEnd", point.y + 1)
                    )
                    .foregroundStyle(point.color)
                    // Uncommenting annotations causes code to not compile, 
                    // unless either chartYAxis or chartXAxis is commented
//                    .annotation(position: .overlay) {
//                        Text(String(format: "%.0f", point.val))
//                    }
                }
                .chartYAxis {
                    AxisMarks(values: .automatic(desiredCount: grid.numRows, roundLowerBound: false, roundUpperBound: false)) { _ in
                        AxisGridLine()
                        AxisTick()
                        AxisValueLabel(centered: true)
                    }
                }
                .chartXAxis {
                    AxisMarks(values: .automatic(desiredCount: grid.numCols, roundLowerBound: false, roundUpperBound: false)) { _ in
                        AxisGridLine()
                        AxisTick()
                        AxisValueLabel(centered: true)
                    }
                }
                .aspectRatio(contentMode: .fit)
                Spacer()
            }
        } else {
            EmptyView()
        }
    }
}

struct Grid {
    let numRows: Int
    let numCols: Int
    var points = [Point]()

    init(numRows: Int, numCols: Int) {
        self.numRows = numRows
        self.numCols = numCols
        generateData()
    }

    mutating func generateData() {
        for rowIndex in 0..<numRows {
            for colIndex in 0..<numCols {
                let maxValue = numRows + numCols - 2
                let variance = Double.random(in: 0..<20) - 10
                let value = (Double(rowIndex + colIndex) * 100)/Double(maxValue) + variance
                let point = Point(x: colIndex, y: rowIndex, val: value)
                points.append(point)
            }
        }
    }

    struct Point: Hashable, Identifiable {
        let id = UUID()
        let x: Int
        let y: Int
        let val: Double

        var color: Color {
            switch val {
            case _ where val < 20.0:
                return .blue
            case 20..<40:
                return .green
            case 40..<60:
                return .yellow
            case 60..<80:
                return .orange
            case _ where val >= 80:
                return .red
            default:
                return .red
            }
        }
    }
}

Issue still exists in Xcode 14 beta 5.