mach: wasm: implement logging and panic handler

src/mach.js

@@ -26,6 +26,19 @@ const mach = {
     }
   },
 
+  machLogWrite(str, len) {
+    log_buf += mach.getString(str, len);
+  },
+
+  machLogFlush() {
+    console.log(log_buf);
+    log_buf = "";
+  },
+
+  machPanic(str, len) {
+    throw Error(mach.getString(str, len));
+  },
+
   machCanvasInit(width, height, id) {
     let canvas = document.createElement("canvas");
     canvas.id = "#mach-canvas-" + mach.canvases.length;

src/wasm.zig

@@ -11,6 +11,11 @@ const js = struct {
     extern fn machCanvasSetSize(canvas: CanvasId, width: u32, height: u32) void;
     extern fn machCanvasGetWidth(canvas: CanvasId) u32;
     extern fn machCanvasGetHeight(canvas: CanvasId) u32;
+
+    extern fn machLog(str: [*]const u8, len: u32) void;
+    extern fn machLogWrite(str: [*]const u8, len: u32) void;
+    extern fn machLogFlush() void;
+    extern fn machPanic(str: [*]const u8, len: u32) void;
 };
 
 pub const CanvasId = u32;
@@ -75,3 +80,31 @@ export fn wasmUpdate() bool {
 export fn wasmDeinit() void {
     app.deinit(&engine);
 }
+
+pub const log_level = .info;
+
+const LogError = error{};
+const LogWriter = std.io.Writer(void, LogError, writeLog);
+
+fn writeLog(_: void, msg: []const u8) LogError!usize {
+    js.machLogWrite(msg.ptr, msg.len);
+    return msg.len;
+}
+
+pub fn log(
+    comptime message_level: std.log.Level,
+    comptime scope: @Type(.EnumLiteral),
+    comptime format: []const u8,
+    args: anytype,
+) void {
+    const prefix = if (scope == .default) ": " else "(" ++ @tagName(scope) ++ "): ";
+    const writer = LogWriter{ .context = {} };
+
+    writer.print(message_level.asText() ++ prefix ++ format ++ "\n", args) catch return;
+    js.machLogFlush();
+}
+
+pub fn panic(msg: []const u8, _: ?*std.builtin.StackTrace) noreturn {
+    js.machPanic(msg.ptr, msg.len);
+    unreachable;
+}