runtime: fix returning an empty array crash

Author: krichprollsch

src/runtime/js.zig

@@ -3469,11 +3469,16 @@ fn simpleZigValueToJs(isolate: v8.Isolate, value: anytype, comptime fail: bool)
                     else => @compileError("Invalid TypeArray type: " ++ @typeName(value_type)),
                 };
 
-                const buffer_len = len * bits / 8;
-                const backing_store = v8.BackingStore.init(isolate, buffer_len);
-                const data: [*]u8 = @alignCast(@ptrCast(backing_store.getData()));
-                @memcpy(data[0..buffer_len], @as([]const u8, @ptrCast(values))[0..buffer_len]);
-                const array_buffer = v8.ArrayBuffer.initWithBackingStore(isolate, &backing_store.toSharedPtr());
+                var array_buffer: v8.ArrayBuffer = undefined;
+                if (len == 0) {
+                    array_buffer = v8.ArrayBuffer.init(isolate, 0);
+                } else {
+                    const buffer_len = len * bits / 8;
+                    const backing_store = v8.BackingStore.init(isolate, buffer_len);
+                    const data: [*]u8 = @alignCast(@ptrCast(backing_store.getData()));
+                    @memcpy(data[0..buffer_len], @as([]const u8, @ptrCast(values))[0..buffer_len]);
+                    array_buffer = v8.ArrayBuffer.initWithBackingStore(isolate, &backing_store.toSharedPtr());
+                }
 
                 switch (@typeInfo(value_type)) {
                     .int => |n| switch (n.signedness) {

src/runtime/test_primitive_types.zig

@@ -118,6 +118,10 @@ const Primitives = struct {
         }
     }
 
+    pub fn _returnEmptyUint8(_: *const Primitives) Env.TypedArray(u8) {
+        return .{ .values = &.{} };
+    }
+
     pub fn _returnUint8(_: *const Primitives) Env.TypedArray(u8) {
         return .{ .values = &.{ 10, 20, 250 } };
     }
@@ -325,6 +329,7 @@ test "JS: primitive types" {
         .{ "try { p.intu64(arr_i64) } catch(e) { e instanceof TypeError; }", "true" },
         .{ "try { p.intu64(arr_u32) } catch(e) { e instanceof TypeError; }", "true" },
 
+        .{ "p.returnEmptyUint8()", "" },
         .{ "p.returnUint8()", "10,20,250" },
         .{ "p.returnInt8()", "10,-20,-120" },
         .{ "p.returnUint16()", "10,200,2050" },