WPF - how to hide menu item if command's CanExecute is false?

<Style.Triggers>
    <Trigger Property="IsEnabled" Value="False">
        <Setter Property="Visibility" Value="Collapsed"/>
    </Trigger>
</Style.Triggers>

CanExecute toggles the IsEnabled property so just watch this and keep everything in the UI. Create a separate style if you want to reuse this.

Binding Visibility to IsEnabled does the trick, but the required XAML is unpleasantly long and complicated:

Visibility="{Binding Path=IsEnabled, RelativeSource={RelativeSource Self}, Mode=OneWay, Converter={StaticResource booleanToVisibilityConverter}}"

You can use an attached property to hide all the binding details and clearly convey your intent.

Here is the attached property:

using System.Windows;
using System.Windows.Controls;
using System.Windows.Data;

namespace MyNamespace
{
    public static class Bindings
    {
        public static bool GetVisibilityToEnabled(DependencyObject obj)
        {
            return (bool)obj.GetValue(VisibilityToEnabledProperty);
        }

        public static void SetVisibilityToEnabled(DependencyObject obj, bool value)
        {
            obj.SetValue(VisibilityToEnabledProperty, value);
        }
        public static readonly DependencyProperty VisibilityToEnabledProperty =
            DependencyProperty.RegisterAttached("VisibilityToEnabled", typeof(bool), typeof(Bindings), new PropertyMetadata(false, OnVisibilityToEnabledChanged));

        private static void OnVisibilityToEnabledChanged(object sender, DependencyPropertyChangedEventArgs args)
        {
            if (sender is FrameworkElement element)
            {
                if ((bool)args.NewValue)
                {
                    Binding b = new Binding
                    {
                        Source = element,
                        Path = new PropertyPath(nameof(FrameworkElement.IsEnabled)),
                        Converter = new BooleanToVisibilityConverter()
                    };
                    element.SetBinding(UIElement.VisibilityProperty, b);
                }
                else
                {
                    BindingOperations.ClearBinding(element, UIElement.VisibilityProperty);
                }
            }
        }
    }
}

And here is how you would use it:

<Window x:Class="MyNamespace.SomeClass"
        xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
        xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
        xmlns:local="clr-namespace:MyNamespace">

    <ContextMenu x:Key="bazContextMenu">
        <MenuItem Header="Open"
                  Command="{x:Static local:FooCommand}"
                  local:Bindings.VisibilityToEnabled="True"/>
    </ContextMenu>
</Window>