GD0111: The exported tool button must be an expression-bodied property
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                                      Value
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**Rule ID**                           GD0111
**Category**                          Usage
**Fix is breaking or non-breaking**   Non-breaking
**Enabled by default**                Yes
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Cause
-----

A property is annotated with the ``[ExportToolButton]`` attribute but it's not
an `expression-bodied property`_.

Rule description
----------------

When reloading the .NET assembly, Godot will attempt to serialize exported
members to preserve their values. A field or a property with a backing field
that stores a ``Callable`` may prevent the unloading of the assembly.

An expression-bodied property doesn't have a backing field and won't store
the ``Callable``, so Godot won't attempt to serialize it, which should result
in the successful reloading of the .NET assembly.

.. code-block:: csharp

    [ExportToolButton("Click me!")]
    public Callable ValidClickMeButton => Callable.From(ClickMe);

    // Invalid because the Callable will be stored in the property's backing field.
    [ExportToolButton("Click me!")]
    public Callable InvalidClickMeButton { get; } = Callable.From(ClickMe);

How to fix violations
---------------------

To fix a violation of this rule, replace the property implementation with an
`expression-bodied property`_.

When to suppress warnings
-------------------------

Do not suppress a warning from this rule. ``Callable`` instances may prevent
the .NET assembly from unloading.

.. _expression-bodied property: https://learn.microsoft.com/en-us/dotnet/csharp/programming-guide/statements-expressions-operators/expression-bodied-members#properties