Merging functional `slotProps` of a theme

[GerardasB]

Steps to reproduce

Steps:

1. Open this link to live example: https://stackblitz.com/edit/github-nxqwy3jw?file=src%2FApp.tsx
2. Click the "Dashboard" button
3. Observe that the aria-labelledby attribute is not set on the list of a Menu component (element with role="menu".

Additionally, you can uncomment the lines that set the slotProps of the list as an object (in the theme) and observe that both the aria-labelledby of the theme and className of the component are merged.

Current behavior

The functional slotProps prop behaves differently than the object variant when set via the defaultProps of a theme.

When the object is used, the slotProps set on the component are merged with the slotProps of the theme. However, the function(al) slotProps of the theme is overridden entirely if the slotProps is set on the component.

This behavior is not ideal, as theme level customizations might be overridden unintentionally and pushes the theme customization towards the slots prop (when the ownerState is needed) - which is not ideal either, as it overrides MUI's default slots (usually just styling, but might include other functionality or internal components).

Expected behavior

(returned) Functional slotProps set via the defaultProps of a theme should be merged with slotProps set via the component.

Context

Working on a theme that customizes both the styling and semantics of MUI components - the ownerState is helpful to get the props passed in the component (or internal component state).

Your environment

No response

Search keywords: slotProps merging theme functional

[silviuaavram]

The usage is quite strange, since you're using the theme for non-theme use case. Not going to address, feel free to wrap the Menu and change it accordingly if you need it.

[GerardasB]

Why is this deemed a non-theme use-case? The theme allows customizing default props of a component or it's slots. There are two ways to customize slots: object or a function, I'm simply using the function.

EDIT: in our case we are trying to avoid wrapper components.