Facing the same issue, can't define default elevation for dialog via i.e. { defaultProps: { PaperProps: { elevation: 5 } } }.
Anytime anybody provides some PaperProps when using dialog, elevation is lost.

@mnajdova you have any update on this?

I did some digging and found out that this MR happened, which seem to resolve deep merge, but only for *slotProps properties.

However, not all of the components internals customisable via slotProps, i.e. Paper is not a slot for Dialog component. Same goes for original example by @guoyunhe.

As an idea perhaps that deep merge could be applied to any prop that ends with Props (e.g. /[a-z]+Props$/) ?
Summoning @flaviendelangle @siriwatknp as authors of the change for slot props

Just in case it needs any more reproduction:
https://codesandbox.io/p/devbox/default-props-deep-merge-issue-h46fxm?file=%2Fsrc%2FDemo.tsx%3A36%2C52

At first, the plan was to add missing slotProps to all components in v6 but we are still discussing the possibility of splitting each component into smaller subcomponents. That's why we haven't move forward with the missing slotProps.

Anyway, I still want to add the missing slotProps to make v6 complete because I don't think we will remove them in v7 regardless of subcomponents. What I picture in v7 is that the component + its slots will be exported and users can decide which one to use based on their use cases, for example, an Autocomplete:

// v7
// use case I: simple use case
import Autocomplete from '@mui/material/Autocomplete';

<Autocomplete … slotProps={{ input: { … }, arrow: {…} }} />


// use case II: composition
import { AutocompleteRoot, AutocompleteInput, Autocomplete… } from '@mui/material/Autocomplete';

<AutocompleteRoot>…</AutocompleteRoot>

What's your thought? @DiegoAndai @aarongarciah

@siriwatknp

to add missing slotProps to all components in v6

Does it mean that all component will have ability to provide any of their children Props via slotProps? i.e. for Dialog, PaperProps would appear as part of slotProps (cause right now PaperProps is just a part of DIalog's props).

Does it mean that all component will have ability to provide any of their children Props via slotProps? i.e. for Dialog, PaperProps would appear as part of slotProps (cause right now PaperProps is just a part of DIalog's props).

Yes, that's correct. @DiegoAndai I think we miss the Dialog, it haven't been migrated to slotProps from https://next.mui.com/material-ui/migration/migrating-from-deprecated-apis/.

@siriwatknp If I willing to contribute to expedite this issue, could you perhaps point me to some PR example for this change?

@alexey-kozlenkov you can follow the progress on slots being implemented here: #41281

But this issue is on hold as we discuss the path forward regarding slots. @siriwatknp's suggestion makes sense to me, but there's no agreement yet. When there's an agreement, which should come soon, we'll know the next step to solve this issue.

@DiegoAndai I see, thanks for replying here.
I'll follow noted issue then and wait for the updates