CustomSystemProps is not used in SystemProps anymore

[IgnusG]

Duplicates

• I have searched the existing issues

Latest version

• I have tested the latest version

Steps to reproduce 🕹

Reference to types: https://github.com/mui/material-ui/blob/master/packages/mui-system/src/Box/Box.d.ts#L144

See context below on what I suggest is missing.

Current behavior 😯

Overwriting CustomSystemProps doesn't do anything since it's not actually used anywhere in the code anymore.

Expected behavior 🤔

CustomSystemProps is used in SystemProps so that augmenting it will properly work on components.

Eg. doing:

declare module '@mui/system/Box' {
  interface CustomSystemProps {
    customProp: number;
  }
}

would cause this prop to be available on components such as <Typography customProp={2} />

Specifically modifying packages/mui-system/src/Box/Box.d.ts like this worked:

export type SystemProps<Theme extends object = {}> = {
  [K in StandardSystemKeys]?:
    | ResponsiveStyleValue<AllSystemCSSProperties[K]>
    | ((theme: Theme) => ResponsiveStyleValue<AllSystemCSSProperties[K]>);
} & CustomSystemProps; // Added this bit

Context 🔦

This issue (#25771 (comment)) originally discussed a different issue but the fix seems to have removed the usage of the CustomSystemProps. I would assume this was by accident since this interface is not used anywhere else and could otherwise be removed entirely if it isn't supposed to be used anymore (although I find it useful).

Your environment 🌎

No response

[mnajdova]

Agree, seems like this is broken now. Would you like to work on a pull request on it, based on #25771 (comment)?

[IgnusG]

@mnajdova sure I can take a look 👍 Shouldn't be a big change