[typescript] Replace Array API with ReadonlyArray

[oliviertassinari]

Steps to reproduce

A good number of API use Array while using ReadonlyArray would be better DX, examples of such cases

• material-ui/packages/mui-base/src/Unstable_Popup/Popup.types.ts

  Line 60 in 48a2922

  middleware?: Array<PopupMiddleware | null | undefined | false>;

• material-ui/packages/mui-base/src/useSlider/useSlider.ts

  Line 145 in 48a2922

  newValue: number | Array<number>,

• material-ui/packages/mui-base/src/useSlider/useSlider.types.ts

  Line 102 in 48a2922

  value?: number | number[];

Current behavior

No response

Expected behavior

No response

Context

Compare:

vs.

We have solved this twice already:

#25155
#40481

We might as well solve it once for all.

Your environment

npx @mui/envinfo

  Don't forget to mention which browser you used.
  Output from `npx @mui/envinfo` goes here.

Search keywords: ReadonlyArray

[DiegoAndai]

This could be a good improvement to ship in v6, will add it to the milestone

[ant-plotnikov]

hey everyone. can I pick this up?

[oliviertassinari]

This could be a good improvement to ship in v6, will add it to the milestone

@DiegoAndai I wonder, I feel that major milestones should be focused on changes that require breaking changes (big features that require breaking changes or new major features to offset the removal of deprecated APIs) to decorelate things.
(e.g. I think it's closer to how MUI X operates for majors)

The rest could go into iteration plans like TypeScript has microsoft/TypeScript#56948 (3 months) or VS Code has microsoft/vscode#201255 (1 month).

This issue is small, we could add "good to take" and delegate to the community, optimizing for whenever a community member has time to donate (overall maximizing "time donation" for the community).

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It's also a Base UI issue.

[oliviertassinari]

We migrated a good chunk in #40754 and #40972 which is great but I think the issue should be about updating all our public APIs to accept read only arrays, there are more e.g.

material-ui/packages/mui-system/src/Unstable_Grid/GridProps.ts

Line 7 in 4a884da

type ResponsiveStyleValue<T> = T | Array<T | null> | { [key in Breakpoint]?: T | null };

material-ui/packages/mui-base/src/useAutocomplete/useAutocomplete.d.ts

Line 31 in 4a884da

? Array<Value | AutocompleteFreeSoloValueMapping<FreeSolo>>