[@types/wordpress__block-editor] MediaPlaceholder value attribute is wrong #75586

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Pinging the DT module owners: @dsifford, @sirreal, @dmsnell, @joshualip-plaudit.

Yes — the current declaration is describing the value that MediaPlaceholder passes down to MediaUpload (number | number[]), not the public MediaPlaceholder.value prop.

In Gutenberg, MediaPlaceholder accepts media objects and converts them immediately before rendering MediaUpload:

value={
  Array.isArray(value)
    ? value.map(({ id }) => id)
    : value.id
}

That matches the component documentation: value is an object or array of objects containing an id.

The conditional should therefore mirror onSelect and keep the single/multiple cases separate. For the declaration's existing generic shape, a minimal correction would be:

type MediaValue = { id: number | string } & { [key: string]: any };

value?: T extends true ? MediaValue[] : MediaValue | undefined;

(Only one | undefined is needed; the repeated ones in the current declaration collapse to the same type.)

There is one additional edge case worth covering in a PR: multiple also accepts "add", but the current generic is only T extends boolean. Since "add" is a multiple-selection mode, a union of prop shapes or a generic over boolean | "add" would model it more accurately, e.g.:

type IsMultiple<T> = T extends true | "add" ? true : false;

type Props<T extends boolean | "add" = false> = {
  multiple?: T;
  value?: IsMultiple<T> extends true ? MediaValue[] : MediaValue;
  onSelect(value: IsMultiple<T> extends true ? MediaValue[] : MediaValue): void;
  // ...the remaining props
};

For the immediate bug, though, changing value from IDs to media object(s) is the important fix. A DT test should exercise all three calls: default/single object, multiple={true} array, and multiple="add" array. That will prevent the value and onSelect types from drifting apart again.