Add a typed meta slot to column leaves and forward it from built-in columns

[matej21]

Summary

Add a typed extension slot to column leaves. ColumnLeafProps declares no place for per-column data that the code consuming useDataViewContext().columns needs, so an extra prop on a custom leaf reaches columns only through the undocumented ...leaf spread in resolveColumnNames, and the built-in column factories drop it.

Environment

• @contember/bindx-dataview@0.1.52 (version installed in the reporting project)
• Reproduces on contember/bindx@main as of 78c1712
• Failing test: tests/react/dataview/columnLeafMeta.test.tsx
• Branch: bug/column-leaf-extension-props

Reproduction

A downstream spreadsheet export needs each computed column to say how its cell is written as text. The column type owns that knowledge, so it has to travel on the leaf:

declare module '@contember/bindx-dataview' {
	interface ColumnLeafProps {
		// Not part of the bindx contract: survives only because resolveColumnNames spreads `...leaf`.
		readonly exportCell?: ((row: ExportRow) => string | null) | null
	}
}

const leafProps: ColumnLeafProps = {
	name: 'composed',
	fieldName: null,
	fieldRef: null,
	sortingField: null,
	filterName: null,
	filterHandler: undefined,
	isTextSearchable: false,
	header: 'Composed',
	renderCell: accessor => <ComposedCell accessor={accessor} />,
	exportCell: row => composedText(row),
}
return <ColumnLeaf {...leafProps} />

// consumer
const { columns } = useDataViewContext()
columns.map(column => column.exportCell)

The failing test expresses the contract we would like instead, a meta slot typed by an interface the consumer augments:

declare module '@contember/bindx-dataview' {
	interface ColumnLeafMeta {
		readonly exportHeader?: string
	}
}

<ColumnLeaf {...leafProps} meta={{ exportHeader }} />
<DataGridTextColumn field={it.title} header="Title" meta={{ exportHeader: 'Title (export)' }} />

const { columns } = useDataViewContext()
columns.map(it => it.meta?.exportHeader)

Expected behavior

• ColumnLeafProps has a documented slot for consumer data, typed by an augmentable interface, so no consumer has to augment ColumnLeafProps itself.
• The slot reaches DataViewColumn through resolveColumnNames and the runtime-bound columns built in useDataGridSetup.
• Every built-in column component (createColumn, createRelationColumn, the enum columns) accepts the slot and forwards it to its leaf.

Actual behavior

• bun run typecheck rejects the test:

  tests/react/dataview/columnLeafMeta.test.tsx(54,5): error TS2353: Object literal may only specify known properties, and 'meta' does not exist in type 'ColumnLeafProps'.
  tests/react/dataview/columnLeafMeta.test.tsx(63,79): error TS2339: Property 'meta' does not exist on type 'DataViewColumn'.
  tests/react/dataview/columnLeafMeta.test.tsx(100,59): error TS2322: Type '{ field: FieldRef<string> & FieldAccessor<string>; header: string; meta: { exportHeader: string; }; }' is not assignable to type 'IntrinsicAttributes & ColumnComponentProps<string> & object'.
    Property 'meta' does not exist on type 'IntrinsicAttributes & ColumnComponentProps<string> & object'.
  

• At runtime the custom leaf's extra prop does reach columns (the first test passes), but only as a side effect of the spread. The built-in column drops it (the second test fails):

  Expected: "title:Title (export)"
  Received: "title:-"
  

Suspected root cause

• packages/bindx-dataview/src/columnLeaf.ts: ColumnLeafProps is a closed interface with no consumer slot. resolveColumnNames passes unknown props through only because it builds each column with { ...leaf, name }.
• packages/bindx-dataview/src/createColumn.ts (createColumnStaticRender) and packages/bindx-dataview/src/createRelationColumn.tsx build leafProps field by field from the component props, so a prop they do not list never reaches the leaf.

Suggested fix

• In columnLeaf.ts, export interface ColumnLeafMeta {} and add readonly meta?: ColumnLeafMeta to ColumnLeafProps (and so to DataViewColumn), documented as the place for consumer data.
• Add meta?: ColumnLeafMeta to ColumnComponentProps and forward props['meta'] in createColumnStaticRender, in createRelationColumn and in the enum columns in columns.tsx.

A documented guarantee that resolveColumnNames and useDataGridSetup keep unknown leaf props would also work, but it leaves the consumer augmenting a core interface and does not cover the built-in columns.

Workaround shipped downstream

We applied a temporary workaround in our project, marked
TODO [BindX] (<this-issue-url>): <description>. The workaround augments ColumnLeafProps with an exportCell property and relies on resolveColumnNames spreading ...leaf; only our own column components set it. We will remove it once this issue is resolved.