[nstepien]

Since #4159, getRowGroupKey and getGroupId return strings, so TreeDataGrid only ever produces string group keys and IDs, but the types still said unknown. Apps had to cast groupKey as string, or keep expandedGroupIds in a ReadonlySet<unknown> that could hold values the grid never produces. This types them all as string, and exports GroupRow, which already appeared in public types (RenderGroupCellContentProps.row, RowHeightArgs) but couldn't be named.

This is the first PR of a stack of four: #4264 builds on it, and #4272 renames GroupRow to RowGroup.

Breaking change

- const [expandedGroupIds, setExpandedGroupIds] = useState((): ReadonlySet<unknown> => new Set());
+ const [expandedGroupIds, setExpandedGroupIds] = useState((): ReadonlySet<string> => new Set());

expandedGroupIds, onExpandedGroupIdsChange, GroupRow.groupKey, GroupRow.parentId, and RenderGroupCellContentProps.groupKey are typed with string instead of unknown, which is what getRowGroupKey and getGroupId produce. GroupRow is now exported.

Changes

• GroupRow.parentId is string | undefined (undefined on the first level) and GroupRow.groupKey is string; every GroupRow member now has JSDoc, checked against expandGroups and setStartRowIndexes.
• RenderGroupCellContentProps.groupKey is string; RenderGroupCellContentProps: pass the group row only #4264 then removes it in favor of row.groupKey.
• The internal toggleGroup parameters of TreeDataGrid, GroupedRow, and GroupCell are string, and renderToggleGroup no longer casts groupKey as string.
• GroupRow is exported from src/index.ts; its README entry is no longer "(internal)" and sits next to RenderGroupCellContentProps, and the RenderGroupCellContentProps and RowHeightArgs entries link to it.
• The ReadonlySet<unknown> state in the row grouping demo and in TreeDataGrid.test.tsx is now ReadonlySet<string>. The new Set() literals passed to expandedGroupIds infer Set<string> and need no change.

Verification

vp run ci passes. No tests are added, because the existing code already type-checks the new types: setup() in TreeDataGrid.test.tsx and the row grouping demo pass ReadonlySet<string> state and its setter to the grid, toggleGroup passes new Set(expandedGroupIds) to onExpandedGroupIdsChange, and renderToggleGroup renders groupKey without a cast. A consumer type-check of the built lib/index.d.ts, with and without exactOptionalPropertyTypes, confirms that ReadonlySet<unknown> state is a type error at expandedGroupIds and that ReadonlySet<string> state accepts the Set<string> from onExpandedGroupIdsChange.

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Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 99.27%. Comparing base (0f4c62c) to head (b32633a).

Additional details and impacted files

@@           Coverage Diff           @@
##             main    #4263   +/-   ##
=======================================
  Coverage   99.27%   99.27%           
=======================================
  Files          44       44           
  Lines        2216     2216           
  Branches      974      974           
=======================================
  Hits         2200     2200           
  Misses         16       16           

Files with missing lines	Coverage Δ
src/GroupCell.tsx	100.00% <ø> (ø)
src/GroupedRow.tsx	100.00% <ø> (ø)
src/TreeDataGrid.tsx	98.66% <100.00%> (ø)
src/cellRenderers/renderToggleGroup.tsx	100.00% <100.00%> (ø)

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