Found bug, ugh

packages/two_dimensional_scrollables/lib/src/table_view/table.dart

@@ -24,10 +24,16 @@ import 'table_span.dart';
 /// vertically. If there is not enough space for all the columns, it will
 /// scroll horizontally.
 ///
-/// Each child [Widget] can belong to exactly one row and one column as
-/// represented by its [TableVicinity]. The table supports lazy rendering and
-/// will only instantiate those cells that are currently visible in the table's
-/// viewport and those that extend into the [cacheExtent].
+/// Each child [TableViewCell] can belong to exactly one row and one column as
+/// represented by its [TableVicinity], or it can span multiple rows and columns
+/// through merging. The table supports lazy rendering and will only instantiate
+/// those cells that are currently visible in the table's viewport and those
+/// that extend into the [cacheExtent]. Therefore, when merging cells in a
+/// [TableView], the same child should be returned from every vicinity the
+/// merged cell contains. The `build` method will only be called once for a
+/// merged cell, but since the table's children are lazily laid out, returning
+/// the same child ensures the merged cell can be built no matter which part of
+/// it is visible.
 ///
 /// The layout of the table (e.g. how many rows/columns there are and their
 /// extents) as well as the content of the individual cells is defined by
@@ -751,6 +757,9 @@ class RenderTableViewport extends RenderTwoDimensionalViewport {
 
         if (cell != null) {
           final TableViewParentData cellParentData = parentDataOf(cell);
+          if (vicinity == TableVicinity.zero) {
+            print(cellParentData);
+          }
 
           // Merged cell handling
           if (cellParentData.rowMergeStart != null ||
@@ -817,6 +826,12 @@ class RenderTableViewport extends RenderTwoDimensionalViewport {
                   mergedRowHeight! + _rowMetrics[currentRow]!.extent;
               int currentColumn = columnMergeStart;
               while (currentColumn <= lastColumn) {
+                if (vicinity == TableVicinity.zero) {
+                  print(TableVicinity(
+                    row: currentRow,
+                    column: currentColumn,
+                  ));
+                }
                 _mergedColumns.add(currentColumn);
                 mergedColumnWidth =
                     mergedColumnWidth! + _columnMetrics[currentColumn]!.extent;
@@ -830,6 +845,11 @@ class RenderTableViewport extends RenderTwoDimensionalViewport {
             }
           }
 
+          if (vicinity == TableVicinity.zero) {
+            print('mergedColumnWidth $mergedColumnWidth');
+            print('mergedRowHeight $mergedRowHeight');
+          }
+
           final BoxConstraints cellConstraints = BoxConstraints.tightFor(
             width: mergedColumnWidth ?? standardColumnWidth,
             height: mergedRowHeight ?? standardRowHeight,
@@ -1112,12 +1132,14 @@ class RenderTableViewport extends RenderTwoDimensionalViewport {
           columnSpan = _columnMetrics[columnIndex]!.configuration;
           if (columnSpan.backgroundDecoration != null) {
             final Rect rect = getColumnRect(
-                columnSpan.backgroundDecoration!.consumeSpanPadding,);
+              columnSpan.backgroundDecoration!.consumeSpanPadding,
+            );
             backgroundColumns[rect] = columnSpan.backgroundDecoration!;
           }
           if (columnSpan.foregroundDecoration != null) {
             final Rect rect = getColumnRect(
-                columnSpan.foregroundDecoration!.consumeSpanPadding,);
+              columnSpan.foregroundDecoration!.consumeSpanPadding,
+            );
             foregroundColumns[rect] = columnSpan.foregroundDecoration!;
           }
         }
@@ -1228,13 +1250,15 @@ class RenderTableViewport extends RenderTwoDimensionalViewport {
               parentDataOf(leadingCell).tableVicinity.row;
           rowSpan = _rowMetrics[rowIndex]!.configuration;
           if (rowSpan.backgroundDecoration != null) {
-            final Rect rect =
-                getRowRect(rowSpan.backgroundDecoration!.consumeSpanPadding,);
+            final Rect rect = getRowRect(
+              rowSpan.backgroundDecoration!.consumeSpanPadding,
+            );
             backgroundRows[rect] = rowSpan.backgroundDecoration!;
           }
           if (rowSpan.foregroundDecoration != null) {
-            final Rect rect =
-                getRowRect(rowSpan.foregroundDecoration!.consumeSpanPadding,);
+            final Rect rect = getRowRect(
+              rowSpan.foregroundDecoration!.consumeSpanPadding,
+            );
             foregroundRows[rect] = rowSpan.foregroundDecoration!;
           }
         }

packages/two_dimensional_scrollables/lib/src/table_view/table_cell.dart

@@ -32,10 +32,10 @@ class TableVicinity extends ChildVicinity {
   /// Equivalent to the [xIndex].
   int get column => xIndex;
 
-  ///
+  /// The origin vicinity of the [TableView], (0,0).
   static const TableVicinity zero = TableVicinity(row: 0, column: 0);
 
-  /// Returns a new TableVicinity, copying over the row and column fields with
+  /// Returns a new [TableVicinity], copying over the row and column fields with
   /// those provided, or maintaining the original values.
   TableVicinity copyWith({
     int? row,
@@ -98,7 +98,14 @@ class TableViewParentData extends TwoDimensionalViewportParentData {
   }
 }
 
+/// Creates a cell of the [TableView], along with information regarding merged
+/// cells and [RepaintBoundary]s.
 ///
+/// When merging cells in a [TableView], the same child should be returned from
+/// every vicinity the merged cell contains. The `build` method will only be
+/// called once for a merged cell, but since the table's children are lazily
+/// laid out, returning the same child ensures the merged cell can be built no
+/// matter which part of it is visible.
 class TableViewCell extends StatelessWidget {
   /// Creates a widget that controls how a child of a [TableView] spans across
   /// multiple rows or columns.
@@ -115,11 +122,15 @@ class TableViewCell extends StatelessWidget {
               (rowMergeStart != null && rowMergeSpan != null),
           'Row merge start and span must both be set, or both unset.',
         ),
+        assert(rowMergeStart == null || rowMergeStart >= 0),
+        assert(rowMergeSpan == null || rowMergeSpan > 0),
         assert(
           (columnMergeStart == null && columnMergeSpan == null) ||
               (columnMergeStart != null && columnMergeSpan != null),
           'Column merge start and span must both be set, or both unset.',
-        );
+        ),
+        assert(columnMergeStart == null || columnMergeStart >= 0),
+        assert(columnMergeSpan == null || columnMergeSpan > 0);
 
   /// The child contained in this cell of the [TableView].
   final Widget child;
@@ -184,16 +195,7 @@ class _TableViewCell extends ParentDataWidget<TableViewParentData> {
     this.columnMergeStart,
     this.columnMergeSpan,
     required super.child,
-  })  : assert(
-          (rowMergeStart == null && rowMergeSpan == null) ||
-              (rowMergeStart != null && rowMergeSpan != null),
-          'Row merge start and span must both be set, or both unset.',
-        ),
-        assert(
-          (columnMergeStart == null && columnMergeSpan == null) ||
-              (columnMergeStart != null && columnMergeSpan != null),
-          'Column merge start and span must both be set, or both unset.',
-        );
+  });
 
   final int? rowMergeStart;
   final int? rowMergeSpan;
@@ -206,18 +208,22 @@ class _TableViewCell extends ParentDataWidget<TableViewParentData> {
         renderObject.parentData! as TableViewParentData;
     bool needsLayout = false;
     if (parentData.rowMergeStart != rowMergeStart) {
+      assert(rowMergeStart == null || rowMergeStart! >= 0);
       parentData.rowMergeStart = rowMergeStart;
       needsLayout = true;
     }
     if (parentData.rowMergeSpan != rowMergeSpan) {
+      assert(rowMergeSpan == null || rowMergeSpan! > 0);
       parentData.rowMergeSpan = rowMergeSpan;
       needsLayout = true;
     }
     if (parentData.columnMergeStart != columnMergeStart) {
+      assert(columnMergeStart == null || columnMergeStart! >= 0);
       parentData.columnMergeStart = columnMergeStart;
       needsLayout = true;
     }
     if (parentData.columnMergeSpan != columnMergeSpan) {
+      assert(columnMergeSpan == null || columnMergeSpan! > 0);
       parentData.columnMergeSpan = columnMergeSpan;
       needsLayout = true;
     }

packages/two_dimensional_scrollables/lib/src/table_view/table_delegate.dart

@@ -148,7 +148,8 @@ class TableCellBuilderDelegate extends TwoDimensionalChildBuilderDelegate
               cellBuilder(context, vicinity as TableVicinity),
           maxXIndex: columnCount - 1,
           maxYIndex: rowCount - 1,
-          addRepaintBoundaries: false, // repaintBoundaries handled by TableViewCell
+          addRepaintBoundaries:
+              false, // repaintBoundaries handled by TableViewCell
         );
 
   @override
@@ -237,7 +238,8 @@ class TableCellListDelegate extends TwoDimensionalChildListDelegate
         _pinnedRowCount = pinnedRowCount,
         super(
           children: cells,
-          addRepaintBoundaries: false, // repaintBoundaries handled by TableViewCell
+          addRepaintBoundaries:
+              false, // repaintBoundaries handled by TableViewCell
         ) {
     // Even if there are merged cells, they should be represented by the same
     // child in each cell location. This ensures that no matter which direction