chore: add zIndex placeholder

Author: zombieJ

src/Footer/Cell.tsx

@@ -28,11 +28,9 @@ export default function SummaryCell({
   const lastIndex = index + colSpan - 1;
   const mergedColSpan = lastIndex + 1 === scrollColumnIndex ? colSpan + 1 : colSpan;
 
-  const fixedInfo = getCellFixedInfo(
-    index,
-    index + mergedColSpan - 1,
-    flattenColumns,
-    stickyOffsets,
+  const fixedInfo = React.useMemo(
+    () => getCellFixedInfo(index, index + mergedColSpan - 1, flattenColumns, stickyOffsets),
+    [index, mergedColSpan, flattenColumns, stickyOffsets],
   );
 
   return (

src/hooks/useFixedInfo.ts

@@ -2,13 +2,18 @@ import useMemo from '@rc-component/util/lib/hooks/useMemo';
 import isEqual from '@rc-component/util/lib/isEqual';
 import type { ColumnType, StickyOffsets } from '../interface';
 import { getCellFixedInfo } from '../utils/fixUtil';
+import * as React from 'react';
 
 export default function useFixedInfo<RecordType>(
   flattenColumns: readonly ColumnType<RecordType>[],
   stickyOffsets: StickyOffsets,
 ) {
-  const fixedInfoList = flattenColumns.map((_, colIndex) =>
-    getCellFixedInfo(colIndex, colIndex, flattenColumns, stickyOffsets),
+  const fixedInfoList = React.useMemo(
+    () =>
+      flattenColumns.map((_, colIndex) =>
+        getCellFixedInfo(colIndex, colIndex, flattenColumns, stickyOffsets),
+      ),
+    [flattenColumns, stickyOffsets],
   );
 
   return useMemo(

src/utils/fixUtil.ts

@@ -11,6 +11,7 @@ export interface FixedInfo {
   fixedStartShadow?: boolean;
   /** `fixed: end` with shadow */
   fixedEndShadow?: boolean;
+
   zIndex?: number;
 }
 
@@ -39,12 +40,19 @@ export function getCellFixedInfo(
     fixEnd = stickyOffsets.end[colEnd];
   }
 
+  console.log('fixStart:', colStart);
+
   // check if need to add shadow
   const fixedStartShadow =
     fixStart !== null && (!columns[colStart + 1] || !isFixedStart(columns[colStart + 1]));
   const fixedEndShadow =
     fixEnd !== null && (!columns[colEnd - 1] || !isFixedEnd(columns[colEnd - 1]));
 
+  // Calc `zIndex`.
+  // first fixed start (start -> end) column `zIndex` should be greater than next column.
+  // first fixed end (end -> start) column `zIndex` should be greater than next column.
+  // TODO: handle this
+
   return {
     fixStart,
     fixEnd,