refactor: improve grid column group auto-width performance (#5122) (#5125)

Co-authored-by: Sascha Ißbrücker <sissbruecker@vaadin.com>

Author: vaadin-bot

packages/grid/src/vaadin-grid.js

@@ -543,6 +543,18 @@ class Grid extends ElementMixin(
 
   /** @private */
   __getIntrinsicWidth(col) {
+    if (this.__intrinsicWidthCache.has(col)) {
+      return this.__intrinsicWidthCache.get(col);
+    }
+
+    const width = this.__calculateIntrinsicWidth(col);
+    this.__intrinsicWidthCache.set(col, width);
+
+    return width;
+  }
+
+  /** @private */
+  __calculateIntrinsicWidth(col) {
     const initialWidth = col.width;
     const initialFlexGrow = col.flexGrow;
 
@@ -615,6 +627,8 @@ class Grid extends ElementMixin(
       this._debouncerHiddenChanged.flush();
     }
 
+    this.__intrinsicWidthCache = new Map();
+
     cols.forEach((col) => {
       col.width = `${this.__getDistributedWidth(col)}px`;
     });

packages/grid/test/column-auto-width.test.js

@@ -148,6 +148,18 @@ describe('column auto-width', () => {
     await recalculateWidths();
     expectColumnWidthsToBeOk(columns);
   });
+
+  it('should update column width when recalculating widths', async () => {
+    grid.items = testItems;
+    await recalculateWidths();
+    expectColumnWidthsToBeOk(columns, [74]);
+
+    // Update item text in first column
+    grid.items = [{ a: 'foo bar baz' }];
+    await nextFrame();
+    grid.recalculateColumnWidths();
+    expectColumnWidthsToBeOk(columns, [114]);
+  });
 });
 
 describe('tree column', () => {