[EuiDataGrid] Add new beta rowHeightsOptions.autoBelowLineCount feature flag

packages/eui/src/components/datagrid/data_grid_types.ts

@@ -1108,6 +1108,14 @@ export interface EuiDataGridRowHeightsOptions {
    * Defines the default size for all rows. It can be line count or just height.
    */
   defaultHeight?: EuiDataGridRowHeightOption;
+  /**
+   * Feature flag for custom `lineCount` behavior, where `lineCount` acts like a
+   * *max* number of lines (instead of a set number of lines for all rows).
+   *
+   * This functionality is in beta and has performance implications;
+   * we do not yet fully recommend/support it for heavy production usage.
+   */
+  autoBelowLineCount?: boolean;
   /**
    * Defines the height for a specific row. It can be line count or just height.
    *

packages/eui/src/components/datagrid/utils/__mocks__/row_heights.ts

@@ -24,6 +24,7 @@ export const RowHeightUtils = jest.fn().mockImplementation(() => {
 
   const rowHeightUtilsMock: RowHeightUtilsPublicAPI = {
     getHeightType: jest.fn(rowHeightUtils.getHeightType),
+    isAutoBelowLineCount: jest.fn(() => false),
     isAutoHeight: jest.fn(() => false),
     setRowHeight: jest.fn(),
     pruneHiddenColumnHeights: jest.fn(),

packages/eui/src/components/datagrid/utils/row_heights.test.ts

@@ -223,6 +223,56 @@ describe('RowHeightUtils', () => {
         ); // 5 * 24 + 6 + 6
       });
     });
+
+    describe('isAutoBelowLineCount', () => {
+      it('returns true when the feature flag is enabled and a lineCount above 1 exists', () => {
+        expect(
+          rowHeightUtils.isAutoBelowLineCount(
+            { autoBelowLineCount: true },
+            { lineCount: 3 }
+          )
+        ).toEqual(true);
+      });
+
+      it('returns false if the feature flag is not enabled', () => {
+        expect(
+          rowHeightUtils.isAutoBelowLineCount(
+            { autoBelowLineCount: false },
+            { lineCount: 3 }
+          )
+        ).toEqual(false);
+        expect(
+          rowHeightUtils.isAutoBelowLineCount(undefined, { lineCount: 3 })
+        ).toEqual(false);
+      });
+
+      it('returns false if height type is not lineCount', () => {
+        expect(
+          rowHeightUtils.isAutoBelowLineCount({ autoBelowLineCount: true }, 50)
+        ).toEqual(false);
+        expect(
+          rowHeightUtils.isAutoBelowLineCount(
+            { autoBelowLineCount: true },
+            'auto'
+          )
+        ).toEqual(false);
+      });
+
+      it('returns false if lineCount is 1 (treated as single line/undefined)', () => {
+        expect(
+          rowHeightUtils.isAutoBelowLineCount(
+            { autoBelowLineCount: true },
+            { lineCount: 1 }
+          )
+        ).toEqual(false);
+        expect(
+          rowHeightUtils.isAutoBelowLineCount(
+            { autoBelowLineCount: true },
+            undefined
+          )
+        ).toEqual(false);
+      });
+    });
   });
 
   describe('auto height utils', () => {
@@ -240,6 +290,15 @@ describe('RowHeightUtils', () => {
         ).toEqual(true);
       });
 
+      it('returns true if the grid if the conditions for `.isAutoBelowLineCount` are met`', () => {
+        expect(
+          rowHeightUtils.isAutoHeight(1, {
+            autoBelowLineCount: true,
+            defaultHeight: { lineCount: 2 },
+          })
+        ).toEqual(true);
+      });
+
       it('returns false otherwise', () => {
         expect(
           rowHeightUtils.isAutoHeight(1, {

packages/eui/src/components/datagrid/utils/row_heights.ts

@@ -115,6 +115,15 @@ export class RowHeightUtils {
     return contentHeight + padding * 2;
   }
 
+  isAutoBelowLineCount(
+    options?: EuiDataGridRowHeightsOptions,
+    option?: EuiDataGridRowHeightOption
+  ) {
+    if (!options?.autoBelowLineCount) return false;
+    if ((this.getLineCount(option) ?? 0) > 1) return true;
+    return false;
+  }
+
   /**
    * Auto height utils
    */
@@ -128,6 +137,9 @@ export class RowHeightUtils {
     if (height === AUTO_HEIGHT) {
       return true;
     }
+    if (this.isAutoBelowLineCount(rowHeightsOptions, height)) {
+      return true;
+    }
     return false;
   }