fix(data-table): handle dynamic headers gracefully (#2195)

Fixes #2193

src/DataTable/DataTable.svelte

@@ -263,12 +263,13 @@
     expanded = expandedRowIds.length === expandableRowIds.length;
   }
   $: if (radio || batchSelection) selectable = true;
-  $: headerKeys = headers.map(({ key }) => key);
   $: tableCellsByRowId = rows.reduce((rows, row) => {
-    rows[row.id] = headerKeys.map((key, index) => ({
-      key,
-      value: resolvePath(row, key),
-      display: headers[index].display,
+    rows[row.id] = headers.map((header, index) => ({
+      key: header.key || `key-${index}`,
+      value: header.key ? resolvePath(row, header.key) : undefined,
+      display: header.display,
+      empty: header.empty,
+      columnMenu: header.columnMenu,
     }));
     return rows;
   }, {});
@@ -557,8 +558,8 @@
             </td>
           {/if}
           {#each tableCellsByRowId[row.id] as cell, j (cell.key)}
-            {#if headers[j].empty}
-              <td class:bx--table-column-menu={headers[j].columnMenu}>
+            {#if cell.empty}
+              <td class:bx--table-column-menu={cell.columnMenu}>
                 <slot name="cell" {row} {cell} rowIndex={i} cellIndex={j}>
                   {cell.display ? cell.display(cell.value, row) : cell.value}
                 </slot>

tests/DataTable/DataTable.test.ts

@@ -772,4 +772,90 @@ describe("DataTable", () => {
       expect.any(Object),
     );
   });
+
+  it("should handle changing number of headers without crashing", async () => {
+    const rows = [
+      {
+        id: "a",
+        name: "Load Balancer 3",
+        protocol: "HTTP",
+        port: 3000,
+        rule: "Round robin",
+      },
+      {
+        id: "b",
+        name: "Load Balancer 1",
+        protocol: "HTTP",
+        port: 443,
+        rule: "Round robin",
+      },
+    ];
+
+    const headers5 = [
+      { key: "name", value: "Name" },
+      { key: "protocol", value: "Protocol" },
+      { key: "port", value: "Port" },
+      { key: "rule", value: "Rule" },
+      { key: "actions", value: "Actions" },
+    ];
+
+    const headers3 = [
+      { key: "name", value: "Name" },
+      { key: "protocol", value: "Protocol" },
+      { key: "port", value: "Port" },
+    ];
+
+    const { component, rerender } = render(DataTable, {
+      props: {
+        rows,
+        headers: headers5,
+      },
+    });
+
+    // First render with 5 headers
+    expect(component).toBeTruthy();
+
+    // Change to 3 headers - this should not crash
+    await rerender({
+      rows,
+      headers: headers3,
+    });
+
+    expect(component).toBeTruthy();
+
+    // Change back to 5 headers - this should not crash
+    await rerender({
+      rows,
+      headers: headers5,
+    });
+
+    expect(component).toBeTruthy();
+  });
+
+  it("should handle empty headers correctly", async () => {
+    const rows = [
+      {
+        id: "a",
+        name: "Load Balancer 3",
+        protocol: "HTTP",
+        port: 3000,
+        rule: "Round robin",
+      },
+    ];
+
+    const headersWithEmpty = [
+      { key: "name", value: "Name" },
+      { key: "protocol", value: "Protocol" },
+      { key: "actions", value: "", empty: true, columnMenu: true },
+    ];
+
+    const { component } = render(DataTable, {
+      props: {
+        rows,
+        headers: headersWithEmpty,
+      },
+    });
+
+    expect(component).toBeTruthy();
+  });
 });