[WIP] fix(DataGrid): Allow columns with empty titles to be used in DataGrid

js/data-frame/index.tsx

@@ -244,6 +244,7 @@ const ShinyDataGrid: FC<ShinyDataGridProps<unknown>> = ({
             }
           },
           enableSorting,
+          ...(colname === "" && { id: findUnusedColumnName(columns, " ") }),
         };
       }),
     [columns, typeHints]
@@ -1018,6 +1019,21 @@ const ShinyDataGrid: FC<ShinyDataGridProps<unknown>> = ({
   );
 };
 
+/**
+ * Solves the problem arising when there's more than one column with the same name (or when
+ * the column name is illegal, like in the case of an empty name) by returning a name with
+ * enough spaces appended so that it becomes unique.
+ * @param columns Names of existing columns.
+ * @param initName String to start the search with.
+ * @returns A string that does not exist in columns and thus can be used as column ID.
+ */
+function findUnusedColumnName(columns: ReadonlyArray<string>, initName = " "): string {
+  while (columns.includes(initName)) {
+    initName += " ";
+  }
+  return initName;
+}
+
 function findKeysBetween<TData>(
   rowModel: RowModel<TData>,
   fromKey: string,

tests/playwright/shiny/bugs/1844-datagrid-empty-column/app.py

@@ -0,0 +1,26 @@
+import pandas as pd
+
+from shiny import App, Inputs, reactive, render, ui
+
+app_ui = ui.page_fluid(
+    ui.output_data_frame("df1"),
+)
+
+
+def server(input: Inputs):
+    df = reactive.Value(
+        pd.DataFrame(
+            {
+                "": [1, 2],
+                "A": [4, 5],
+                " ": [7, 8],
+            }
+        )
+    )
+
+    @render.data_frame
+    def df1():
+        return render.DataGrid(df())
+
+
+app = App(app_ui, server)

tests/playwright/shiny/bugs/1844-datagrid-empty-column/test_1844_datagrid_empty_column.py

@@ -0,0 +1,20 @@
+from __future__ import annotations
+
+from playwright.sync_api import Page
+
+from shiny.playwright import controller
+from shiny.run import ShinyAppProc
+
+
+def test_empty_column_name(page: Page, local_app: ShinyAppProc) -> None:
+    page.goto(local_app.url)
+
+    df = controller.OutputDataFrame(page, "df1")
+    df.expect_nrow(2)
+    df.expect_ncol(3)
+    df.expect_column_labels(["", "A", " "])
+
+    df.expect_cell("1", row=0, col=0)
+    df.expect_cell("2", row=1, col=0)
+    df.expect_cell("4", row=0, col=1)
+    df.expect_cell("8", row=1, col=2)