From 97496d5a672c78271735dd77abde3248eea8b967 Mon Sep 17 00:00:00 2001
From: Simon Willison <swillison@gmail.com>
Date: Sun, 21 Dec 2025 19:52:49 -0800
Subject: [PATCH] ?_extra=render_cells for tables, refs #2619

---
 datasette/views/table.py | 31 ++++++++++++++++++++
 tests/test_table_api.py  | 62 ++++++++++++++++++++++++++++++++++++++++
 2 files changed, 93 insertions(+)

diff --git a/datasette/views/table.py b/datasette/views/table.py
index 007c0c85..c8f209d6 100644
--- a/datasette/views/table.py
+++ b/datasette/views/table.py
@@ -1492,6 +1492,36 @@ async def table_view_data(
     async def extra_display_rows(run_display_columns_and_rows):
         return run_display_columns_and_rows["rows"]
 
+    async def extra_render_cells():
+        "Rendered HTML for each cell using the render_cell plugin hook"
+        columns = [col[0] for col in results.description]
+        rendered_rows = []
+        for row in rows:
+            rendered_row = {}
+            for value, column in zip(row, columns):
+                # Call render_cell plugin hook
+                plugin_display_value = None
+                for candidate in pm.hook.render_cell(
+                    row=row,
+                    value=value,
+                    column=column,
+                    table=table_name,
+                    database=database_name,
+                    datasette=datasette,
+                    request=request,
+                ):
+                    candidate = await await_me_maybe(candidate)
+                    if candidate is not None:
+                        plugin_display_value = candidate
+                        break
+                if plugin_display_value:
+                    rendered_row[column] = str(plugin_display_value)
+                else:
+                    # Default: convert value to string
+                    rendered_row[column] = "" if value is None else str(value)
+            rendered_rows.append(rendered_row)
+        return rendered_rows
+
     async def extra_query():
         "Details of the underlying SQL query"
         return {
@@ -1678,6 +1708,7 @@ async def table_view_data(
         run_display_columns_and_rows,
         extra_display_columns,
         extra_display_rows,
+        extra_render_cells,
         extra_debug,
         extra_request,
         extra_query,
diff --git a/tests/test_table_api.py b/tests/test_table_api.py
index 653679e4..d5a8ca41 100644
--- a/tests/test_table_api.py
+++ b/tests/test_table_api.py
@@ -1383,3 +1383,65 @@ async def test_table_extras(ds_client, extra, expected_json):
     )
     assert response.status_code == 200
     assert response.json() == expected_json
+
+
+@pytest.mark.asyncio
+async def test_extra_render_cells():
+    """Test that _extra=render_cells returns rendered HTML from render_cell plugin hook"""
+    from datasette import hookimpl
+    from datasette.app import Datasette
+
+    class TestRenderCellPlugin:
+        __name__ = "TestRenderCellPlugin"
+
+        @hookimpl
+        def render_cell(self, value, column, table, database):
+            # Only modify cells in our test table
+            if table == "test_render" and column == "name":
+                return f"<strong>{value}</strong>"
+            return None
+
+    ds = Datasette(memory=True)
+    await ds.invoke_startup()
+    db = ds.add_memory_database("test")
+    await db.execute_write(
+        "create table test_render (id integer primary key, name text)"
+    )
+    await db.execute_write("insert into test_render values (1, 'Alice')")
+    await db.execute_write("insert into test_render values (2, 'Bob')")
+
+    # Register our test plugin
+    ds.pm.register(TestRenderCellPlugin(), name="TestRenderCellPlugin")
+
+    try:
+        # Request with _extra=render_cells
+        response = await ds.client.get("/test/test_render.json?_extra=render_cells")
+        assert response.status_code == 200
+        data = response.json()
+
+        # Verify the response structure
+        assert "render_cells" in data
+        assert "rows" in data
+
+        # render_cells should be a list of rows, each row being a dict of column -> rendered HTML
+        render_cells = data["render_cells"]
+        assert len(render_cells) == 2
+
+        # First row: id=1, name='Alice'
+        # The 'name' column should be rendered by our plugin as <strong>Alice</strong>
+        assert render_cells[0]["name"] == "<strong>Alice</strong>"
+        # The 'id' column should use default rendering (just the value as string)
+        assert render_cells[0]["id"] == "1"
+
+        # Second row: id=2, name='Bob'
+        assert render_cells[1]["name"] == "<strong>Bob</strong>"
+        assert render_cells[1]["id"] == "2"
+
+        # The regular rows should still contain raw values
+        assert data["rows"] == [
+            {"id": 1, "name": "Alice"},
+            {"id": 2, "name": "Bob"},
+        ]
+
+    finally:
+        ds.pm.unregister(name="TestRenderCellPlugin")