fix: notebook cell_ids for MarimoConvert.to_notebook_v1()

marimo/_convert/notebook.py

@@ -1,6 +1,8 @@
 # Copyright 2026 Marimo. All rights reserved.
 from __future__ import annotations
 
+from marimo._ast.cell_id import CellIdGenerator
+from marimo._ast.names import SETUP_CELL_NAME
 from marimo._schemas.notebook import (
     NotebookCell,
     NotebookCellConfig,
@@ -12,6 +14,7 @@
     CellDef,
     NotebookSerialization,
     NotebookSerializationV1,
+    SetupCell,
 )
 from marimo._utils.code import hash_code
 from marimo._version import __version__
@@ -28,11 +31,18 @@ def convert_from_ir_to_notebook_v1(
     Returns:
         NotebookV1: The notebook v1.
     """
+    cell_id_generator = CellIdGenerator()
     cells: list[NotebookCell] = []
-    for data in notebook_ir.cells:
+    for i, data in enumerate(notebook_ir.cells):
+        if isinstance(data, SetupCell) or (
+            i == 0 and data.name == SETUP_CELL_NAME
+        ):
+            cell_id = SETUP_CELL_NAME
+        else:
+            cell_id = cell_id_generator.create_cell_id()
         cells.append(
             NotebookCell(
-                id=None,
+                id=cell_id,
                 code=data.code,
                 code_hash=hash_code(data.code) if data.code else None,
                 name=data.name,

tests/_convert/test_notebook_cell_ids.py

@@ -0,0 +1,125 @@
+# Copyright 2026 Marimo. All rights reserved.
+from __future__ import annotations
+
+from textwrap import dedent
+
+from marimo._ast.cell_id import CellIdGenerator
+from marimo._ast.names import SETUP_CELL_NAME
+from marimo._convert.converters import MarimoConvert
+
+
+def _kernel_cell_ids(source: str) -> list[str]:
+    """Simulate the cell IDs the kernel would generate for a notebook."""
+    from marimo._ast.parse import parse_notebook
+    from marimo._schemas.serialization import SetupCell
+
+    ir = parse_notebook(source)
+    assert ir is not None
+    gen = CellIdGenerator()
+    ids = []
+    for i, cell_def in enumerate(ir.cells):
+        if isinstance(cell_def, SetupCell) or (
+            i == 0 and cell_def.name == SETUP_CELL_NAME
+        ):
+            ids.append(SETUP_CELL_NAME)
+        else:
+            ids.append(gen.create_cell_id())
+    return ids
+
+
+def test_snapshot_ids_match_kernel_ids():
+    source = dedent('''
+        import marimo
+
+        __generated_with = "0.1.0"
+        app = marimo.App()
+
+        @app.cell
+        def hello():
+            x = 1
+            return (x,)
+
+        @app.cell
+        def world(x):
+            y = x + 1
+            return (y,)
+
+        if __name__ == "__main__":
+            app.run()
+    ''').strip()
+
+    notebook = MarimoConvert.from_py(source).to_notebook_v1()
+    snapshot_ids = [c["id"] for c in notebook["cells"]]
+    kernel_ids = _kernel_cell_ids(source)
+
+    assert snapshot_ids == kernel_ids
+    assert all(id is not None for id in snapshot_ids)
+
+
+def test_snapshot_ids_match_kernel_ids_with_setup_cell():
+    source = dedent('''
+        import marimo
+
+        __generated_with = "0.1.0"
+        app = marimo.App()
+
+        with app.setup:
+            import numpy as np
+
+        @app.cell
+        def hello():
+            x = 1
+            return (x,)
+
+        @app.cell
+        def world(x):
+            y = x + 1
+            return (y,)
+
+        if __name__ == "__main__":
+            app.run()
+    ''').strip()
+
+    notebook = MarimoConvert.from_py(source).to_notebook_v1()
+    snapshot_ids = [c["id"] for c in notebook["cells"]]
+    kernel_ids = _kernel_cell_ids(source)
+
+    assert snapshot_ids == kernel_ids
+    assert snapshot_ids[0] == SETUP_CELL_NAME
+
+
+def test_snapshot_ids_are_deterministic():
+    source = dedent('''
+        import marimo
+
+        __generated_with = "0.1.0"
+        app = marimo.App()
+
+        @app.cell
+        def _():
+            x = 1
+            return (x,)
+
+        @app.cell
+        def _():
+            y = 2
+            return (y,)
+
+        @app.cell
+        def _():
+            z = 3
+            return (z,)
+
+        if __name__ == "__main__":
+            app.run()
+    ''').strip()
+
+    ids_1 = [
+        c["id"] for c in MarimoConvert.from_py(source).to_notebook_v1()["cells"]
+    ]
+    ids_2 = [
+        c["id"] for c in MarimoConvert.from_py(source).to_notebook_v1()["cells"]
+    ]
+
+    assert ids_1 == ids_2
+    assert len(set(ids_1)) == 3  # all unique