Fix Nx.slice crash on scalar tensor

nx/lib/nx.ex

@@ -13654,13 +13654,32 @@ defmodule Nx do
 
       iex> Nx.slice(Nx.tensor([[1, 2, 3], [4, 5, 6]]), [Nx.tensor(1.0), Nx.tensor(0)], [1, 1])
       ** (ArgumentError) index must be integer type, got {:f, 32} for axis 0
+
+  ## Scalars
+
+  Slicing a scalar tensor returns the scalar itself:
+
+      iex> Nx.slice(Nx.tensor(42), [], [])
+      #Nx.Tensor<
+        s32
+        42
+      >
   """
   @doc type: :indexed
   def slice(tensor, start_indices, lengths, opts \\ [])
       when is_list(start_indices) and is_list(lengths) and is_list(opts) do
     opts = keyword!(opts, strides: 1)
     %T{vectorized_axes: vectorized_axes, shape: shape} = tensor = to_tensor(tensor)
 
+    # Slicing a scalar tensor is a no-op — return unchanged
+    if shape == {} and start_indices == [] and lengths == [] do
+      tensor
+    else
+      slice_non_scalar(tensor, start_indices, lengths, opts, vectorized_axes, shape)
+    end
+  end
+
+  defp slice_non_scalar(tensor, start_indices, lengths, opts, vectorized_axes, shape) do
     if Enum.any?(start_indices, &(is_struct(&1, T) and &1.vectorized_axes != [])) do
       # if any of the indices is vectorized, we instead treat this slice as a gather
       [%{vectorized_axes: [{first_axis, _} | _] = vectorized_axes} | _] =

nx/test/nx_test.exs

@@ -3574,4 +3574,18 @@ defmodule NxTest do
       assert 28 = Nx.bit_size(tensor)
     end
   end
+
+  describe "slice of scalar tensor" do
+    test "returns scalar" do
+      t = Nx.tensor(42)
+      result = Nx.slice(t, [], [])
+      assert Nx.to_number(result) == 42
+    end
+
+    test "slice of scalar f64 tensor" do
+      t = Nx.tensor(3.14, type: :f64)
+      result = Nx.slice(t, [], [])
+      assert_in_delta Nx.to_number(result), 3.14, 1.0e-10
+    end
+  end
 end