Add option to not raise if output is none, resolves #538

lib/axon.ex

@@ -3405,7 +3405,7 @@ defmodule Axon do
   """
   @doc type: :graph
   def get_output_shape(%Axon{} = axon, inputs, opts \\ []) do
-    {init_fn, forward_fn} = build(axon, opts)
+    {init_fn, forward_fn} = build(axon, opts ++ [raise_on_none: false])
 
     out =
       Nx.Defn.jit(

lib/axon/compiler.ex

@@ -48,6 +48,7 @@ defmodule Axon.Compiler do
   @doc false
   def build(%Axon{output: id, nodes: nodes}, opts) do
     debug? = Keyword.get(opts, :debug, false)
+    raise_on_none? = Keyword.get(opts, :raise_on_none, true)
     mode = Keyword.get(opts, :mode, :inference)
     seed = Keyword.get_lazy(opts, :seed, fn -> :erlang.system_time() end)
     global_layer_options = Keyword.get(opts, :global_layer_options, [])
@@ -105,10 +106,12 @@ defmodule Axon.Compiler do
       end
 
       with %Axon.None{} <- result do
-        raise ArgumentError,
-              "the compiled model will always result in %Axon.None{}." <>
-                " This most likely means you specified optional output and " <>
-                " did not handle the case when it is missing"
+        if raise_on_none? do
+          raise ArgumentError,
+                "the compiled model will always result in %Axon.None{}." <>
+                  " This most likely means you specified optional output and " <>
+                  " did not handle the case when it is missing"
+        end
       end
 
       result

test/axon_test.exs

@@ -1076,5 +1076,19 @@ defmodule AxonTest do
       assert shape = Axon.get_output_shape(model, Nx.template({1, 1}, :f32))
       assert shape == {{1, 2}, {1, 2}}
     end
+
+    test "doesn't raise on none output" do
+      values = Axon.input("values")
+      mask = Axon.input("mask", optional: true)
+
+      model =
+        values
+        |> Axon.dense(10)
+        |> Axon.multiply(mask)
+        |> Axon.dense(1)
+        |> Axon.sigmoid()
+
+      assert %Axon.None{} = Axon.get_output_shape(model, %{"values" => Nx.template({1, 1}, :f32)})
+    end
   end
 end