feat: raise proper error if function being compiled returns something unsupported

concrete/numpy/tracing/tracer.py

@@ -65,12 +65,29 @@ class Tracer:
             input_indices[node] = index
 
         Tracer._is_tracing = True
-        output_tracers = function(**arguments)
+        output_tracers: Any = function(**arguments)
         Tracer._is_tracing = False
 
-        if isinstance(output_tracers, Tracer):
+        if not isinstance(output_tracers, tuple):
             output_tracers = (output_tracers,)
 
+        sanitized_tracers = []
+        for tracer in output_tracers:
+            if isinstance(tracer, Tracer):
+                sanitized_tracers.append(tracer)
+                continue
+
+            try:
+                sanitized_tracers.append(Tracer._sanitize(tracer))
+            except Exception as error:
+                raise ValueError(
+                    f"Function '{function.__name__}' "
+                    f"returned '{tracer}', "
+                    f"which is not supported"
+                ) from error
+
+        output_tracers = tuple(sanitized_tracers)
+
         def create_graph_from_output_tracers(output_tracers: Tuple[Tracer, ...]) -> nx.MultiDiGraph:
             graph = nx.MultiDiGraph()
 

tests/compilation/test_compiler.py

@@ -2,6 +2,7 @@
 Tests of `Compiler` class.
 """
 
+import numpy as np
 import pytest
 
 from concrete.numpy.compilation import Compiler
@@ -126,6 +127,9 @@ def test_compiler_bad_trace(helpers):
 
     configuration = helpers.configuration()
 
+    # without inputset
+    # ----------------
+
     def f(x, y, z):
         return x + y + z
 
@@ -138,6 +142,18 @@ def test_compiler_bad_trace(helpers):
 
     assert str(excinfo.value) == "Tracing function 'f' without an inputset is not supported"
 
+    # bad return
+    # ----------
+
+    def g():
+        return np.array([{}, ()], dtype=object)
+
+    with pytest.raises(ValueError) as excinfo:
+        compiler = Compiler(g, {})
+        compiler.trace(inputset=[()], configuration=configuration)
+
+    assert str(excinfo.value) == "Function 'g' returned '[{} ()]', which is not supported"
+
 
 def test_compiler_bad_compile(helpers):
     """