feat: raise error if tracers are tried to be converted to bool

concrete/numpy/tracing/tracer.py

@@ -175,6 +175,12 @@ class Tracer:
     def __hash__(self) -> int:
         return id(self)
 
+    def __bool__(self) -> bool:
+        # pylint: disable=invalid-bool-returned
+
+        message = "Branching within circuits is not possible"
+        raise RuntimeError(message)
+
     @staticmethod
     def sanitize(value: Any) -> Any:
         """

tests/tracing/test_tracer.py

@@ -45,6 +45,12 @@ from concrete.numpy.values import EncryptedTensor
             "`astype` method must be called with a "
             "numpy type for compilation (e.g., value.astype(np.int64))",
         ),
+        pytest.param(
+            lambda x: x + 1 if x else x + x,
+            {"x": EncryptedTensor(UnsignedInteger(7), shape=())},
+            RuntimeError,
+            "Branching within circuits is not possible",
+        ),
     ],
 )
 def test_tracer_bad_trace(function, parameters, expected_error, expected_message):