Improve prior build error message

src/orion/algo/space.py

@@ -880,13 +880,13 @@ class Fidelity(Dimension):
     # pylint:disable=super-init-not-called
     def __init__(self, name, low, high, base=2):
         if low <= 0:
-            raise AttributeError("Minimum resources must be a positive number.")
+            raise ValueError("Minimum resources must be a positive number.")
         elif low > high:
-            raise AttributeError(
+            raise ValueError(
                 "Minimum resources must be smaller than maximum resources."
             )
         if base < 1:
-            raise AttributeError("Base should be greater than or equal to 1")
+            raise ValueError("Base should be greater than or equal to 1")
         self.name = name
         self.low = int(low)
         self.high = int(high)

src/orion/core/io/space_builder.py

@@ -193,6 +193,16 @@ def loguniform(self, *args, **kwargs):
         klass = _real_or_int(kwargs)
         return klass(name, "reciprocal", *args, **kwargs)
 
+    def _build_custom(self, expression, globals_, locals_):
+        name = expression.split("(")[0]
+        if not hasattr(self, name):
+            return None
+        try:
+            dimension = eval("self." + expression, globals_, locals_)
+            return dimension
+        except AttributeError as error:
+            raise AttributeError(f"Parameter '{name}': {error}") from error
+
     def _build(self, name, expression):
         """Build a `Dimension` object using a string as its `name` and another
         string, `expression`, from configuration as a "function" to create it.
@@ -205,12 +215,10 @@ def _build(self, name, expression):
         import numpy as np
 
         globals_["np"] = np
-        try:
-            dimension = eval("self." + expression, globals_, {"self": self})
-
+        locals_ = {"self": self}
+        dimension = self._build_custom(expression, globals_, locals_)
+        if dimension is not None:
             return dimension
-        except AttributeError:
-            pass
 
         # If not found in the methods of `DimensionBuilder`.
         # try to see if it is legit scipy stuff and call a `Dimension`

tests/unittests/core/io/test_space_builder.py

@@ -127,6 +127,17 @@ def test_build_fails_because_of_ValueError_on_init(self, dimbuilder):
         assert "Parameter" in str(exc.value)
         assert "size" in str(exc.value.__cause__)
 
+    def test_build_fails_because_of_invalid_arguments_for_custom_prior(
+        self, dimbuilder
+    ):
+        """Build fails because ValueError happens on init of builtin prior."""
+        with pytest.raises(ValueError) as exc:
+            dimbuilder.build("yolo2", "fidelity(0, 10, base=1)")
+        assert "Parameter" in str(exc.value)
+        assert "Minimum resources must be a positive number." in str(
+            exc.value.__cause__
+        )
+
     def test_build_gaussian(self, dimbuilder):
         """Check that gaussian/normal/norm is built into reciprocal correctly."""
         dim = dimbuilder.build("yolo", "gaussian(3, 5)")