environment: call prepare for children by default, closes #545

RELEASE_NOTES.rst

@@ -8,6 +8,8 @@ Release notes
 
 * The --embed option of applets is replaced with the environment variable
   ARTIQ_APPLET_EMBED.
+* EnvExperiment's prepare calls prepare for all its children.
+
 
 2.0rc1
 ------

artiq/language/environment.py

@@ -194,6 +194,7 @@ class HasEnvironment:
     """Provides methods to manage the environment of an experiment (arguments,
     devices, datasets)."""
     def __init__(self, managers_or_parent, *args, **kwargs):
+        self.children = []
         if isinstance(managers_or_parent, tuple):
             self.__device_mgr = managers_or_parent[0]
             self.__dataset_mgr = managers_or_parent[1]
@@ -202,11 +203,15 @@ class HasEnvironment:
             self.__device_mgr = managers_or_parent.__device_mgr
             self.__dataset_mgr = managers_or_parent.__dataset_mgr
             self.__argument_mgr = managers_or_parent.__argument_mgr
+            managers_or_parent.register_child(self)
 
         self.__in_build = True
         self.build(*args, **kwargs)
         self.__in_build = False
 
+    def register_child(self, child):
+        self.children.append(child)
+
     def build(self):
         """Should be implemented by the user to request arguments.
 
@@ -373,7 +378,11 @@ class EnvExperiment(Experiment, HasEnvironment):
     environment manager.
 
     Most experiment should derive from this class."""
-    pass
+    def prepare(self):
+        """The default prepare method calls prepare for all children, in the
+        order of instantiation."""
+        for child in self.children:
+            child.prepare()
 
 
 def is_experiment(o):