element.py: Extract environment as classmethod

To clarify the data flow for extraction of environment variables,
make the relevant functions into classmethods and add an expansion
function which relies on the Variables instance.

Signed-off-by: Daniel Silverstone <daniel.silverstone@codethink.co.uk>

1 files changed, 16 insertions, 10 deletions

diff --git a/buildstream/element.py b/buildstream/element.py
index 1190b0ed0..72779915b 100644
--- a/buildstream/element.py
+++ b/buildstream/element.py
@@ -250,10 +250,11 @@ class Element(Plugin):
         self.__variables = Variables(variables)
 
         # Collect the composited environment now that we have variables
-        self.__environment = self.__extract_environment(meta)
+        unexpanded_env = self.__extract_environment(project, meta)
+        self.__environment = self.__expand_environment(unexpanded_env)
 
         # Collect the environment nocache blacklist list
-        nocache = self.__extract_env_nocache(meta)
+        nocache = self.__extract_env_nocache(project, meta)
         self.__env_nocache = nocache
 
         # Grab public domain data declared for this instance
@@ -2474,22 +2475,28 @@ class Element(Plugin):
             # Set the data class wide
             cls.__defaults = defaults
 
-    # This will resolve the final environment to be used when
+    # This will acquire the environment to be used when
     # creating sandboxes for this element
     #
-    def __extract_environment(self, meta):
-        default_env = _yaml.node_get(self.__defaults, Mapping, 'environment', default_value={})
+    @classmethod
+    def __extract_environment(cls, project, meta):
+        default_env = _yaml.node_get(cls.__defaults, Mapping, 'environment', default_value={})
 
         if meta.kind == "junction":
             environment = _yaml.new_empty_node()
         else:
-            project = self._get_project()
             environment = _yaml.node_copy(project.base_environment)
 
         _yaml.composite(environment, default_env)
         _yaml.composite(environment, meta.environment)
         _yaml.node_final_assertions(environment)
 
+        return environment
+
+    # This will resolve the final environment to be used when
+    # creating sandboxes for this element
+    #
+    def __expand_environment(self, environment):
         # Resolve variables in environment value strings
         final_env = {}
         for key, _ in self.node_items(environment):
@@ -2497,15 +2504,14 @@ class Element(Plugin):
 
         return final_env
 
-    def __extract_env_nocache(self, meta):
+    @classmethod
+    def __extract_env_nocache(cls, project, meta):
         if meta.kind == "junction":
             project_nocache = []
         else:
-            project = self._get_project()
-            project.ensure_fully_loaded()
             project_nocache = project.base_env_nocache
 
-        default_nocache = _yaml.node_get(self.__defaults, list, 'environment-nocache', default_value=[])
+        default_nocache = _yaml.node_get(cls.__defaults, list, 'environment-nocache', default_value=[])
         element_nocache = meta.env_nocache
 
         # Accumulate values from the element default, the project and the element