plugin.py: Added _configure() and _get_configuring() private APIs

Keeps track of whether the plugin is currently being configured.

Adjusted Element and Source classes to call _configure() in place
of calling configure() directly.

This is a part of #620

3 files changed, 29 insertions, 2 deletions

diff --git a/buildstream/element.py b/buildstream/element.py
index 70e12313c..6a6d1a9b8 100644
--- a/buildstream/element.py
+++ b/buildstream/element.py
@@ -262,7 +262,7 @@ class Element(Plugin):
         # Collect the composited element configuration and
         # ask the element to configure itself.
         self.__config = self.__extract_config(meta)
-        self.configure(self.__config)
+        self._configure(self.__config)
 
         # Extract Sandbox config
         self.__sandbox_config = self.__extract_sandbox_config(meta)
diff --git a/buildstream/plugin.py b/buildstream/plugin.py
index 836b60834..f57c0e15c 100644
--- a/buildstream/plugin.py
+++ b/buildstream/plugin.py
@@ -162,6 +162,7 @@ class Plugin():
         self.__provenance = provenance  # The Provenance information
         self.__type_tag = type_tag      # The type of plugin (element or source)
         self.__unique_id = _plugin_register(self)  # Unique ID
+        self.__configuring = False      # Whether we are currently configuring
 
         # Infer the kind identifier
         modulename = type(self).__module__
@@ -651,7 +652,32 @@ class Plugin():
         else:
             yield log
 
+    # _configure():
+    #
+    # Calls configure() for the plugin, this must be called by
+    # the core instead of configure() directly, so that the
+    # _get_configuring() state is up to date.
+    #
+    # Args:
+    #    node (dict): The loaded configuration dictionary
+    #
+    def _configure(self, node):
+        self.__configuring = True
+        self.configure(node)
+        self.__configuring = False
+
+    # _get_configuring():
+    #
+    # Checks whether the plugin is in the middle of having
+    # its Plugin.configure() method called
+    #
+    # Returns:
+    #    (bool): Whether we are currently configuring
+    def _get_configuring(self):
+        return self.__configuring
+
     # _preflight():
+    #
     # Calls preflight() for the plugin, and allows generic preflight
     # checks to be added
     #
@@ -659,6 +685,7 @@ class Plugin():
     #    SourceError: If it's a Source implementation
     #    ElementError: If it's an Element implementation
     #    ProgramNotFoundError: If a required host tool is not found
+    #
     def _preflight(self):
         self.preflight()
 
diff --git a/buildstream/source.py b/buildstream/source.py
index 15acba732..bec01553b 100644
--- a/buildstream/source.py
+++ b/buildstream/source.py
@@ -247,7 +247,7 @@ class Source(Plugin):
         self.__config = self.__extract_config(meta)
         self.__first_pass = meta.first_pass
 
-        self.configure(self.__config)
+        self._configure(self.__config)
 
     COMMON_CONFIG_KEYS = ['kind', 'directory']
     """Common source config keys