BuildCommand: Validate multiple root morphologies

When you attempt to build a stratum or chunk, the ArtifactResolver can
return multiple root artifacts, since the root source produces multiple
artifacts.

Rather than having the BuildCommand complain that there's multiple root
artifacts, it now validates all the produced artifacts too, since that
will validate the kinds of artifacts produced, and give a more useful
error message, that you're trying to build a stratum or chunk directly.

If all the produced artifacts validate, then an exception is raised to
signal that it got multiple artifacts, when it only expected one.

1 files changed, 21 insertions, 11 deletions

diff --git a/morphlib/buildcommand.py b/morphlib/buildcommand.py
index 4b3b2108..6485f510 100644
--- a/morphlib/buildcommand.py
+++ b/morphlib/buildcommand.py
@@ -1,4 +1,4 @@
-# Copyright (C) 2011-2013  Codethink Limited
+# Copyright (C) 2011-2014  Codethink Limited
 #
 # This program is free software; you can redistribute it and/or modify
 # it under the terms of the GNU General Public License as published by
@@ -22,6 +22,14 @@ import tempfile
 import morphlib
 
 
+class MultipleRootArtifactsError(morphlib.Error):
+
+    def __init__(self, artifacts):
+        self.msg = ('System build has multiple root artifacts: %r'
+                    % [a.name for a in artifacts])
+        self.artifacts = artifacts
+
+
 class BuildCommand(object):
 
     '''High level logic for building.
@@ -142,7 +150,15 @@ class BuildCommand(object):
         artifacts = ar.resolve_artifacts(srcpool)
 
         self.app.status(msg='Computing build order', chatty=True)
-        root_artifact = self._find_root_artifact(artifacts)
+        root_artifacts = self._find_root_artifacts(artifacts)
+        if len(root_artifacts) > 1:
+            # Validate root artifacts, since validation covers errors
+            # such as trying to build a chunk or stratum directly,
+            # and this is one cause for having multiple root artifacts
+            for root_artifact in root_artifacts:
+                self._validate_root_artifact(root_artifact)
+            raise MultipleRootArtifactsError(root_artifacts)
+        root_artifact = root_artifacts[0]
 
         # Validate the root artifact here, since it's a costly function
         # to finalise it, so any pre finalisation validation is better
@@ -231,8 +247,8 @@ class BuildCommand(object):
                          other.morphology['kind'],
                          wanted))
 
-    def _find_root_artifact(self, artifacts):
-        '''Find the root artifact among a set of artifacts in a DAG.
+    def _find_root_artifacts(self, artifacts):
+        '''Find all the root artifacts among a set of artifacts in a DAG.
         
         It would be nice if the ArtifactResolver would return its results in a
         more useful order to save us from needing to do this -- the root object
@@ -240,13 +256,7 @@ class BuildCommand(object):
         
         '''
 
-        maybe = set(artifacts)
-        for a in artifacts:
-            for dep in a.dependencies:
-                if dep in maybe:
-                    maybe.remove(dep)
-        assert len(maybe) == 1
-        return maybe.pop()
+        return [a for a in artifacts if not a.dependents]
 
     def build_in_order(self, root_artifact):
         '''Build everything specified in a build order.'''