_versions.py: Added new file just to hold basic symbolic versions

This is where we're going to store BST_CORE_ARTIFACT_VERSION
and BST_FORMAT_VERSION from now on.

This was a little bit weirdly defined before, and now we need to
at least have BST_FORMAT_VERSION available from the frontend/cli
without onerous imports (we need to import it there, but dont want
to slow down load time for bash completion runs).

3 files changed, 40 insertions, 18 deletions

diff --git a/buildstream/_project.py b/buildstream/_project.py
index 6c8bda69a..c7f535e23 100644
--- a/buildstream/_project.py
+++ b/buildstream/_project.py
@@ -33,16 +33,10 @@ from ._artifactcache import artifact_cache_specs_from_config_node
 from ._elementfactory import ElementFactory
 from ._sourcefactory import SourceFactory
 from ._projectrefs import ProjectRefs, ProjectRefStorage
+from ._versions import BST_FORMAT_VERSION
 from ._workspaces import Workspaces
 
 
-# The base BuildStream format version
-#
-# This version is bumped whenever enhancements are made
-# to the `project.conf` format or the core element format.
-#
-BST_FORMAT_VERSION = 6
-
 # The separator we use for user specified aliases
 _ALIAS_SEPARATOR = ':'
 
diff --git a/buildstream/_versions.py b/buildstream/_versions.py
new file mode 100644
index 000000000..b08048c1f
--- /dev/null
+++ b/buildstream/_versions.py
@@ -0,0 +1,37 @@
+#!/usr/bin/env python3
+#
+#  Copyright (C) 2016 Codethink Limited
+#
+#  This program is free software; you can redistribute it and/or
+#  modify it under the terms of the GNU Lesser General Public
+#  License as published by the Free Software Foundation; either
+#  version 2 of the License, or (at your option) any later version.
+#
+#  This library is distributed in the hope that it will be useful,
+#  but WITHOUT ANY WARRANTY; without even the implied warranty of
+#  MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.	 See the GNU
+#  Lesser General Public License for more details.
+#
+#  You should have received a copy of the GNU Lesser General Public
+#  License along with this library. If not, see <http://www.gnu.org/licenses/>.
+#
+#  Authors:
+#        Tristan Van Berkom <tristan.vanberkom@codethink.co.uk>
+
+
+# The base BuildStream format version
+#
+# This version is bumped whenever enhancements are made
+# to the `project.conf` format or the core element format.
+#
+BST_FORMAT_VERSION = 6
+
+
+# The base BuildStream artifact version
+#
+# The artifact version changes whenever the cache key
+# calculation algorithm changes in an incompatible way
+# or if buildstream was changed in a way which can cause
+# the same cache key to produce something that is no longer
+# the same.
+BST_CORE_ARTIFACT_VERSION = 1
diff --git a/buildstream/element.py b/buildstream/element.py
index f63812f4d..76a6e0b73 100644
--- a/buildstream/element.py
+++ b/buildstream/element.py
@@ -36,6 +36,7 @@ import shutil
 
 from . import _yaml
 from ._variables import Variables
+from ._versions import BST_CORE_ARTIFACT_VERSION
 from ._exceptions import BstError, LoadError, LoadErrorReason, ImplError, ErrorDomain
 from . import Plugin, Consistency
 from . import SandboxFlags
@@ -47,16 +48,6 @@ from ._platform import Platform
 from .sandbox._config import SandboxConfig
 
 
-# The base BuildStream artifact version
-#
-# The artifact version changes whenever the cache key
-# calculation algorithm changes in an incompatible way
-# or if buildstream was changed in a way which can cause
-# the same cache key to produce something that is no longer
-# the same.
-_BST_CORE_ARTIFACT_VERSION = 1
-
-
 # _KeyStrength():
 #
 # Strength of cache key
@@ -1011,7 +1002,7 @@ class Element(Plugin):
             project = self._get_project()
 
             self.__cache_key_dict = {
-                'artifact-version': "{}.{}".format(_BST_CORE_ARTIFACT_VERSION,
+                'artifact-version': "{}.{}".format(BST_CORE_ARTIFACT_VERSION,
                                                    self.BST_ARTIFACT_VERSION),
                 'context': context.get_cache_key(),
                 'project': project.get_cache_key(),