project.py: Load new definitions of project version requirements

  o Define the base buildstream format as BST_FORMAT_VERSION
    in the project module

  o Load and cache any required versions of plugins

  o Assert overall project version is supported at load time

2 files changed, 59 insertions, 0 deletions

diff --git a/buildstream/data/projectconfig.yaml b/buildstream/data/projectconfig.yaml
index 5ebed682d..aa9605358 100644
--- a/buildstream/data/projectconfig.yaml
+++ b/buildstream/data/projectconfig.yaml
@@ -4,6 +4,29 @@
 #
 # name: myproject
 
+# Format version requirements
+#
+# Indicates the minimum required format version the
+# project requires.
+#
+required-versions:
+
+  # The minimum base BuildStream format
+  project: 0
+
+  # A minimum plugin format version for each individual
+  # plugin (as advertized by the plugin BST_FORMAT_VERSION
+  # class attributes), may be asserted here.
+  #
+  # E.g., to require version 3 of the the autotools
+  # element format:
+  #
+  #   elements:
+  #     autotools: 3
+  #
+  elements: {}
+  sources: {}
+
 # Base project relative element path, elements will be loaded
 # from this base.
 
diff --git a/buildstream/project.py b/buildstream/project.py
index 095fac137..e6e088e2e 100644
--- a/buildstream/project.py
+++ b/buildstream/project.py
@@ -49,6 +49,14 @@ class _ProjectVariant():
         del self.data['variant']
 
 
+BST_FORMAT_VERSION = 0
+"""The base BuildStream format version
+
+This version is bumped whenever enhancements are made
+to the ``project.conf`` format or the format in general.
+"""
+
+
 class Project():
     """Project Configuration
 
@@ -82,6 +90,8 @@ class Project():
         self._variants = []
         self._host_arch = host_arch
         self._target_arch = target_arch or host_arch
+        self._source_format_versions = {}
+        self._element_format_versions = {}
 
         profile_start(Topics.LOAD_PROJECT, self.directory.replace(os.sep, '-'))
         self._unresolved_config = self._load_first_half()
@@ -210,6 +220,32 @@ class Project():
         # The project name
         self.name = _yaml.node_get(self._unresolved_config, str, 'name')
 
+        # Version requirements
+        versions = _yaml.node_get(self._unresolved_config, Mapping, 'required-versions')
+
+        # Assert project version first
+        format_version = _yaml.node_get(versions, int, 'project')
+        if BST_FORMAT_VERSION < format_version:
+            major, minor = utils.get_bst_version()
+            raise LoadError(
+                LoadErrorReason.UNSUPPORTED_PROJECT,
+                "Project requested format version {}, but BuildStream {}.{} only supports up until format version {}"
+                .format(format_version, major, minor, BST_FORMAT_VERSION))
+
+        # The source versions
+        source_versions = _yaml.node_get(versions, Mapping, 'sources', default_value={})
+        for key, _ in source_versions.items():
+            if key == _yaml.PROVENANCE_KEY:
+                continue
+            self._source_format_versions[key] = _yaml.node_get(source_versions, int, key)
+
+        # The element versions
+        element_versions = _yaml.node_get(versions, Mapping, 'elements', default_value={})
+        for key, _ in element_versions.items():
+            if key == _yaml.PROVENANCE_KEY:
+                continue
+            self._element_format_versions[key] = _yaml.node_get(element_versions, int, key)
+
         # Load the plugin paths
         plugins = _yaml.node_get(self._unresolved_config, Mapping, 'plugins', default_value={})
         self._plugin_source_paths = [os.path.join(self.directory, path)