_plugincontext.py: Add plugin version assertion for non BuildStream 1 plugins.

From BuildStream 2, we added BST_MIN_VERSION which must be specified by
all plugins. This new assertion in BuildStream 1 detects the presence of this
in order to issue an early assertion informing the user that they should
use BuildStream 1 plugins for BuildStream 1 projects.

2 files changed, 32 insertions, 2 deletions

diff --git a/buildstream/_plugincontext.py b/buildstream/_plugincontext.py
index 5a7097485..10e32e58a 100644
--- a/buildstream/_plugincontext.py
+++ b/buildstream/_plugincontext.py
@@ -22,6 +22,7 @@ import inspect
 
 from ._exceptions import PluginError, LoadError, LoadErrorReason
 from . import utils
+from .utils import UtilError
 
 
 # A Context for loading plugin types
@@ -223,6 +224,31 @@ class PluginContext():
                                   plugin_type.BST_REQUIRED_VERSION_MAJOR,
                                   plugin_type.BST_REQUIRED_VERSION_MINOR))
 
+        # If a BST_MIN_VERSION was specified, then we need to raise an error
+        # that we are loading a plugin which targets the wrong BuildStream version.
+        #
+        try:
+            min_version = plugin_type.BST_MIN_VERSION
+        except AttributeError:
+            return
+
+        # Handle malformed version string specified by plugin
+        #
+        try:
+            major, minor = utils._parse_version(min_version)
+        except UtilError as e:
+            raise PluginError(
+                "Loaded plugin '{}' is not a BuildStream 1 plugin".format(kind),
+                detail="Error parsing BST_MIN_VERSION: {}".format(e),
+                reason="plugin-version-mismatch"
+            ) from e
+
+        raise PluginError(
+            "Loaded plugin '{}' is a BuildStream {} plugin".format(kind, major),
+            detail="You need to use BuildStream 1 plugins with BuildStream 1 projects",
+            reason="plugin-version-mismatch"
+        )
+
     # _assert_plugin_format()
     #
     # Helper to raise a PluginError if the loaded plugin is of a lesser version then
diff --git a/buildstream/utils.py b/buildstream/utils.py
index 3a2372262..f141cb15d 100644
--- a/buildstream/utils.py
+++ b/buildstream/utils.py
@@ -1222,11 +1222,15 @@ def _deduplicate(iterable, key=None):
 #
 def _parse_version(version):
 
-    versions = version.split(".")
+    try:
+        versions = version.split(".")
+    except AttributeError as e:
+        raise UtilError("Malformed version string: {}".format(version),)
+
     try:
         major = int(versions[0])
         minor = int(versions[1])
     except (IndexError, ValueError):
         raise UtilError("Malformed version string: {}".format(version),)
 
-    return (major, minor)
+    return major, minor