fix(legacy): export sources method to local plugins

Support legacy local plugins that invoke `snapcraft.sources.get`
by redirecting imports to `snapcraft_legacy`. This is similar
to the strategy used for V1 and V2 plugins.

Fixes #4285

Signed-off-by: Claudio Matsuoka <claudio.matsuoka@canonical.com>

snapcraft/__init__.py

@@ -20,6 +20,9 @@
 
 import pkg_resources
 
+# For legacy compatibility
+import snapcraft.sources  # noqa: F401
+
 
 def _get_version():
     if os.environ.get("SNAP_NAME") == "snapcraft":

snapcraft/sources.py

@@ -0,0 +1,23 @@
+# -*- Mode:Python; indent-tabs-mode:nil; tab-width:4 -*-
+#
+# Copyright 2023 Canonical Ltd.
+#
+# This program is free software: you can redistribute it and/or modify
+# it under the terms of the GNU General Public License version 3 as
+# published by the Free Software Foundation.
+#
+# This program 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 General Public License for more details.
+#
+# You should have received a copy of the GNU General Public License
+# along with this program.  If not, see <http://www.gnu.org/licenses/>.
+
+"""Legacy support for local plugins."""
+
+from snapcraft_legacy.sources import get
+
+__all__ = [
+    "get",
+]

tests/spread/plugins/v1/x-local/local-plugin/task.yaml

@@ -4,6 +4,7 @@ environment:
   SNAP_DIR/baseplugin: ../snaps/from-baseplugin
   SNAP_DIR/nilplugin: ../snaps/from-nilplugin
   SNAP_DIR/pluginv1: ../snaps/from-pluginv1
+  SNAP_DIR/sourceget: ../snaps/source-get
 
 prepare: |
   #shellcheck source=tests/spread/tools/snapcraft-yaml.sh

tests/spread/plugins/v1/x-local/snaps/source-get/snap/plugins/x_local_plugin.py

@@ -0,0 +1,43 @@
+# -*- Mode:Python; indent-tabs-mode:nil; tab-width:4 -*-
+#
+# Copyright 2023 Canonical Ltd.
+#
+# This program is free software: you can redistribute it and/or modify
+# it under the terms of the GNU General Public License version 3 as
+# published by the Free Software Foundation.
+#
+# This program 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 General Public License for more details.
+#
+# You should have received a copy of the GNU General Public License
+# along with this program.  If not, see <http://www.gnu.org/licenses/>.
+
+import snapcraft
+from snapcraft.plugins.v1 import PluginV1
+
+
+class LocalPlugin(PluginV1):
+    @classmethod
+    def schema(cls):
+        schema = super().schema()
+
+        schema["properties"]["foo"] = {"type": "string"}
+
+        return schema
+
+    @classmethod
+    def get_pull_properties(cls):
+        return ["foo", "stage-packages"]
+
+    @classmethod
+    def get_build_properties(cls):
+        return ["foo", "stage-packages"]
+
+    def pull(self):
+        super().pull()
+        x = snapcraft.sources.get
+
+    def build(self):
+        return self.run(["touch", "build-stamp"], self.installdir)

tests/spread/plugins/v1/x-local/snaps/source-get/snap/snapcraft.yaml

@@ -0,0 +1,12 @@
+name: test-local-plugins
+base: core18
+version: "0.1"
+summary: local plugin using snapcraft.sources.get
+description: Tests if local plugins load and can build
+confinement: strict
+grade: devel
+
+parts:
+    x-local-plugin:
+      plugin: x-local-plugin
+      source: .