Add migration scripts for historical versions of the definitions format

See README for more information on how the migrations are intended work.

These migrations are probably not widely useful, as our definitions have
already been migrated manually. However, I want to come up with a good
pattern for writing migration scripts, and actually doing it seems like
the best way.

There is a 'migrations/indent' tool, which reformats a set of
definitions according to how the ruamel.yaml program writes them out.
This tool is nice if you like everything to have consistent indent and
line wrapping, and you can run it before running the migrations to
ensure that the migrations don't do any reformatting when writing the
.moprh files back to disk.

The migration scripts require the ruamel.yaml Python library. I have
sent a separate change to add this to the 'build' and 'devel' reference
systems.

Change-Id: Ibd62ba140d3f7e8e638beed6d714f671405bdc79

1 files changed, 59 insertions, 0 deletions

diff --git a/migrations/004-install-files-overwrite-symlink.py b/migrations/004-install-files-overwrite-symlink.py
new file mode 100755
index 00000000..6853dcb5
--- /dev/null
+++ b/migrations/004-install-files-overwrite-symlink.py
@@ -0,0 +1,59 @@
+#!/usr/bin/env python
+# Copyright (C) 2015  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
+# the Free Software Foundation; version 2 of the License.
+#
+# 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/>.
+
+'''Migration to Baserock Definitions format version 4.
+
+This change to the format was made to work around a bug in a deployment
+extension present in morph.git.
+
+Automated migration is not really possible for this change, and unless you
+are experiencing the install-files.configure extension crashing, you can ignore
+it completely.
+
+We have now moved all .configure and .write extensions into the definitions.git
+repository. Changes like this no longer require a marking a new version of the
+Baserock definitions format in order to prevent build tools crashing.
+
+Morph commit c373f5a403b0ec introduces version 4 of the definitions format. In
+older versions of Morph the install-files.configure extension would crash if it
+tried to overwrite a symlink. This bug is fixed in the version of Morph that
+can build definitions version 4.
+
+If you need to overwrite a symlink at deploytime using install-files.configure,
+please use VERSION to 4 or above in your definitions.git repo so older versions
+of Morph gracefully refuse to deploy, instead of crashing.
+
+'''
+
+
+import sys
+
+import migrations
+
+
+TO_VERSION = 4
+
+
+try:
+    if migrations.check_definitions_version(TO_VERSION - 1):
+        migrations.set_definitions_version(TO_VERSION)
+        sys.stdout.write("Migration completed successfully.\n")
+        sys.exit(0)
+    else:
+        sys.stdout.write("Nothing to do.\n")
+        sys.exit(0)
+except RuntimeError as e:
+    sys.stderr.write("Error: %s\n" % e.message)
+    sys.exit(1)