update-source-catalog: support version 2 scheme

Version 1 of install-sources.yaml is a top-level list of the sources to
be offered.
Version 2 extends this by placing the list under a top-level key
`sources`, adding a `version` field, and adding a `kernel` field which
supplants the current kernel-meta-package file.  `kernel.default` is
read to know which kernel to use - unless we need to fallback to the
bridge kernel.

live-build/lb_binary_layered

@@ -185,7 +185,7 @@ build_layered_squashfs () {
 			if [ -f config/seeded-languages ]; then
 				usc_opts="$usc_opts --langs $(cat config/seeded-languages)"
 			fi
-			/usr/share/livecd-rootfs/update-source-catalog $usc_opts
+			/usr/share/livecd-rootfs/update-source-catalog source $usc_opts
 		else
 			echo "No catalog entry template for $pass"
 		fi

live-build/ubuntu-core-installer/hooks/05-prepare-image.binary

@@ -56,4 +56,4 @@ PROJECT_FULL=$PROJECT${SUBARCH:+-$SUBARCH}
 usc_opts="--output livecd.${PROJECT_FULL}.install-sources.yaml \
           --template config/edge.catalog-in.yaml \
           --size 0"
-/usr/share/livecd-rootfs/update-source-catalog $usc_opts
+/usr/share/livecd-rootfs/update-source-catalog source $usc_opts

update-source-catalog

@@ -7,29 +7,43 @@ import os
 import sys
 import yaml
 
+
+def get_opts():
     parser = argparse.ArgumentParser()
-parser.add_argument('--output', required=True)
+    subparsers = parser.add_subparsers(dest="subcommand")
-parser.add_argument('--size', required=True)
-parser.add_argument('--squashfs', default='')
-parser.add_argument('--translations')
-parser.add_argument('--template')
-parser.add_argument('--langs', default=None)
 
-opts = parser.parse_args(sys.argv[1:])
+    parser_source = subparsers.add_parser('source')
+    parser_source.add_argument('--output', required=True)
+    parser_source.add_argument('--template', required=True)
+    parser_source.add_argument('--size', required=True)
+    parser_source.add_argument('--squashfs', default='')
+    parser_source.add_argument('--translations')
+    parser_source.add_argument('--langs')
+    parser_source.set_defaults(func=on_source)
 
-if os.path.exists(opts.output):
+    parser_merge = subparsers.add_parser('merge')
-    with open(opts.output) as fp:
+    parser_merge.add_argument('--output', required=True)
-        output = yaml.safe_load(fp)
+    parser_merge.add_argument('--template', required=True)
-else:
+    parser_merge.set_defaults(func=on_merge)
-    output = []
+
+    return parser.parse_args()
 
 
-with open(opts.template) as fp:
+def yaml_load(filename):
-    template = yaml.safe_load(fp)
+    with open(filename) as fp:
+        return yaml.safe_load(fp)
 
 
+def yaml_dump(filename, content):
+    with open(filename, 'w') as fp:
+        yaml.dump(content, fp)
+
+
+def on_source(opts, output):
+    template = yaml_load(opts.template)
+
     id = template['id']
-for entry in output:
+    for entry in output["sources"]:
         # First, look if this source catalogue template id is already present.
         # If so, use the template to extend the existing entry with additional
         # variations.
@@ -73,10 +87,10 @@ else:
                 if opts.langs is not None:
                     template['preinstalled_langs'] = opts.langs.split(',')
 
-    output.append(template)
+        output["sources"].append(template)
 
         default_count = 0
-for entry in output:
+        for entry in output["sources"]:
             if entry.get('default', False):
                 default_count += 1
 
@@ -84,5 +98,22 @@ if default_count > 1:
             print("Too many defaults in source catalog!")
             sys.exit(1)
 
-with open(opts.output, 'w') as fp:
+
-    yaml.dump(output, fp)
+def on_merge(opts, output):
+    output.update(yaml_load(opts.template))
+
+
+if __name__ == "__main__":
+    opts = get_opts()
+
+    if os.path.exists(opts.output):
+        output = yaml_load(opts.output)
+    else:
+        output = {
+            "version": 2,
+            "sources": [],
+        }
+
+    opts.func(opts, output)
+
+    yaml_dump(opts.output, output)