add upgrade_metadata, fix getnikola/nikola#1692

Signed-off-by: Chris Warrick <kwpolska@gmail.com>

v7/upgrade_metadata/upgrade_metadata.plugin

@@ -0,0 +1,12 @@
+[Core]
+Name = upgrade_metadata
+Module = upgrade_metadata
+
+[Nikola]
+MinVersion = 7.4.0
+
+[Documentation]
+Author = Chris Warrick
+Version = 0.1.0
+Website = http://plugins.getnikola.com/#upgrade_metadata
+Description = Upgrade old-style metadata

v7/upgrade_metadata/upgrade_metadata.py

@@ -0,0 +1,80 @@
+# -*- coding: utf-8 -*-
+
+# Copyright © 2014–2015, Chris Warrick.
+
+# Permission is hereby granted, free of charge, to any
+# person obtaining a copy of this software and associated
+# documentation files (the "Software"), to deal in the
+# Software without restriction, including without limitation
+# the rights to use, copy, modify, merge, publish,
+# distribute, sublicense, and/or sell copies of the
+# Software, and to permit persons to whom the Software is
+# furnished to do so, subject to the following conditions:
+#
+# The above copyright notice and this permission notice
+# shall be included in all copies or substantial portions of
+# the Software.
+#
+# THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY
+# KIND, EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE
+# WARRANTIES OF MERCHANTABILITY, FITNESS FOR A PARTICULAR
+# PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS
+# OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR
+# OTHER LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR
+# OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION WITH THE
+# SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.
+
+from __future__ import unicode_literals
+import io
+
+from nikola.plugin_categories import Command
+from nikola import utils
+
+
+class UpgradeMetadata(Command):
+    """Upgrade metadata from the old no-descriptions format to the new reST-esque format."""
+
+    name = 'upgrade_metadata'
+    doc_purpose = 'upgrade old-style metadata'
+    cmd_options = [
+        {
+            'name': 'yes',
+            'short': 'y',
+            'long': 'yes',
+            'type': bool,
+            'default': False,
+            'help': 'Proceed without confirmation',
+        },
+    ]
+    fields = ('title', 'slug', 'date', 'tags', 'link', 'description', 'type')
+
+    def _execute(self, options, args):
+        L = utils.get_logger('upgrade_metadata', self.site.loghandlers)
+        # scan posts
+        self.site.scan_posts()
+        flagged = []
+        for post in self.site.timeline:
+            if not post.newstylemeta:
+                flagged.append(post)
+        if flagged:
+            if len(flagged) == 1:
+                L.info('1 post contains old-style metadata:')
+            else:
+                L.info('{0} posts contain old-style metadata:'.format(len(flagged)))
+            for post in flagged:
+                L.info('    ' + post.metadata_path)
+            if not options['yes']:
+                yesno = utils.ask_yesno("Proceed with metadata upgrade?")
+            if options['yes'] or yesno:
+                for post in flagged:
+                    with io.open(post.metadata_path, 'r', encoding='utf-8') as fh:
+                        meta = fh.readlines()
+                    with io.open(post.metadata_path, 'w', encoding='utf-8') as fh:
+                        for k, v in zip(self.fields, meta):
+                            fh.write('.. {0}: {1}'.format(k, v))
+                L.info('{0} posts upgraded.'.format(len(flagged)))
+            else:
+                L.info('Metadata not upgraded.')
+        else:
+            L.info('No old-style metadata posts found.  No action is required.')
+