Add category to post list (via #1889)

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

CHANGES.txt

@@ -4,6 +4,7 @@ New in master
 Features
 --------
 
+* Add categories filter to post list directive (via Issue #1889)
 * Remove empty directories with nikola check --clean-files (Issue #1873)
 
 Bugfixes

docs/manual.txt

@@ -1737,7 +1737,10 @@ The following options are recognized:
 
 * ``tags`` : string [, string...]
       Filter posts to show only posts having at least one of the ``tags``.
+      Defaults to None.
 
+* ``categories`` : string [, string...]
+      Filter posts to show only posts having one of the ``categories``.
       Defaults to None.
 
 * ``slugs`` : string [, string...]

nikola/plugins/compile/rest/post_list.py

@@ -54,7 +54,7 @@ class PostList(Directive):
     Post List
     =========
     :Directive Arguments: None.
-    :Directive Options: lang, start, stop, reverse, sort, tags, template, id
+    :Directive Options: lang, start, stop, reverse, sort, tags, categories, slugs, all, template, id
     :Directive Content: None.
 
     Provides a reStructuredText directive to create a list of posts.
@@ -87,6 +87,10 @@ class PostList(Directive):
         Filter posts to show only posts having at least one of the ``tags``.
         Defaults to None.
 
+    ``categories`` : string [, string...]
+        Filter posts to show only posts having one of the ``categories``.
+        Defaults to None.
+
     ``slugs`` : string [, string...]
         Filter posts to show only posts having at least one of the ``slugs``.
         Defaults to None.
@@ -113,6 +117,7 @@ class PostList(Directive):
         'reverse': directives.flag,
         'sort': directives.unchanged,
         'tags': directives.unchanged,
+        'categories': directives.unchanged,
         'slugs': directives.unchanged,
         'all': directives.flag,
         'lang': directives.unchanged,
@@ -126,6 +131,8 @@ def run(self):
         reverse = self.options.get('reverse', False)
         tags = self.options.get('tags')
         tags = [t.strip().lower() for t in tags.split(',')] if tags else []
+        categories = self.options.get('categories')
+        categories = [c.strip().lower() for c in categories.split(',')] if categories else []
         slugs = self.options.get('slugs')
         slugs = [s.strip() for s in slugs.split(',')] if slugs else []
         show_all = self.options.get('all', False)
@@ -145,6 +152,9 @@ def run(self):
         else:
             timeline = [p for p in self.site.timeline if p.use_in_feeds]
 
+        if categories:
+            timeline = [p for p in timeline if p.meta('category', lang=lang).lower() in categories]
+
         for post in timeline:
             if tags:
                 cont = True