Fix followed tags posts in stream for posts with multiple tags

When there were posts with many followed tags they were returned
multiple times, resulting in less than 15 unique posts. That resulted in
some posts to be missed in the stream.

Fixes #4503

closes #7715

Changelog.md

@@ -8,6 +8,7 @@
 * Prevent duplicate mention notifications when the post is received twice [#7721](https://github.com/diaspora/diaspora/pull/7721)
 * Fixed a compatiblitiy issue with non-diaspora\* webfingers [#7718](https://github.com/diaspora/diaspora/pull/7718)
 * Don't retry federation for accounts without a valid public key [#7717](https://github.com/diaspora/diaspora/pull/7717)
+* Fix stream generation for tagged posts with many followed tags [#7715](https://github.com/diaspora/diaspora/pull/7715)
 
 ## Features
 * Add basic html5 audio/video embedding support [#6418](https://github.com/diaspora/diaspora/pull/6418)

app/models/status_message.rb

@@ -46,7 +46,7 @@ class StatusMessage < Post
   end
 
   def self.public_tag_stream(tag_ids)
-    all_public.tag_stream(tag_ids)
+    all_public.select("DISTINCT #{table_name}.*").tag_stream(tag_ids)
   end
 
   def self.tag_stream(tag_ids)

spec/models/status_message_spec.rb

@@ -51,6 +51,14 @@ describe StatusMessage, type: :model do
         it "returns public status messages tagged with the tag" do
           expect(StatusMessage.public_tag_stream([@tag_id])).to eq([@status_message_1])
         end
+
+        it "returns a post with two tags only once" do
+          status_message = FactoryGirl.create(:status_message, text: "#hashtag #test", public: true)
+          test_tag_id = ActsAsTaggableOn::Tag.where(name: "test").first.id
+
+          expect(StatusMessage.public_tag_stream([@tag_id, test_tag_id]))
+            .to match_array([@status_message_1, status_message])
+        end
       end
 
       describe ".user_tag_stream" do