Implement PlaylistInfo.getDescription()

Implement PlaylistExtractor.getDescription() for PeerTube and SoundCloud.
Anotate   PlaylistExtractor.getDescription() as Nonnull

extractor/src/main/java/org/schabi/newpipe/extractor/playlist/PlaylistExtractor.java

@@ -22,6 +22,7 @@ public abstract class PlaylistExtractor extends ListExtractor<StreamInfoItem> {
 
     public abstract long getStreamCount() throws ParsingException;
 
+    @Nonnull
     public abstract Description getDescription() throws ParsingException;
 
     @Nonnull

extractor/src/main/java/org/schabi/newpipe/extractor/playlist/PlaylistInfo.java

@@ -8,6 +8,7 @@ import org.schabi.newpipe.extractor.StreamingService;
 import org.schabi.newpipe.extractor.exceptions.ExtractionException;
 import org.schabi.newpipe.extractor.exceptions.ParsingException;
 import org.schabi.newpipe.extractor.linkhandler.ListLinkHandler;
+import org.schabi.newpipe.extractor.stream.Description;
 import org.schabi.newpipe.extractor.stream.StreamInfoItem;
 import org.schabi.newpipe.extractor.utils.ExtractorHelper;
 
@@ -102,6 +103,11 @@ public final class PlaylistInfo extends ListInfo<StreamInfoItem> {
         } catch (final Exception e) {
             info.addError(e);
         }
+        try {
+            info.setDescription(extractor.getDescription());
+        } catch (final Exception e) {
+            info.addError(e);
+        }
         try {
             info.setThumbnailUrl(extractor.getThumbnailUrl());
         } catch (final Exception e) {
@@ -174,6 +180,7 @@ public final class PlaylistInfo extends ListInfo<StreamInfoItem> {
     private String subChannelName;
     private String subChannelAvatarUrl;
     private long streamCount = 0;
+    private Description description;
     private PlaylistType playlistType;
 
     public String getThumbnailUrl() {
@@ -248,6 +255,14 @@ public final class PlaylistInfo extends ListInfo<StreamInfoItem> {
         this.streamCount = streamCount;
     }
 
+    public Description getDescription() {
+        return description;
+    }
+
+    public void setDescription(final Description description) {
+        this.description = description;
+    }
+
     public PlaylistType getPlaylistType() {
         return playlistType;
     }

extractor/src/main/java/org/schabi/newpipe/extractor/services/bandcamp/extractors/BandcampPlaylistExtractor.java

@@ -109,6 +109,7 @@ public class BandcampPlaylistExtractor extends PlaylistExtractor {
         return trackInfo.size();
     }
 
+    @Nonnull
     @Override
     public Description getDescription() throws ParsingException {
         return Description.EMPTY_DESCRIPTION;

extractor/src/main/java/org/schabi/newpipe/extractor/services/peertube/extractors/PeertubePlaylistExtractor.java

@@ -66,9 +66,14 @@ public class PeertubePlaylistExtractor extends PlaylistExtractor {
         return playlistInfo.getLong("videosLength");
     }
 
+    @Nonnull
     @Override
     public Description getDescription() throws ParsingException {
-        return Description.EMPTY_DESCRIPTION;
+        final String description = playlistInfo.getString("description");
+        if (isNullOrEmpty(description)) {
+            return Description.EMPTY_DESCRIPTION;
+        }
+        return new Description(description, Description.PLAIN_TEXT);
     }
 
     @Nonnull

extractor/src/main/java/org/schabi/newpipe/extractor/services/soundcloud/extractors/SoundcloudPlaylistExtractor.java

@@ -119,9 +119,14 @@ public class SoundcloudPlaylistExtractor extends PlaylistExtractor {
         return playlist.getLong("track_count");
     }
 
+    @Nonnull
     @Override
     public Description getDescription() throws ParsingException {
-        return Description.EMPTY_DESCRIPTION;
+        final String description = playlist.getString("description");
+        if (isNullOrEmpty(description)) {
+            return Description.EMPTY_DESCRIPTION;
+        }
+        return new Description(description, Description.PLAIN_TEXT);
     }
 
     @Nonnull

extractor/src/main/java/org/schabi/newpipe/extractor/services/youtube/extractors/YoutubeMixPlaylistExtractor.java

@@ -170,6 +170,7 @@ public class YoutubeMixPlaylistExtractor extends PlaylistExtractor {
         return ListExtractor.ITEM_COUNT_INFINITE;
     }
 
+    @Nonnull
     @Override
     public Description getDescription() throws ParsingException {
         return Description.EMPTY_DESCRIPTION;

extractor/src/main/java/org/schabi/newpipe/extractor/services/youtube/extractors/YoutubePlaylistExtractor.java

@@ -295,6 +295,7 @@ public class YoutubePlaylistExtractor extends PlaylistExtractor {
         return ITEM_COUNT_UNKNOWN;
     }
 
+    @Nonnull
     @Override
     public Description getDescription() throws ParsingException {
         final String description = getTextFromObject(

extractor/src/test/java/org/schabi/newpipe/extractor/services/peertube/PeertubePlaylistExtractorTest.java

@@ -60,6 +60,11 @@ public class PeertubePlaylistExtractorTest {
             ExtractorAsserts.assertGreaterOrEqual(39, extractor.getStreamCount());
         }
 
+        @Test
+        void testGetDescription() throws ParsingException {
+            ExtractorAsserts.assertContains("épisodes de Shocking", extractor.getDescription().getContent());
+        }
+
         @Test
         void testGetSubChannelUrl() {
             assertEquals("https://skeptikon.fr/video-channels/metadechoc_channel", extractor.getSubChannelUrl());