Youtube --flat-playlist extractor on filters=playlist search url results in video id instead of playlist id

[Crypto90]

Checklist

• [ X ] I'm reporting a broken site support issue
• [ X ] I've verified that I'm running youtube-dl version 2020.06.06
• [ X ] I've checked that all provided URLs are alive and playable in a browser
• [ X ] I've checked that all URLs and arguments with special characters are properly quoted or escaped
• [ X ] I've searched the bugtracker for similar bug reports including closed ones
• [ X ] I've read bugs section in FAQ

Verbose log

python youtube-dl -v -4 --default-search ytsearch1 "https://www.youtube.com/results?search_query=nightcore&filters=playlist&lclk=video" --dump-single-json --playlist-start 1 --playlist-end 1 --flat-playlist
[debug] System config: []
[debug] User config: []
[debug] Custom config: []
[debug] Command-line args: [u'-v', u'-4', u'--default-search', u'ytsearch1', u'https://www.youtube.com/results?search_query=nightcore&filters=playlist&lclk=video', u'--dump-single-json', u'--playlist-start', u'1', u'--playlist-end', u'1', u'--flat-playlist']
[debug] Encodings: locale UTF-8, fs UTF-8, out UTF-8, pref UTF-8
[debug] youtube-dl version 2020.06.06
[debug] Python version 2.7.13 (CPython) - Linux-4.9.0-9-amd64-x86_64-with-debian-9.9
[debug] exe versions: ffmpeg 4.0, ffprobe 4.0
[debug] Proxy map: {}
{"extractor": "youtube:search_url", "_type": "playlist", "title": "nightcore", "extractor_key": "YoutubeSearchURL", "webpage_url": "https://www.youtube.com/results?search_query=nightcore&filters=playlist&lclk=video", "entries": [{"url": "cvaIgq5j2Q8", "_type": "url", "ie_key": "Youtube", "id": "cvaIgq5j2Q8", "title": "Most Viewed Nightcore"}], "webpage_url_basename": "results"}

Description

Searched for https://www.youtube.com/results?search_query=nightcore&filters=playlist&lclk=video
with --default-search ytsearch1 --dump-single-json --playlist-start 1 --playlist-end 1 --flat-playlist

As we get playlist only results listed from youtube, we need to get the playlist id instead of the first video id inside the playlist.
So we have to make sure if the resulted id/url contains &list=XXXXXXXXXXXXXXXXXXX and add the list id as result id instead of the video id. Otherwise its not possible to get the correct playlist id/url.

Result from youtube.com:
https://www.youtube.com/watch?v=cvaIgq5j2Q8&list=PL0wqt_um4x0bsdViTJBmnl6KGMoSqxfZy

We need the playlist id "PL0wqt_um4x0bsdViTJBmnl6KGMoSqxfZy" but youtube-dl results the video id "cvaIgq5j2Q8" which is wrong.

[dstftw]

https://github.com/ytdl-org/youtube-dl#is-the-description-of-the-issue-itself-sufficient

[Crypto90]

How is this unclear?

Wrong:
{"url": "cvaIgq5j2Q8", "_type": "url", "ie_key": "Youtube", "id": "cvaIgq5j2Q8", "title": "Most Viewed Nightcore"}], "webpage_url_basename": "results"}

Right:
{"url": "PL0wqt_um4x0bsdViTJBmnl6KGMoSqxfZy", "_type": "url", "ie_key": "Youtube", "id": "PL0wqt_um4x0bsdViTJBmnl6KGMoSqxfZy", "title": "Most Viewed Nightcore"}], "webpage_url_basename": "results"}

[Crypto90]

@dstftw ?

[dstftw]

Duplicate of #16627.