{"action":"created","issue":{"url":"https://api.github.com/repos/vim/vim/issues/2424","repository_url":"https://api.github.com/repos/vim/vim","labels_url":"https://api.github.com/repos/vim/vim/issues/2424/labels{/name}","comments_url":"https://api.github.com/repos/vim/vim/issues/2424/comments","events_url":"https://api.github.com/repos/vim/vim/issues/2424/events","html_url":"https://github.com/vim/vim/issues/2424","id":280276957,"number":2424,"title":"`t_Cs` set on unsupported terminal; Undercurl fallback broken","user":{"login":"joshklod","id":28229839,"avatar_url":"https://avatars2.githubusercontent.com/u/28229839?v=4","gravatar_id":"","url":"https://api.github.com/users/joshklod","html_url":"https://github.com/joshklod","followers_url":"https://api.github.com/users/joshklod/followers","following_url":"https://api.github.com/users/joshklod/following{/other_user}","gists_url":"https://api.github.com/users/joshklod/gists{/gist_id}","starred_url":"https://api.github.com/users/joshklod/starred{/owner}{/repo}","subscriptions_url":"https://api.github.com/users/joshklod/subscriptions","organizations_url":"https://api.github.com/users/joshklod/orgs","repos_url":"https://api.github.com/users/joshklod/repos","events_url":"https://api.github.com/users/joshklod/events{/privacy}","received_events_url":"https://api.github.com/users/joshklod/received_events","type":"User","site_admin":false},"labels":[],"state":"closed","locked":false,"assignee":null,"assignees":[],"milestone":null,"comments":7,"created_at":"2017-12-07T21:00:15Z","updated_at":"2018-03-06T06:00:07Z","closed_at":"2017-12-22T20:12:54Z","author_association":"NONE","body":"I noticed a while ago that `'t_Cs'` is somehow getting a value assigned, though nothing is assigning it.  It is neither in the terminfo entry, nor (as far as I can tell) the built-in termcaps.  It is definitely not getting set in a script.  (Yes, even with plugins disabled via `vim -N -u NONE`.)  So where does it come from?\r\n\r\nIts value happens to be the xterm cursor color escape sequence.\r\n\r\nBefore 8b9e20afb0da79a21155988a38704b5777cc2efe, this code was never used, so it didn't really matter. But now it is causing a problem. As of this patch, Vim notices the presence of this option and assumes the terminal is capable of displaying undercurl.  As such, it no longer falls back to a normal underline.\r\n\r\nEven manually clearing the option has no effect.  It seems once Vim detects that the feature is present, it will never attempt to fall back again.\r\n\r\n### How to Reproduce:\r\n\r\nI was able to reproduce the issue with several xterm-compatible terminals on Debian and Cygwin, using Vim v8.0.1376.\r\n\r\n    iThis sentence has a spelilng mistake<Esc>\r\n    :hi SpellBad cterm=undercurl\r\n    :set spell\r\n        -> 'spelilng' is not underlined\r\n    :set t_Cs?\r\n        -> t_Cs=^[]12;%p1%s^G\r\n    :set t_Cs=\r\n        -> 'spelilng' is still not underlined\r\n    :hi SpellBad cterm=underline\r\n        -> This works fine\r\n"},"comment":{"url":"https://api.github.com/repos/vim/vim/issues/comments/370673158","html_url":"https://github.com/vim/vim/issues/2424#issuecomment-370673158","issue_url":"https://api.github.com/repos/vim/vim/issues/2424","id":370673158,"user":{"login":"redeyes2015","id":93420,"avatar_url":"https://avatars2.githubusercontent.com/u/93420?v=4","gravatar_id":"","url":"https://api.github.com/users/redeyes2015","html_url":"https://github.com/redeyes2015","followers_url":"https://api.github.com/users/redeyes2015/followers","following_url":"https://api.github.com/users/redeyes2015/following{/other_user}","gists_url":"https://api.github.com/users/redeyes2015/gists{/gist_id}","starred_url":"https://api.github.com/users/redeyes2015/starred{/owner}{/repo}","subscriptions_url":"https://api.github.com/users/redeyes2015/subscriptions","organizations_url":"https://api.github.com/users/redeyes2015/orgs","repos_url":"https://api.github.com/users/redeyes2015/repos","events_url":"https://api.github.com/users/redeyes2015/events{/privacy}","received_events_url":"https://api.github.com/users/redeyes2015/received_events","type":"User","site_admin":false},"created_at":"2018-03-06T06:00:07Z","updated_at":"2018-03-06T06:00:07Z","author_association":"NONE","body":"> However, t_Cs is still being set when it shouldn't be\r\n\r\nI was also troubled by this issue, while trying out vim 8 recently (using Jonathon F's [ppa], previously on v8.0.1542) . However, version 8.0.1567, released today, has seemed to solve this issue, well, at least for me. The terminal emulator is xfce4-terminal. I can confirm that `t_Cs` is no longer set by default, and undercurl falls back to underline correctly.\r\n\r\nI have no idea which patch fixes this. (I would guess it is [patch 8.0.1556].) Hope this is a good news for others also having this `t_Cs` issue.\r\n\r\n[ppa]: https://launchpad.net/~jonathonf/+archive/ubuntu/vim/+packages\r\n[patch 8.0.1556]: https://github.com/vim/vim/commit/590ec878a52b3b3d4453475f1eb4899f2b37969f"}}
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