How to not block shift-tab unindent?

[himat]

Issue Prelude

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Issue Details

Provide a clear description of the problem, including the following key questions:

• What did you do? Adding the tabnine vim plugin, breaks the shift-tab functionality I had previously.

Include steps to reproduce here.

Add inoremap <S-Tab> <C-d> to your .vimrc And add the tabnine-vim plugin to your vim as well

Include description of a minimal test case, including any actual code required to reproduce the issue.

• What did you expect to happen?

  Include description of the expected behaviour.

Previously, without the tabnine plugin, I would be able to use <Tab> to indent, and then <S-tab> to unindent (back to the left). I expected this behavior to be the same now with the plugin.

• What actually happened?

  Include description of the observed behaviour, including actual output, screenshots, etc.

<S-tab> now just behaves like the normal tab, and indents the line forward.

I find this weird only because although tabnine and YCM also use the tab and shift-tab keys for cycling through the autocomplete list, the regular tab key works fine for indenting when a YCM window is not displayed. So I would have expected the shift-tab to work just as normally when a YCM window is not displayed.

So is it possible to fix this breaking my <S-tab> mapping?

Diagnostic data

Output of vim --version

Place the output here, or a link to a gist.

Output of YcmDebugInfo

Place the output here, or a link to a gist.

Contents of YCM, ycmd and completion engine logfiles

Add let g:ycm_log_level = 'debug' to vimrc, restart Vim, reproduce the issue, and include link here to a gist containing the entire logfiles for ycm, ycmd and any completer logfiles listed by :YcmToggleLogs.

OS version, distribution, etc.

Include system information here.

MacOS 10.14.5 Mojave

$ vim --version
VIM - Vi IMproved 8.1 (2018 May 18, compiled Apr 23 2019 20:02:08)
macOS version
Included patches: 1-1200
Compiled by Homebrew

Printing YouCompleteMe debug information...
-- Client logfile: /var/folders/lk/gqfw8vmx5hb02t8v6l0qb5dh0000gn/T/ycm_g536qu4r.log
-- Server errored, no debug info from server
-- Server running at: http://127.0.0.1:55627
-- Server process ID: 71265
-- Server logfiles:
--   /var/folders/lk/gqfw8vmx5hb02t8v6l0qb5dh0000gn/T/ycmd_55627_stdout_8jsshhya.log
--   /var/folders/lk/gqfw8vmx5hb02t8v6l0qb5dh0000gn/T/ycmd_55627_stderr_61fmjt68.log

Output of build/install commands

Include link to a gist containing the invocation and entire output of install.py if reporting an installation issue.