Issue Prelude

Please complete these steps and check these boxes (by putting an x inside
the brackets) before filing your issue:

• I have read and understood YCM's CONTRIBUTING document.
• I have read and understood YCM's CODE_OF_CONDUCT document.
• I have read and understood YCM's README, especially the
  Frequently Asked Questions section.
• I have searched YCM's issue tracker to find issues similar to the one I'm
  about to report and couldn't find an answer to my problem. (Example Google
  search.)
• If filing a bug report, I have included the output of vim --version.
• If filing a bug report, I have included the output of :YcmDebugInfo.
• If filing a bug report, I have attached the contents of the logfiles using
  the :YcmToggleLogs command.
• If filing a bug report, I have included which OS (including specific OS
  version) I am using.
• If filing a bug report, I have included a minimal test case that reproduces
  my issue, using vim -Nu /path/to/YCM/vimrc_ycm_minimal, including what I
  expected to happen and what actually happened.
• If filing a installation failure report, I have included the entire output
  of install.py (or cmake/make/ninja) including its invocation
• I understand this is an open-source project staffed by volunteers and
  that any help I receive is a selfless, heartfelt gift of their free time. I
  know I am not entitled to anything and will be polite and courteous.
• I understand my issue may be closed if it becomes obvious I didn't
  actually perform all of these steps.

Thank you for adhering to this process! It ensures your issue is resolved
quickly and that neither your nor our time is needlessly wasted.

Issue Details

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

• What did you do?

Try using YCM in .NET 6.0 project on Linux without mono installed.

Per log:

No mono executable at None

failure is caused by cs_completer.py:72 requiring mono on Linux, despite cs_completer.py:441,443 only requiring mono if roslyn_path ends with .exe.

Include steps to reproduce here.

1. Install YCM with --cs-completer
2. Follow .NET 6.0 instructions in README
3. Create C# file with var x = "";
4. Run :YcmCompleter GetType with cursor on x

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

If you made changes to vimrc_ycm_minimal, pase them here:

• What did you expect to happen?

Include description of the expected behaviour.

System.String is shown

• What actually happened?

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

ValueError: No semantic completer exists for filetypes: ['cs']

Diagnostic data

Output of vim --version

NVIM v0.9.5
Build type: Release
LuaJIT 2.1.1692716794

   system vimrc file: "$VIM/sysinit.vim"
  fall-back for $VIM: "/__w/neovim/neovim/build/nvim.AppDir/usr/share/nvim"

Run :checkhealth for more info

Output of YcmDebugInfo

Printing YouCompleteMe debug information...
-- Resolve completions: Never
-- Client logfile: /tmp/ycm_8_vtjvb_.log
-- Server Python interpreter: /usr/bin/python3
-- Server Python version: 3.10.12
-- Server has Clang support compiled in: False
-- Clang version: None
-- No extra configuration file found
-- Server running at: http://127.0.0.1:58993
-- Server process ID: 4034667
-- Server logfiles:
--   /tmp/ycmd_58993_stdout_8g29j64y.log
--   /tmp/ycmd_58993_stderr_oyi0l59g.log
-- Semantic highlighting supported: False
-- Virtual text supported: False
-- Popup windows supported: False

Output of YcmDiags

Native filetype completion not supported for current file, cannot force recompilation.  

Output of git rev-parse HEAD in YouCompleteMe installation directory

52618aeebf12ca4c8e31c45551d903160e201038

Contents of YCM, ycmd and completion engine logfiles

Reproduce the issue with vim -Nu /path/to/YCM/vimrc_ycm_minimal, which
enabled debug logging and other useful diagnostics. Include a link to a
gist containing all of the log files listed by :YcmToggleLogs.

ycm_8_vtjvb_.log
ycmd_58993_stderr_oyi0l59g.log

OS version, distribution, etc.

Include system information here.

OS: Ubuntu 22.04.4 LTS x86_64 
Host: VirtualBox 1.2 
Kernel: 6.5.0-44-generic 
Uptime: 22 hours, 31 mins 
Packages: 1740 (dpkg), 11 (snap) 
Shell: bash 5.1.16 
Terminal: /dev/pts/0 
CPU: 12th Gen Intel i5-1245U (8) @ 2.495GHz 
Memory: 2675MiB / 7931MiB 

Output of build/install commands

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