This post goes over how to set up YouCompleteMe for Vim 8.

Problem

If you updated YouCompleteMe, you might get the error:

YouCompleteMe unavailable: requires Vim 9.1.0016+.

You have 2 solutions:

1. Upgrade Vim to 9.1
2. Use a YouCompleteMe version that supports Vim 8

Solution

I tried upgrading Vim with Homebrew:

brew install vim

But the install took forever (see Stack Overflow and Reddit) so I canceled it. I decided to downgrade YouCompleteMe to support an older Vim version.

First, I deleted the plugin:

rm -rf bundle/YouCompleteMe/

Then I cloned the repository:

cd bundle && git clone https://github.com/ycm-core/YouCompleteMe.git

Afterwards, I checked out the branch legacy-vim-8.2:

cd YouCompleteMe && git checkout legacy-vim-8.2

I installed the submodules:

git submodule update --init --recursive

Finally, I built ycmd:

python3 install.py --all