Comment 4 for bug 1874508

it works for me

apt-get dist-upgrade
Reading package lists... Done
Building dependency tree
Reading state information... Done

Calculating upgrade... Done
The following package was automatically installed and is no longer required:
  libllvm9
Use 'sudo apt autoremove' to remove it.
The following NEW packages will be installed:
  libllvm10

The following packages will be upgraded:
  ccls
1 upgraded, 1 newly installed, 0 to remove and 0 not upgraded.
Need to get 21.1 MB of archives.
After this operation, 75.4 MB of additional disk space will be used.
0% [Working]to continue? [Y/n]
Get:1 http://archive.ubuntu.com/ubuntu focal/main amd64 libllvm10 amd64 1:10.0.0-4ubuntu1 [15.3 MB]
Get:2 http://archive.ubuntu.com/ubuntu focal-proposed/universe amd64 ccls amd64 0.20190823.6-1~ubuntu1.20.04.1 [5753 kB]
Fetched 9324 kB in 6s (1446 kB/s)
debconf: delaying package configuration, since apt-utils is not installed
Selecting previously unselected package libllvm10:amd64.
(Reading database ... 11501 files and directories currently installed.)
Preparing to unpack .../libllvm10_1%3a10.0.0-4ubuntu1_amd64.deb ...
Unpacking libllvm10:amd64 (1:10.0.0-4ubuntu1) ...
Preparing to unpack .../ccls_0.20190823.6-1~ubuntu1.20.04.1_amd64.deb ...
Unpacking ccls (0.20190823.6-1~ubuntu1.20.04.1) over (0.20190823.5-1) ...
Setting up libllvm10:amd64 (1:10.0.0-4ubuntu1) ...
Setting up ccls (0.20190823.6-1~ubuntu1.20.04.1) ...
Processing triggers for libc-bin (2.31-0ubuntu9) ...
root@Unimatrix05-Bionic:/# ccls --version
ccls version 0.20190823.6-1~ubuntu1.20.04.1
clang version 10.0.0-4ubuntu1