bash: line 210: stretch-backports: command not found, resolver fails to find packages

I noticed that my MariaDB 10.5 build stage build stretch-backports stopped working yesterday.

When I compare the build logs there is a massive difference in how dependencies are resolved.

The old version successfully installed:

1)     libzstd-dev [1.3.8+dfsg-3~bpo9+1 (stretch-backports)]
2)     libzstd1 [1.3.8+dfsg-3~bpo9+1 (stretch-backports)] 
...
Setting up krb5-multidev (1.15-1+deb9u3) ...
Setting up libkrb5-dev (1.15-1+deb9u3) ...
Setting up odbcinst1debian2:amd64 (2.3.4-1) ...
Setting up unixodbc-dev (2.3.4-1) ...
Setting up odbcinst (2.3.4-1) ...
Processing triggers for libc-bin (2.24-11+deb9u4) ...
Reading package lists...
Building dependency tree...
Reading state information...
Reading extended state information...
Initializing package states...
Writing extended state information...
Building tag database...
 -> Finished installing the build-deps

The new version just fails:

Setting up dpkg-dev (1.18.25) ...
Setting up cpp-6 (6.3.0-18+deb9u1) ...
Setting up cpp (4:6.3.0-4) ...
Setting up gcc-6 (6.3.0-18+deb9u1) ...
Setting up g++-6 (6.3.0-18+deb9u1) ...
Setting up gcc (4:6.3.0-4) ...
Setting up g++ (4:6.3.0-4) ...
update-alternatives: using /usr/bin/g++ to provide /usr/bin/c++ (c++) in auto mode
Setting up build-essential (12.3) ...
Processing triggers for libc-bin (2.24-11+deb9u4) ...
/bin/bash: line 210: stretch-backports: command not found
/bin/bash: line 210: stretch-backports: command not found
Note, using directory '.' to get the build dependencies
Reading package lists...
Building dependency tree...
Reading state information...
Some packages could not be installed. This may mean that you have
requested an impossible situation or if you are using the unstable
distribution that some required packages have not yet been created
or been moved out of Incoming.
The following information may help to resolve the situation:

The following packages have unmet dependencies:
 builddeps:. : Depends: libzstd-dev (>= 1.3.3) but 1.1.2-1+deb9u1 is to be installed
E: Unable to correct problems, you have held broken packages.

This is most likely due to the commit 58880fce where the resolver was changed in Salsa-CI.

Please revert the commit or make a version of it that does not affect Bullseye or Buster builds (actual or backports) as there is no way for me to start doing any dependency changes for mariadb-10.5 in bullseye or backports.

Edited Nov 27, 2021 by Otto Kekäläinen

To upload designs, you'll need to enable LFS and have an admin enable hashed storage. More information