https://bugzilla.redhat.com/show_bug.cgi?id=2124697
--- Comment #46 from Stefan Hajnoczi stefanha@redhat.com --- meson 0.64.0 added a new optimization level called "plain" that means "don't set explicit compiler optimization options" (apparently nix needs this because it controls the compiler options). libblkio's src/cargo-build.sh script parses the meson_optimization option and doesn't know how to deal with "plain".
I am investigating further to see how to solve this.