I got a bit further, and the 400 Client Error is gone. I added a .spec file into release tar files. Having downloaded a release tar ball, I try to build, but it fails:
$ rpmbuild -tb topnfiles-4.1.2.tar.gz ... Executing(%generate_buildrequires): /bin/sh -e /var/tmp/rpm-tmp.DUSPMl + umask 022 + cd /home/troels/rpmbuild/BUILD/topnfiles-4.1.2-build + cd topnfiles-4.1.2 + /usr/bin/cargo2rpm --path Cargo.toml buildrequires --with-check + RPM_EC=0 ++ jobs -p + exit 0 error: Failed build dependencies: (crate(anyhow/default) >= 1.0.0 with crate(anyhow/default) < 2.0.0~) is needed by topnfiles-4.1.2-1.fc42.x86_64 (crate(chrono) >= 0.4.0 with crate(chrono) < 0.5.0~) is needed by topnfiles-4.1.2-1.fc42.x86_64 (crate(chrono/clock) >= 0.4.0 with crate(chrono/clock) < 0.5.0~) is needed by topnfiles-4.1.2-1.fc42.x86_64 (crate(clap/cargo) >= 4.0.0 with crate(clap/cargo) < 5.0.0~) is needed by topnfiles-4.1.2-1.fc42.x86_64 (crate(clap/default) >= 4.0.0 with crate(clap/default) < 5.0.0~) is needed by topnfiles-4.1.2-1.fc42.x86_64 (crate(clap/wrap_help) >= 4.0.0 with crate(clap/wrap_help) < 5.0.0~) is needed by topnfiles-4.1.2-1.fc42.x86_64 (crate(env_logger/default) >= 0.11.0 with crate(env_logger/default) < 0.12.0~) is needed by topnfiles-4.1.2-1.fc42.x86_64 (crate(log/default) >= 0.4.0 with crate(log/default) < 0.5.0~) is needed by topnfiles-4.1.2-1.fc42.x86_64 (crate(regex/default) >= 1.11.0 with crate(regex/default) < 2.0.0~) is needed by topnfiles-4.1.2-1.fc42.x86_64 (crate(serde/default) >= 1.0.0 with crate(serde/default) < 2.0.0~) is needed by topnfiles-4.1.2-1.fc42.x86_64 (crate(serde/derive) >= 1.0.0 with crate(serde/derive) < 2.0.0~) is needed by topnfiles-4.1.2-1.fc42.x86_64 (crate(serde_json/default) >= 1.0.0 with crate(serde_json/default) < 2.0.0~) is needed by topnfiles-4.1.2-1.fc42.x86_64 (crate(tempfile/default) >= 3.21.0 with crate(tempfile/default) < 4.0.0~) is needed by topnfiles-4.1.2-1.fc42.x86_64 (crate(utf8-supported/default) >= 1.0.0 with crate(utf8-supported/default) < 2.0.0~) is needed by topnfiles-4.1.2-1.fc42.x86_64 (crate(walkdir/default) >= 2.5.0 with crate(walkdir/default) < 3.0.0~) is needed by topnfiles-4.1.2-1.fc42.x86_64 Wrote: /home/troels/rpmbuild/SRPMS/topnfiles-4.1.2-1.fc42.buildreqs.nosrc.rpm
How can I proceed?