ncm-spma: update_pkgs in yum plugin tries to remove empty list of packages

[lexming]

SPMA is failing to complete in one of our systems because it tries to execute yum remove without any packages

[DEBUG] Running transaction: remove
install libstdc++.i686 kernel-firmware procps sssd-client.i686 compat-libstdc++-33.i686 python-argparse module-init-tools
transaction solve
transaction run

[DEBUG] keeps_state set
[VERB] Executing command: yum -c /etc/yum.conf -y shell with options: stderr=SCALAR(0x38cf5e8) stdin=remove
install libstdc++.i686 kernel-firmware procps sssd-client.i686 compat-libstdc++-33.i686 python-argparse module-init-tools
transaction solve
transaction run
stdout=SCALAR(0x38d5b00)
[WARN] running transaction produced warnings: Error: Need to pass a list of pkgs to remove
Mini usage:

erase PACKAGE...

Remove a package or packages from your system

aliases: remove, autoremove, erase-n, erase-na, erase-nevra, autoremove-n, autoremove-na, autoremove-nevra, remove-n, > remove-na, remove-nevra

[VERB] running transaction output: Loaded plugins: priorities, product-id, search-disabled-repos, subscription-
: manager, versionlock

This system is not registered with an entitlement server. You can use subscription-manager to register.

Excluding 38 updates due to versionlock (use "yum versionlock status" to show them)
Package libstdc++-4.8.5-44.el7.i686 already installed and latest version
Package linux-firmware-20200421-80.git78c0348.el7_9.noarch already installed and latest version
Package procps-ng-3.3.10-28.el7.x86_64 already installed and latest version
Package sssd-client-1.16.5-10.el7_9.13.i686 already installed and latest version
Package compat-libstdc++-33-3.2.3-72.el7.i686 already installed and latest version
Package python-2.7.5-92.el7_9.x86_64 already installed and latest version
Package kmod-20-28.el7.x86_64 already installed and latest version
--> Finding unneeded leftover dependencies
Found and removing 0 unneeded dependencies
Success resolving dependencies
Leaving Shell

[WARN] Command output: Loaded plugins: priorities, product-id, search-disabled-repos, subscription-
: manager, versionlock

This system is not registered with an entitlement server. You can use subscription-manager to register.

Excluding 38 updates due to versionlock (use "yum versionlock status" to show them)
Package libstdc++-4.8.5-44.el7.i686 already installed and latest version
Package linux-firmware-20200421-80.git78c0348.el7_9.noarch already installed and latest version
Package procps-ng-3.3.10-28.el7.x86_64 already installed and latest version
Package sssd-client-1.16.5-10.el7_9.13.i686 already installed and latest version
Package compat-libstdc++-33-3.2.3-72.el7.i686 already installed and latest version
Package python-2.7.5-92.el7_9.x86_64 already installed and latest version
Package kmod-20-28.el7.x86_64 already installed and latest version
--> Finding unneeded leftover dependencies
Found and removing 0 unneeded dependencies
Success resolving dependencies
Leaving Shell

[ERROR] Failed running transaction: Error: Need to pass a list of pkgs to remove

I tracked down this issue to update_pkgs():

configuration-modules-core/ncm-spma/src/main/perl/spma/yum.pm

Lines 907 to 910 in bdb85e6

	$to_rm = $self->packages_to_remove($wanted);
	defined($to_rm) or return 0;
	$self->spare_dependencies($to_rm, $to_install, $error_is_warn);
	$tx = $self->schedule(REMOVE, $to_rm);

In the affected system, packages_to_remove() returns an empty $to_rm list. This is the result of spare_deps_required(), which generates the following list of leaves:

[DEBUG] List of packages flagged as leaves:
[DEBUG] ( SINDES-ca-certificate-cerberus;noarch SOAPpy;noarch acpid;x86_64 autofs;x86_64 biosdevname;x86_64 cabundle-hpcvub;noarch cdp-listend;noarch cluster-modules;noarch compat-libstdc++-33;i686 compat-libstdc++-33;x86_64 config-templates-metaconfig-ugent;noarch dos2unix;x86_64 dstat;noarch e2fsprogs;x86_64 emacs-nox;x86_64 figlet;x86_64 fprintd-pam;x86_64 grub2;x86_64 htop;x86_64 hwloc;x86_64 icinga-checks-ugent;noarch iotop;noarch iperf3;x86_64 ipmitool;x86_64 ipset;x86_64 kernel-tools;x86_64 kernel;x86_64 kexec-tools;x86_64 lldpd;x86_64 lsof;x86_64 lsscsi;x86_64 lvm2;x86_64 mc;x86_64 mcelog;x86_64 microcode_ctl;x86_64 mlocate;x86_64 nagios-plugins-bonding;x86_64 nagios-plugins-disk;x86_64 nagios-plugins-dns;x86_64 nagios-plugins-http;x86_64 nagios-plugins-ldap;x86_64 nagios-plugins-procs;x86_64 nagios-plugins-time;x86_64 nano;x86_64 ncm-accounts;noarch ncm-altlogrotate;noarch ncm-authconfig;noarch ncm-autofs;noarch ncm-ccm;noarch ncm-cdispd;noarch ncm-cdp;noarch ncm-chkconfig;noarch ncm-cron;noarch ncm-dirperm;noarch ncm-download;noarch ncm-filecopy;noarch ncm-fstab;noarch ncm-grub;noarch ncm-metaconfig;noarch ncm-modprobe;noarch ncm-named;noarch ncm-network;noarch ncm-nrpe;noarch ncm-query;noarch ncm-shorewall;noarch ncm-sindes_getcert;noarch ncm-spma;noarch ncm-sudo;noarch ncm-symlink;noarch ncm-sysconfig;noarch ncm-systemd;noarch ncm-useraccess;noarch ncm-validate;noarch nfs-utils;x86_64 nmap-ncat;x86_64 nrpe;x86_64 numactl;x86_64 nuttcp;x86_64 openssh-server;x86_64 pakiti2-client;noarch parted;x86_64 pbzip2;x86_64 pciutils;x86_64 pigz;x86_64 podman;x86_64 ptpd;x86_64 pyOpenSSL;x86_64 python-perf;x86_64 python-vsc-host-tools;noarch redhat-lsb-core;x86_64 rootfiles;noarch rsyslog;x86_64 screen;x86_64 service_sanity;noarch shorewall-init;noarch smartmontools;x86_64 sssd-client;i686 sssd-tools;x86_64 sssd;x86_64 strace;x86_64 sudo;x86_64 sysstat;x86_64 tcpdump;x86_64 tcsh;x86_64 telnet;x86_64 tmux;x86_64 traceroute;x86_64 unzip;x86_64 update-firmware-ugent;x86_64 vim-enhanced;x86_64 vsc-profiles-brussel;noarch vsc-scripts-brussel;noarch wget;x86_64 zabbix-module-systemd;x86_64)

All of the packages are subsequently deleted from the list as false positives, which is reasonable, and $to_rm stays empty. However, defined($to_rm) still evaluates to true and the execution continues with the empty list.