libb-debug-perl 1.26-2 (amd64 binary) in ubuntu focal

 The B::Debug module walks the Perl syntax tree, printing debug info about
 ops.
 .
 The B module supplies classes which allow a Perl program to delve
 into its own innards. It is the module used to implement the
 "backends" of the Perl compiler.
 .
 B::Debug in perl core is deprecated in 5.27.3 and will be removed in the
 future.