Not exactly what you're asking, but Devel::Symdump has (among other useful things) two methods inh_tree() and isa_tree() that might help.  It works by analyzing the symbol table for a set of packages (all those which are loaded at the time of the call).

...
... your code here
...
package main;

use Devel::Symdump;

print Devel::Symdump->inh_tree();
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Output:

Element
    Circle
    Line
    Square
Exporter
    Carp
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(The presence of Exporter / Carp in the output is a side effect of the warnings pragma being loaded, which in turn loads Carp and Exporter as a dependency.)