$ perl -Mdiagnostics -wMstrict -le 'my $x if 0'
Deprecated use of my() in false conditional at -e line 1 (#1)
(D deprecated) You used a declaration similar to my $x if 0.  There
has been a long-standing bug in Perl that causes a lexical variable
not to be cleared at scope exit when its declaration includes a false
conditional.  Some people have exploited this bug to achieve a kind of
static variable.  Since we intend to fix this bug, we don't want
people relying on this behavior.  ...