Don't try to Sv[PI]V() on an undef index SV in find_uninit_var()

When trying to evaluate:

  $x{$y}

or

  $x[$y]

where both the index and the hash or array entry was undefined,
when trying to report the entry as uninitialised, find_uninit_var()
would try to get the string or numeric value of the index,
recursively trying to produce a warning.

This would end up overflowing the stack, producing a segmentation fault.

Fixes #19147.

1 files changed, 13 insertions, 0 deletions

diff --git a/t/lib/warnings/sv b/t/lib/warnings/sv
index be04b8457e..8524c2c25a 100644
--- a/t/lib/warnings/sv
+++ b/t/lib/warnings/sv
@@ -211,6 +211,19 @@ Use of uninitialized value $a in join or string at - line 4.
 Use of uninitialized value $a in concatenation (.) or string at - line 5.
 Use of uninitialized value $a in concatenation (.) or string at - line 6.
 ########
+# NAME https://github.com/Perl/perl5/issues/19147
+use warnings 'uninitialized';
+my %x;
+my @z;
+my $y;
+-$x{$y};
+-$z[$y];
+EXPECT
+Use of uninitialized value $y in hash element at - line 5.
+Use of uninitialized value $x{""} in negation (-) at - line 5.
+Use of uninitialized value $y in array element at - line 6.
+Use of uninitialized value $z[0] in negation (-) at - line 6.
+########
 # sv.c 
 use warnings 'numeric' ;
 sub TIESCALAR{bless[]} ;