avoid vivifying UNIVERSAL::isa:: in Carp

The test added to Carp by commit 915a6810d3e3198d759f025f85d1fd6f3171dd27
for UNIVERSAL::isa being loaded had the side effect of vivifying the
UNIVERSAL::isa stash.  Take more care about checking for UNIVERSAL::isa
to avoid vivifying it, as for the other checks for things in optional
modules.  Fixes [perl #132788].

3 files changed, 22 insertions, 6 deletions

diff --git a/dist/Carp/lib/Carp.pm b/dist/Carp/lib/Carp.pm
index 65d22b1b2b..eb7ad7bb06 100644
--- a/dist/Carp/lib/Carp.pm
+++ b/dist/Carp/lib/Carp.pm
@@ -116,7 +116,7 @@ BEGIN {
 	;
 }
 
-our $VERSION = '1.45';
+our $VERSION = '1.46';
 $VERSION =~ tr/_//d;
 
 our $MaxEvalLen = 0;
@@ -277,6 +277,20 @@ sub caller_info {
     return wantarray() ? %call_info : \%call_info;
 }
 
+sub _univisa_loaded {
+    return 0 unless exists($::{"UNIVERSAL::"});
+    for ($::{"UNIVERSAL::"}) {
+	return 0 unless ref \$_ eq "GLOB" && *$_{HASH} && exists $$_{"isa::"};
+	for ($$_{"isa::"}) {
+	    return 0 unless ref \$_ eq "GLOB" && *$_{HASH} && exists $$_{"VERSION"};
+	    for ($$_{"VERSION"}) {
+		return 0 unless ref \$_ eq "GLOB";
+		return ${*$_{SCALAR}};
+	    }
+	}
+    }
+}
+
 # Transform an argument to a function into a string.
 our $in_recurse;
 sub format_arg {
@@ -286,7 +300,7 @@ sub format_arg {
 
         # lazy check if the CPAN module UNIVERSAL::isa is used or not
         #   if we use a rogue version of UNIVERSAL this would lead to infinite loop
-        my $isa = $UNIVERSAL::isa::VERSION ? sub { 1 } : \&UNIVERSAL::isa;
+        my $isa = _univisa_loaded() ? sub { 1 } : _fetch_sub(UNIVERSAL => "isa");
 
          # legitimate, let's not leak it.
         if (!$in_recurse && $isa->( $arg, 'UNIVERSAL' ) &&
diff --git a/dist/Carp/lib/Carp/Heavy.pm b/dist/Carp/lib/Carp/Heavy.pm
index 6575c63d84..1d4bab613f 100644
--- a/dist/Carp/lib/Carp/Heavy.pm
+++ b/dist/Carp/lib/Carp/Heavy.pm
@@ -2,7 +2,7 @@ package Carp::Heavy;
 
 use Carp ();
 
-our $VERSION = '1.45';
+our $VERSION = '1.46';
 $VERSION =~ tr/_//d;
 
 # Carp::Heavy was merged into Carp in version 1.12.  Any mismatched versions
diff --git a/dist/Carp/t/vivify_stash.t b/dist/Carp/t/vivify_stash.t
index 0ac66d89e0..455aded7c1 100644
--- a/dist/Carp/t/vivify_stash.t
+++ b/dist/Carp/t/vivify_stash.t
@@ -1,8 +1,9 @@
-BEGIN { print "1..5\n"; }
+BEGIN { print "1..6\n"; }
 
 our $has_utf8; BEGIN { $has_utf8 = exists($::{"utf8::"}); }
 our $has_overload; BEGIN { $has_overload = exists($::{"overload::"}); }
 our $has_B; BEGIN { $has_B = exists($::{"B::"}); }
+our $has_UNIVERSAL_isa; BEGIN { $has_UNIVERSAL_isa = exists($UNIVERSAL::{"isa::"}); }
 
 use Carp;
 sub { sub { Carp::longmess("x") }->() }->(\1, "\x{2603}", qr/\x{2603}/);
@@ -10,16 +11,17 @@ sub { sub { Carp::longmess("x") }->() }->(\1, "\x{2603}", qr/\x{2603}/);
 print !(exists($::{"utf8::"}) xor $has_utf8) ? "" : "not ", "ok 1\n";
 print !(exists($::{"overload::"}) xor $has_overload) ? "" : "not ", "ok 2\n";
 print !(exists($::{"B::"}) xor $has_B) ? "" : "not ", "ok 3\n";
+print !(exists($UNIVERSAL::{"isa::"}) xor $has_UNIVERSAL_isa) ? "" : "not ", "ok 4\n";
 
 # Autovivify $::{"overload::"}
 () = \$::{"overload::"};
 () = \$::{"utf8::"};
 eval { sub { Carp::longmess() }->(\1) };
-print $@ eq '' ? "ok 4\n" : "not ok 4\n# $@";
+print $@ eq '' ? "ok 5\n" : "not ok 5\n# $@";
 
 # overload:: glob without hash
 undef *{"overload::"};
 eval { sub { Carp::longmess() }->(\1) };
-print $@ eq '' ? "ok 5\n" : "not ok 5\n# $@";
+print $@ eq '' ? "ok 6\n" : "not ok 6\n# $@";
 
 1;