detect Carp/Carp::Heavy version mismatch

[rt.cpan.org #79649]  If an old Carp, requiring old-style Carp::Heavy
that provides subroutines, gets a newer stub-style Carp::Heavy, due to
@INC having changed, the resulting error messages were not awesome.

2 files changed, 13 insertions, 0 deletions

diff --git a/dist/Carp/lib/Carp/Heavy.pm b/dist/Carp/lib/Carp/Heavy.pm
index f0de26373a..f8c409e9f3 100644
--- a/dist/Carp/lib/Carp/Heavy.pm
+++ b/dist/Carp/lib/Carp/Heavy.pm
@@ -4,6 +4,11 @@ use Carp ();
 
 our $VERSION = '1.32';
 
+my $cv = defined($Carp::VERSION) ? $Carp::VERSION : "undef";
+if($cv ne $VERSION) {
+	die "Version mismatch between Carp $cv ($INC{q(Carp.pm)}) and Carp::Heavy $VERSION ($INC{q(Carp/Heavy.pm)}).  Did you alter \@INC after Carp was loaded?\n";
+}
+
 1;
 
 # Most of the machinery of Carp used to be here.
diff --git a/dist/Carp/t/heavy_mismatch.t b/dist/Carp/t/heavy_mismatch.t
new file mode 100644
index 0000000000..233bc5ace3
--- /dev/null
+++ b/dist/Carp/t/heavy_mismatch.t
@@ -0,0 +1,8 @@
+print "1..1\n";
+
+$INC{"Carp.pm"} = "<faked>";
+$Carp::VERSION = "0.90";
+eval { require Carp::Heavy; };
+print $@ =~ /\AVersion mismatch between Carp 0\.90 \(<faked>\) and Carp::Heavy [0-9._]+ \(.+\)\.  Did you alter \@INC after Carp was loaded\?\n/ ? "" : "not ", "ok 1\n";
+
+1;