Fix perl #132902 - Carp: avoid infinite loops when checking for overloads

We use $obj->can("((") to see if a package has enabled overloads,
however in some cases can() is overridden with a custom implementation,
which may be unaware of these methods and then call Carp itself. This
then results in an infinite loop. An example is Class::Std v0.013.
While technically this is a bug in whatever overrides UNIVERSAL::can(),
Carp is so prolific in its use that we might as well treat it as a Carp
bug also and avoid the problem outright.

See also: https://github.com/chorny/Class-Std/pull/2

3 files changed, 43 insertions, 14 deletions

diff --git a/dist/Carp/Changes b/dist/Carp/Changes
index c0f378cbf9..db3920329b 100644
--- a/dist/Carp/Changes
+++ b/dist/Carp/Changes
@@ -1,3 +1,27 @@
+version 1.48
+
+ * guard against hand-rolled UNIVERSAL::can() implementations
+   which throw exceptions when we call $obj->can("((").
+
+version 1.47, 1.47_02
+
+  * Deal with overloading when overload.pm is not use
+
+  * Note 1.47_02 only existed for one commit in blead-perl,
+    and in fact no 1.47 should ever see the wild.
+
+version 1.47, 1.47_01
+
+  * Do not die on trappable stack-not-refcounted bugs while
+    serializing the stack.
+
+  * Note 1.47_01 only existed for one commit in blead-perl,
+    and in fact no 1.47 should ever see the wild.
+
+version 1.46
+
+  * avoid vivifying UNIVERSAL::isa:: in Carp
+
 version 1.45
 
   * Optimize format_arg when arguments contain many references
diff --git a/dist/Carp/lib/Carp.pm b/dist/Carp/lib/Carp.pm
index 3de78d9f6f..9956f128d1 100644
--- a/dist/Carp/lib/Carp.pm
+++ b/dist/Carp/lib/Carp.pm
@@ -116,7 +116,7 @@ BEGIN {
 	;
 }
 
-our $VERSION = '1.47';
+our $VERSION = '1.48';
 $VERSION =~ tr/_//d;
 
 our $MaxEvalLen = 0;
@@ -336,18 +336,23 @@ sub format_arg {
         }
         else
         {
-            if ($pack->can("((")) {
-		# Argument is blessed into a class with overloading, and
-		# so might have an overloaded stringification.	We don't
-		# want to risk getting the overloaded stringification,
-		# so we need to use overload::StrVal() below.  But it's
-		# possible that the overload module hasn't been loaded:
-		# overload methods can be installed without it.  So load
-		# the module here.  The bareword form of require is here
-		# eschewed to avoid iths compile-time effect of vivifying
-		# vivifying the target module's stash.
-                require "overload.pm"
-                    or return "use overload failed";
+            # overload uses the presence of a special "method" name "((" to signal
+            # it is in effect.  This test seeks to see if it has been set up.
+            # In theory we should be able to use 'can' without the $in_recurse guard,
+            # but this breaks modules that call overloads or croak during can(), for
+            # instance Class::Std v0.013, so if we end up here twice, we will just
+            # load overload outright.
+            if ($in_recurse || do{ local $in_recurse = 1; $pack->can("((") }) {
+                # Argument is blessed into a class with overloading, and
+                # so might have an overloaded stringification.  We don't
+                # want to risk getting the overloaded stringification,
+                # so we need to use overload::StrVal() below.  But it's
+                # possible that the overload module hasn't been loaded:
+                # overload methods can be installed without it.  So load
+                # the module here.  The bareword form of require is here
+                # eschewed to avoid this compile-time effect of vivifying
+                # the target module's stash.
+                require "overload.pm";
             }
             my $sub = _fetch_sub(overload => 'StrVal');
             return $sub ? &$sub($arg) : "$arg";
diff --git a/dist/Carp/lib/Carp/Heavy.pm b/dist/Carp/lib/Carp/Heavy.pm
index a82325f4ce..5188f40d0e 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 = '1.47';
+our $VERSION = '1.48';
 $VERSION =~ tr/_//d;
 
 # Carp::Heavy was merged into Carp in version 1.12.  Any mismatched versions