revert commit 114f948 (gh #54)

The existing code falls back to URI::urn and already caches the implementor after it's done. It therefore can never try to load one twice if it previously failed.

lib/URI/urn.pm

@@ -10,7 +10,6 @@ use parent 'URI';
 use Carp qw(carp);
 
 my %implementor;
-my %require_attempted;
 
 sub _init {
     my $class = shift;
@@ -30,21 +29,18 @@ sub _init {
 	$impclass = "URI::urn::$id";
 	no strict 'refs';
 	unless (@{"${impclass}::ISA"}) {
-            if (not exists $require_attempted{$impclass}) {
                 # Try to load it
                 my $_old_error = $@;
                 eval "require $impclass";
                 die $@ if $@ && $@ !~ /Can\'t locate.*in \@INC/;
                 $@ = $_old_error;
-            }
 	    $impclass = "URI::urn" unless @{"${impclass}::ISA"};
 	}
     }
     else {
 	carp("Illegal namespace identifier '$nid' for URN '$self'") if $^W;
     }
     $implementor{$nid} = $impclass;
-
     return $impclass->_urn_init($self, $nid);
 }
 

t/urn-scheme-exceptions.t

@@ -0,0 +1,19 @@
+use strict;
+use warnings;
+
+use Test::More;
+use URI::urn;
+
+plan tests => 6;
+
+{
+    require URI::_foreign;    # load this before disabling @INC
+    my $count = 0;
+    local @INC = sub { $count++; return };
+    for ( 0 .. 1 ) {
+        my $uri = URI->new('urn:asdfasdf:1.2.3.4.5.6.7.8.9.10');
+        is( $count, 1, 'only attempt to load the scheme package once' );
+        is( $@, '', 'no exception when trying to load a scheme handler class' );
+        ok( $uri->isa('URI'), 'but URI still instantiated as foreign' );
+    }
+}