toke.c: Make _charnames check more robust

Assuming that $^H{charnames} exists and contains a code ref can result
in crashes.  See the tests in the diff.

It’s not a good idea to do $INC{"_charnames.pm"}++, but perl still
shouldn’t crash.

1 files changed, 24 insertions, 1 deletions

diff --git a/t/op/lex.t b/t/op/lex.t
index 0789077b5c..c009f2d13c 100644
--- a/t/op/lex.t
+++ b/t/op/lex.t
@@ -4,7 +4,7 @@ use warnings;
 
 require './test.pl';
 
-plan(tests => 4);
+plan(tests => 7);
 
 {
     no warnings 'deprecated';
@@ -45,3 +45,26 @@ curr_test(3);
 
 }
 
+fresh_perl_is(
+  'BEGIN{ ++$_ for @INC{"charnames.pm","_charnames.pm"} } "\N{a}"',
+  'Constant(\N{a}) unknown at - line 1, within string' . "\n"
+ ."Execution of - aborted due to compilation errors.\n",
+   { stderr => 1 },
+  'correct output (and no crash) when charnames cannot load for \N{...}'
+);
+fresh_perl_is(
+  'BEGIN{ ++$_ for @INC{"charnames.pm","_charnames.pm"};
+          $^H{charnames} = "foo" } "\N{a}"',
+  "Undefined subroutine &main::foo called at - line 2.\n"
+ ."Propagated at - line 2, within string\n"
+ ."Execution of - aborted due to compilation errors.\n",
+   { stderr => 1 },
+  'no crash when charnames cannot load and %^H holds string'
+);
+fresh_perl_is(
+  'BEGIN{ ++$_ for @INC{"charnames.pm","_charnames.pm"} } "\N{a}"',
+  'Constant(\N{a}) unknown at - line 1, within string' . "\n"
+ ."Execution of - aborted due to compilation errors.\n",
+   { stderr => 1 },
+  'no crash when charnames cannot load and %^H holds string reference'
+);