Fix buffer overflow with overlong identifiers

This was introduced by commit 32833930e32dc in 5.17.10.

$  ./perl -Ilib -e Foooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooo
Identifier too long at -e line 1.
Segmentation fault: 11

(That was an amusing use of macro parentheses for the while condition,
at least while it lasted.)

(cherry picked from commit eaaaaa32882752f15fc0db1c73a1adbe34b49642)

Conflicts:
	t/comp/parser.t

2 files changed, 10 insertions, 2 deletions

diff --git a/t/comp/parser.t b/t/comp/parser.t
index 7c0db7fa37..4f2da90f50 100644
--- a/t/comp/parser.t
+++ b/t/comp/parser.t
@@ -3,7 +3,7 @@
 # Checks if the parser behaves correctly in edge cases
 # (including weird syntax errors)
 
-print "1..154\n";
+print "1..155\n";
 
 sub failed {
     my ($got, $expected, $name) = @_;
@@ -450,6 +450,14 @@ for my $pkg(()){}
 $pkg = 3;
 is $pkg, 3, '[perl #114942] for my $foo()){} $foo';
 
+eval 'Fooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooo'
+    .'oooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooo'
+    .'oooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooo'
+    .'oooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooo'
+    .'oooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooo'
+    .'ooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooo';
+like $@, "^Identifier too long at ", 'ident buffer overflow';
+
 # Add new tests HERE (above this line)
 
 # bug #74022: Loop on characters in \p{OtherIDContinue}
diff --git a/toke.c b/toke.c
index 10807d5f1e..fc53c7978e 100644
--- a/toke.c
+++ b/toke.c
@@ -9244,7 +9244,7 @@ S_parse_ident(pTHX_ char **s, char **d, char * const e, int allow_package, bool
         else if ( isWORDCHAR_A(**s) ) {
             do {
                 *(*d)++ = *(*s)++;
-            } while isWORDCHAR_A(**s);
+            } while (isWORDCHAR_A(**s) && *d < e);
         }
         else if (allow_package && **s == '\'' && isIDFIRST_lazy_if(*s+1,is_utf8)) {
             *(*d)++ = ':';