op.c: call class_wrap_method_body() for lexical methods

Class method bodies must be wrapped by this function, which adds the
OP_METHSTART op at the beginning, which is responsible for shifting
the `$self` lexical from the arguments array, and setting up field
bindings. This was already done for non-lexical (i.e. package) methods
but was forgotten for lexical methods, so they didn't work properly,
leading to the bug found in GH#23030 whereby the argument count in a
signatured lexical method did not take account of the `$self` argument
properly.

In addition, fields accessed by the method body would not have been
working, though originally this wasn't reported or tested either. A test
for this has also been added.

Author: leonerd

op.c

@@ -10657,6 +10657,8 @@ Perl_newMYSUB(pTHX_ I32 floor, OP *o, OP *proto, OP *attrs, OP *block)
     }
 
     if (block) {
+        if (CvIsMETHOD(PL_compcv))
+            block = class_wrap_method_body(block);
         /* This makes sub {}; work as expected.  */
         if (block->op_type == OP_STUB) {
             const line_t l = PL_parser->copline;

t/class/method.t

@@ -106,8 +106,10 @@ no warnings 'experimental::class';
 # ->& operator can invoke methods with lexical scope
 {
     class Testcase8 {
+        field $f = "private-result";
+
         my method priv {
-            return "private-result";
+            return $f;
         }
 
         method notpriv {
@@ -134,4 +136,22 @@ no warnings 'experimental::class';
         '->&m operator does not follow inheritance');
 }
 
+# lexical methods with signatures work correctly (GH#23030)
+{
+    class Testcase9 {
+        field $x = 123;
+
+        my method priv ( $y ) {
+            return "X is $x and Y is $y for $self";
+        }
+
+        method test {
+            $self->&priv(456);
+        }
+    }
+
+    like(Testcase9->new->test, qr/^X is 123 and Y is 456 for Testcase9=OBJECT\(0x.*\)$/,
+        'lexical method with signature counts $self correctly');
+}
+
 done_testing;