assertion failure on foo(my $x : bar)

RT #126257

'my var : attr' injects a void-context sub call just after the
pad op. However, Perl_ck_entersub_args_list() tries to impose lvalue
context on each of its args, which causes an assertion failure.

This commit makes Perl_ck_entersub_args_list() skip calling op_lvalue()
on any args which are OP_ENTERSUB/OPf_WANT_VOID. Strictly
speaking it should check that the sub call is actually an attribute
method call (e.g. first child is a const("attibutes") etc), but this
was far too much like hard work.

Author: iabyn

op.c

@@ -11156,11 +11156,20 @@ OP *
 Perl_ck_entersub_args_list(pTHX_ OP *entersubop)
 {
     OP *aop;
+
     PERL_ARGS_ASSERT_CK_ENTERSUB_ARGS_LIST;
+
     aop = cUNOPx(entersubop)->op_first;
     if (!OpHAS_SIBLING(aop))
 	aop = cUNOPx(aop)->op_first;
     for (aop = OpSIBLING(aop); OpHAS_SIBLING(aop); aop = OpSIBLING(aop)) {
+        /* skip the extra attributes->import() call implicitly added in
+         * something like foo(my $x : bar)
+         */
+        if (   aop->op_type == OP_ENTERSUB
+            && (aop->op_flags & OPf_WANT) == OPf_WANT_VOID
+        )
+            continue;
         list(aop);
         op_lvalue(aop, OP_ENTERSUB);
     }

t/op/attrs.t

@@ -428,4 +428,23 @@ package _123817 {
     eval 'return my $x : m';
 }
 
+# [perl #126257]
+# attributed lex var as function arg caused assertion failure
+
+package P126257 {
+    sub MODIFY_SCALAR_ATTRIBUTES {}
+    sub MODIFY_ARRAY_ATTRIBUTES  {}
+    sub MODIFY_HASH_ATTRIBUTES   {}
+    sub MODIFY_CODE_ATTRIBUTES   {}
+    sub foo {}
+    eval { foo(my $x : bar); };
+    ::is $@, "", "RT 126257 scalar";
+    eval { foo(my @x : bar); };
+    ::is $@, "", "RT 126257 array";
+    eval { foo(my %x : bar); };
+    ::is $@, "", "RT 126257 hash";
+    eval { foo(sub : bar {}); };
+    ::is $@, "", "RT 126257 sub";
+}
+
 done_testing();