attributes.pm: warn & don’t apply :lvalue to defined subs

This is something that ‘sub foo :lvalue;’ declarations do.  This brings
attributes.pm in line with them.

See commits fff96ff and 885ef6f, ticket #68758, and
<364E1F98-FDCC-49A7-BADB-BD844626B8AE@cpan.org>.

1 files changed, 10 insertions, 5 deletions

diff --git a/pod/perldiag.pod b/pod/perldiag.pod
index 7954739f77..51a19e7d1c 100644
--- a/pod/perldiag.pod
+++ b/pod/perldiag.pod
@@ -2474,13 +2474,18 @@ You may wish to switch to using L<Math::BigInt> explicitly.
 by that?  lstat() makes sense only on filenames.  (Perl did a fstat()
 instead on the filehandle.)
 
+=item lvalue attribute cannot be removed after the subroutine has been defined
+
+(W misc) The lvalue attribute on a Perl subroutine cannot be turned off
+once the subroutine is defined.
+
 =item lvalue attribute ignored after the subroutine has been defined
 
-(W misc) Making a subroutine an lvalue subroutine after it has been defined
-by declaring the subroutine with an lvalue attribute is not
-possible. To make the subroutine an lvalue subroutine add the
-lvalue attribute to the definition, or put the declaration before
-the definition.
+(W misc) Making a Perl subroutine an lvalue subroutine after it has been
+defined, whether by declaring the subroutine with an lvalue attribute
+or by using L<attributes.pm|attributes>, is not possible.  To make the subroutine an
+lvalue subroutine, add the lvalue attribute to the definition, or put
+the declaration before the definition.
 
 =item Malformed integer in [] in pack