Revert "we can catch this earlier now that we optimize out unused att…

…ributes"

This reverts commit 50d8ed5.

this actually doesn't work, because a method might look like

    method wrap ($app, @Args) {
        if (ref $self) {
            $!app = $app;
        } else {
            $self = $self->new({ app => $app, @Args });
        }
        return $self->to_app;
    }

mop.xs

@@ -333,6 +333,28 @@ mg_attr_set(pTHX_ SV *sv, MAGIC *mg)
     return 0;
 }
 
+static int
+mg_err_get(pTHX_ SV *sv, MAGIC *mg)
+{
+    PERL_UNUSED_ARG(sv);
+
+    assert(mg->mg_obj && SvPOK(mg->mg_obj));
+
+    croak("Cannot access the attribute:(%"SVf") in a method "
+          "without a blessed invocant", SVfARG(mg->mg_obj));
+}
+
+static int
+mg_err_set(pTHX_ SV *sv, MAGIC *mg)
+{
+    PERL_UNUSED_ARG(sv);
+
+    assert(mg->mg_obj && SvPOK(mg->mg_obj));
+
+    croak("Cannot assign to the attribute:(%"SVf") in a method "
+          "without a blessed invocant", SVfARG(mg->mg_obj));
+}
+
 static MGVTBL attr_vtbl = {
     mg_attr_get,                /* get */
     mg_attr_set,                /* set */
@@ -343,6 +365,16 @@ static MGVTBL attr_vtbl = {
     0,                          /* dup */
     0,                          /* local */
 };
+static MGVTBL err_vtbl = {
+    mg_err_get,                 /* get */
+    mg_err_set,                 /* set */
+    0,                          /* len */
+    0,                          /* clear */
+    0,                          /* free */
+    0,                          /* copy */
+    0,                          /* dup */
+    0,                          /* local */
+};
 
 #define set_attr_magic(var, name, meta, self) THX_set_attr_magic(aTHX_ var, name, meta, self)
 static void
@@ -357,6 +389,13 @@ THX_set_attr_magic(pTHX_ SV *var, SV *name, SV *meta, SV *self)
     sv_magicext(var, (SV *)data, PERL_MAGIC_ext, &attr_vtbl, "attr", 0);
 }
 
+#define set_err_magic(var, name) THX_set_err_magic(aTHX_ var, name)
+static void
+THX_set_err_magic(pTHX_ SV *var, SV *name)
+{
+    sv_magicext(var, name, PERL_MAGIC_ext, &err_vtbl, "err", 0);
+}
+
 /* }}} */
 /* version helpers {{{ */
 
@@ -1332,11 +1371,10 @@ pp_init_attr(pTHX)
     attr_name       = POPs;
     meta_class      = get_meta(meta_class_name);
 
-    if (!sv_isobject(invocant))
-        croak("Cannot access the attribute:(%"SVf") in a method "
-              "without a blessed invocant", SVfARG(attr_name));
-
-    set_attr_magic(TARG, attr_name, meta_class, invocant);
+    if (sv_isobject(invocant))
+        set_attr_magic(TARG, attr_name, meta_class, invocant);
+    else
+        set_err_magic(TARG, attr_name);
 
     RETURN;
 }

t/010-basics/007-class-methods.t

@@ -19,7 +19,7 @@ class Foo {
 eval { Foo->bar(10) };
 like(
     $@,
-    qr/^Cannot access the attribute\:\(\$!bar\) in a method without a blessed invocant/,
+    qr/^Cannot assign to the attribute\:\(\$!bar\) in a method without a blessed invocant/,
     '... got the error we expected'
 );
 

t/010-basics/028-attributes-in-class-methods.t

@@ -0,0 +1,28 @@
+#!/usr/bin/env perl
+use strict;
+use warnings;
+use Test::More;
+
+use mop;
+
+# this comes up in, for instance, Plack::Middleware::wrap
+
+class Foo {
+    has $!bar is ro;
+
+    method baz ($bar) {
+        if (ref($self)) {
+            $!bar = $bar;
+        }
+        else {
+            $self = __CLASS__->new(bar => $bar);
+        }
+
+        return $self->bar;
+    }
+}
+
+is(Foo->baz('BAR-class'), 'BAR-class');
+is(Foo->new->baz('BAR-instance'), 'BAR-instance');
+
+done_testing;