implement fn item -> trait object conversion

src/interpreter/vtable.rs

@@ -58,11 +58,14 @@ impl<'a, 'tcx> EvalContext<'a, 'tcx> {
                 }
                 traits::VtableFnPointer(
                     traits::VtableFnPointerData {
-                        fn_ty: _bare_fn_ty,
+                        fn_ty,
                         nested: _ }) => {
-                    let _trait_closure_kind = tcx.lang_items.fn_trait_kind(trait_ref.def_id()).unwrap();
-                    //vec![trans_fn_pointer_shim(ccx, trait_closure_kind, bare_fn_ty)].into_iter()
-                    unimplemented!()
+                    match fn_ty.sty {
+                        ty::TyFnDef(did, substs, bare_fn_ty) => {
+                            vec![Some(self.memory.create_fn_ptr(did, substs, bare_fn_ty))].into_iter()
+                        },
+                        _ => bug!("bad VtableFnPointer fn_ty: {:?}", fn_ty),
+                    }
                 }
                 traits::VtableObject(ref data) => {
                     // this would imply that the Self type being erased is

tests/run-pass/issue-30530.rs

@@ -0,0 +1,35 @@
+// Copyright 2012-2016 The Rust Project Developers. See the COPYRIGHT
+// file at the top-level directory of this distribution and at
+// http://rust-lang.org/COPYRIGHT.
+//
+// Licensed under the Apache License, Version 2.0 <LICENSE-APACHE or
+// http://www.apache.org/licenses/LICENSE-2.0> or the MIT license
+// <LICENSE-MIT or http://opensource.org/licenses/MIT>, at your
+// option. This file may not be copied, modified, or distributed
+// except according to those terms.
+
+// Regression test for Issue #30530: alloca's created for storing
+// intermediate scratch values during brace-less match arms need to be
+// initialized with their drop-flag set to "dropped" (or else we end
+// up running the destructors on garbage data at the end of the
+// function).
+
+pub enum Handler {
+    Default,
+    #[allow(dead_code)]
+    Custom(*mut Box<Fn()>),
+}
+
+fn main() {
+    take(Handler::Default, Box::new(main));
+}
+
+#[inline(never)]
+pub fn take(h: Handler, f: Box<Fn()>) -> Box<Fn()> {
+    unsafe {
+        match h {
+            Handler::Custom(ptr) => *Box::from_raw(ptr),
+            Handler::Default => f,
+        }
+    }
+}