Fix translation of unboxing shim for rust-call ABI methods

src/librustc/middle/trans/callee.rs

@@ -281,8 +281,32 @@ pub fn trans_unboxing_shim(bcx: Block,
     };
     let boxed_function_type =
         ty::mk_bare_fn(tcx, boxed_function_type).subst(tcx, &substs);
-    let function_type =
-        ty::mk_bare_fn(tcx, (*fty).clone()).subst(tcx, &substs);
+    let function_type = match fty.abi {
+        synabi::RustCall => {
+            // We're passing through to a RustCall ABI function, but
+            // because the shim will already perform untupling, we
+            // need to pretend the shimmed function does not use
+            // RustCall so the untupled arguments can be passed
+            // through verbatim.  This is kind of ugly.
+            let fake_ty = ty::FnSig {
+                binder_id: fty.sig.binder_id,
+                inputs: type_of::untuple_arguments_if_necessary(ccx,
+                                                                fty.sig.inputs.as_slice(),
+                                                                fty.abi),
+                output: fty.sig.output,
+                variadic: false,
+            };
+            let fake_ty = ty::BareFnTy {
+                fn_style: fty.fn_style,
+                abi: synabi::Rust,
+                sig: fake_ty,
+            };
+            ty::mk_bare_fn(tcx, fake_ty).subst(tcx, &substs)
+        }
+        _ => {
+            ty::mk_bare_fn(tcx, (*fty).clone()).subst(tcx, &substs)
+        }
+    };
 
     let function_name = ty::with_path(tcx, method_id, |path| {
         link::mangle_internal_name_by_path_and_seq(path, "unboxing_shim")

src/librustc/middle/trans/type_of.rs

@@ -44,10 +44,10 @@ pub fn type_of_explicit_arg(ccx: &CrateContext, arg_ty: ty::t) -> Type {
 /// Yields the types of the "real" arguments for this function. For most
 /// functions, these are simply the types of the arguments. For functions with
 /// the `RustCall` ABI, however, this untuples the arguments of the function.
-fn untuple_arguments_if_necessary(ccx: &CrateContext,
-                                  inputs: &[ty::t],
-                                  abi: abi::Abi)
-                                  -> Vec<ty::t> {
+pub fn untuple_arguments_if_necessary(ccx: &CrateContext,
+                                      inputs: &[ty::t],
+                                      abi: abi::Abi)
+                                      -> Vec<ty::t> {
     if abi != abi::RustCall {
         return inputs.iter().map(|x| (*x).clone()).collect()
     }

src/test/run-pass/issue-16739.rs

@@ -0,0 +1,42 @@
+// Copyright 2014 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.
+
+#![feature(unboxed_closures)]
+
+// Test that unboxing shim for calling rust-call ABI methods through a
+// trait box works and does not cause an ICE
+
+struct Foo { foo: uint }
+
+impl FnOnce<(), uint> for Foo {
+    #[rust_call_abi_hack]
+    fn call_once(self, _: ()) -> uint { self.foo }
+}
+
+impl FnOnce<(uint,), uint> for Foo {
+    #[rust_call_abi_hack]
+    fn call_once(self, (x,): (uint,)) -> uint { self.foo + x }
+}
+
+impl FnOnce<(uint, uint), uint> for Foo {
+    #[rust_call_abi_hack]
+    fn call_once(self, (x, y): (uint, uint)) -> uint { self.foo + x + y }
+}
+
+fn main() {
+    let f = box Foo { foo: 42 } as Box<FnOnce<(), uint>>;
+    assert_eq!(f.call_once(()), 42);
+
+    let f = box Foo { foo: 40 } as Box<FnOnce<(uint,), uint>>;
+    assert_eq!(f.call_once((2,)), 42);
+
+    let f = box Foo { foo: 40 } as Box<FnOnce<(uint, uint), uint>>;
+    assert_eq!(f.call_once((1, 1)), 42);
+}