resolve type vars with obligations in more places

This fixes a few cases of inference misses, some of them regressions
caused by the impl selected for a method not being immediately evaluated.

Author: arielb1

src/librustc_typeck/check/mod.rs

@@ -2818,6 +2818,7 @@ impl<'a, 'gcx, 'tcx> FnCtxt<'a, 'gcx, 'tcx> {
                                            formal_ret: Ty<'tcx>,
                                            formal_args: &[Ty<'tcx>])
                                            -> Vec<Ty<'tcx>> {
+        let formal_ret = self.resolve_type_vars_with_obligations(formal_ret);
         let expected_args = expected_ret.only_has_type(self).and_then(|ret_ty| {
             self.fudge_regions_if_ok(&RegionVariableOrigin::Coercion(call_span), || {
                 // Attempt to apply a subtyping relationship between the formal
@@ -3978,6 +3979,7 @@ impl<'a, 'gcx, 'tcx> FnCtxt<'a, 'gcx, 'tcx> {
           }
           hir::ExprTup(ref elts) => {
             let flds = expected.only_has_type(self).and_then(|ty| {
+                let ty = self.resolve_type_vars_with_obligations(ty);
                 match ty.sty {
                     ty::TyTuple(ref flds, _) => Some(&flds[..]),
                     _ => None

src/test/run-pass/method-argument-inference-associated-type.rs

@@ -0,0 +1,37 @@
+// Copyright 2017 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.
+
+pub struct ClientMap;
+pub struct ClientMap2;
+
+pub trait Service {
+    type Request;
+    fn call(&self, _req: Self::Request);
+}
+
+pub struct S<T>(T);
+
+impl Service for ClientMap {
+    type Request = S<Box<Fn(i32)>>;
+    fn call(&self, _req: Self::Request) {}
+}
+
+
+impl Service for ClientMap2 {
+    type Request = (Box<Fn(i32)>,);
+    fn call(&self, _req: Self::Request) {}
+}
+
+
+fn main() {
+    ClientMap.call(S { 0: Box::new(|_msgid| ()) });
+    ClientMap.call(S(Box::new(|_msgid| ())));
+    ClientMap2.call((Box::new(|_msgid| ()),));
+}