Register fn-ptr coercion obligations out of a snapshot

src/librustc_typeck/check/coercion.rs

@@ -807,8 +807,7 @@ impl<'a, 'gcx, 'tcx> FnCtxt<'a, 'gcx, 'tcx> {
             let lub_ty = self.commit_if_ok(|_| {
                 self.at(cause, self.param_env)
                     .lub(prev_ty, new_ty)
-                    .map(|ok| self.register_infer_ok_obligations(ok))
-            });
+            }).map(|ok| self.register_infer_ok_obligations(ok));
 
             if lub_ty.is_ok() {
                 // We have a LUB of prev_ty and new_ty, just return it.
@@ -884,8 +883,7 @@ impl<'a, 'gcx, 'tcx> FnCtxt<'a, 'gcx, 'tcx> {
                 return self.commit_if_ok(|_| {
                     self.at(cause, self.param_env)
                         .lub(prev_ty, new_ty)
-                        .map(|ok| self.register_infer_ok_obligations(ok))
-                });
+                }).map(|ok| self.register_infer_ok_obligations(ok));
             }
         }
 
@@ -898,8 +896,7 @@ impl<'a, 'gcx, 'tcx> FnCtxt<'a, 'gcx, 'tcx> {
                     self.commit_if_ok(|_| {
                         self.at(cause, self.param_env)
                             .lub(prev_ty, new_ty)
-                            .map(|ok| self.register_infer_ok_obligations(ok))
-                    })
+                    }).map(|ok| self.register_infer_ok_obligations(ok))
                 }
             }
             Ok(ok) => {

src/librustc_typeck/check/regionck.rs

@@ -1815,12 +1815,12 @@ impl<'a, 'gcx, 'tcx> RegionCtxt<'a, 'gcx, 'tcx> {
                     // check whether this predicate applies to our current projection
                     let cause = self.fcx.misc(span);
                     match self.at(&cause, self.fcx.param_env).eq(outlives.0, ty) {
-                        Ok(ok) => {
-                            self.register_infer_ok_obligations(ok);
-                            Ok(outlives.1)
-                        }
-                        Err(_) => { Err(()) }
+                        Ok(ok) => Ok((ok, outlives.1)),
+                        Err(_) => Err(())
                     }
+                }).map(|(ok, result)| {
+                    self.register_infer_ok_obligations(ok);
+                    result
                 });
 
                 debug!("projection_bounds: region_result={:?}",

src/test/run-pass/issue-43923.rs

@@ -0,0 +1,19 @@
+// 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.
+
+struct A<T: ?Sized> { ptr: T }
+
+fn foo<T>(x: &A<[T]>) {}
+
+fn main() {
+    let a = foo;
+    let b = A { ptr: [a, a, a] };
+    a(&A { ptr: [()] });
+}