Auto merge of #28626 - arielb1:closure-needs-infer, r=nikomatsakis

Fixes #28550

Author: bors

Diff for: src/librustc/middle/infer/mod.rs

@@ -1394,9 +1394,16 @@ impl<'a, 'tcx> InferCtxt<'a, 'tcx> {
         self.resolve_type_vars_or_error(&ty)
     }
 
+    pub fn tables_are_tcx_tables(&self) -> bool {
+        let tables: &RefCell<ty::Tables> = &self.tables;
+        let tcx_tables: &RefCell<ty::Tables> = &self.tcx.tables;
+        tables as *const _ == tcx_tables as *const _
+    }
+
     pub fn type_moves_by_default(&self, ty: Ty<'tcx>, span: Span) -> bool {
         let ty = self.resolve_type_vars_if_possible(&ty);
-        if ty.needs_infer() {
+        if ty.needs_infer() ||
+            (ty.has_closure_types() && !self.tables_are_tcx_tables()) {
             // this can get called from typeck (by euv), and moves_by_default
             // rightly refuses to work with inference variables, but
             // moves_by_default has a cache, which we want to use in other

Diff for: src/test/run-pass/issue-28550.rs

@@ -0,0 +1,25 @@
+// Copyright 2015 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<F: FnOnce()->T,T>(F::Output);
+struct B<F: FnOnce()->T,T>(A<F,T>);
+
+// Removing Option causes it to compile.
+fn foo<T,F: FnOnce()->T>(f: F) -> Option<B<F,T>> {
+    Some(B(A(f())))
+}
+
+fn main() {
+    let v = (|| foo(||4))();
+    match v {
+        Some(B(A(4))) => {},
+        _ => unreachable!()
+    }
+}