try to fix lvalue ops for real

Hopefully this is the last PR needed.

Fixes #41726.
Fixes #41742.
Fixes #41774.

src/test/compile-fail/issue-41726.rs

@@ -0,0 +1,17 @@
+// 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.
+
+use std::collections::HashMap;
+fn main() {
+    let things: HashMap<String, Vec<String>> = HashMap::new();
+    for src in things.keys() {
+        things[src.as_str()].sort(); //~ ERROR cannot borrow immutable
+    }
+}

src/test/compile-fail/issue-41742.rs

@@ -0,0 +1,35 @@
+// 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.
+
+use std::ops::{Index, IndexMut};
+
+struct S;
+struct H;
+
+impl S {
+    fn f(&mut self) {}
+}
+
+impl Index<u32> for H {
+    type Output = S;
+    fn index(&self, index: u32) -> &S {
+        unimplemented!()
+    }
+}
+
+impl IndexMut<u32> for H {
+    fn index_mut(&mut self, index: u32) -> &mut S {
+        unimplemented!()
+    }
+}
+
+fn main() {
+    H["?"].f(); //~ ERROR mismatched types
+}

src/test/compile-fail/regions-adjusted-lvalue-op.rs

@@ -0,0 +1,26 @@
+// 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.
+
+// check that we link regions in mutable lvalue ops correctly - issue #41774
+
+struct Data(i32);
+
+trait OhNo {
+    fn oh_no(&mut self, other: &Vec<Data>) { loop {} }
+}
+
+impl OhNo for Data {}
+impl OhNo for [Data] {}
+
+fn main() {
+    let mut v = vec![Data(0)];
+    v[0].oh_no(&v); //~ ERROR cannot borrow `v` as immutable because
+    (*v).oh_no(&v); //~ ERROR cannot borrow `v` as immutable because
+}