5 files changed, 46 insertions, 0 deletions
diff --git a/src/test/ui/borrowck/index-mut-help-with-impl.nll.stderr b/src/test/ui/borrowck/index-mut-help-with-impl.nll.stderr
new file mode 100644
index 00000000000..8e7ffa67b06
--- /dev/null
+++ b/src/test/ui/borrowck/index-mut-help-with-impl.nll.stderr
@@ -0,0 +1,11 @@
+error[E0596]: cannot borrow data in a `&` reference as mutable
+  --> $DIR/index-mut-help-with-impl.rs:19:5
+   |
+LL |     Index::index(&v, 1..2).make_ascii_uppercase(); //~ ERROR
+   |     ^^^^^^^^^^^^^^^^^^^^^^ cannot borrow as mutable
+   |
+   = help: trait `IndexMut` is required to modify indexed content
+
+error: aborting due to previous error
+
+For more information about this error, try `rustc --explain E0596`.
diff --git a/src/test/ui/borrowck/index-mut-help-with-impl.rs b/src/test/ui/borrowck/index-mut-help-with-impl.rs
new file mode 100644
index 00000000000..a5bab48c5cc
--- /dev/null
+++ b/src/test/ui/borrowck/index-mut-help-with-impl.rs
@@ -0,0 +1,20 @@
+// Copyright 2018 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.
+
+// When mutably indexing a type that implements `Index` and `IndexMut` but
+// `Index::index` is being used specifically, the normal special help message
+// should not mention a missing `IndexMut` impl.
+
+fn main() {
+    use std::ops::Index;
+
+    let v = String::from("dinosaur");
+    Index::index(&v, 1..2).make_ascii_uppercase(); //~ ERROR
+}
diff --git a/src/test/ui/borrowck/index-mut-help-with-impl.stderr b/src/test/ui/borrowck/index-mut-help-with-impl.stderr
new file mode 100644
index 00000000000..9c28b86c45a
--- /dev/null
+++ b/src/test/ui/borrowck/index-mut-help-with-impl.stderr
@@ -0,0 +1,9 @@
+error[E0596]: cannot borrow immutable borrowed content as mutable
+  --> $DIR/index-mut-help-with-impl.rs:19:5
+   |
+LL |     Index::index(&v, 1..2).make_ascii_uppercase(); //~ ERROR
+   |     ^^^^^^^^^^^^^^^^^^^^^^ cannot borrow as mutable
+
+error: aborting due to previous error
+
+For more information about this error, try `rustc --explain E0596`.
diff --git a/src/test/ui/borrowck/index-mut-help.nll.stderr b/src/test/ui/borrowck/index-mut-help.nll.stderr
index cc058f1fde5..a15f37684e7 100644
--- a/src/test/ui/borrowck/index-mut-help.nll.stderr
+++ b/src/test/ui/borrowck/index-mut-help.nll.stderr
@@ -3,6 +3,8 @@ error[E0596]: cannot borrow data in a `&` reference as mutable
    |
 LL |     map["peter"].clear();           //~ ERROR
    |     ^^^^^^^^^^^^ cannot borrow as mutable
+   |
+   = help: trait `IndexMut` is required to modify indexed content, but it is not implemented for `std::collections::HashMap<&str, std::string::String>`
 
 error[E0594]: cannot assign to data in a `&` reference
   --> $DIR/index-mut-help.rs:22:5
@@ -15,6 +17,8 @@ error[E0596]: cannot borrow data in a `&` reference as mutable
    |
 LL |     let _ = &mut map["peter"];      //~ ERROR
    |             ^^^^^^^^^^^^^^^^^ cannot borrow as mutable
+   |
+   = help: trait `IndexMut` is required to modify indexed content, but it is not implemented for `std::collections::HashMap<&str, std::string::String>`
 
 error: aborting due to 3 previous errors
 
diff --git a/src/test/ui/issues/issue-41726.nll.stderr b/src/test/ui/issues/issue-41726.nll.stderr
index 06ff743a0f5..9f727881bea 100644
--- a/src/test/ui/issues/issue-41726.nll.stderr
+++ b/src/test/ui/issues/issue-41726.nll.stderr
@@ -3,6 +3,8 @@ error[E0596]: cannot borrow data in a `&` reference as mutable
    |
 LL |         things[src.as_str()].sort(); //~ ERROR cannot borrow immutable
    |         ^^^^^^^^^^^^^^^^^^^^ cannot borrow as mutable
+   |
+   = help: trait `IndexMut` is required to modify indexed content, but it is not implemented for `std::collections::HashMap<std::string::String, std::vec::Vec<std::string::String>>`
 
 error: aborting due to previous error