Add help message for mutation though overloaded place operators

10 files changed, 97 insertions, 75 deletions

diff --git a/src/test/ui/borrowck/borrowck-borrow-overloaded-auto-deref.rs b/src/test/ui/borrowck/borrowck-borrow-overloaded-auto-deref.rs
index 01dc0af8550..83eab7fdeab 100644
--- a/src/test/ui/borrowck/borrowck-borrow-overloaded-auto-deref.rs
+++ b/src/test/ui/borrowck/borrowck-borrow-overloaded-auto-deref.rs
@@ -2,18 +2,7 @@
 // Deref and not DerefMut is implemented.
 
 use std::ops::Deref;
-
-struct Rc<T> {
-    value: *const T
-}
-
-impl<T> Deref for Rc<T> {
-    type Target = T;
-
-    fn deref(&self) -> &T {
-        unsafe { &*self.value }
-    }
-}
+use std::rc::Rc;
 
 struct Point {
     x: isize,
diff --git a/src/test/ui/borrowck/borrowck-borrow-overloaded-auto-deref.stderr b/src/test/ui/borrowck/borrowck-borrow-overloaded-auto-deref.stderr
index dc52685363e..d262c578843 100644
--- a/src/test/ui/borrowck/borrowck-borrow-overloaded-auto-deref.stderr
+++ b/src/test/ui/borrowck/borrowck-borrow-overloaded-auto-deref.stderr
@@ -1,86 +1,114 @@
-error[E0596]: cannot borrow data in a `&` reference as mutable
-  --> $DIR/borrowck-borrow-overloaded-auto-deref.rs:47:19
+error[E0596]: cannot borrow data in an `Rc` as mutable
+  --> $DIR/borrowck-borrow-overloaded-auto-deref.rs:36:19
    |
 LL |     let __isize = &mut x.y;
    |                   ^^^^^^^^ cannot borrow as mutable
+   |
+   = help: trait `DerefMut` is required to modify through a dereference, but it is not implemented for `std::rc::Rc<Point>`
 
-error[E0596]: cannot borrow data in a `&` reference as mutable
-  --> $DIR/borrowck-borrow-overloaded-auto-deref.rs:51:19
+error[E0596]: cannot borrow data in an `Rc` as mutable
+  --> $DIR/borrowck-borrow-overloaded-auto-deref.rs:40:19
    |
 LL |     let __isize = &mut x.y;
    |                   ^^^^^^^^ cannot borrow as mutable
+   |
+   = help: trait `DerefMut` is required to modify through a dereference, but it is not implemented for `std::rc::Rc<Point>`
 
-error[E0596]: cannot borrow data in a `&` reference as mutable
-  --> $DIR/borrowck-borrow-overloaded-auto-deref.rs:59:5
+error[E0596]: cannot borrow data in an `Rc` as mutable
+  --> $DIR/borrowck-borrow-overloaded-auto-deref.rs:48:5
    |
 LL |     &mut x.y
    |     ^^^^^^^^ cannot borrow as mutable
+   |
+   = help: trait `DerefMut` is required to modify through a dereference, but it is not implemented for `std::rc::Rc<Point>`
 
-error[E0596]: cannot borrow data in a `&` reference as mutable
-  --> $DIR/borrowck-borrow-overloaded-auto-deref.rs:63:5
+error[E0596]: cannot borrow data in an `Rc` as mutable
+  --> $DIR/borrowck-borrow-overloaded-auto-deref.rs:52:5
    |
 LL |     &mut x.y
    |     ^^^^^^^^ cannot borrow as mutable
+   |
+   = help: trait `DerefMut` is required to modify through a dereference, but it is not implemented for `std::rc::Rc<Point>`
 
-error[E0594]: cannot assign to data in a `&` reference
-  --> $DIR/borrowck-borrow-overloaded-auto-deref.rs:67:5
+error[E0594]: cannot assign to data in an `Rc`
+  --> $DIR/borrowck-borrow-overloaded-auto-deref.rs:56:5
    |
 LL |     x.y = 3;
    |     ^^^^^^^ cannot assign
+   |
+   = help: trait `DerefMut` is required to modify through a dereference, but it is not implemented for `std::rc::Rc<Point>`
 
-error[E0594]: cannot assign to data in a `&` reference
-  --> $DIR/borrowck-borrow-overloaded-auto-deref.rs:71:5
+error[E0594]: cannot assign to data in an `Rc`
+  --> $DIR/borrowck-borrow-overloaded-auto-deref.rs:60:5
    |
 LL |     x.y = 3;
    |     ^^^^^^^ cannot assign
+   |
+   = help: trait `DerefMut` is required to modify through a dereference, but it is not implemented for `std::rc::Rc<Point>`
 
-error[E0594]: cannot assign to data in a `&` reference
-  --> $DIR/borrowck-borrow-overloaded-auto-deref.rs:75:5
+error[E0594]: cannot assign to data in an `Rc`
+  --> $DIR/borrowck-borrow-overloaded-auto-deref.rs:64:5
    |
 LL |     x.y = 3;
    |     ^^^^^^^ cannot assign
+   |
+   = help: trait `DerefMut` is required to modify through a dereference, but it is not implemented for `std::rc::Rc<Point>`
 
-error[E0596]: cannot borrow data in a `&` reference as mutable
-  --> $DIR/borrowck-borrow-overloaded-auto-deref.rs:83:5
+error[E0596]: cannot borrow data in an `Rc` as mutable
+  --> $DIR/borrowck-borrow-overloaded-auto-deref.rs:72:5
    |
 LL |     x.set(0, 0);
    |     ^ cannot borrow as mutable
+   |
+   = help: trait `DerefMut` is required to modify through a dereference, but it is not implemented for `std::rc::Rc<Point>`
 
-error[E0596]: cannot borrow data in a `&` reference as mutable
-  --> $DIR/borrowck-borrow-overloaded-auto-deref.rs:87:5
+error[E0596]: cannot borrow data in an `Rc` as mutable
+  --> $DIR/borrowck-borrow-overloaded-auto-deref.rs:76:5
    |
 LL |     x.set(0, 0);
    |     ^ cannot borrow as mutable
+   |
+   = help: trait `DerefMut` is required to modify through a dereference, but it is not implemented for `std::rc::Rc<Point>`
 
-error[E0596]: cannot borrow data in a `&` reference as mutable
-  --> $DIR/borrowck-borrow-overloaded-auto-deref.rs:95:5
+error[E0596]: cannot borrow data in an `Rc` as mutable
+  --> $DIR/borrowck-borrow-overloaded-auto-deref.rs:84:5
    |
 LL |     x.y_mut()
    |     ^ cannot borrow as mutable
+   |
+   = help: trait `DerefMut` is required to modify through a dereference, but it is not implemented for `std::rc::Rc<Point>`
 
-error[E0596]: cannot borrow data in a `&` reference as mutable
-  --> $DIR/borrowck-borrow-overloaded-auto-deref.rs:99:5
+error[E0596]: cannot borrow data in an `Rc` as mutable
+  --> $DIR/borrowck-borrow-overloaded-auto-deref.rs:88:5
    |
 LL |     x.y_mut()
    |     ^ cannot borrow as mutable
+   |
+   = help: trait `DerefMut` is required to modify through a dereference, but it is not implemented for `std::rc::Rc<Point>`
 
-error[E0596]: cannot borrow data in a `&` reference as mutable
-  --> $DIR/borrowck-borrow-overloaded-auto-deref.rs:103:6
+error[E0596]: cannot borrow data in an `Rc` as mutable
+  --> $DIR/borrowck-borrow-overloaded-auto-deref.rs:92:6
    |
 LL |     *x.y_mut() = 3;
    |      ^ cannot borrow as mutable
+   |
+   = help: trait `DerefMut` is required to modify through a dereference, but it is not implemented for `std::rc::Rc<Point>`
 
-error[E0596]: cannot borrow data in a `&` reference as mutable
-  --> $DIR/borrowck-borrow-overloaded-auto-deref.rs:107:6
+error[E0596]: cannot borrow data in an `Rc` as mutable
+  --> $DIR/borrowck-borrow-overloaded-auto-deref.rs:96:6
    |
 LL |     *x.y_mut() = 3;
    |      ^ cannot borrow as mutable
+   |
+   = help: trait `DerefMut` is required to modify through a dereference, but it is not implemented for `std::rc::Rc<Point>`
 
-error[E0596]: cannot borrow data in a `&` reference as mutable
-  --> $DIR/borrowck-borrow-overloaded-auto-deref.rs:111:6
+error[E0596]: cannot borrow data in an `Rc` as mutable
+  --> $DIR/borrowck-borrow-overloaded-auto-deref.rs:100:6
    |
 LL |     *x.y_mut() = 3;
    |      ^ cannot borrow as mutable
+   |
+   = help: trait `DerefMut` is required to modify through a dereference, but it is not implemented for `std::rc::Rc<Point>`
 
 error: aborting due to 14 previous errors
 
diff --git a/src/test/ui/borrowck/borrowck-borrow-overloaded-deref.rs b/src/test/ui/borrowck/borrowck-borrow-overloaded-deref.rs
index 39fa70c4e59..2b98a7b9483 100644
--- a/src/test/ui/borrowck/borrowck-borrow-overloaded-deref.rs
+++ b/src/test/ui/borrowck/borrowck-borrow-overloaded-deref.rs
@@ -2,18 +2,7 @@
 // Deref and not DerefMut is implemented.
 
 use std::ops::Deref;
-
-struct Rc<T> {
-    value: *const T
-}
-
-impl<T> Deref for Rc<T> {
-    type Target = T;
-
-    fn deref<'a>(&'a self) -> &'a T {
-        unsafe { &*self.value }
-    }
-}
+use std::rc::Rc;
 
 fn deref_imm(x: Rc<isize>) {
     let __isize = &*x;
diff --git a/src/test/ui/borrowck/borrowck-borrow-overloaded-deref.stderr b/src/test/ui/borrowck/borrowck-borrow-overloaded-deref.stderr
index 1755b22f59d..8cacc29414d 100644
--- a/src/test/ui/borrowck/borrowck-borrow-overloaded-deref.stderr
+++ b/src/test/ui/borrowck/borrowck-borrow-overloaded-deref.stderr
@@ -1,44 +1,58 @@
-error[E0596]: cannot borrow data in a `&` reference as mutable
-  --> $DIR/borrowck-borrow-overloaded-deref.rs:23:19
+error[E0596]: cannot borrow data in an `Rc` as mutable
+  --> $DIR/borrowck-borrow-overloaded-deref.rs:12:19
    |
 LL |     let __isize = &mut *x;
    |                   ^^^^^^^ cannot borrow as mutable
+   |
+   = help: trait `DerefMut` is required to modify through a dereference, but it is not implemented for `std::rc::Rc<isize>`
 
-error[E0596]: cannot borrow data in a `&` reference as mutable
-  --> $DIR/borrowck-borrow-overloaded-deref.rs:27:19
+error[E0596]: cannot borrow data in an `Rc` as mutable
+  --> $DIR/borrowck-borrow-overloaded-deref.rs:16:19
    |
 LL |     let __isize = &mut *x;
    |                   ^^^^^^^ cannot borrow as mutable
+   |
+   = help: trait `DerefMut` is required to modify through a dereference, but it is not implemented for `std::rc::Rc<isize>`
 
-error[E0596]: cannot borrow data in a `&` reference as mutable
-  --> $DIR/borrowck-borrow-overloaded-deref.rs:35:5
+error[E0596]: cannot borrow data in an `Rc` as mutable
+  --> $DIR/borrowck-borrow-overloaded-deref.rs:24:5
    |
 LL |     &mut **x
    |     ^^^^^^^^ cannot borrow as mutable
+   |
+   = help: trait `DerefMut` is required to modify through a dereference, but it is not implemented for `std::rc::Rc<isize>`
 
-error[E0596]: cannot borrow data in a `&` reference as mutable
-  --> $DIR/borrowck-borrow-overloaded-deref.rs:39:5
+error[E0596]: cannot borrow data in an `Rc` as mutable
+  --> $DIR/borrowck-borrow-overloaded-deref.rs:28:5
    |
 LL |     &mut **x
    |     ^^^^^^^^ cannot borrow as mutable
+   |
+   = help: trait `DerefMut` is required to modify through a dereference, but it is not implemented for `std::rc::Rc<isize>`
 
-error[E0594]: cannot assign to data in a `&` reference
-  --> $DIR/borrowck-borrow-overloaded-deref.rs:43:5
+error[E0594]: cannot assign to data in an `Rc`
+  --> $DIR/borrowck-borrow-overloaded-deref.rs:32:5
    |
 LL |     *x = 3;
    |     ^^^^^^ cannot assign
+   |
+   = help: trait `DerefMut` is required to modify through a dereference, but it is not implemented for `std::rc::Rc<isize>`
 
-error[E0594]: cannot assign to data in a `&` reference
-  --> $DIR/borrowck-borrow-overloaded-deref.rs:47:5
+error[E0594]: cannot assign to data in an `Rc`
+  --> $DIR/borrowck-borrow-overloaded-deref.rs:36:5
    |
 LL |     **x = 3;
    |     ^^^^^^^ cannot assign
+   |
+   = help: trait `DerefMut` is required to modify through a dereference, but it is not implemented for `std::rc::Rc<isize>`
 
-error[E0594]: cannot assign to data in a `&` reference
-  --> $DIR/borrowck-borrow-overloaded-deref.rs:51:5
+error[E0594]: cannot assign to data in an `Rc`
+  --> $DIR/borrowck-borrow-overloaded-deref.rs:40:5
    |
 LL |     **x = 3;
    |     ^^^^^^^ cannot assign
+   |
+   = help: trait `DerefMut` is required to modify through a dereference, but it is not implemented for `std::rc::Rc<isize>`
 
 error: aborting due to 7 previous errors
 
diff --git a/src/test/ui/borrowck/borrowck-overloaded-index-ref-index.rs b/src/test/ui/borrowck/borrowck-overloaded-index-ref-index.rs
index cb20873432b..8adafaa8e93 100644
--- a/src/test/ui/borrowck/borrowck-overloaded-index-ref-index.rs
+++ b/src/test/ui/borrowck/borrowck-overloaded-index-ref-index.rs
@@ -54,6 +54,6 @@ fn main() {
         x: 1,
     };
     s[2] = 20;
-    //~^ ERROR cannot assign to data in a `&` reference
+    //~^ ERROR cannot assign to data in an index of `Bar`
     drop(rs);
 }
diff --git a/src/test/ui/borrowck/borrowck-overloaded-index-ref-index.stderr b/src/test/ui/borrowck/borrowck-overloaded-index-ref-index.stderr
index fcbfe72a34b..84fe17d8544 100644
--- a/src/test/ui/borrowck/borrowck-overloaded-index-ref-index.stderr
+++ b/src/test/ui/borrowck/borrowck-overloaded-index-ref-index.stderr
@@ -21,11 +21,13 @@ LL |     f[&s] = 10;
 LL |     drop(rs);
    |          -- mutable borrow later used here
 
-error[E0594]: cannot assign to data in a `&` reference
+error[E0594]: cannot assign to data in an index of `Bar`
   --> $DIR/borrowck-overloaded-index-ref-index.rs:56:5
    |
 LL |     s[2] = 20;
    |     ^^^^^^^^^ cannot assign
+   |
+   = help: trait `IndexMut` is required to modify indexed content, but it is not implemented for `Bar`
 
 error: aborting due to 3 previous errors
 
diff --git a/src/test/ui/borrowck/index-mut-help-with-impl.stderr b/src/test/ui/borrowck/index-mut-help-with-impl.stderr
index 4b29beb02b3..89391f4099a 100644
--- a/src/test/ui/borrowck/index-mut-help-with-impl.stderr
+++ b/src/test/ui/borrowck/index-mut-help-with-impl.stderr
@@ -3,8 +3,6 @@ error[E0596]: cannot borrow data in a `&` reference as mutable
    |
 LL |     Index::index(&v, 1..2).make_ascii_uppercase();
    |     ^^^^^^^^^^^^^^^^^^^^^^ cannot borrow as mutable
-   |
-   = help: trait `IndexMut` is required to modify indexed content
 
 error: aborting due to previous error
 
diff --git a/src/test/ui/borrowck/index-mut-help.stderr b/src/test/ui/borrowck/index-mut-help.stderr
index fbc427a6e6d..47f2171f88c 100644
--- a/src/test/ui/borrowck/index-mut-help.stderr
+++ b/src/test/ui/borrowck/index-mut-help.stderr
@@ -1,4 +1,4 @@
-error[E0596]: cannot borrow data in a `&` reference as mutable
+error[E0596]: cannot borrow data in an index of `std::collections::HashMap<&str, std::string::String>` as mutable
   --> $DIR/index-mut-help.rs:11:5
    |
 LL |     map["peter"].clear();
@@ -6,13 +6,15 @@ LL |     map["peter"].clear();
    |
    = 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
+error[E0594]: cannot assign to data in an index of `std::collections::HashMap<&str, std::string::String>`
   --> $DIR/index-mut-help.rs:12:5
    |
 LL |     map["peter"] = "0".to_string();
    |     ^^^^^^^^^^^^ cannot assign
+   |
+   = help: trait `IndexMut` is required to modify indexed content, but it is not implemented for `std::collections::HashMap<&str, std::string::String>`
 
-error[E0596]: cannot borrow data in a `&` reference as mutable
+error[E0596]: cannot borrow data in an index of `std::collections::HashMap<&str, std::string::String>` as mutable
   --> $DIR/index-mut-help.rs:13:13
    |
 LL |     let _ = &mut map["peter"];
diff --git a/src/test/ui/issues/issue-41726.rs b/src/test/ui/issues/issue-41726.rs
index ed056293890..39631912c00 100644
--- a/src/test/ui/issues/issue-41726.rs
+++ b/src/test/ui/issues/issue-41726.rs
@@ -2,6 +2,6 @@ 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 data in a `&` reference as mutable
+        things[src.as_str()].sort(); //~ ERROR cannot borrow data in an index of
     }
 }
diff --git a/src/test/ui/issues/issue-41726.stderr b/src/test/ui/issues/issue-41726.stderr
index c92753d6e3d..aa7f23511dd 100644
--- a/src/test/ui/issues/issue-41726.stderr
+++ b/src/test/ui/issues/issue-41726.stderr
@@ -1,4 +1,4 @@
-error[E0596]: cannot borrow data in a `&` reference as mutable
+error[E0596]: cannot borrow data in an index of `std::collections::HashMap<std::string::String, std::vec::Vec<std::string::String>>` as mutable
   --> $DIR/issue-41726.rs:5:9
    |
 LL |         things[src.as_str()].sort();