Handle exclusive refs in suggestion to copy/clone

Author: clubby789

Diff for: compiler/rustc_hir_typeck/src/fn_ctxt/suggestions.rs

@@ -1110,7 +1110,7 @@ impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
         {
             let expr_inner_ty = args.type_at(0);
             let expected_inner_ty = expected_args.type_at(0);
-            if let &ty::Ref(_, ty, hir::Mutability::Not) = expr_inner_ty.kind()
+            if let &ty::Ref(_, ty, mutability) = expr_inner_ty.kind()
                     && self.can_eq(self.param_env, ty, expected_inner_ty)
                 {
                     let def_path = self.tcx.def_path_str(adt_def.did());
@@ -1119,7 +1119,11 @@ impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
                         errors::OptionResultRefMismatch::Copied {
                             span, def_path
                         }
-                    } else if let Some(expected_ty_expr) = expected_ty_expr {
+                    } else if let Some(expected_ty_expr) = expected_ty_expr
+                            // FIXME: suggest changes to both expressions to convert both to
+                            // Option/Result<&T>
+                            && mutability.is_not()
+                        {
                         errors::OptionResultRefMismatch::AsRef {
                             span: expected_ty_expr.span.shrink_to_hi(), expected_ty, expr_ty, def_path
                         }

Diff for: tests/ui/suggestions/copied-and-cloned.fixed

@@ -28,4 +28,18 @@ fn main() {
     //~^ ERROR mismatched types
     //~| HELP use `Option::as_ref` to convert `Option<String>` to `Option<&String>`
 
+
+    let mut s = ();
+    let x = Some(s);
+    let y = Some(&mut s);
+    println!("{}", x == y.copied());
+    //~^ ERROR mismatched types
+    //~| HELP use `Option::copied` to copy the value inside the `Option`
+
+    let mut s = String::new();
+    let x = Some(s.clone());
+    let y = Some(&mut s);
+    println!("{}", x == y.cloned());
+    //~^ ERROR mismatched types
+    //~| HELP use `Option::cloned` to clone the value inside the `Option`
 }

Diff for: tests/ui/suggestions/copied-and-cloned.rs

@@ -28,4 +28,18 @@ fn main() {
     //~^ ERROR mismatched types
     //~| HELP use `Option::as_ref` to convert `Option<String>` to `Option<&String>`
 
+
+    let mut s = ();
+    let x = Some(s);
+    let y = Some(&mut s);
+    println!("{}", x == y);
+    //~^ ERROR mismatched types
+    //~| HELP use `Option::copied` to copy the value inside the `Option`
+
+    let mut s = String::new();
+    let x = Some(s.clone());
+    let y = Some(&mut s);
+    println!("{}", x == y);
+    //~^ ERROR mismatched types
+    //~| HELP use `Option::cloned` to clone the value inside the `Option`
 }

Diff for: tests/ui/suggestions/copied-and-cloned.stderr

@@ -91,6 +91,32 @@ help: use `Option::as_ref` to convert `Option<String>` to `Option<&String>`
 LL |     println!("{}", x.as_ref() == y);
    |                     +++++++++
 
-error: aborting due to 5 previous errors
+error[E0308]: mismatched types
+  --> $DIR/copied-and-cloned.rs:35:25
+   |
+LL |     println!("{}", x == y);
+   |                         ^ expected `Option<()>`, found `Option<&mut ()>`
+   |
+   = note: expected enum `Option<()>`
+              found enum `Option<&mut ()>`
+help: use `Option::copied` to copy the value inside the `Option`
+   |
+LL |     println!("{}", x == y.copied());
+   |                          +++++++++
+
+error[E0308]: mismatched types
+  --> $DIR/copied-and-cloned.rs:42:25
+   |
+LL |     println!("{}", x == y);
+   |                         ^ expected `Option<String>`, found `Option<&mut String>`
+   |
+   = note: expected enum `Option<String>`
+              found enum `Option<&mut String>`
+help: use `Option::cloned` to clone the value inside the `Option`
+   |
+LL |     println!("{}", x == y.cloned());
+   |                          +++++++++
+
+error: aborting due to 7 previous errors
 
 For more information about this error, try `rustc --explain E0308`.