Use suggestions instead of notes ref mismatches

On type mismatch errors, use a suggestion when encountering minimal
differences in type differences due to refs, instead of a note.

src/librustc_typeck/check/demand.rs

@@ -134,10 +134,8 @@ pub fn demand_coerce_diag(&self,
             }
         }
 
-        if let Some(suggestion) = self.check_ref(expr,
-                                                 checked_ty,
-                                                 expected) {
-            err.help(&suggestion);
+        if let Some((msg, suggestion)) = self.check_ref(expr, checked_ty, expected) {
+            err.span_suggestion(expr.span, msg, suggestion);
         } else {
             let mode = probe::Mode::MethodCall;
             let suggestions = self.probe_for_return_type(syntax_pos::DUMMY_SP,
@@ -214,7 +212,7 @@ fn check_ref(&self,
                  expr: &hir::Expr,
                  checked_ty: Ty<'tcx>,
                  expected: Ty<'tcx>)
-                 -> Option<String> {
+                 -> Option<(&'static str, String)> {
         match (&expected.sty, &checked_ty.sty) {
             (&ty::TyRef(_, exp), &ty::TyRef(_, check)) => match (&exp.ty.sty, &check.ty.sty) {
                 (&ty::TyStr, &ty::TyArray(arr, _)) |
@@ -222,7 +220,8 @@ fn check_ref(&self,
                     if let hir::ExprLit(_) = expr.node {
                         let sp = self.sess().codemap().call_span_if_macro(expr.span);
                         if let Ok(src) = self.tcx.sess.codemap().span_to_snippet(sp) {
-                            return Some(format!("try `{}`", &src[1..]));
+                            return Some(("consider removing the leading `b`",
+                                         src[1..].to_string()));
                         }
                     }
                     None
@@ -232,7 +231,8 @@ fn check_ref(&self,
                     if let hir::ExprLit(_) = expr.node {
                         let sp = self.sess().codemap().call_span_if_macro(expr.span);
                         if let Ok(src) = self.tcx.sess.codemap().span_to_snippet(sp) {
-                            return Some(format!("try `b{}`", src));
+                            return Some(("consider adding a leading `b`",
+                                         format!("b{}", src)));
                         }
                     }
                     None
@@ -260,12 +260,14 @@ fn check_ref(&self,
                     // Use the callsite's span if this is a macro call. #41858
                     let sp = self.sess().codemap().call_span_if_macro(expr.span);
                     if let Ok(src) = self.tcx.sess.codemap().span_to_snippet(sp) {
-                        return Some(format!("try with `{}{}`",
-                                            match mutability.mutbl {
-                                                hir::Mutability::MutMutable => "&mut ",
-                                                hir::Mutability::MutImmutable => "&",
-                                            },
-                                            &src));
+                        return Some(match mutability.mutbl {
+                            hir::Mutability::MutMutable => {
+                                ("consider mutably borrowing here", format!("&mut {}", src))
+                            }
+                            hir::Mutability::MutImmutable => {
+                                ("consider borrowing here", format!("&{}", src))
+                            }
+                        });
                     }
                 }
                 None
@@ -284,7 +286,8 @@ fn check_ref(&self,
                         // Maybe remove `&`?
                         hir::ExprAddrOf(_, ref expr) => {
                             if let Ok(code) = self.tcx.sess.codemap().span_to_snippet(expr.span) {
-                                return Some(format!("try with `{}`", code));
+                                return Some(("consider removing the borrow",
+                                             code));
                             }
                         }
 
@@ -295,7 +298,8 @@ fn check_ref(&self,
                                                                 expr.span) {
                                 let sp = self.sess().codemap().call_span_if_macro(expr.span);
                                 if let Ok(code) = self.tcx.sess.codemap().span_to_snippet(sp) {
-                                    return Some(format!("try with `*{}`", code));
+                                    return Some(("consider dereferencing the borrow",
+                                                 format!("*{}", code)));
                                 }
                             }
                         },

src/test/compile-fail/issue-13058.rs

@@ -35,5 +35,5 @@ fn check<'r, I: Iterator<Item=usize>, T: Itble<'r, usize, I>>(cont: &T) -> bool
 fn main() {
     check((3, 5));
 //~^ ERROR mismatched types
-//~| HELP try with `&(3, 5)`
+//~| HELP consider borrowing here
 }

src/test/ui/deref-suggestion.stderr

@@ -17,31 +17,37 @@ error[E0308]: mismatched types
   --> $DIR/deref-suggestion.rs:23:10
    |
 23 |     foo3(u); //~ ERROR mismatched types
-   |          ^ expected u32, found &u32
+   |          ^
+   |          |
+   |          expected u32, found &u32
+   |          help: consider dereferencing the borrow: `*u`
    |
    = note: expected type `u32`
               found type `&u32`
-   = help: try with `*u`
 
 error[E0308]: mismatched types
   --> $DIR/deref-suggestion.rs:30:9
    |
 30 |     foo(&"aaa".to_owned()); //~ ERROR mismatched types
-   |         ^^^^^^^^^^^^^^^^^ expected struct `std::string::String`, found reference
+   |         ^^^^^^^^^^^^^^^^^
+   |         |
+   |         expected struct `std::string::String`, found reference
+   |         help: consider removing the borrow: `"aaa".to_owned()`
    |
    = note: expected type `std::string::String`
               found type `&std::string::String`
-   = help: try with `"aaa".to_owned()`
 
 error[E0308]: mismatched types
   --> $DIR/deref-suggestion.rs:31:9
    |
 31 |     foo(&mut "aaa".to_owned()); //~ ERROR mismatched types
-   |         ^^^^^^^^^^^^^^^^^^^^^ expected struct `std::string::String`, found mutable reference
+   |         ^^^^^^^^^^^^^^^^^^^^^
+   |         |
+   |         expected struct `std::string::String`, found mutable reference
+   |         help: consider removing the borrow: `"aaa".to_owned()`
    |
    = note: expected type `std::string::String`
               found type `&mut std::string::String`
-   = help: try with `"aaa".to_owned()`
 
 error[E0308]: mismatched types
   --> $DIR/deref-suggestion.rs:12:20

src/test/ui/span/coerce-suggestions.rs

@@ -23,7 +23,7 @@ fn main() {
     //~^ ERROR E0308
     //~| NOTE expected &str, found struct `std::string::String`
     //~| NOTE expected type `&str`
-    //~| HELP try with `&String::new()`
+    //~| HELP consider borrowing here
     let y = String::new();
     test(&y);
     //~^ ERROR E0308

src/test/ui/span/coerce-suggestions.stderr

@@ -14,11 +14,13 @@ error[E0308]: mismatched types
   --> $DIR/coerce-suggestions.rs:22:19
    |
 22 |     let x: &str = String::new();
-   |                   ^^^^^^^^^^^^^ expected &str, found struct `std::string::String`
+   |                   ^^^^^^^^^^^^^
+   |                   |
+   |                   expected &str, found struct `std::string::String`
+   |                   help: consider borrowing here: `&String::new()`
    |
    = note: expected type `&str`
               found type `std::string::String`
-   = help: try with `&String::new()`
 
 error[E0308]: mismatched types
   --> $DIR/coerce-suggestions.rs:28:10
@@ -48,11 +50,13 @@ error[E0308]: mismatched types
   --> $DIR/coerce-suggestions.rs:42:9
    |
 42 |     s = format!("foo");
-   |         ^^^^^^^^^^^^^^ expected mutable reference, found struct `std::string::String`
+   |         ^^^^^^^^^^^^^^
+   |         |
+   |         expected mutable reference, found struct `std::string::String`
+   |         help: consider mutably borrowing here: `&mut format!("foo")`
    |
    = note: expected type `&mut std::string::String`
               found type `std::string::String`
-   = help: try with `&mut format!("foo")`
    = note: this error originates in a macro outside of the current crate (in Nightly builds, run with -Z external-macro-backtrace for more info)
 
 error: aborting due to 6 previous errors

src/test/ui/str-lit-type-mismatch.stderr

@@ -2,31 +2,37 @@ error[E0308]: mismatched types
   --> $DIR/str-lit-type-mismatch.rs:13:20
    |
 13 |     let x: &[u8] = "foo"; //~ ERROR mismatched types
-   |                    ^^^^^ expected slice, found str
+   |                    ^^^^^
+   |                    |
+   |                    expected slice, found str
+   |                    help: consider adding a leading `b`: `b"foo"`
    |
    = note: expected type `&[u8]`
               found type `&'static str`
-   = help: try `b"foo"`
 
 error[E0308]: mismatched types
   --> $DIR/str-lit-type-mismatch.rs:14:23
    |
 14 |     let y: &[u8; 4] = "baaa"; //~ ERROR mismatched types
-   |                       ^^^^^^ expected array of 4 elements, found str
+   |                       ^^^^^^
+   |                       |
+   |                       expected array of 4 elements, found str
+   |                       help: consider adding a leading `b`: `b"baaa"`
    |
    = note: expected type `&[u8; 4]`
               found type `&'static str`
-   = help: try `b"baaa"`
 
 error[E0308]: mismatched types
   --> $DIR/str-lit-type-mismatch.rs:15:19
    |
 15 |     let z: &str = b"foo"; //~ ERROR mismatched types
-   |                   ^^^^^^ expected str, found array of 3 elements
+   |                   ^^^^^^
+   |                   |
+   |                   expected str, found array of 3 elements
+   |                   help: consider removing the leading `b`: `"foo"`
    |
    = note: expected type `&str`
               found type `&'static [u8; 3]`
-   = help: try `"foo"`
 
 error: aborting due to 3 previous errors
 

src/test/ui/suggestions/str-array-assignment.rs

@@ -28,5 +28,5 @@ fn main() { //~ NOTE expected `()` because of default return type
   //~^ ERROR mismatched types
   //~| NOTE expected &str, found str
   //~| NOTE expected type
-  //~| HELP try with `&s[..2]`
+  //~| HELP consider borrowing here
 }

src/test/ui/suggestions/str-array-assignment.stderr

@@ -34,11 +34,13 @@ error[E0308]: mismatched types
   --> $DIR/str-array-assignment.rs:27:17
    |
 27 |   let w: &str = s[..2];
-   |                 ^^^^^^ expected &str, found str
+   |                 ^^^^^^
+   |                 |
+   |                 expected &str, found str
+   |                 help: consider borrowing here: `&s[..2]`
    |
    = note: expected type `&str`
               found type `str`
-   = help: try with `&s[..2]`
 
 error: aborting due to 4 previous errors