Put backticks around field names, types and paths in error messages

Added to `DispatchFromDyn` and `CoerceUnsized` error messages

Author: mikeyhew

src/librustc_typeck/coherence/builtin.rs

@@ -215,7 +215,7 @@ fn visit_implementation_of_dispatch_from_dyn<'a, 'tcx>(
                             &format!(
                                 "the trait `DispatchFromDyn` may only be implemented \
                                 for a coercion between structures with the same \
-                                definition; expected {}, found {}",
+                                definition; expected `{}`, found `{}`",
                                 source_path, target_path,
                             )
                         ).emit();
@@ -271,7 +271,7 @@ fn visit_implementation_of_dispatch_from_dyn<'a, 'tcx>(
                                 "currently, {} fields need coercions: {}",
                                 coerced_fields.len(),
                                 coerced_fields.iter().map(|field| {
-                                    format!("{} ({} to {})",
+                                    format!("`{}` (`{}` to `{}`)",
                                         field.ident,
                                         field.ty(tcx, substs_a),
                                         field.ty(tcx, substs_b),
@@ -398,7 +398,7 @@ pub fn coerce_unsized_info<'a, 'gcx>(gcx: TyCtxt<'a, 'gcx, 'gcx>,
                               E0377,
                               "the trait `CoerceUnsized` may only be implemented \
                                for a coercion between structures with the same \
-                               definition; expected {}, found {}",
+                               definition; expected `{}`, found `{}`",
                               source_path,
                               target_path);
                     return err_info;
@@ -503,7 +503,7 @@ pub fn coerce_unsized_info<'a, 'gcx>(gcx: TyCtxt<'a, 'gcx, 'gcx>,
                                       diff_fields.len(),
                                       diff_fields.iter()
                                           .map(|&(i, a, b)| {
-                                              format!("{} ({} to {})", fields[i].ident, a, b)
+                                              format!("`{}` (`{}` to `{}`)", fields[i].ident, a, b)
                                           })
                                           .collect::<Vec<_>>()
                                           .join(", ")));

src/test/ui/error-codes/E0375.stderr

@@ -5,7 +5,7 @@ LL | impl<T, U> CoerceUnsized<Foo<U, T>> for Foo<T, U> {}
    |            ^^^^^^^^^^^^^^^^^^^^^^^^ requires multiple coercions
    |
    = note: `CoerceUnsized` may only be implemented for a coercion between structures with one field being coerced
-   = note: currently, 2 fields need coercions: b (T to U), c (U to T)
+   = note: currently, 2 fields need coercions: `b` (`T` to `U`), `c` (`U` to `T`)
 
 error: aborting due to previous error
 

src/test/ui/invalid_dispatch_from_dyn_impls.stderr

@@ -19,7 +19,7 @@ LL | | {} //~^^^ ERROR [E0378]
    | |__^
    |
    = note: the trait `DispatchFromDyn` may only be implemented for a coercion between structures with a single field being coerced
-   = note: currently, 2 fields need coercions: ptr1 (*const T to *const U), ptr2 (*const T to *const U)
+   = note: currently, 2 fields need coercions: `ptr1` (`*const T` to `*const U`), `ptr2` (`*const T` to `*const U`)
 
 error[E0378]: the trait `DispatchFromDyn` may only be implemented for a coercion between structures with a single field being coerced, none found
   --> $DIR/invalid_dispatch_from_dyn_impls.rs:41:1

src/test/ui/issues/issue-26905.stderr

@@ -5,7 +5,7 @@ LL | impl<T: ?Sized + Unsize<U>, U: ?Sized> CoerceUnsized<MyRc<U>> for MyRc<T>{
    |                                        ^^^^^^^^^^^^^^^^^^^^^^ requires multiple coercions
    |
    = note: `CoerceUnsized` may only be implemented for a coercion between structures with one field being coerced
-   = note: currently, 2 fields need coercions: _ptr (*const T to *const U), _boo (NotPhantomData<T> to NotPhantomData<U>)
+   = note: currently, 2 fields need coercions: `_ptr` (`*const T` to `*const U`), `_boo` (`NotPhantomData<T>` to `NotPhantomData<U>`)
 
 error: aborting due to previous error