Only refer to return type when it matches

src/librustc/hir/map/mod.rs

@@ -664,7 +664,7 @@ impl<'hir> Map<'hir> {
             match *node {
                 NodeExpr(ref expr) => {
                     match expr.node {
-                        ExprWhile(..) | ExprLoop(..) | ExprIf(..) => true,
+                        ExprWhile(..) | ExprLoop(..) => true,
                         _ => false,
                     }
                 }

src/librustc_typeck/check/mod.rs

@@ -95,7 +95,7 @@ use rustc::middle::region::CodeExtent;
 use rustc::ty::subst::{Kind, Subst, Substs};
 use rustc::traits::{self, FulfillmentContext, ObligationCause, ObligationCauseCode};
 use rustc::ty::{ParamTy, LvaluePreference, NoPreference, PreferMutLvalue};
-use rustc::ty::{self, Ty, TyCtxt, Visibility};
+use rustc::ty::{self, Ty, TyCtxt, Visibility, TypeVariants};
 use rustc::ty::adjustment::{Adjust, Adjustment, AutoBorrow};
 use rustc::ty::fold::{BottomUpFolder, TypeFoldable};
 use rustc::ty::maps::Providers;
@@ -4302,7 +4302,6 @@ impl<'a, 'gcx, 'tcx> FnCtxt<'a, 'gcx, 'tcx> {
                                    expected: Ty<'tcx>,
                                    found: Ty<'tcx>,
                                    can_suggest: bool) {
-
         // Only suggest changing the return type for methods that
         // haven't set a return type at all (and aren't `fn main()` or an impl).
         match (&fn_decl.output, found.is_suggestable(), can_suggest) {
@@ -4316,13 +4315,31 @@ impl<'a, 'gcx, 'tcx> FnCtxt<'a, 'gcx, 'tcx> {
             }
             (&hir::FunctionRetTy::DefaultReturn(span), _, _) => {
                 // `fn main()` must return `()`, do not suggest changing return type
-                err.span_label(span, "expected `()` because of default return type");
+                err.span_label(span, "expected () because of default return type");
             }
             (&hir::FunctionRetTy::Return(ref ty), _, _) => {
                 // Only point to return type if the expected type is the return type, as if they
                 // are not, the expectation must have been caused by something else.
-                err.span_label(ty.span,
-                               format!("expected `{}` because of return type", expected));
+                debug!("suggest_missing_return_type: return type {:?} node {:?}", ty, ty.node);
+                let sp = ty.span;
+                let ty = AstConv::ast_ty_to_ty(self, ty);
+                debug!("suggest_missing_return_type: return type sty {:?}", ty.sty);
+                debug!("suggest_missing_return_type: expected type sty {:?}", ty.sty);
+                if ty.sty == expected.sty {
+                    let quote = if let TypeVariants::TyTuple(ref slice, _) = expected.sty {
+                        if slice.len() == 0 {  // don't use backtics for ()
+                            ""
+                        } else {
+                            "`"
+                        }
+                    } else {
+                        "`"
+                    };
+                    err.span_label(sp, format!("expected {}{}{} because of return type",
+                                               quote,
+                                               expected,
+                                               quote));
+                }
             }
         }
     }

src/test/ui/block-result/block-must-not-have-result-res.stderr

@@ -2,7 +2,7 @@ error[E0308]: mismatched types
   --> $DIR/block-must-not-have-result-res.rs:15:9
    |
 14 |     fn drop(&mut self) {
-   |                        - expected `()` because of default return type
+   |                        - expected () because of default return type
 15 |         true //~  ERROR mismatched types
    |         ^^^^ expected (), found bool
    |

src/test/ui/block-result/issue-13624.stderr

@@ -2,7 +2,7 @@ error[E0308]: mismatched types
   --> $DIR/issue-13624.rs:17:5
    |
 16 |   pub fn get_enum_struct_variant() -> () {
-   |                                       -- expected `()` because of return type
+   |                                       -- expected () because of return type
 17 |     Enum::EnumStructVariant { x: 1, y: 2, z: 3 }
    |     ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ expected (), found enum `a::Enum`
    |

src/test/ui/block-result/issue-22645.stderr

@@ -12,7 +12,7 @@ error[E0308]: mismatched types
   --> $DIR/issue-22645.rs:25:3
    |
 23 | fn main() {
-   |           - expected `()` because of default return type
+   |           - expected () because of default return type
 24 |   let b = Bob + 3.5;
 25 |   b + 3 //~ ERROR E0277
    |   ^^^^^ expected (), found struct `Bob`

src/test/ui/block-result/issue-5500.stderr

@@ -2,7 +2,7 @@ error[E0308]: mismatched types
   --> $DIR/issue-5500.rs:12:5
    |
 11 | fn main() {
-   |           - expected `()` because of default return type
+   |           - expected () because of default return type
 12 |     &panic!()
    |     ^^^^^^^^^ expected (), found reference
    |

src/test/ui/impl-trait/equality.stderr

@@ -1,9 +1,6 @@
 error[E0308]: mismatched types
   --> $DIR/equality.rs:25:5
    |
-21 | fn two(x: bool) -> impl Foo {
-   |                    -------- expected `_` because of return type
-...
 25 |     0_u32
    |     ^^^^^ expected i32, found u32
    |