Point at return type when appropriate

Author: estebank

src/librustc_typeck/check/coercion.rs

@@ -1250,14 +1250,26 @@ impl<'gcx, 'tcx, 'exprs, E> CoerceMany<'gcx, 'tcx, 'exprs, E>
                             }
                         }
                     }
-                    _ => {
+                    ObligationCauseCode::ReturnType(_id) => {
                         db = fcx.report_mismatched_types(cause, expected, found, err);
-                        if let Some(sp) = fcx.ret_coercion_span.borrow().as_ref() {
+                        let _id = fcx.tcx.hir().get_parent_node(_id);
+                        let mut pointing_at_return_type = false;
+                        if let Some((fn_decl, can_suggest)) = fcx.get_fn_decl(_id) {
+                            pointing_at_return_type = fcx.suggest_missing_return_type(
+                                &mut db, &fn_decl, expected, found, can_suggest);
+                        }
+                        if let (Some(sp), false) = (
+                            fcx.ret_coercion_span.borrow().as_ref(),
+                            pointing_at_return_type,
+                        ) {
                             if !sp.overlaps(cause.span) {
                                 db.span_label(*sp, reason_label);
                             }
                         }
                     }
+                    _ => {
+                        db = fcx.report_mismatched_types(cause, expected, found, err);
+                    }
                 }
 
                 if let Some(augment_error) = augment_error {

src/test/ui/fully-qualified-type/fully-qualified-type-name2.stderr

@@ -1,6 +1,8 @@
 error[E0308]: mismatched types
   --> $DIR/fully-qualified-type-name2.rs:12:12
    |
+LL | fn bar(x: x::Foo) -> y::Foo {
+   |                      ------ expected `y::Foo` because of return type
 LL |     return x;
    |            ^ expected enum `y::Foo`, found enum `x::Foo`
    |

src/test/ui/fully-qualified-type/fully-qualified-type-name4.stderr

@@ -1,6 +1,8 @@
 error[E0308]: mismatched types
   --> $DIR/fully-qualified-type-name4.rs:6:12
    |
+LL | fn bar(x: usize) -> Option<usize> {
+   |                     ------------- expected `std::option::Option<usize>` because of return type
 LL |     return x;
    |            ^ expected enum `std::option::Option`, found usize
    |

src/test/ui/liveness/liveness-forgot-ret.stderr

@@ -2,7 +2,7 @@ error[E0308]: mismatched types
   --> $DIR/liveness-forgot-ret.rs:3:19
    |
 LL | fn f(a: isize) -> isize { if god_exists(a) { return 5; }; }
-   |    -              ^^^^^ expected isize, found ()    - expected because of this statement
+   |    -              ^^^^^ expected isize, found ()
    |    |
    |    this function's body doesn't return
    |

src/test/ui/proc-macro/span-preservation.stderr

@@ -15,6 +15,9 @@ LL |     let x: usize = "hello";;;;; //~ ERROR mismatched types
 error[E0308]: mismatched types
   --> $DIR/span-preservation.rs:19:29
    |
+LL | fn b(x: Option<isize>) -> usize {
+   |                           ----- expected `usize` because of return type
+LL |     match x {
 LL |         Some(x) => { return x }, //~ ERROR mismatched types
    |                             ^ expected usize, found isize
 

src/test/ui/return/return-from-diverging.stderr

@@ -1,6 +1,8 @@
 error[E0308]: mismatched types
   --> $DIR/return-from-diverging.rs:4:12
    |
+LL | fn fail() -> ! {
+   |              - expected `!` because of return type
 LL |     return "wow"; //~ ERROR mismatched types
    |            ^^^^^ expected !, found reference
    |

src/test/ui/tail-typeck.stderr

@@ -2,7 +2,9 @@ error[E0308]: mismatched types
   --> $DIR/tail-typeck.rs:3:26
    |
 LL | fn f() -> isize { return g(); }
-   |                          ^^^ expected isize, found usize
+   |           -----          ^^^ expected isize, found usize
+   |           |
+   |           expected `isize` because of return type
 
 error: aborting due to previous error
 

src/test/ui/wrong-ret-type.stderr

@@ -2,7 +2,9 @@ error[E0308]: mismatched types
   --> $DIR/wrong-ret-type.rs:2:49
    |
 LL | fn mk_int() -> usize { let i: isize = 3; return i; }
-   |                                                 ^ expected usize, found isize
+   |                -----                            ^ expected usize, found isize
+   |                |
+   |                expected `usize` because of return type
 
 error: aborting due to previous error