Merge #10798

10798: ide: show go to for function hover return type r=Veykril a=jhgg

I've found myself wanting this...  adds to the hover quick go-to for a function's return type:

![image](https://user-images.githubusercontent.com/5489149/142375722-4a385216-494b-45a4-be1c-59664213b8d6.png)

This is particularly useful when you are hovering over a function in a long chain, like:

```rust
foo.bar().b$0az().some_trait_fn();
```

where `baz`'s return type is not immediately obvious, but the chain is not long enough to trigger chain inlay hints... 

i guess I could just select `foo.bar().baz()` too to get the types too... 

Co-authored-by: Jake Heinz <jh@discordapp.com>

crates/ide/src/hover.rs

@@ -314,6 +314,7 @@ fn goto_type_action_for_def(db: &RootDatabase, def: Definition) -> Option<HoverA
             Definition::Local(it) => it.ty(db),
             Definition::GenericParam(hir::GenericParam::ConstParam(it)) => it.ty(db),
             Definition::Field(field) => field.ty(db),
+            Definition::Function(function) => function.ret_type(db),
             _ => return None,
         };
 

crates/ide/src/hover/tests.rs

@@ -1750,6 +1750,9 @@ fn foo_$0test() {}
                         cfg: None,
                     },
                 ),
+                GoToType(
+                    [],
+                ),
             ]
         "#]],
     );