11173: Allow adding partially resolved types r=Veykril a=SomeoneToIgnore Sometimes when writing something like `let foo = Arc::new(Mutex::new(CrazyGenerics::new(HashMap::new())))`, I want/have to specify an explicit type for the expression. Using turbofish isn't very readable and not always appreciated by guidelines, so `let foo: T` has to be filled. To ease that, the PR enables the `add_explicit_type` assist on types that contain unknown types and some generics. Fully unresolved types, arrays with unknown types and other known cases behave the same. `_` placeholder was chosen to replace an unknown type: ```rust let foo = HashMap::new(); // after assist usage, turns into let foo: HashMap<_, _> = HashMap::new(); ``` Co-authored-by: Kirill Bulatov <[email protected]>