intellij-rust: Quick fixes on type mismatch

A very basic type checking just merged #1727 Now it’s possible to attach quick fixes to a type mismatch annotations (on this line). I can imagine the following quick fixes (we assume that A is actual type, B is expected type and so a is a var of type A. e.g. let a: A = ...; let _: B = a;):

Coercions:

• If both types are numerics, we can suggest to add a cast a as B.
• We can have a set of special cases like str.to_string()/String.as_str()
• We can try to find impl From<A> for B, and if it is exists, suggest B::from(a)
• From is not the one type conversion trait. We can also deal with ToOwned/AsRef/AsMut/Borrow/BorrowMut or even TryFrom/FromStr
• We can try to deref *a to match required type
• We can also get more references &a/&mut a
• And any combinations of these, like &*a
• Or even &S::from(*a)

Refactorings:

• Suggest to change type of local variable/function/struct field etc. https://github.com/intellij-rust/intellij-rust/pull/5647
• Suggest to change (or add) return type in current function signature #1772

You can find examples of quick fixes in the org.rust.ide.annotator.fixes package.

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