Extra typechecks or simple diagnostics on Swift code

Inspiration

Generating Diagnostics for Unintentional Optionals in String Interpolation https://github.com/apple/swift/pull/5248/files

I'd like to learn to implement similar diagnostics checks.

What it does

compiler generates warnings for with some specific special conditions:

try Swift()
try? Swift()

but does not generate warnings for this case:

try! Swift()

(It's not a simple string or regex matching!) Swift is not always literally Swift. but conforming to SwiftConf protocol is needed to be checked by this diagnostics.

A full example input swift file.

protocol Conf {}

struct Swift: Conf {
  init() throws {  }
}

struct Riko {
  init() throws {  }
}

_ = try Swift() // diagnostics warning: use try! Swift
_ = try? Swift() // diagnostics warning: use try! Swift
_ = try! Swift()
_ = try? Riko()

func f() throws {
  _ = try Swift() // diagnostics warning: use try! Swift
  _ = try? Swift() // diagnostics warning: use try! Swift
  _ = try! Swift()
  _ = try? Riko()
}

/Users/banjun/Downloads/tryswiftchecked.swift:11:5: warning: use try! Swift
_ = try Swift()
    ^~~~~~~~~~~
/Users/banjun/Downloads/tryswiftchecked.swift:12:5: warning: use try! Swift
_ = try? Swift()
    ^~~~~~~~~~~~
/Users/banjun/Downloads/tryswiftchecked.swift:17:7: warning: use try! Swift
  _ = try Swift()
      ^~~~~~~~~~~
/Users/banjun/Downloads/tryswiftchecked.swift:18:7: warning: use try! Swift
  _ = try? Swift()
      ^~~~~~~~~~~~