[SR-9201] Incorrect error message when using optional chaining

[bjhomer]

Previous ID	SR-9201
Radar	None
Original Reporter	@bjhomer
Type	Bug
Status	Resolved
Resolution	Done

Environment

Swift 4.2
Swift 5 (master, as of Nov 6, 2018)

Additional Detail from JIRA

Votes	0
Component/s	Compiler
Labels	Bug, DiagnosticsQoI, StarterBug
Assignee	@bjhomer
Priority	Medium

md5: c734879d228c03881746c3e4d483304a

Issue Description:

An incorrect error message is produced here:

struct Thing {
  func produceDoubleOptional() -> Int?? { return 3 }
}

let optThing: Thing? = Thing()

// error: Value of optional type 'Int?' must be unwrapped to a value of type 'Int'
let _: Int? = optThing?.produceDoubleOptional()

The error is suggesting a change like this:

let _: Int? = (optThing?.produceDoubleOptional())!

But

[belkadan]

cc @xedin. Starter bug?

[xedin]

I actually don't think it's a problem because the contextual type is `Int?` which matches what `(optThing?.produceDoubleOptional())!` is going to produce by unwrapping one level of optional from `Int??`. @bjhomer Could you please clarify what seems to be the issue here?

[belkadan]

The message is wrong, not the fix-it.

[bjhomer]

It's telling me that I need to turn an `Int?` into an `Int`, when I actually need to turn an `Int??` into an `Int?`. There is no reason the compiler should telling me something needs to be unwrapped into an plain `Int` here, because nothing requires a plain `Int`.

[xedin]

@bjhomer Ah the error message itself, I see, sorry! Yes, that's definitely a starter bug.

[xedin]

@bjhomer Issue has been resolved by #22050 thanks to @theblixguy for contribution! Please use next available snapshot to verify.