[SR-10199] Swift 5 Force unwrapped optional is getting warning of casting optional to Any

[swift-ci]

Previous ID	SR-10199
Radar	None
Original Reporter	murthyveda2000 (JIRA User)
Type	Bug
Status	Resolved
Resolution	Done

Additional Detail from JIRA

Votes	0
Component/s	Compiler
Labels	Bug, 5.0Regression, DiagnosticsQoI, StarterBug, TypeChecker
Assignee	@theblixguy
Priority	Medium

md5: 4fa37f2df1e096a8d1e88933647f691e

Issue Description:

After upgrading to XCode 10.2 and converting to Swift 5, I am getting a ton of new warnings related to force unwrapped optionals.

Here is a very simple example, but I'm getting the example this error all over the place (especially for the first argument in NSLayoutContraint constructor).

If a property is defined as such:

@IBOutlet weak var shutterButton : UIButton! 

And then later I reference it as an Any:

var views : [Any] = []
views.append(shutterButton) // Expression implicitly coerced from 'UIButton?' to 'Any'

I get the error which I put into the comment there.

Since shutterButter is actually a UIButton and not a UIButton?, I don't think I should be getting this warning and don't get this warning in Swift 4.2.

[belkadan]

The rule for IUOs is "try to treat them as Optional before trying to unwrap", but I agree that the diagnostic doesn't make sense here. Still, you can work around it with an explicit ! or as.

cc @xedin

[xedin]

It looks like when IUO was made an attribute of the decl, we didn't fix all of the places to check for that attribute...

[xedin]

Do you want to take a look at this one, @theblixguy?

[theblixguy]

Sure. Do we not want to emit this diagnostic if we're implicitly unwrapping to Any?

[xedin]

@theblixguy No, we should keep that, but before emitting such diagnostic we should check if that optional type is actually optional and not IUO.

[theblixguy]

Hmm, seems like it's not possible to use `OptionalTypeKind` for this. Probably need to check the type repr.

[xedin]

@theblixguy Since the attribute is attached to declaration you'd have to get declaration for optional and go from there similar to https://github.com/apple/swift/blob/master/lib/Sema/ConstraintSystem.cpp#L2116

[theblixguy]

Hmm something like this doesn't work:

if (srcType->getOptionalObjectType()) {
  auto decl = srcType->getEnumOrBoundGenericEnum();
  if (decl->getAttrs().hasAttribute<ImplicitlyUnwrappedOptionalAttr>()) {
      return;
  }
}

I do get the declaration for optional, but it doesn't have that attribute.

[theblixguy]

Maybe what we need to do is

if (srcType->getOptionalObjectType() && hasImplicitlyUnwrappedResult(subExpr)) { 
  return;
} 

[xedin]

I'd expect that attribute to be associated with declaration of the entity IOU type is associated with e.g. property in this case, instead of Optional itself (which is what you are checking). I would be great if we could extract that warning from MiscDiagnostic and use a fix to diagnose it, it could be done in matchTypes.

[theblixguy]

Sounds good, I have a fix ready for it, just trying to figure out why it's not diagnosing (even after passing `warning=true` to ConstraintFix). Maybe the fix is being ignored somehow by matchTypes().

[theblixguy]

Nevermind, I fixed it. I'll create a PR now

[theblixguy]

PR: #23617

[belkadan]

Can you cherry-pick this to 5.1 when you and Pavel are done with it?

[theblixguy]

Sure!