[5.8] Collection literal inferred as Any when function type argument is Any

[keith]

With this code:

func asJSON(_ a: [String: Any]) { print(a) }

asJSON([
    "a": [
        "b": "c",
        "d": [
            "e": "f",
        ],
    ],
])

Swift 5.8 from Xcode 14.3 beta 2 warns that the collection is inferred as Any:

foo.swift:4:10: warning: heterogeneous collection literal could only be inferred to '[String : Any]'; add explicit type annotation if this is intentional
    "a": [
         ^

In this case I'm surprised to see this warning since the function it's being passed to explicitly takes [String: Any], so it being inferred as Any seems expected and I don't think needs a warning

[xedin]

The type of dictionary is inferred to [String: Any] before it's converted to the parameter type. The warning has been made more aggressive by #60323. cc @AnthonyLatsis

[xedin]

I'm not sure how I feel about this myself, on one side this seems reasonable because collection is indeed heterogeneous but on other other hand we could consider parameter to be an explicit type annotation as well.

[keith]

on other other hand we could consider parameter to be an explicit type annotation as well

yea that's what I was expecting

[AnthonyLatsis]

After looking at 1d21b4e, which introduced this diagnostic, I think I might have misinterpreted its purpose. I agree with Keith that whether the literal has a defaulted type should not matter if it gets type-erased anyway. On its turn, an erasure expression implies the presence of an explicit type annotation somewhere.

[ian-sayles]

Since upgrading to Xcode 14.3 I I get the following warning, which I think maybe related:
Heterogeneous collection literal could only be inferred to '[String : Any]'; add explicit type annotation if this is intentional

My app uses Firestore and as many statements like below which are impacted by the new change:

 assetDocument.setData([
                "alerts": [
                    "service": [
                        "end": Timestamp(date: newDate),
                        ],
                    ],
            ], merge: true) { err in
                if let err = err {
                    print("Error updating document: \(err)")
                }
            }

Does anyone know if this is a bug that will be fixed in the next release of Xcode or do I have to find a fix to the issue that does not break my app?

[xedin]

Should the changes be reverted then, @AnthonyLatsis?

[AnthonyLatsis]

Yes, I will see if there is anything useful worth keeping while there’s still time until 5.9 converges. Do you want me to fully revert it for upcoming 5.8 patches now?

[xedin]

Let’s revert on main and 5.9.

[AnthonyLatsis]

@lattner Do you remember why you added this diagnostic (1d21b4e)? Was it to avoid semantic source breaks caused by potential improvements to the type join?

[lattner]

no recollection sorry