Incorrect warning: '#require(_:_:)' is redundant because '<expression>' never equals 'nil'

[mhrawdon]

Description

In a Swift Testing test, use of #require can in some cases result in a build warning about how the expression in the macro can never equal nil, even though it clearly can.

For example, in swift-build, some tests have checks like this:

if let fileRef = try? #require(fileGroup.children[1] as? FileReference) {

This results in the warning:

'#require(_:_:)' is redundant because 'fileGroup.children[1] as? FileReference' never equals 'nil' (from macro 'require')

But fileGroup.children is of type [GroupTreeReference], so the check is downcasting it to FileReference, which seems entirely valid to do, and could end up being nil if the instance is not a FileReference. It works correctly, so the warning seems incorrect.

#require is being used here because it will emit an issue automatically if the expression is false or nil, which is the desired behavior. This could be worked around by not using #require and instead handling that case with explicit code, but that seems unnecessary and contrary to the intent of #require.

Reproduction

See Description.

Expected behavior

This warning should not be emitted in cases such as the one in the Description.

Environment

Swift 6

Additional information

No response