[SR-7066] Compiler does not warn on duplicate keys for dictionary literals

[swift-ci]

Previous ID	SR-7066
Radar	None
Original Reporter	erica (JIRA User)
Type	Bug

Environment

Version 9.2 (9C40b)

Additional Detail from JIRA

Votes	0
Component/s	Compiler, Standard Library
Labels	Bug
Assignee	None
Priority	Medium

md5: 55fa9f54aa6d8465d1df9a15dab092cf

Issue Description:

let insets: UIEdgeInsets = [.left: 4, .right: 4, .left: 8]

The compiler accepts this without warning. I think it probably should warn/error if the literal can be checked at compile time.

[swift-ci]

Comment by erica sadun (JIRA)

The problem may be with the name, as a dictionary literal is initialized as an ordered array of tuples (thanks Stephen Celis). Maybe it should be a "tuple sequence literal".

See Also: https://developer.apple.com/documentation/swift/dictionaryliteral

[belkadan]

Yeah, I think this behavior is deliberate, and it'd also be hard to do for non-literal types. (We'd need some kind of notion of structurally-equivalent expressions, which is not unreasonable but isn't something the compiler currently has.). @moiseev, @airspeedswift, thoughts?

[swift-ci]

Comment by erica sadun (JIRA)

There are really two questions here:

1. Is including the same key in a dictionary literal a bug, and if so, can it be caught?

2. If the problem is in the name, which promises a dictionary literal (which this isn't due to key duplication), can it be solved by renaming to a more accurate `DictionaryStyleLiteral` or `DictionaryStyleTupleSequence` or `DictionaryStyleLiteralInitializable` sort of thing?