[SR-11160] Inconsistent behavior with exhaustive switching over optionals of tuples

[tayloraswift]

Previous ID	SR-11160
Radar	rdar://problem/53312914
Original Reporter	@Kelvin13
Type	Bug
Status	Resolved
Resolution	Done

Environment

$ swift --version
Swift version 5.1-dev (LLVM 200186e28b, Swift 75a5496)
Target: x86_64-unknown-linux-gnu

Additional Detail from JIRA

Votes	0
Component/s	Compiler
Labels	Bug
Assignee	@typesanitizer
Priority	Medium

md5: 17cc87614deb65870fadbaf0dd67d61d

is blocked by:

• SR-11212 Ill-typed patterns are permitted to compile (implicit tupling/untupling)

Issue Description:

why does this work:
{{}}

func foo<T, U>(_ bar1:T?, _ bar2:U?) 
{
    switch (bar1, bar2) 
    { 
    case (let a?, let b?):
        print(a, b) 
    case (let a?, nil): 
        print(a, -1) 
    case(nil, let b?):
        print(-1, b) 
    case (nil, nil): 
        print("") 
    } 
}

{{}}
but not this?

switch (Optional<Int>(1), Optional<(Int, Int)>((5, 6))) 
{ 
case (let a?, let b?):
    print(a, b) 
case (let a?, nil): 
    print(a, -1) 
case(nil, let b?):
    print(-1, b) 
case (nil, nil): 
    print("") 
} 

error: switch must be exhaustive
switch (Optional<Int>(1), Optional<(Int, Int)>((5, 6))) 
^
note: add missing case: '(_, .some(_, _))'
switch (Optional<Int>(1), Optional<(Int, Int)>((5, 6))) 

{{}}

[belkadan]

@swift-ci create

[amomchilov]

The tupleness isn't actually necessary. This errors out:

switch (Optional<(Int, Int)>((5, 6))) { 
case let b?: print(b) 
case nil:    print(-1)
}

But this works:

switch (Optional<(Int, Int)>((5, 6))) { 
case let b?: print(b) 
case nil:    print(-1)

// Adding this case fixes it:
case let (b, c)?: print(-1, b, c)

[typesanitizer]

Somewhat related: we compile the following code today even though we shouldn't

switch Optional<(Int, Int)>((5, 6)) {
case .some(let a, let b): () // ought to be .some((let a, let b))
case .none: ()
}

We need to preserve this while fixing the bug, although we could consider adding
a new warning.

Opened SR-11212 for this.

[typesanitizer]

Fix merged with [GitHub PR #26357 | #26357]. Thanks for reporting the issue. 🙂