Behavior of postfix operator has been changed in Swift6.1

[muukii]

Description

No response

Reproduction

the below code works in Swift6.0.
but it gets errors in Swift6.1

postfix operator &>

public postfix func &> <T>(argument: consuming T) -> _FlowDownBox<T> {
  .init(consume argument)
}

public struct _FlowDownBox<Value>: ~Copyable {
  
  public var value: Value
  
  public init(_ value: consuming Value) {
    self.value = consume value
  }
  
  
  public consuming func perform<U>(_ transform: (consuming Value) throws -> U) rethrows -> U {
    try transform(value)
  }
  
}

func test() {
  
  var x: Int?
  
  x&>.perform { (v: Int?) in
    
  }
  
  x?&>.perform { (v: Int) in
    
  }
  
  var box: Box? = Box(value: 1)
  
  box?.value&>.perform { (v: Int) in
    
  }
  
}

struct Box {
  var value: Int
}

Swift 6.1

Expected behavior

It should work the same way, I guess.

Environment

swift-driver version: 1.120.5 Apple Swift version 6.1 (swiftlang-6.1.0.110.21 clang-1700.0.13.3)
Target: arm64-apple-macosx15.0

Additional information

No response

[airspeedswift]

Shorter reduction:

extension Int {
    func f() { print("I am an Int") }
}

postfix operator §
postfix func §(argument: Int) -> Int {
    argument
}

var x: Int? = 1
x?§.f() // compiles in 6.0.3, in more recent compilers Value of optional type 'Int?' must be unwrapped to refer to member 'f' of wrapped base type 'Int'

[xedin]

It looks like the problem here is related to pre-check, optional evaluation expression used to be at the top but now it wraps postfix unary expression for §. cc @hamishknight and @rintaro

[hamishknight]

This would have regressed with #76981, I can take it

[muukii]

@hamishknight Thank you!