[SR-10231] Overloading Overriden Method By Inout-ness Causes Compile Error

[swift-ci]

Previous ID	SR-10231
Radar	None
Original Reporter	trevorthoele (JIRA User)
Type	Bug
Status	Resolved
Resolution	Done

Environment

Swift 4.2

XCode 10.2

Additional Detail from JIRA

Votes	0
Component/s	Compiler
Labels	Bug, 5.0Regression
Assignee	@slavapestov
Priority	Medium

md5: 1d2b0351efbb0962eb5ccace68a59193

relates to:

• SR-10198 Cannot override more than one superclass declaration

Issue Description:

Overriding a base class function and introducing an overload in the derived class based solely on the inout status of the parameter causes the compiler to think that the method is overridden twice.

This appears to happen regardless of whether an inout parameter is overridden or a non-inout parameter is overridden. This worked prior to upgrading to XCode 10.2.

Below, XCode reports the 'f(i: Int)' function declared in Derived as already overridden.

class Base {
    func f(i: inout Int) {
        
    }
}


class Derived : Base {
    override func f(i: inout Int) {
        
    }
    
    func f(i: Int) {
        
    }
}

[slavapestov]

Recall that parameter types no longer include an InOutType, so the problem here is that override checking is not checking parameter flags. In 4.2 I think we just compared tuple types.

[slavapestov]

#23754