[SR-3470] Compiler displays wrong error message when calling a constructor to cause a type mismatch

[swift-ci]

Previous ID	SR-3470
Radar	None
Original Reporter	Sweeper (JIRA User)
Type	Bug

Attachment: Download

Environment

Xcode 8.1

macOS Sierra 10.12

Apple Swift version 3.0.1 (swiftlang-800.0.58.6 clang-800.0.42.1)
Target: x86_64-apple-macosx10.9

Additional Detail from JIRA

Votes	0
Component/s	Compiler
Labels	Bug, DiagnosticsQoI, TypeChecker
Assignee	None
Priority	Medium

md5: 01e588e13a060ad512276df0a96a822f

Issue Description:

If you compile the code in the attachment, you will see two different compiler error messages on line 6 and 7.

On line 6,

— Cannot convert value of type 'A' to specified type 'Void' (aka '()')

On line 7,

— Cannot invoke initializer for type 'A' with an argument list of type '(x: Int, y: Double)'

But in theory, the real problem of the two lines are the same - assigning A to Void. I expected the messages to both be

— Cannot convert value of type 'A' to specified type 'Void' (aka '()')

[belkadan]

struct A {
    init(x: Double, y: Double) { }
    init(x: Int, y: Int) { }
}

let a: Void = A(x: 1, y: 2)
let b: Void = A(x: 1, y: 2.0)

Indeed, commenting out the second initializer makes both error messages the same.

[jtbandes]

Problem seems to be the use of typeCheckArgumentChildIndependently to typecheck the arguments alone during failure diagnosis, then trying to match them to callee candidates, as opposed to solving the whole call at once.

[gregomni]

Swift 5.10, this is fixed:

bug.swift:6:15: error: cannot convert value of type 'A' to specified type 'Void'
let a: Void = A(x: 1, y: 2)
              ^~~~~~~~~~~~~
bug.swift:7:15: error: cannot convert value of type 'A' to specified type 'Void'
let b: Void = A(x: 1, y: 2.0)
              ^~~~~~~~~~~~~~~