[SR-10558] Failed to cast to a concrete class type after sequence's init(elements: Sequence)

[swift-ci]

Previous ID	SR-10558
Radar	rdar://problem/50245539
Original Reporter	davionliu30 (JIRA User)
Type	Bug
Status	Resolved
Resolution	Duplicate

Additional Detail from JIRA

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

md5: 307874635addc56b0dbbc8c59870d49d

duplicates:

• SR-10285 Subclass of a class that conforms to a protocol and extends NSObject is not instantiate correctly

Issue Description:

Failed to cast to a concrete class type after sequence's init(elements: Sequence)

Please refer ChartsOrg/Charts#3917

This seems introduced with Xcode 10.2

for code like:

// demo code       
        let chartView = BarChartView()
        view.addSubview(chartView)
        chartView.frame = view.bounds
        chartView.autoresizingMask = [.flexibleWidth, .flexibleHeight]


        let count = 10


        let values = (1...count).enumerated().map { BarChartDataEntry(x: (Double)($0.offset), y: (Double)($0.element)) }
        
        let set = BarChartDataSet(values)
        let data = BarChartData(dataSet: set)
        chartView.data = data

let set = BarChartDataSet(values) is eventually calling

Swift.RangeReplaceableCollection.init<A where A1: Swift.Sequence, A.Element == A1.Element>(A1) -> A

but later in BarChartRenderer's initBuffers() func

line 75: let set = barData.dataSets[i] as! IBarChartDataSet

it failed to cast to IBarChartDataSet or BarChartDataSet

I checked when break at

let set = BarChartDataSet(values)
let data = BarChartData(dataSet: set)

set is still BarChartDatSet:

> (lldb) fr v set
(Charts.BarChartDataSet) set = 0x000000028109c000 

but in

let set = barData.dataSets[i] as! IBarChartDataSet

it's

>(lldb) p barData.dataSets[i]
(_TtC6Charts12ChartDataSet) $R6 = 0x000000028109c000

note the pointer address is still the same, but failed to cast to BarChartDataSet or IBarChartDataSet

[belkadan]

Thanks for the reproducer! Reduced:

import Foundation

protocol Foo {
  init()
}
extension Foo {
  init(oops: Int) {
    print("protocol extension")
    self.init()
  }
}

class Base: NSObject, Foo {
  override required init() {
    print("init base")
  }
}

class Sub: Base {
  required init() {
    print("init sub")
  }
}

print("\t", type(of: Sub() as Any)) // Sub
print("\t", type(of: Sub(oops: 0) as Any)) // Base

Looks like the NSObject-ness is relevant here, though I'm not sure how yet. @slavapestov, does this look familiar?

[slavapestov]

Smells like SR-10285. I'll take a look. Thanks for the reduction Jordan!