[SR-4450] "type(of:)" detects class type but returns false for "type(of:) is AnyClass"

[regexident]

Previous ID	SR-4450
Radar	rdar://problem/31372306
Original Reporter	@regexident
Type	Bug
Status	Resolved
Resolution	Done

Additional Detail from JIRA

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

md5: dc6ab6dfd3eb9653018884543bf399dc

Issue Description:

protocol Bar {}
class FooClass: Bar {}
struct FooStruct: Bar {}

func test1<T>(instance: T, `protocol`: T.Type) {
    let type = type(of: instance as Any)
    let typeIsClass = type is AnyClass
    print("\(type) is a class: \(typeIsClass)")
}

func test2<T>(instance: T) {
    let type = type(of: instance as Any)
    let typeIsClass = type is AnyClass
    print("\(type) is a class: \(typeIsClass)")
}

test1(instance: FooClass(), protocol: Bar.self)
test1(instance: FooStruct(), protocol: Bar.self)

test2(instance: FooClass())
test2(instance: FooStruct())

// test1:
// FooClass is a class: false
// FooStruct is a class: false

// test2:
// FooClass is a class: true
// FooStruct is a class: false

One would expect test1 to behave like test2.

type(of: instance as Any) was suggested by Joe Groff as a workaround for https://bugs.swift.org/browse/SR-4420, which revealed this bug.

[jckarter]

@swift-ci create

[gparker42]

I blame the compiler. I can change the result of is AnyClass by introducing any other use of the value of instance as Any.

protocol Bar {}
class FooClass: Bar {}
struct FooStruct: Bar {}

var A: Any = 0

func test1<T>(instance: T, proto: T.Type) -> Bool {
  let a = instance as Any
  return type(of: a) is AnyClass
}

func test2<T>(instance: T, proto: T.Type) -> Bool {
  let a = instance as Any
  A = a
  return type(of: a) is AnyClass
}

print(test1(instance: FooClass(), proto: Bar.self))
// false
print(test2(instance: FooClass(), proto: Bar.self))
// true

[gparker42]

I also hit an assertion failure in constant propagation in a modified version of the test (rdar://32124747). Perhaps they are related?

[regexident]

With …

Apple Swift version 4.0 (swiftlang-900.0.54.11 clang-900.0.31)
Target: x86_64-apple-macosx10.9

… I'm now getting …

FooClass is a class: true
FooStruct is a class: false
FooClass is a class: true
FooStruct is a class: false

… with my snippet, which is the result I expected in the first place.

And I'm getting …

true
true

… with @gparker42's snippet.

So it looks like it's fixed? Can you confirm, @gparker42/@jckarter?

[gparker42]

We fixed this a while ago but forgot to update this report. Recent betas of Xcode 9 should have the fix.

[gparker42]

#9521