[SR-9774] Forbid the syntax "dynamic static func"

[swift-ci]

Previous ID	SR-9774
Radar	None
Original Reporter	bang.nguyen (JIRA User)
Type	Improvement

Additional Detail from JIRA

| | | |------------------|-----------------| |Votes | 0 | |Component/s | Compiler | |Labels | Improvement | |Assignee | None | |Priority | Medium | md5: 836b0a2566d616fb175a8f25b7a2e488

Issue Description:

In both Xcode 9.4 (Swift 4.1.2) and Xcode 10 (Swift 4.2), we can declare a function like this:

@objc dynamic static func test() {

}

Xcode 10, this function will be dynamic dispatch. But in Xcode 9, it's static dispatch. It's confusing. In fact, the syntax "dynamic static", "dynamic private static",... should be forbidden, because a function can't be "dynamic" and "static" at the same time.

Eg: this swizzling code works on Xcode 10 (Swift 4.2) but doesn't work on Xcode 9 (Swift 4.1):

class TestSwizzle {

static func swizzle() {

    let sel1 = \#selector(TestSwizzle.doSomething)

    let sel2 = \#selector(TestSwizzle.swizzled_doSomething)

    let cls: AnyClass = TestSwizzle.self

    guard let m1 = class_getClassMethod(cls, sel1),

        let m2 = class_getClassMethod(cls, sel2) else

{ return assertionFailure() }

    method_exchangeImplementations(m1, m2)

}

@objc dynamic static func doSomething()

{ print("orignal") }

@objc dynamic static func swizzled_doSomething()

{ print("swizzled one") swizzled_doSomething() }

}

[belkadan]

static means class + final in a class context, so it's not entirely unreasonable: "subclasses can't override this, but the implementation for all instances might get changed out at run time". I agree that it looks silly, though, since the two words are normally opposites. Any ideas for how to improve the situation?

[belkadan]

cc @slavapestov

[swift-ci]

Comment by Bang Nguyen (JIRA)

@belkadan but in Xcode 9.4 (Swift 4.1), Swizzling a `dynamic static function` doesn't work (I put an example in the Description). Swizzling successfully, but when we call this function, it doesn't go through Objective C runtime.