Grammar missing optional mutation-modifier in willSet/didSet-clause

[sarahcantohyatt]

Location

https://github.com/apple/swift-book/blob/main/TSPL.docc/ReferenceManual/Declarations.md?plain=1#L568

Description

Below is a subsection of a program pulled from the swift test suite.

@propertyWrapper
struct State {
  var wrappedValue: Int {
    get { 0 }
    nonmutating set {}
  }
}

struct MutatingDidSet {
  @State private var value: Int {
    mutating didSet {}
  }

  mutating func test() {
    value = 10
  }

}
struct MutatingWillSet {
  @State private var value: Int {
    mutating willSet {}
  }

  mutating func test() {
    value = 10
  }
}

The important things to look at in this program are:

@State private var value: Int {
    mutating didSet {}
  }

and

  @State private var value: Int {
    mutating willSet {}
  }

More specifically, the mutating keyword in front of the respective didSet/willSet.
This is not derivable in the current grammar due to mutation-modifier missing from the willSet/didSet-clause productions respectively.

Current grammar:

willSet-clause → attributes? willSet setter-name? code-block
didSet-clause → attributes? didSet setter-name? code-block

Correction

Proposed change:

willSet-clause → attributes? mutation-modifier? willSet setter-name? code-block
didSet-clause → attributes? mutation-modifier? didSet setter-name? code-block