deprecated-declaration.md

Deprecated Declaration Warnings (DeprecatedDeclaration)

This diagnostic group includes warnings related to deprecated APIs that may be removed in future versions and should be replaced with more current alternatives.

The DeprecatedDeclaration group covers the following warnings:

• Use of a function annotated with @available(<platform>, deprecated: <version>)

  @available(iOS, deprecated: 10.0)
  func oldFunction() {
    // This function is deprecated and should not be used.
  }
  
  oldFunction() // 'oldFunction()' is deprecated

• Use of a function annotated with @available(<platform>, deprecated: <version>, renamed: "<new name>")

  @available(iOS, deprecated: 10.0, renamed: "newFunction")
  func oldFunction() {
    // This function is deprecated and should not be used.
  }
  
  oldFunction() // 'oldFunction()' is deprecated: renamed to 'newFunction'

• Use of a type as an instance of a protocol when the type's conformance to the protocol is marked as deprecated

  struct S {}
  
  protocol P {}
  
  @available(*, deprecated)
  extension S: P {}
  
  func f(_ p: some P) {}
  
  func test() {
    f(S()) // Conformance of 'S' to 'P' is deprecated
  }

• When a protocol requirement has a default implementation marked as deprecated and the type conforming to the protocol doesn't provide that requirement

  protocol P {
    func f()
    func g()
  }
  
  extension P {
    @available(*, deprecated)
    func f() {}
    @available(*, deprecated, message: "write it yourself")
    func g() {}
  }
  
  struct S: P {} // deprecated default implementation is used to satisfy instance method 'f()' required by protocol 'P'
                // deprecated default implementation is used to satisfy instance method 'g()' required by protocol 'P': write it yourself

• When a protocol requirement has been deprecated

  struct S: Hashable {
    var hashValue: Int { // 'Hashable.hashValue' is deprecated as a protocol requirement; conform type 'S' to 'Hashable' by implementing 'hash(into:)' instead
      ...
    }
  }
  final class C: Executor {
    func enqueue(_ job: __owned Job) {} // 'Executor.enqueue(Job)' is deprecated as a protocol requirement; conform type 'C' to 'Executor' by implementing 'func enqueue(ExecutorJob)' instead
  }

Usage Example

swiftc -Werror DeprecatedDeclaration file.swift
swiftc -warnings-as-errors -Wwarning DeprecatedDeclaration file.swift