[Observation] Switch Observable to be a non-marker protocol (swiftlang#66993)

With support for redundant conformance declarations via macros,
the `Observable` protocol can be a non-marker protocol, which
provides more flexibility for evolution in the future.

rdar://111463883

This change also switches to the new ExtensionMacro protocol,
the requirement for which includes information about whether the
conformance to the Observable protocol has already been added, either
in the declaration or in a superclass to the macro-attributed type.
This allows the @observable macro to be applied to subclasses of
observable types without redundant-conformance errors.

Author: natecook1000

lib/Macros/Sources/ObservationMacros/Extensions.swift

@@ -58,7 +58,7 @@ extension VariableDeclSyntax {
       guard let decl = accessor.as(AccessorDeclSyntax.self) else {
         return nil
       }
-      if predicate(decl.accessorKind.tokenKind) {
+      if predicate(decl.accessorSpecifier.tokenKind) {
         return decl
       } else {
         return nil
@@ -85,7 +85,7 @@ extension VariableDeclSyntax {
 
 
   var isImmutable: Bool {
-    return bindingKeyword.tokenKind == .keyword(.let)
+    return bindingSpecifier.tokenKind == .keyword(.let)
   }
 
   func isEquivalent(to other: VariableDeclSyntax) -> Bool {
@@ -198,9 +198,9 @@ extension FunctionDeclSyntax {
   var signatureStandin: SignatureStandin {
     var parameters = [String]()
     for parameter in signature.input.parameterList {
-      parameters.append(parameter.firstName.text + ":" + (parameter.type.genericSubstitution(genericParameterClause?.genericParameterList) ?? "" ))
+      parameters.append(parameter.firstName.text + ":" + (parameter.type.genericSubstitution(genericParameterClause?.parameters) ?? "" ))
     }
-    let returnType = signature.output?.returnType.genericSubstitution(genericParameterClause?.genericParameterList) ?? "Void"
+    let returnType = signature.output?.returnType.genericSubstitution(genericParameterClause?.parameters) ?? "Void"
     return SignatureStandin(isInstance: isInstance, identifier: identifier.text, parameters: parameters, returnType: returnType)
   }
 

lib/Macros/Sources/ObservationMacros/ObservableMacro.swift

@@ -71,7 +71,7 @@ public struct ObservableMacro {
   static var ignoredAttribute: AttributeSyntax {
     AttributeSyntax(
       leadingTrivia: .space,
-      atSignToken: .atSignToken(),
+      atSign: .atSignToken(),
       attributeName: SimpleTypeIdentifierSyntax(name: .identifier(ignoredMacroName)),
       trailingTrivia: .space
     )
@@ -173,12 +173,14 @@ extension PatternBindingListSyntax {
 }
 
 extension VariableDeclSyntax {
-    func privatePrefixed(_ prefix: String, addingAttribute attribute: AttributeSyntax) -> VariableDeclSyntax {
-    VariableDeclSyntax(
+  func privatePrefixed(_ prefix: String, addingAttribute attribute: AttributeSyntax) -> VariableDeclSyntax {
+    let newAttributes = AttributeListSyntax(
+      (attributes.map(Array.init) ?? []) + [.attribute(attribute)])
+    return VariableDeclSyntax(
       leadingTrivia: leadingTrivia,
-      attributes: attributes?.appending(.attribute(attribute)) ?? [.attribute(attribute)],
+      attributes: newAttributes,
       modifiers: modifiers?.privatePrefixed(prefix) ?? ModifierListSyntax(keyword: .private),
-      bindingKeyword: TokenSyntax(bindingKeyword.tokenKind, leadingTrivia: .space, trailingTrivia: .space, presence: .present),
+      bindingSpecifier: TokenSyntax(bindingSpecifier.tokenKind, leadingTrivia: .space, trailingTrivia: .space, presence: .present),
       bindings: bindings.privatePrefixed(prefix),
       trailingTrivia: trailingTrivia
     )
@@ -265,30 +267,27 @@ extension ObservableMacro: MemberAttributeMacro {
   }
 }
 
-extension ObservableMacro: ConformanceMacro {
-  public static func expansion<Declaration: DeclGroupSyntax, Context: MacroExpansionContext>(
+extension ObservableMacro: ExtensionMacro {
+  public static func expansion(
     of node: AttributeSyntax,
-    providingConformancesOf declaration: Declaration,
-    in context: Context
-  ) throws -> [(TypeSyntax, GenericWhereClauseSyntax?)] {
-    let inheritanceList: InheritedTypeListSyntax?
-    if let classDecl = declaration.as(ClassDeclSyntax.self) {
-      inheritanceList = classDecl.inheritanceClause?.inheritedTypeCollection
-    } else if let structDecl = declaration.as(StructDeclSyntax.self) {
-      inheritanceList = structDecl.inheritanceClause?.inheritedTypeCollection
-    } else {
-      inheritanceList = nil
-    }
-    
-    if let inheritanceList {
-      for inheritance in inheritanceList {
-        if inheritance.typeName.identifier == ObservableMacro.conformanceName {
-          return []
-        }
-      }
+    attachedTo declaration: some DeclGroupSyntax,
+    providingExtensionsOf type: some TypeSyntaxProtocol,
+    conformingTo protocols: [TypeSyntax],
+    in context: some MacroExpansionContext
+  ) throws -> [ExtensionDeclSyntax] {
+    // This method can be called twice - first with an empty `protocols` when
+    // no conformance is needed, and second with a `MissingTypeSyntax` instance.
+    if protocols.isEmpty {
+      return []
     }
-    
-    return [(ObservableMacro.observableConformanceType, nil)]
+
+    let decl: DeclSyntax = """
+      extension \(raw: type.trimmedDescription): \(raw: qualifiedConformanceName) {}
+      """
+
+    return [
+      decl.cast(ExtensionDeclSyntax.self)
+    ]
   }
 }
 

stdlib/public/Observation/Sources/Observation/CMakeLists.txt

@@ -24,6 +24,7 @@ add_swift_target_library(swiftObservation ${SWIFT_STDLIB_LIBRARY_BUILD_TYPES} IS
   SWIFT_COMPILE_FLAGS
     ${SWIFT_STANDARD_LIBRARY_SWIFT_FLAGS}
     "-enable-experimental-feature" "Macros"
+    "-enable-experimental-feature" "ExtensionMacros"
     -Xfrontend -disable-implicit-string-processing-module-import
 
   C_COMPILE_FLAGS

stdlib/public/Observation/Sources/Observation/Observable.swift

@@ -18,7 +18,7 @@
 /// the ``Observation/Observable-swift.macro`` macro when adding observation
 /// support to a type.
 @available(SwiftStdlib 5.9, *)
-@_marker public protocol Observable { }
+public protocol Observable { }
 
 #if $Macros && hasAttribute(attached)
 
@@ -46,7 +46,7 @@
 @attached(member, names: named(_$observationRegistrar), named(access), named(withMutation), arbitrary)
 #endif
 @attached(memberAttribute)
-@attached(conformance)
+@attached(extension, conformances: Observable)
 public macro Observable() =
   #externalMacro(module: "ObservationMacros", type: "ObservableMacro")
 

test/stdlib/Observation/Observable.swift

@@ -1,9 +1,9 @@
 // REQUIRES: swift_swift_parser, executable_test
 
-// RUN: %target-run-simple-swift( -Xfrontend -disable-availability-checking -parse-as-library -enable-experimental-feature InitAccessors -enable-experimental-feature Macros -Xfrontend -plugin-path -Xfrontend %swift-host-lib-dir/plugins)
+// RUN: %target-run-simple-swift( -Xfrontend -disable-availability-checking -parse-as-library -enable-experimental-feature InitAccessors -enable-experimental-feature Macros -enable-experimental-feature ExtensionMacros -Xfrontend -plugin-path -Xfrontend %swift-host-lib-dir/plugins)
 
 // Run this test via the swift-plugin-server
-// RUN: %target-run-simple-swift( -Xfrontend -disable-availability-checking -parse-as-library -enable-experimental-feature InitAccessors -enable-experimental-feature Macros -Xfrontend -external-plugin-path -Xfrontend %swift-host-lib-dir/plugins#%swift-plugin-server)
+// RUN: %target-run-simple-swift( -Xfrontend -disable-availability-checking -parse-as-library -enable-experimental-feature InitAccessors -enable-experimental-feature Macros -enable-experimental-feature ExtensionMacros -Xfrontend -external-plugin-path -Xfrontend %swift-host-lib-dir/plugins#%swift-plugin-server)
 
 // Asserts is required for '-enable-experimental-feature InitAccessors'.
 // REQUIRES: asserts

test/stdlib/Observation/ObservableDidSetWillSet.swift

@@ -1,6 +1,6 @@
 // REQUIRES: swift_swift_parser, executable_test
 
-// RUN: %target-run-simple-swift( -Xfrontend -disable-availability-checking -enable-experimental-feature InitAccessors -enable-experimental-feature Macros -Xfrontend -plugin-path -Xfrontend %swift-host-lib-dir/plugins) | %FileCheck %s
+// RUN: %target-run-simple-swift( -Xfrontend -disable-availability-checking -enable-experimental-feature InitAccessors -enable-experimental-feature Macros -enable-experimental-feature ExtensionMacros -Xfrontend -plugin-path -Xfrontend %swift-host-lib-dir/plugins) | %FileCheck %s
 
 // Asserts is required for '-enable-experimental-feature InitAccessors'.
 // REQUIRES: asserts