[Macros] Accessor macros can decide not to emit getter/setter if the property has one

If an accessor macro is placed on a computed property, then opts not to
produce a getter/setter, we would produce an error because the macro
didn't make the computed property... computed. Fix that; it's already
computed, and it's fine not to add accessors.

Fixes rdar://111586568.

Author: DougGregor

lib/Sema/TypeCheckMacros.cpp

@@ -1328,11 +1328,7 @@ llvm::Optional<unsigned> swift::expandAccessors(AbstractStorageDecl *storage,
   // declaration, so there is nothing further to do.
   bool foundNonObservingAccessor = false;
   bool foundInitAccessor = false;
-  for (auto decl : macroSourceFile->getTopLevelItems()) {
-    auto accessor = dyn_cast_or_null<AccessorDecl>(decl.dyn_cast<Decl *>());
-    if (!accessor)
-      continue;
-
+  for (auto accessor : storage->getAllAccessors()) {
     if (accessor->isInitAccessor())
       foundInitAccessor = true;
 

test/Macros/Inputs/syntax_macro_definitions.swift

@@ -467,6 +467,55 @@ extension PropertyWrapperMacro: PeerMacro {
   }
 }
 
+extension PatternBindingSyntax.Accessor {
+  var hasGetter: Bool {
+    switch self {
+    case .accessors(let accessors):
+      for accessor in accessors.accessors {
+        if accessor.accessorKind.text == "get" {
+          return true
+        }
+      }
+
+      return false
+    case .getter:
+      return true
+    }
+  }
+}
+
+public struct PropertyWrapperSkipsComputedMacro {}
+
+extension PropertyWrapperSkipsComputedMacro: AccessorMacro, Macro {
+  public static func expansion(
+    of node: AttributeSyntax,
+    providingAccessorsOf declaration: some DeclSyntaxProtocol,
+    in context: some MacroExpansionContext
+  ) throws -> [AccessorDeclSyntax] {
+    guard let varDecl = declaration.as(VariableDeclSyntax.self),
+      let binding = varDecl.bindings.first,
+      let identifier = binding.pattern.as(IdentifierPatternSyntax.self)?.identifier, !(binding.accessor?.hasGetter ?? false)
+    else {
+      return []
+    }
+
+    return [
+      """
+
+        get {
+          _\(identifier).wrappedValue
+        }
+      """,
+      """
+
+        set {
+          _\(identifier).wrappedValue = newValue
+        }
+      """,
+    ]
+  }
+}
+
 public struct WrapAllProperties: MemberAttributeMacro {
   public static func expansion(
     of node: AttributeSyntax,

test/Macros/accessor_macros.swift

@@ -23,6 +23,10 @@
 macro myPropertyWrapper() =
     #externalMacro(module: "MacroDefinition", type: "PropertyWrapperMacro")
 
+@attached(accessor)
+macro myPropertyWrapperSkipsComputed() =
+    #externalMacro(module: "MacroDefinition", type: "PropertyWrapperSkipsComputedMacro")
+
 struct Date { }
 
 struct MyWrapperThingy<T> {
@@ -64,6 +68,11 @@ struct MyStruct {
   // CHECK-DUMP: set {
   // CHECK-DUMP:   _birthDate.wrappedValue = newValue
   // CHECK-DUMP: }
+
+  @myPropertyWrapperSkipsComputed
+  var age: Int? {
+    get { nil }
+  }
 }
 
 // Test that the fake-property-wrapper-introduced accessors execute properly at