MacroSystem should remove the initializer for an accessor macro

SE-0389 specifies that a macro returning either a getter or setter
should remove the initializer, if one exists.

Resolves rdar://117442713 (#2310)

Author: bnbarham

Examples/Tests/MacroExamples/Implementation/ComplexMacros/DictionaryIndirectionMacroTests.swift

@@ -32,15 +32,15 @@ final class DictionaryStorageMacroTests: XCTestCase {
       """,
       expandedSource: """
         struct Point {
-          var x: Int = 1 {
+          var x: Int {
             get {
               _storage["x", default: 1] as! Int
             }
             set {
               _storage["x"] = newValue
             }
           }
-          var y: Int = 2 {
+          var y: Int {
             get {
               _storage["y", default: 2] as! Int
             }

Examples/Tests/MacroExamples/Implementation/ComplexMacros/ObservableMacroTests.swift

@@ -77,7 +77,7 @@ final class ObservableMacroTests: XCTestCase {
             }
           }
 
-          var isHappy: Bool = true {
+          var isHappy: Bool {
             get {
               _registrar.beginAccess(\.isHappy)
               defer {

Sources/SwiftSyntaxMacroExpansion/MacroSystem.swift

@@ -307,7 +307,7 @@ private func expandAccessorMacroWithExistingAccessors(
     return nil
   }
 
-  // Separate the accessor from any existing accessors by two spaces
+  // Separate the accessor from any existing accessors by an empty line
   let indentedSource = "\n" + expanded.indented(by: attachedTo.indentationOfFirstLine + indentationWidth)
   return "\(raw: indentedSource)"
 }
@@ -702,13 +702,26 @@ private class MacroApplication<Context: MacroExpansionContext>: SyntaxRewriter {
       context.addDiagnostics(from: MacroApplicationError.accessorMacroOnVariableWithMultipleBindings, node: node)
       return DeclSyntax(node)
     }
-    node.bindings[node.bindings.startIndex].accessorBlock = expandAccessors(of: node, existingAccessors: binding.accessorBlock)
+
+    let expansion = expandAccessors(of: node, existingAccessors: binding.accessorBlock)
+    if expansion.accessors != binding.accessorBlock {
+      if binding.initializer != nil, expansion.expandsGetSet {
+        // The accessor block will have a leading space, but there will already be a
+        // space between the variable and the to-be-removed initializer. Remove the
+        // leading trivia on the accessor block so we don't double up.
+        node.bindings[node.bindings.startIndex].accessorBlock = expansion.accessors?.with(\.leadingTrivia, [])
+        node.bindings[node.bindings.startIndex].initializer = nil
+      } else {
+        node.bindings[node.bindings.startIndex].accessorBlock = expansion.accessors
+      }
+    }
+
     return DeclSyntax(node)
   }
 
   override func visit(_ node: SubscriptDeclSyntax) -> DeclSyntax {
     var node = super.visit(node).cast(SubscriptDeclSyntax.self)
-    node.accessorBlock = expandAccessors(of: node, existingAccessors: node.accessorBlock)
+    node.accessorBlock = expandAccessors(of: node, existingAccessors: node.accessorBlock).accessors
     return DeclSyntax(node)
   }
 }
@@ -869,14 +882,23 @@ extension MacroApplication {
     }
   }
 
-  /// Expand all 'accessor' macros attached to `storage` and return the `storage`
-  /// node.
+  /// Expand all 'accessor' macros attached to `storage`.
   ///
-  /// - Returns: The storage node with all macro-synthesized accessors applied.
-  private func expandAccessors(of storage: some DeclSyntaxProtocol, existingAccessors: AccessorBlockSyntax?) -> AccessorBlockSyntax? {
+  /// - Returns: The final accessors block that includes both the existing
+  ///   and expanded accessors, as well as whether any `get`/`set` were
+  ///   expanded (in which case any initializer on `storage` should be
+  ///   removed).
+  private func expandAccessors(of storage: some DeclSyntaxProtocol, existingAccessors: AccessorBlockSyntax?) -> (
+    accessors: AccessorBlockSyntax?, expandsGetSet: Bool
+  ) {
     let accessorMacros = macroAttributes(attachedTo: DeclSyntax(storage), ofType: AccessorMacro.Type.self)
 
     var newAccessorsBlock = existingAccessors
+    var expandsGetSet = false
+    func checkExpansions(_ accessors: AccessorDeclListSyntax?) {
+      guard let accessors else { return }
+      expandsGetSet = expandsGetSet || accessors.contains(where: \.isGetOrSet)
+    }
 
     for macro in accessorMacros {
       do {
@@ -894,6 +916,8 @@ extension MacroApplication {
             in: context,
             indentationWidth: indentationWidth
           ) {
+            checkExpansions(newAccessors)
+
             // If existingAccessors is not `nil`, then we also set
             // `newAccessorBlock` above to a a non-nil value, so
             // `newAccessorsBlock` also isn’t `nil`.
@@ -902,31 +926,33 @@ extension MacroApplication {
               indentationWidth: self.indentationWidth
             )
           }
-        } else {
-          let newAccessors = try expandAccessorMacroWithoutExistingAccessors(
-            definition: macro.definition,
-            attributeNode: macro.attributeNode,
-            attachedTo: DeclSyntax(storage),
-            in: context,
-            indentationWidth: indentationWidth
-          )
-          if newAccessorsBlock == nil {
-            newAccessorsBlock = newAccessors
-          } else if let newAccessors = newAccessors {
-            guard case .accessors(let accessorList) = newAccessors.accessors else {
-              throw MacroApplicationError.malformedAccessor
-            }
-            newAccessorsBlock = newAccessorsBlock!.addingAccessors(
+        } else if let newAccessors = try expandAccessorMacroWithoutExistingAccessors(
+          definition: macro.definition,
+          attributeNode: macro.attributeNode,
+          attachedTo: DeclSyntax(storage),
+          in: context,
+          indentationWidth: indentationWidth
+        ) {
+          guard case .accessors(let accessorList) = newAccessors.accessors else {
+            throw MacroApplicationError.malformedAccessor
+          }
+
+          checkExpansions(accessorList)
+
+          if let oldBlock = newAccessorsBlock {
+            newAccessorsBlock = oldBlock.addingAccessors(
               from: accessorList,
               indentationWidth: self.indentationWidth
             )
+          } else {
+            newAccessorsBlock = newAccessors
           }
         }
       } catch {
         context.addDiagnostics(from: error, node: macro.attributeNode)
       }
     }
-    return newAccessorsBlock
+    return (newAccessorsBlock, expandsGetSet)
   }
 }
 
@@ -1130,3 +1156,9 @@ private extension AttributeSyntax {
     return (detach(in: context, foldingWith: operatorTable) as Syntax).cast(Self.self)
   }
 }
+
+private extension AccessorDeclSyntax {
+  var isGetOrSet: Bool {
+    return accessorSpecifier.tokenKind == .keyword(.get) || accessorSpecifier.tokenKind == .keyword(.set)
+  }
+}

Tests/SwiftSyntaxMacroExpansionTest/AccessorMacroTests.swift

@@ -320,4 +320,95 @@ final class AccessorMacroTests: XCTestCase {
       macros: ["Test": TestMacro.self]
     )
   }
+
+  func testInitializerRemovedForGetSet() {
+    assertMacroExpansion(
+      """
+      @constantOne
+      var x: Int = 1
+      """,
+      expandedSource: """
+        var x: Int {
+          get {
+            return 1
+          }
+        }
+        """,
+      macros: ["constantOne": ConstantOneGetter.self],
+      indentationWidth: indentationWidth
+    )
+
+    // Bit of an odd case, compiler has the type but we don't know it in `MacroSystem`
+    assertMacroExpansion(
+      """
+      @constantOne
+      var x = 1
+      """,
+      expandedSource: """
+        var x {
+          get {
+            return 1
+          }
+        }
+        """,
+      macros: ["constantOne": ConstantOneGetter.self],
+      indentationWidth: indentationWidth
+    )
+  }
+
+  func testInitializerRemainsForObserver() {
+    struct DidSetAdder: AccessorMacro {
+      static func expansion(
+        of node: AttributeSyntax,
+        providingAccessorsOf declaration: some DeclSyntaxProtocol,
+        in context: some MacroExpansionContext
+      ) throws -> [AccessorDeclSyntax] {
+        return [
+          """
+          didSet {
+          }
+          """
+        ]
+      }
+    }
+
+    assertMacroExpansion(
+      """
+      @addDidSet
+      var x = 1
+      """,
+      expandedSource: """
+        var x = 1 {
+          didSet {
+          }
+        }
+        """,
+      macros: ["addDidSet": DidSetAdder.self],
+      indentationWidth: indentationWidth
+    )
+
+    // Invalid semantically, but we shouldn't remove the initializer as the
+    // macro did not produce a getter/setter
+    assertMacroExpansion(
+      """
+      @addDidSet
+      var x = 1 {
+        get {
+          return 1
+        }
+      }
+      """,
+      expandedSource: """
+        var x = 1 {
+          get {
+            return 1
+          }
+          didSet {
+          }
+        }
+        """,
+      macros: ["addDidSet": DidSetAdder.self],
+      indentationWidth: indentationWidth
+    )
+  }
 }