Fix newline closing brace and opening brace for expanded macros

Author: kimdv

Sources/SwiftSyntaxMacroExpansion/MacroSystem.swift

@@ -762,10 +762,8 @@ private class MacroApplication<Context: MacroExpansionContext>: SyntaxRewriter {
     return CodeBlockItemListSyntax(newItems)
   }
 
-  override func visit(_ node: MemberBlockItemListSyntax) -> MemberBlockItemListSyntax {
+  override func visit(_ node: MemberBlockSyntax) -> MemberBlockSyntax {
     let parentDeclGroup = node
-      .parent?
-      .as(MemberBlockSyntax.self)?
       .parent?
       .as(DeclSyntax.self)
     var newItems: [MemberBlockItemSyntax] = []
@@ -792,7 +790,7 @@ private class MacroApplication<Context: MacroExpansionContext>: SyntaxRewriter {
       extensions += expandExtensions(of: node.decl)
     }
 
-    for var item in node {
+    for var item in node.members {
       // Expand member attribute members attached to the declaration context.
       // Note that MemberAttribute macros are _not_ applied to generated members
       if let parentDeclGroup, let decl = item.decl.asProtocol(WithAttributesSyntax.self) {
@@ -825,7 +823,29 @@ private class MacroApplication<Context: MacroExpansionContext>: SyntaxRewriter {
       }
     }
 
-    return .init(newItems)
+    /// Returns an leading trivia for the member blocks closing brace.
+    /// It will add a leading newline, if there is none.
+    var leadingTriviaForClosingBrace: Trivia {
+      if (node.members.isEmpty || newItems.isEmpty) && newItems.isEmpty {
+        return node.rightBrace.leadingTrivia
+      }
+
+      if node.rightBrace.leadingTrivia.contains(where: { $0.isNewline }) {
+        return node.rightBrace.leadingTrivia
+      }
+
+      if newItems.last?.trailingTrivia.pieces.last?.isNewline ?? false {
+        return node.rightBrace.leadingTrivia
+      } else {
+        return .newline + node.rightBrace.leadingTrivia
+      }
+    }
+
+    return MemberBlockSyntax(
+      leftBrace: node.leftBrace,
+      members: MemberBlockItemListSyntax(newItems),
+      rightBrace: node.rightBrace.with(\.leadingTrivia, leadingTriviaForClosingBrace)
+    )
   }
 
   override func visit(_ node: VariableDeclSyntax) -> DeclSyntax {

Tests/SwiftSyntaxMacroExpansionTest/MemberMacroTests.swift

@@ -299,4 +299,129 @@ final class MemberMacroTests: XCTestCase {
       ]
     )
   }
+
+  func testAddMemberToEmptyDeclaration() {
+    struct TestMacro: MemberMacro {
+      static func expansion(
+        of node: AttributeSyntax,
+        providingMembersOf declaration: some DeclGroupSyntax,
+        conformingTo protocols: [TypeSyntax],
+        in context: some MacroExpansionContext
+      ) throws -> [DeclSyntax] {
+        return [DeclSyntax("var x = 0")]
+      }
+    }
+
+    assertMacroExpansion(
+      """
+      @Test
+      struct Foo {}
+      """,
+      expandedSource: """
+        struct Foo {
+
+          var x = 0
+        }
+        """,
+      macros: [
+        "Test": TestMacro.self
+      ],
+      indentationWidth: indentationWidth
+    )
+  }
+
+  func testAddTwoMembersToEmptyDeclaration() {
+    struct TestMacro: MemberMacro {
+      static func expansion(
+        of node: AttributeSyntax,
+        providingMembersOf declaration: some DeclGroupSyntax,
+        conformingTo protocols: [TypeSyntax],
+        in context: some MacroExpansionContext
+      ) throws -> [DeclSyntax] {
+        return [DeclSyntax("var x = 0"), DeclSyntax("var x = 0")]
+      }
+    }
+
+    assertMacroExpansion(
+      """
+      @Test
+      struct Foo {}
+      """,
+      expandedSource: """
+        struct Foo {
+
+          var x = 0
+
+          var x = 0
+        }
+        """,
+      macros: [
+        "Test": TestMacro.self
+      ],
+      indentationWidth: indentationWidth
+    )
+  }
+
+  func testAddMemberToEmptyDeclarationWithEndingNewline() {
+    struct TestMacro: MemberMacro {
+      static func expansion(
+        of node: AttributeSyntax,
+        providingMembersOf declaration: some DeclGroupSyntax,
+        conformingTo protocols: [TypeSyntax],
+        in context: some MacroExpansionContext
+      ) throws -> [DeclSyntax] {
+        return [DeclSyntax("var x = 0\n")]
+      }
+    }
+
+    assertMacroExpansion(
+      """
+      @Test
+      struct Foo {}
+      """,
+      expandedSource: """
+        struct Foo {
+
+          var x = 0
+        }
+        """,
+      macros: [
+        "Test": TestMacro.self
+      ],
+      indentationWidth: indentationWidth
+    )
+  }
+
+  func testAddMemberToDeclarationWithASingleVariable() {
+    struct TestMacro: MemberMacro {
+      static func expansion(
+        of node: AttributeSyntax,
+        providingMembersOf declaration: some DeclGroupSyntax,
+        conformingTo protocols: [TypeSyntax],
+        in context: some MacroExpansionContext
+      ) throws -> [DeclSyntax] {
+        return [DeclSyntax("var x = 0\n")]
+      }
+    }
+
+    assertMacroExpansion(
+      """
+      @Test
+      struct Foo {
+        var y = 0
+      }
+      """,
+      expandedSource: """
+        struct Foo {
+          var y = 0
+
+          var x = 0
+        }
+        """,
+      macros: [
+        "Test": TestMacro.self
+      ],
+      indentationWidth: indentationWidth
+    )
+  }
 }