[5.9] Automatically format expanded macros

Sources/SwiftCompilerPluginMessageHandling/CMakeLists.txt

@@ -16,6 +16,7 @@ add_swift_host_library(SwiftCompilerPluginMessageHandling
 
 target_link_libraries(SwiftCompilerPluginMessageHandling PUBLIC
   SwiftSyntax
+  SwiftBasicFormat
   SwiftDiagnostics
   SwiftParser
   SwiftSyntaxMacros

Sources/SwiftCompilerPluginMessageHandling/Macros.swift

@@ -10,6 +10,7 @@
 //
 //===----------------------------------------------------------------------===//
 
+import SwiftBasicFormat
 import SwiftDiagnostics
 import SwiftSyntax
 import SwiftSyntaxMacros
@@ -49,21 +50,21 @@ extension CompilerPluginMessageHandler {
           try exprMacroDef.expansion(of: node, in: context)
         }
         let rewritten = try _openExistential(macroSyntax, do: _expand)
-        expandedSource = rewritten.description
+        expandedSource = rewritten.formattedExpansion(macroDefinition.formatMode)
 
       case let declMacroDef as DeclarationMacro.Type:
         func _expand<Node: FreestandingMacroExpansionSyntax>(node: Node) throws -> [DeclSyntax] {
           try declMacroDef.expansion(of: node, in: context)
         }
         let rewritten = try _openExistential(macroSyntax, do: _expand)
-        expandedSource = CodeBlockItemListSyntax(rewritten.map { CodeBlockItemSyntax(item: .decl($0)) }).description
+        expandedSource = CodeBlockItemListSyntax(rewritten.map { CodeBlockItemSyntax(item: .decl($0)) }).formattedExpansion(macroDefinition.formatMode)
 
       case let codeItemMacroDef as CodeItemMacro.Type:
         func _expand<Node: FreestandingMacroExpansionSyntax>(node: Node) throws -> [CodeBlockItemSyntax] {
           try codeItemMacroDef.expansion(of: node, in: context)
         }
         let rewritten = try _openExistential(macroSyntax, do: _expand)
-        expandedSource = CodeBlockItemListSyntax(rewritten).description
+        expandedSource = CodeBlockItemListSyntax(rewritten).formattedExpansion(macroDefinition.formatMode)
 
       default:
         throw MacroExpansionError.unmathedMacroRole
@@ -113,7 +114,7 @@ extension CompilerPluginMessageHandler {
           in: context
         )
         expandedSources = accessors.map {
-          $0.trimmedDescription
+          $0.formattedExpansion(macroDefinition.formatMode)
         }
 
       case (let attachedMacro as MemberAttributeMacro.Type, .memberAttribute):
@@ -145,7 +146,7 @@ extension CompilerPluginMessageHandler {
 
         // Form a buffer containing an attribute list to return to the caller.
         expandedSources = attributes.map {
-          $0.trimmedDescription
+          $0.formattedExpansion(macroDefinition.formatMode)
         }
 
       case (let attachedMacro as MemberMacro.Type, .member):
@@ -170,7 +171,7 @@ extension CompilerPluginMessageHandler {
         let members = try _openExistential(declGroup, do: expandMemberMacro)
 
         // Form a buffer of member declarations to return to the caller.
-        expandedSources = members.map { $0.trimmedDescription }
+        expandedSources = members.map { $0.formattedExpansion(macroDefinition.formatMode) }
 
       case (let attachedMacro as PeerMacro.Type, .peer):
         let peers = try attachedMacro.expansion(
@@ -181,7 +182,7 @@ extension CompilerPluginMessageHandler {
 
         // Form a buffer of peer declarations to return to the caller.
         expandedSources = peers.map {
-          $0.trimmedDescription
+          $0.formattedExpansion(macroDefinition.formatMode)
         }
 
       case (let attachedMacro as ConformanceMacro.Type, .conformance):
@@ -234,3 +235,18 @@ extension CompilerPluginMessageHandler {
     )
   }
 }
+
+fileprivate extension SyntaxProtocol {
+  /// Perform a format if required and then trim any leading/trailing
+  /// whitespace.
+  func formattedExpansion(_ mode: FormatMode) -> String {
+    let formatted: Syntax
+    switch mode {
+    case .auto:
+      formatted = self.formatted()
+    case .disabled:
+      formatted = Syntax(self)
+    }
+    return formatted.trimmedDescription(matching: { $0.isWhitespace })
+  }
+}

Sources/SwiftSyntax/Syntax.swift

@@ -541,13 +541,35 @@ public extension SyntaxProtocol {
     return self.with(\.leadingTrivia, []).with(\.trailingTrivia, [])
   }
 
-  /// The description of this node without the leading trivia of the first token
-  /// in the node and the trailing trivia of the last token in the node.
+  /// A copy of this node with pieces that match `matching` trimmed from the
+  /// leading trivia of the first token and trailing trivia of the last token.
+  func trimmed(matching filter: (TriviaPiece) -> Bool) -> Self {
+    // TODO: Should only need one new node here
+    return self.with(
+      \.leadingTrivia,
+      Trivia(pieces: leadingTrivia.pieces.drop(while: filter))
+    ).with(
+      \.trailingTrivia,
+      Trivia(pieces: trailingTrivia.pieces.reversed().drop(while: filter).reversed())
+    )
+  }
+
+  /// The description of this node with leading whitespace of the first token
+  /// and trailing whitespace of the last token removed.
   var trimmedDescription: String {
-    // TODO: We shouldn't need to create to copies just to get the description
-    // without trivia.
+    // TODO: We shouldn't need to create to copies just to get the trimmed
+    // description.
     return self.trimmed.description
   }
+
+  /// The description of this node with pieces that match `matching` removed
+  /// from the leading trivia of the first token and trailing trivia of the
+  /// last token.
+  func trimmedDescription(matching filter: (TriviaPiece) -> Bool) -> String {
+    // TODO: We shouldn't need to create to copies just to get the trimmed
+    // description.
+    return self.trimmed(matching: filter).description
+  }
 }
 
 /// Provides debug descriptions for a node

Sources/SwiftSyntaxMacros/CMakeLists.txt

@@ -15,6 +15,7 @@ add_swift_host_library(SwiftSyntaxMacros
   MacroProtocols/ExpressionMacro.swift
   MacroProtocols/FreestandingMacro.swift
   MacroProtocols/Macro.swift
+  MacroProtocols/Macro+Format.swift
   MacroProtocols/MemberAttributeMacro.swift
   MacroProtocols/MemberMacro.swift
   MacroProtocols/PeerMacro.swift

Sources/SwiftSyntaxMacros/MacroProtocols/Macro+Format.swift

@@ -0,0 +1,29 @@
+//===----------------------------------------------------------------------===//
+//
+// This source file is part of the Swift.org open source project
+//
+// Copyright (c) 2014 - 2023 Apple Inc. and the Swift project authors
+// Licensed under Apache License v2.0 with Runtime Library Exception
+//
+// See https://swift.org/LICENSE.txt for license information
+// See https://swift.org/CONTRIBUTORS.txt for the list of Swift project authors
+//
+//===----------------------------------------------------------------------===//
+
+/// Describes the mode to use to format the result of an expansion.
+public enum FormatMode {
+  /// Perform a basic format of the expansion. This is primarily for inserting
+  /// whitespace as required (eg. between two keywords), but also adds simple
+  /// newline and indentation.
+  case auto
+
+  /// Disable automatically formatting the expanded macro. Trivia must be
+  /// manually inserted where required (eg. adding spaces between keywords).
+  case disabled
+}
+
+public extension Macro {
+  static var formatMode: FormatMode {
+    return .auto
+  }
+}

Sources/SwiftSyntaxMacros/MacroProtocols/Macro.swift

@@ -11,4 +11,8 @@
 //===----------------------------------------------------------------------===//
 
 /// Describes a macro.
-public protocol Macro {}
+public protocol Macro {
+  /// How the resulting expansion should be formatted, `.auto` by default.
+  /// Use `.disabled` for the expansion to be used as is.
+  static var formatMode: FormatMode { get }
+}

lit_tests/compiler_plugin_basic.swift

@@ -23,7 +23,9 @@ class MyClass {
 }
 
 // For '@Metadata'
-// CHECK: static var __metadata__: [String: String] { ["name": "MyClass"] }
+// CHECK: {{^}}static var __metadata__: [String: String] {
+// CHECK-NEXT: {{^}}    ["name": "MyClass"]
+// CHECK-NEXT: {{^}}}
 
 // For '#echo(12)'
 // CHECK: /* echo */12