Make all AdditionalTrailingClosures children non-optional

Author: ahoppen

CodeGeneration/Sources/SyntaxSupport/Child.swift

@@ -32,7 +32,7 @@ public enum ChildKind {
   /// The child always contains a node that matches one of the `choices`.
   case nodeChoices(choices: [Child])
   /// The child is a collection of `kind`.
-  case collection(kind: SyntaxNodeKind, collectionElementName: String, deprecatedCollectionElementName: String? = nil)
+  case collection(kind: SyntaxNodeKind, collectionElementName: String, defaultsToEmpty: Bool = false, deprecatedCollectionElementName: String? = nil)
   /// The child is a token that matches one of the given `choices`.
   /// If `requiresLeadingSpace` or `requiresTrailingSpace` is not `nil`, it
   /// overrides the default leading/trailing space behavior of the token.
@@ -91,7 +91,7 @@ public class Child {
       return kind
     case .nodeChoices:
       return .syntax
-    case .collection(kind: let kind, _, _):
+    case .collection(kind: let kind, _, _, _):
       return kind
     case .token:
       return .token
@@ -150,7 +150,7 @@ public class Child {
   /// Whether this child has syntax kind `UnexpectedNodes`.
   public var isUnexpectedNodes: Bool {
     switch kind {
-    case .collection(kind: .unexpectedNodes, _, _):
+    case .collection(kind: .unexpectedNodes, _, _, _):
       return true
     default:
       return false
@@ -165,7 +165,7 @@ public class Child {
       return choices.isEmpty
     case .node(let kind):
       return kind.isBase
-    case .collection(let kind, _, _):
+    case .collection(kind: let kind, _, _, _):
       return kind.isBase
     case .token:
       return false

CodeGeneration/Sources/SyntaxSupport/DeclNodes.swift

@@ -1450,8 +1450,7 @@ public let DECL_NODES: [Node] = [
       ),
       Child(
         name: "AdditionalTrailingClosures",
-        kind: .collection(kind: .multipleTrailingClosureElementList, collectionElementName: "AdditionalTrailingClosure"),
-        isOptional: true
+        kind: .collection(kind: .multipleTrailingClosureElementList, collectionElementName: "AdditionalTrailingClosure", defaultsToEmpty: true)
       ),
     ]
   ),

CodeGeneration/Sources/SyntaxSupport/ExprNodes.swift

@@ -828,9 +828,8 @@ public let EXPR_NODES: [Node] = [
       ),
       Child(
         name: "AdditionalTrailingClosures",
-        kind: .collection(kind: .multipleTrailingClosureElementList, collectionElementName: "AdditionalTrailingClosure"),
-        nameForDiagnostics: "trailing closures",
-        isOptional: true
+        kind: .collection(kind: .multipleTrailingClosureElementList, collectionElementName: "AdditionalTrailingClosure", defaultsToEmpty: true),
+        nameForDiagnostics: "trailing closures"
       ),
     ]
   ),
@@ -1179,8 +1178,7 @@ public let EXPR_NODES: [Node] = [
       ),
       Child(
         name: "AdditionalTrailingClosures",
-        kind: .collection(kind: .multipleTrailingClosureElementList, collectionElementName: "AdditionalTrailingClosure"),
-        isOptional: true
+        kind: .collection(kind: .multipleTrailingClosureElementList, collectionElementName: "AdditionalTrailingClosure", defaultsToEmpty: true)
       ),
     ]
   ),
@@ -1583,9 +1581,8 @@ public let EXPR_NODES: [Node] = [
       ),
       Child(
         name: "AdditionalTrailingClosures",
-        kind: .collection(kind: .multipleTrailingClosureElementList, collectionElementName: "AdditionalTrailingClosure"),
-        nameForDiagnostics: "trailing closures",
-        isOptional: true
+        kind: .collection(kind: .multipleTrailingClosureElementList, collectionElementName: "AdditionalTrailingClosure", defaultsToEmpty: true),
+        nameForDiagnostics: "trailing closures"
       ),
     ]
   ),

CodeGeneration/Sources/SyntaxSupport/GrammarGenerator.swift

@@ -36,7 +36,7 @@ struct GrammarGenerator {
     case .nodeChoices(let choices):
       let choicesDescriptions = choices.map { grammar(for: $0) }
       return "(\(choicesDescriptions.joined(separator: " | ")))\(optionality)"
-    case .collection(let kind, _, _):
+    case .collection(kind: let kind, _, _, _):
       return "``\(kind.syntaxType)``"
     case .token(let choices, _, _):
       if choices.count == 1 {

CodeGeneration/Sources/SyntaxSupport/Node.swift

@@ -367,7 +367,7 @@ fileprivate extension Child {
       return [kind]
     case .nodeChoices(let choices):
       return choices.flatMap(\.kinds)
-    case .collection(let kind, _, _):
+    case .collection(kind: let kind, _, _, _):
       return [kind]
     case .token:
       return [.token]

CodeGeneration/Sources/SyntaxSupport/Traits.swift

@@ -69,7 +69,7 @@ public let TRAITS: [Trait] = [
       Child(name: "ArgumentList", kind: .node(kind: .labeledExprList)),
       Child(name: "RightParen", kind: .token(choices: [.token(.rightParen)]), isOptional: true),
       Child(name: "TrailingClosure", kind: .node(kind: .closureExpr), isOptional: true),
-      Child(name: "AdditionalTrailingClosures", kind: .node(kind: .multipleTrailingClosureElementList), isOptional: true),
+      Child(name: "AdditionalTrailingClosures", kind: .node(kind: .multipleTrailingClosureElementList)),
     ]
   ),
   Trait(

CodeGeneration/Sources/Utils/SyntaxBuildableChild.swift

@@ -33,7 +33,7 @@ public extension Child {
       buildableKind = .node(kind: kind)
     case .nodeChoices:
       buildableKind = .node(kind: .syntax)
-    case .collection(let kind, _, _):
+    case .collection(kind: let kind, _, _, _):
       buildableKind = .node(kind: kind)
     case .token:
       buildableKind = .token(self.tokenKind!)
@@ -65,6 +65,9 @@ public extension Child {
         return ExprSyntax("nil")
       }
     }
+    if case .collection(_, _, defaultsToEmpty: true, _) = kind {
+      return ExprSyntax("[]")
+    }
     guard let token = token, isToken else {
       return type.defaultValue
     }

CodeGeneration/Sources/generate-swiftsyntax/templates/swiftsyntax/RenamedChildrenCompatibilityFile.swift

@@ -38,7 +38,8 @@ let renamedChildrenCompatibilityFile = try! SourceFileSyntax(leadingTrivia: copy
           )
           if let childNode = SYNTAX_NODE_MAP[child.syntaxNodeKind]?.collectionNode,
             !child.isUnexpectedNodes,
-            case .collection(_, let collectionElementName, let deprecatedCollectionElementName) = child.kind,
+            case .collection(_, collectionElementName: let collectionElementName, _, deprecatedCollectionElementName: let deprecatedCollectionElementName) =
+              child.kind,
             let deprecatedCollectionElementName
           {
             let childEltType = childNode.collectionElementType.syntaxBaseName

CodeGeneration/Sources/generate-swiftsyntax/templates/swiftsyntax/SyntaxNodesFile.swift

@@ -193,7 +193,7 @@ func syntaxNode(emitKind: SyntaxNodeKind) -> SourceFileSyntax {
           // If needed, this could be added in the future, but for now withUnexpected should be sufficient.
           if let childNode = SYNTAX_NODE_MAP[child.syntaxNodeKind]?.collectionNode,
             !child.isUnexpectedNodes,
-            case .collection(_, let childElt, _) = child.kind
+            case .collection(_, collectionElementName: let childElt, _, _) = child.kind
           {
             let childEltType = childNode.collectionElementType.syntaxBaseName
 

CodeGeneration/Tests/ValidateSyntaxNodes/ValidateSyntaxNodes.swift

@@ -56,13 +56,13 @@ fileprivate extension ChildKind {
       return kind == otherKind
     case (.nodeChoices(let choices), .nodeChoices(let otherChoices)):
       return choices.count == otherChoices.count && zip(choices, otherChoices).allSatisfy { $0.hasSameType(as: $1) }
-    case (.collection(let kind, _, _), .collection(let otherKind, _, _)):
+    case (.collection(kind: let kind, _, _, _), .collection(kind: let otherKind, _, _, _)):
       return kind == otherKind
     case (.token(let choices, _, _), .token(let otherChoices, _, _)):
       return choices == otherChoices
-    case (.node(let kind), .collection(let otherKind, _, _)):
+    case (.node(let kind), .collection(kind: let otherKind, _, _, _)):
       return kind == otherKind
-    case (.collection(let kind, _, _), .node(let otherKind)):
+    case (.collection(kind: let kind, _, _, _), .node(let otherKind)):
       return kind == otherKind
     default:
       return false

Sources/SwiftParser/Declarations.swift

@@ -1917,15 +1917,15 @@ extension Parser {
 
     // Parse the optional trailing closures.
     let trailingClosure: RawClosureExprSyntax?
-    let additionalTrailingClosures: RawMultipleTrailingClosureElementListSyntax?
+    let additionalTrailingClosures: RawMultipleTrailingClosureElementListSyntax
     if self.at(.leftBrace),
       self.withLookahead({ $0.atValidTrailingClosure(.trailingClosure) })
     {
       (trailingClosure, additionalTrailingClosures) =
         self.parseTrailingClosures(.trailingClosure)
     } else {
       trailingClosure = nil
-      additionalTrailingClosures = nil
+      additionalTrailingClosures = self.emptyCollection(RawMultipleTrailingClosureElementListSyntax.self)
     }
 
     return RawMacroExpansionDeclSyntax(

Sources/SwiftParser/Expressions.swift

@@ -733,12 +733,12 @@ extension Parser {
 
         // If we can parse trailing closures, do so.
         let trailingClosure: RawClosureExprSyntax?
-        let additionalTrailingClosures: RawMultipleTrailingClosureElementListSyntax?
+        let additionalTrailingClosures: RawMultipleTrailingClosureElementListSyntax
         if case .trailingClosure = flavor, self.at(.leftBrace), self.withLookahead({ $0.atValidTrailingClosure(flavor) }) {
           (trailingClosure, additionalTrailingClosures) = self.parseTrailingClosures(flavor)
         } else {
           trailingClosure = nil
-          additionalTrailingClosures = nil
+          additionalTrailingClosures = self.emptyCollection(RawMultipleTrailingClosureElementListSyntax.self)
         }
 
         leadingExpr = RawExprSyntax(
@@ -769,12 +769,12 @@ extension Parser {
 
         // If we can parse trailing closures, do so.
         let trailingClosure: RawClosureExprSyntax?
-        let additionalTrailingClosures: RawMultipleTrailingClosureElementListSyntax?
+        let additionalTrailingClosures: RawMultipleTrailingClosureElementListSyntax
         if case .trailingClosure = flavor, self.at(.leftBrace), self.withLookahead({ $0.atValidTrailingClosure(flavor) }) {
           (trailingClosure, additionalTrailingClosures) = self.parseTrailingClosures(flavor)
         } else {
           trailingClosure = nil
-          additionalTrailingClosures = nil
+          additionalTrailingClosures = self.emptyCollection(RawMultipleTrailingClosureElementListSyntax.self)
         }
 
         leadingExpr = RawExprSyntax(
@@ -1320,12 +1320,12 @@ extension Parser {
 
     // Parse the optional trailing closures.
     let trailingClosure: RawClosureExprSyntax?
-    let additionalTrailingClosures: RawMultipleTrailingClosureElementListSyntax?
+    let additionalTrailingClosures: RawMultipleTrailingClosureElementListSyntax
     if case .trailingClosure = flavor, self.at(.leftBrace), self.withLookahead({ $0.atValidTrailingClosure(flavor) }) {
       (trailingClosure, additionalTrailingClosures) = self.parseTrailingClosures(flavor)
     } else {
       trailingClosure = nil
-      additionalTrailingClosures = nil
+      additionalTrailingClosures = self.emptyCollection(RawMultipleTrailingClosureElementListSyntax.self)
     }
 
     return RawMacroExpansionExprSyntax(
@@ -1908,7 +1908,7 @@ extension Parser {
 
 extension Parser {
   /// Parse the trailing closure(s) following a call expression.
-  mutating func parseTrailingClosures(_ flavor: ExprFlavor) -> (RawClosureExprSyntax, RawMultipleTrailingClosureElementListSyntax?) {
+  mutating func parseTrailingClosures(_ flavor: ExprFlavor) -> (RawClosureExprSyntax, RawMultipleTrailingClosureElementListSyntax) {
     // Parse the closure.
     let closure = self.parseClosureExpression()
 
@@ -1931,7 +1931,10 @@ extension Parser {
       )
     }
 
-    let trailing = elements.isEmpty ? nil : RawMultipleTrailingClosureElementListSyntax(elements: elements, arena: self.arena)
+    let trailing =
+      elements.isEmpty
+      ? self.emptyCollection(RawMultipleTrailingClosureElementListSyntax.self)
+      : RawMultipleTrailingClosureElementListSyntax(elements: elements, arena: self.arena)
     return (closure, trailing)
   }
 }

Sources/SwiftParser/Parser.swift

@@ -129,6 +129,19 @@ public struct Parser {
   static let defaultMaximumNestingLevel = 256
   #endif
 
+  var _emptyRawMultipleTrailingClosureElementListSyntax: RawMultipleTrailingClosureElementListSyntax?
+
+  /// Create an empty collection of the given type.
+  ///
+  /// These empty collections are only created once and the same node is returned
+  /// on subsequent calls, reducing memory usage.
+  mutating func emptyCollection(_: RawMultipleTrailingClosureElementListSyntax.Type) -> RawMultipleTrailingClosureElementListSyntax {
+    if _emptyRawMultipleTrailingClosureElementListSyntax == nil {
+      _emptyRawMultipleTrailingClosureElementListSyntax = RawMultipleTrailingClosureElementListSyntax(elements: [], arena: self.arena)
+    }
+    return _emptyRawMultipleTrailingClosureElementListSyntax!
+  }
+
   /// The delegated initializer for the parser.
   ///
   /// - Parameters

Sources/SwiftRefactor/CallToTrailingClosures.swift

@@ -54,7 +54,7 @@ public struct CallToTrailingClosures: SyntaxRefactoringProvider {
 
 extension FunctionCallExprSyntax {
   fileprivate func convertToTrailingClosures(from startAtArgument: Int) -> FunctionCallExprSyntax? {
-    guard trailingClosure == nil, additionalTrailingClosures == nil, leftParen != nil, rightParen != nil else {
+    guard trailingClosure == nil, additionalTrailingClosures.isEmpty, leftParen != nil, rightParen != nil else {
       // Already have trailing closures
       return nil
     }

Sources/SwiftSyntax/generated/RenamedChildrenCompatibility.swift

@@ -3024,7 +3024,7 @@ extension FunctionCallExprSyntax {
       _ unexpectedBetweenRightParenAndTrailingClosure: UnexpectedNodesSyntax? = nil,
       trailingClosure: ClosureExprSyntax? = nil,
       _ unexpectedBetweenTrailingClosureAndAdditionalTrailingClosures: UnexpectedNodesSyntax? = nil,
-      additionalTrailingClosures: MultipleTrailingClosureElementListSyntax? = nil,
+      additionalTrailingClosures: MultipleTrailingClosureElementListSyntax = [],
       _ unexpectedAfterAdditionalTrailingClosures: UnexpectedNodesSyntax? = nil,
       trailingTrivia: Trivia? = nil
 
@@ -4949,7 +4949,7 @@ extension MacroExpansionDeclSyntax {
       _ unexpectedBetweenRightParenAndTrailingClosure: UnexpectedNodesSyntax? = nil,
       trailingClosure: ClosureExprSyntax? = nil,
       _ unexpectedBetweenTrailingClosureAndAdditionalTrailingClosures: UnexpectedNodesSyntax? = nil,
-      additionalTrailingClosures: MultipleTrailingClosureElementListSyntax? = nil,
+      additionalTrailingClosures: MultipleTrailingClosureElementListSyntax = [],
       _ unexpectedAfterAdditionalTrailingClosures: UnexpectedNodesSyntax? = nil,
       trailingTrivia: Trivia? = nil
 
@@ -5102,7 +5102,7 @@ extension MacroExpansionExprSyntax {
       _ unexpectedBetweenRightParenAndTrailingClosure: UnexpectedNodesSyntax? = nil,
       trailingClosure: ClosureExprSyntax? = nil,
       _ unexpectedBetweenTrailingClosureAndAdditionalTrailingClosures: UnexpectedNodesSyntax? = nil,
-      additionalTrailingClosures: MultipleTrailingClosureElementListSyntax? = nil,
+      additionalTrailingClosures: MultipleTrailingClosureElementListSyntax = [],
       _ unexpectedAfterAdditionalTrailingClosures: UnexpectedNodesSyntax? = nil,
       trailingTrivia: Trivia? = nil
 
@@ -7573,7 +7573,7 @@ extension SubscriptCallExprSyntax {
       _ unexpectedBetweenRightBracketAndTrailingClosure: UnexpectedNodesSyntax? = nil,
       trailingClosure: ClosureExprSyntax? = nil,
       _ unexpectedBetweenTrailingClosureAndAdditionalTrailingClosures: UnexpectedNodesSyntax? = nil,
-      additionalTrailingClosures: MultipleTrailingClosureElementListSyntax? = nil,
+      additionalTrailingClosures: MultipleTrailingClosureElementListSyntax = [],
       _ unexpectedAfterAdditionalTrailingClosures: UnexpectedNodesSyntax? = nil,
       trailingTrivia: Trivia? = nil
 

Sources/SwiftSyntax/generated/SyntaxTraits.swift

@@ -208,7 +208,7 @@ public protocol FreestandingMacroExpansionSyntax: SyntaxProtocol {
     set
   }
 
-  var additionalTrailingClosures: MultipleTrailingClosureElementListSyntax? {
+  var additionalTrailingClosures: MultipleTrailingClosureElementListSyntax {
     get
     set
   }