Add disableSameTypeForUniqueChoice on Node

When elementChoices of a Node has a single syntax node as a choice, it's
`Element` type is of that syntax node type.

Add a flag disableSameTypeForUniqueChoice to disable this behavior.

This is added for a TypeSpecifier node to avoid the api break from
deleting LifetimeTypeSpecifier from its elementChoices.

Author: meg-gupta

CodeGeneration/Sources/SyntaxSupport/Node.swift

@@ -55,6 +55,8 @@ public class Node: NodeChoiceConvertible {
   /// function that should be invoked to create this node.
   public let parserFunction: TokenSyntax?
 
+  public let disableSameTypeForUniqueChoice: Bool
+
   public var syntaxNodeKind: SyntaxNodeKind {
     self.kind
   }
@@ -121,6 +123,7 @@ public class Node: NodeChoiceConvertible {
     experimentalFeature: ExperimentalFeature? = nil,
     nameForDiagnostics: String?,
     documentation: String? = nil,
+    disableSameTypeForUniqueChoice: Bool = false,
     parserFunction: TokenSyntax? = nil,
     traits: [String] = [],
     children: [Child] = []
@@ -133,6 +136,7 @@ public class Node: NodeChoiceConvertible {
     self.experimentalFeature = experimentalFeature
     self.nameForDiagnostics = nameForDiagnostics
     self.documentation = SwiftSyntax.Trivia.docCommentTrivia(from: documentation)
+    self.disableSameTypeForUniqueChoice = disableSameTypeForUniqueChoice
     self.parserFunction = parserFunction
 
     let childrenWithUnexpected: [Child]
@@ -278,6 +282,7 @@ public class Node: NodeChoiceConvertible {
     experimentalFeature: ExperimentalFeature? = nil,
     nameForDiagnostics: String?,
     documentation: String? = nil,
+    disableSameTypeForUniqueChoice: Bool = false,
     parserFunction: TokenSyntax? = nil,
     elementChoices: [SyntaxNodeKind]
   ) {
@@ -287,6 +292,7 @@ public class Node: NodeChoiceConvertible {
     self.experimentalFeature = experimentalFeature
     self.nameForDiagnostics = nameForDiagnostics
     self.documentation = SwiftSyntax.Trivia.docCommentTrivia(from: documentation)
+    self.disableSameTypeForUniqueChoice = disableSameTypeForUniqueChoice
     self.parserFunction = parserFunction
 
     assert(!elementChoices.isEmpty)

CodeGeneration/Sources/SyntaxSupport/TypeNodes.swift

@@ -527,6 +527,7 @@ public let TYPE_NODES: [Node] = [
     kind: .typeSpecifierList,
     base: .syntaxCollection,
     nameForDiagnostics: nil,
+    disableSameTypeForUniqueChoice: true,
     elementChoices: [.simpleTypeSpecifier]
   ),
 ]

CodeGeneration/Sources/generate-swift-syntax/ChildNodeChoices.swift

@@ -89,7 +89,10 @@ extension Node {
           return nil
         }
       }
-    } else if let node = self.collectionNode, node.elementChoices.count > 1 {
+    } else if let node = self.collectionNode, node.elementChoices.count >= 1 {
+      if !node.disableSameTypeForUniqueChoice && node.elementChoices.count == 1 {
+        return []
+      }
       return [
         ChildNodeChoices(
           name: "Element",

CodeGeneration/Sources/generate-swift-syntax/templates/swiftsyntax/RawSyntaxNodesFile.swift

@@ -116,7 +116,9 @@ func rawSyntaxNodesFile(nodesStartingWith: [Character]) -> SourceFileSyntax {
         }
 
         if let node = node.collectionNode {
-          let element = node.elementChoices.only != nil ? node.elementChoices.only!.raw.syntaxType : "Element"
+          let element =
+            !node.disableSameTypeForUniqueChoice && node.elementChoices.only != nil
+            ? node.elementChoices.only!.raw.syntaxType : "Element"
           DeclSyntax(
             """
             public init(elements: [\(element)], arena: __shared SyntaxArena) {

CodeGeneration/Sources/generate-swift-syntax/templates/swiftsyntax/SyntaxCollectionsFile.swift

@@ -31,8 +31,8 @@ let syntaxCollectionsFile = SourceFileSyntax(leadingTrivia: copyrightHeader) {
       public struct \(node.kind.syntaxType): SyntaxCollection, SyntaxHashable
       """
     ) {
-      if let onlyElement = node.elementChoices.only {
-        DeclSyntax("public typealias Element = \(onlyElement.syntaxType)")
+      if !node.disableSameTypeForUniqueChoice && node.elementChoices.only != nil {
+        DeclSyntax("public typealias Element = \(node.elementChoices.only!.syntaxType)")
       } else {
         for childNodeChoices in node.node.childrenNodeChoices() {
           childNodeChoices.enumDecl