Allow putting garbage nodes in between any two children of a Syntax node

Author: ahoppen

Sources/SwiftSyntax/SyntaxAnyVisitor.swift.gyb

@@ -40,10 +40,11 @@
 ///       }
 ///
 open class SyntaxAnyVisitor: SyntaxVisitor {
-  /// Visiting `UnknownSyntax` specifically.
-  ///   - Parameter node: the node we are visiting.
-  ///   - Returns: how should we continue visiting.
+  
   open func visitAny(_ node: Syntax) -> SyntaxVisitorContinueKind {
+    if node.is(GarbageNodesSyntax.self) {
+      return .skipChildren
+    }
     return .visitChildren
   }
 

Sources/SwiftSyntax/SyntaxBuilders.swift.gyb

@@ -34,7 +34,7 @@ public struct ${Builder} {
     Array<RawSyntax?>(repeating: nil, count: ${len(node.children)})
 
   internal init() {}
-%     for child in node.children:
+%     for child in node.non_garbage_children:
 %       child_node = NODE_MAP.get(child.syntax_kind)
 %       if child_node and child_node.is_syntax_collection():
 %         child_elt = child.collection_element_name

Sources/SwiftSyntax/SyntaxFactory.swift.gyb

@@ -52,10 +52,16 @@ public enum SyntaxFactory {
 %   elif node.children:
 %     child_params = []
 %     for child in node.children:
-%         param_type = child.type_name
-%         if child.is_optional:
-%            param_type = param_type + "?"
+%       param_type = child.type_name
+%       if child.is_optional:
+%          param_type = param_type + "?"
+%       end
+%       if child.is_garbage_nodes():
+%         child_params.append("garbage %s: %s = nil" % (child.swift_name, param_type))
+%       else:
 %         child_params.append("%s: %s" % (child.swift_name, param_type))
+%       end
+%     end
 %     child_params = ', '.join(child_params)
   public static func make${node.syntax_kind}(${child_params}) -> ${node.name} {
     let layout: [RawSyntax?] = [

Sources/SwiftSyntax/SyntaxNodes.swift.gyb.template

@@ -115,7 +115,7 @@ public struct ${node.name}: ${base_type}Protocol, SyntaxHashable {
 %       # ===============
 %       # Adding children
 %       # ===============
-%       if child_node and child_node.is_syntax_collection():
+%       if child_node and child_node.is_syntax_collection() and not child.is_garbage_nodes():
 %         child_elt = child.collection_element_name
 %         child_elt_type = child_node.collection_element_type
 %         if not child_elt:

Sources/SwiftSyntax/SyntaxRewriter.swift.gyb

@@ -34,7 +34,11 @@ open class SyntaxRewriter {
   ///   - Parameter node: the node that is being visited
   ///   - Returns: the rewritten node
   open func visit(_ node: ${node.name}) -> ${node.base_type} {
+%     if node.name == 'GarbageNodesSyntax':
+    return ${node.base_type}(node)
+%     else:
     return ${node.base_type}(visitChildren(node))
+%     end
   }
 
 %   end

Sources/SwiftSyntax/SyntaxVisitor.swift.gyb

@@ -43,7 +43,11 @@ open class SyntaxVisitor {
   ///   - Parameter node: the node we are visiting.
   ///   - Returns: how should we continue visiting.
   open func visit(_ node: ${node.name}) -> SyntaxVisitorContinueKind {
+%     if node.name == 'GarbageNodesSyntax':
+    return .skipChildren
+%     else:
     return .visitChildren
+%     end
   }
 
   /// The function called after visiting `${node.name}` and its descendents.

Sources/SwiftSyntax/gyb_generated/Misc.swift

@@ -67,6 +67,12 @@ extension SyntaxNode {
     return CodeBlockSyntax(asSyntaxData)
   }
 
+  public var isGarbageNodes: Bool { return raw.kind == .garbageNodes }
+  public var asGarbageNodes: GarbageNodesSyntax? {
+    guard isGarbageNodes else { return nil }
+    return GarbageNodesSyntax(asSyntaxData)
+  }
+
   public var isInOutExpr: Bool { return raw.kind == .inOutExpr }
   public var asInOutExpr: InOutExprSyntax? {
     guard isInOutExpr else { return nil }
@@ -1557,6 +1563,8 @@ extension Syntax {
       return node
     case .codeBlock(let node):
       return node
+    case .garbageNodes(let node):
+      return node
     case .inOutExpr(let node):
       return node
     case .poundColumnExpr(let node):

Sources/SwiftSyntax/gyb_generated/SyntaxAnyVisitor.swift

@@ -35,10 +35,11 @@
 ///       }
 ///
 open class SyntaxAnyVisitor: SyntaxVisitor {
-  /// Visiting `UnknownSyntax` specifically.
-  ///   - Parameter node: the node we are visiting.
-  ///   - Returns: how should we continue visiting.
+  
   open func visitAny(_ node: Syntax) -> SyntaxVisitorContinueKind {
+    if node.is(GarbageNodesSyntax.self) {
+      return .skipChildren
+    }
     return .visitChildren
   }
 
@@ -120,6 +121,13 @@ open class SyntaxAnyVisitor: SyntaxVisitor {
   override open func visitPost(_ node: CodeBlockSyntax) {
     visitAnyPost(node._syntaxNode)
   }
+  override open func visit(_ node: GarbageNodesSyntax) -> SyntaxVisitorContinueKind {
+    return visitAny(node._syntaxNode)
+  }
+
+  override open func visitPost(_ node: GarbageNodesSyntax) {
+    visitAnyPost(node._syntaxNode)
+  }
   override open func visit(_ node: InOutExprSyntax) -> SyntaxVisitorContinueKind {
     return visitAny(node._syntaxNode)
   }