WIP: Get the first potential token of a node recursively

Author: StevenWong12

CodeGeneration/Sources/SyntaxSupport/Node.swift

@@ -84,6 +84,55 @@ public class Node {
       return CollectionNode(node: self)
     }
   }
+  
+  /// Get the first potential token of a node recursively
+  /// This information is used by incremental parse
+  public var firstPotentialToken: [TokenChoice] {
+    if let children = self.layoutNode?.children,
+       let firstChild = children.first(where: {!$0.isUnexpectedNodes}) {
+      
+      switch firstChild.kind {
+        case .node(kind: let nodeKind):
+          guard let nodeSpec = SYNTAX_NODES.first(where: {$0.kind == nodeKind}) else {
+            return []
+          }
+          return nodeSpec.firstPotentialToken
+        
+        case .nodeChoices(choices: let children):
+          return children.compactMap { child in
+            if let nodeSpec = SYNTAX_NODES.first(where: {$0.kind == child.syntaxNodeKind}) {
+              return nodeSpec.firstPotentialToken
+            }
+            return nil
+          }.flatMap {$0}
+        case .collection(kind: let kind, _):
+          guard let nodeSpec = SYNTAX_NODES.first(where: {$0.kind == kind}),
+                let collection = nodeSpec.collectionNode  else {
+            return []
+          }
+          return collection.elementChoices.compactMap { choiceKind in
+            if let nodeSpec = SYNTAX_NODES.first(where: {$0.kind == choiceKind}) {
+              return nodeSpec.firstPotentialToken
+            }
+            return nil
+          }.flatMap {$0}
+        
+        case .token(choices: let choices, _, _):
+          return choices
+      }
+    }
+    
+    if let collection = self.collectionNode {
+      return collection.elementChoices.compactMap { choiceKind in
+        if let nodeSpec = SYNTAX_NODES.first(where: {$0.kind == choiceKind}) {
+          return nodeSpec.firstPotentialToken
+        }
+        return nil
+      }.flatMap {$0}
+    }
+    
+    return []
+  }
 
   /// Construct the specification for a layout syntax node.
   init(