WIP: Hard code first potential token of children of FunctionCallExpr

Author: StevenWong12

Sources/SwiftParser/Parser.swift

@@ -633,11 +633,27 @@ extension Parser {
 
     var lookUpHelper = IncrementalParseLookup(transition: parseTransition)
     let currentOffset = self.lexemes.getOffsetToStart(self.currentToken)
-    if let node = lookUpHelper.lookUp(currentOffset, kind: kind) {
+    if let node = lookUpHelper.lookUp(currentOffset, kind: kind),
+        nodeCanBeReused(node: node) == true {
+      // for test
+      lookUpHelper.registerReusedNode(node, offset: currentOffset)
       self.lexemes.advance(by: node.byteSize, currentToken: &self.currentToken)
       return node
     }
 
     return nil
   }
+  
+  func nodeCanBeReused(node: Syntax) -> Bool {
+    var lookahead = self.lookahead()
+    lookahead.lexemes.advance(by: node.byteSize, currentToken: &lookahead.currentToken)
+    
+    if let codeBlockItem = node.as(CodeBlockItemSyntax.self),
+       let internalItem = codeBlockItem.item.as(FunctionCallExprSyntax.self),
+       let nextPotentialToken = internalItem.nextPotentialTokenChoices?.decomposeToRaw().rawKind {
+      return lookahead.currentToken.rawTokenKind != nextPotentialToken
+    }
+    
+    return true
+  }
 }

Sources/SwiftSyntax/IncrementalParseTransition.swift

@@ -240,13 +240,16 @@ public struct IncrementalParseLookup {
     }
     let prevPosition = AbsolutePosition(utf8Offset: prevOffset)
     let node = cursorLookup(prevPosition: prevPosition, kind: kind)
-    if let delegate = reusedDelegate, let node {
+    return node
+  }
+  
+  public func registerReusedNode(_ node: Syntax, offset: Int) {
+    if let delegate = reusedDelegate {
       delegate.parserReusedNode(
-        range: ByteSourceRange(offset: newOffset, length: node.byteSizeAfterTrimmingTrivia),
+        range: ByteSourceRange(offset: offset, length: node.byteSizeAfterTrimmingTrivia),
         previousNode: node
       )
     }
-    return node
   }
 
   mutating fileprivate func cursorLookup(

Sources/SwiftSyntax/generated/syntaxNodes/SyntaxExprNodes.swift

@@ -2378,6 +2378,30 @@ public struct FunctionCallExprSyntax: ExprSyntaxProtocol, SyntaxHashable {
           \Self.unexpectedAfterAdditionalTrailingClosures
         ])
   }
+  
+  public var nextPotentialTokenChoices: TokenKind? {
+    if let children = self.raw.layoutView?.children,
+       let lastNonNilChildIdx = children.lastIndex(where: {$0 != nil}),
+       lastNonNilChildIdx != children.endIndex {
+      var targetIntIndex = children.distance(from: children.startIndex, to: children.index(after: lastNonNilChildIdx))
+      // Unexpected Nodes
+      if targetIntIndex % 2 == 0 {
+        targetIntIndex += 1
+      }
+      
+      switch targetIntIndex {
+        case 1: return .identifier("")
+        case 3: return .leftParen
+        case 5: return .identifier("")
+        case 7: return .rightParen
+        case 9: return .leftBrace
+        case 11: return .identifier("")
+        default: break
+      }
+    }
+    
+    return nil
+  }
 }
 
 // MARK: - IdentifierExprSyntax

Tests/SwiftParserTest/IncrementalParsingTests.swift

@@ -39,7 +39,6 @@ public class IncrementalParsingTests: XCTestCase {
   }
 
   public func testTrailingClosure() {
-    XCTExpectFailure("WIP: Add lookahead for incremental parse")
     assertIncrementalParse(
       """
       foo() {}