Using enum case instead of boolean value to indicate how SyntaxVisitor should continue.

Author: nkcsgexi

Sources/SwiftSyntax/RawSyntax.swift

@@ -478,7 +478,7 @@ extension RawSyntax {
       if shouldVisit {
         // Visit this node realizes a syntax node.
         visitor.visitPre()
-        visitChildren = visitor.visit()
+        visitChildren = visitor.visit() == .visitChildren
       }
       if visitChildren {
         for (offset, element) in layout.enumerated() {

Sources/SwiftSyntax/SyntaxClassifier.swift.gyb

@@ -70,7 +70,7 @@ fileprivate class _SyntaxClassifier: SyntaxVisitor {
     }
   }
 
-  override func visit(_ token: TokenSyntax) {
+  override func visit(_ token: TokenSyntax) -> SyntaxVisitorContinueKind {
     assert(token.isPresent)
     // FIXME: We need to come up with some way in which the SyntaxClassifier can
     // classify trivia (i.e. comments). In particular we need to be able to
@@ -91,16 +91,17 @@ fileprivate class _SyntaxClassifier: SyntaxVisitor {
     assert(classifications[token] == nil,
            "\(token) has already been classified")
     classifications[token] = classification
+    return .skipChildren
   }
 
 % for node in SYNTAX_NODES:
 %   if is_visitable(node):
-  override func visit(_ node: ${node.name}) -> Bool {
+  override func visit(_ node: ${node.name}) -> SyntaxVisitorContinueKind {
     if skipNodeIds.contains(node.raw.id) {
-      return false
+      return .skipChildren
     }
 %     if node.is_unknown() or node.is_syntax_collection():
-    return true
+    return .visitChildren
 %     else:
 %       for child in node.children:
 %         if child.is_optional:
@@ -123,7 +124,7 @@ fileprivate class _SyntaxClassifier: SyntaxVisitor {
 %           end
 %         end
 %       end
-    return false
+    return .skipChildren
 %     end
   }
 %   end

Sources/SwiftSyntax/SyntaxRewriter.swift.gyb

@@ -94,24 +94,35 @@ open class SyntaxRewriter {
   }
 }
 
+/// The enum describes how the SyntaxVistor should continue after visiting
+/// the current node.
+public enum SyntaxVisitorContinueKind {
+
+  /// The visitor should visit the descendents of the current node.
+  case visitChildren
+
+  /// The visitor should avoid visiting the descendents of the current node.
+  case skipChildren
+}
+
 open class SyntaxVisitor {
     public init() {}
 % for node in SYNTAX_NODES:
 %   if is_visitable(node):
   /// Visting ${node.name} specifically.
   ///   - Parameter node: the node we are visiting.
-  ///   - Returns: whether we should visit the descendents of node.
-  open func visit(_ node: ${node.name}) -> Bool {
-    return true
+  ///   - Returns: how should we continue visiting.
+  open func visit(_ node: ${node.name}) -> SyntaxVisitorContinueKind {
+    return .visitChildren
   }
 %   end
 % end
 
   /// Visting UnknownSyntax specifically.
   ///   - Parameter node: the node we are visiting.
-  ///   - Returns: whether we should visit the descendents of node.
-  open func visit(_ node: UnknownSyntax) -> Bool {
-    return true
+  ///   - Returns: how should we continue visiting.
+  open func visit(_ node: UnknownSyntax) -> SyntaxVisitorContinueKind {
+    return .visitChildren
   }
 
   /// Whether we should ever visit a given syntax kind.
@@ -128,7 +139,9 @@ open class SyntaxVisitor {
     return true
   }
 
-  open func visit(_ token: TokenSyntax) {}
+  open func visit(_ token: TokenSyntax) -> SyntaxVisitorContinueKind {
+    return .skipChildren
+  }
 
   /// The function called before visiting the node and its descendents.
   ///   - node: the node we are about to visit.
@@ -138,18 +151,17 @@ open class SyntaxVisitor {
   ///   - node: the node we just finished visiting.
   open func visitPost(_ node: Syntax) {}
 
-  public func visit(_ node: Syntax) -> Bool {
+  public func visit(_ node: Syntax) -> SyntaxVisitorContinueKind {
     switch node.raw.kind {
-    case .token: visit(node as! TokenSyntax)
+    case .token: return visit(node as! TokenSyntax)
 % for node in SYNTAX_NODES:
 %   if is_visitable(node):
     case .${node.swift_syntax_kind}: return visit(node as! ${node.name})
 %   end
 % end
     case .unknown: return visit(node as! UnknownSyntax)
-    default: break
+    default: return .skipChildren
     }
-    return false
   }
 }
 
@@ -232,7 +244,7 @@ class RawSyntaxVisitor {
 
   // The current raw syntax node is interesting for the user, so realize a
   // correponding syntax node and feed it into the visitor.
-  func visit() -> Bool {
+  func visit() -> SyntaxVisitorContinueKind {
     return visitor.visit(currentNode.node)
   }
 }

Sources/lit-test-helper/ClassifiedSyntaxTreePrinter.swift

@@ -115,11 +115,12 @@ class ClassifiedSyntaxTreePrinter: SyntaxVisitor {
     }
   }
 
-  override func visit(_ node: TokenSyntax) {
+  override func visit(_ node: TokenSyntax) -> SyntaxVisitorContinueKind {
     visit(node.leadingTrivia)
     let classification = classifications[node] ?? SyntaxClassification.none
     recordCurrentClassification(classification)
     result += node.text
     visit(node.trailingTrivia)
+    return .skipChildren
   }
 }

Tests/SwiftSyntaxTest/AbsolutePosition.swift

@@ -64,9 +64,10 @@ public class AbsolutePositionTestCase: XCTestCase {
           _ = node.byteSize
           _ = node.positionAfterSkippingLeadingTrivia
         }
-        override func visit(_ node: TokenSyntax) {
+        override func visit(_ node: TokenSyntax) -> SyntaxVisitorContinueKind {
           XCTAssertEqual(node.positionAfterSkippingLeadingTrivia.utf8Offset,
             node.position.utf8Offset + node.leadingTrivia.byteSize)
+          return .skipChildren
         }
       }
       parsed.walk(Visitor())

Tests/SwiftSyntaxTest/DiagnosticTest.swift

@@ -76,14 +76,14 @@ public class DiagnosticTestCase: XCTestCase {
         self.url = url
         self.engine = engine
       }
-      override func visit(_ function: FunctionDeclSyntax) -> Bool {
+      override func visit(_ function: FunctionDeclSyntax) -> SyntaxVisitorContinueKind {
         let startLoc = function.identifier.startLocation(in: url)
         let endLoc = function.endLocation(in: url)
         engine.diagnose(.badFunction(function.identifier), location: startLoc) {
           $0.highlight(function.identifier.sourceRange(in: self.url))
         }
         engine.diagnose(.endOfFunction(function.identifier), location: endLoc)
-        return true
+        return .visitChildren
       }
     }
 

Tests/SwiftSyntaxTest/VisitorTest.swift

@@ -13,9 +13,9 @@ public class SyntaxVisitorTestCase: XCTestCase {
   public func testBasic() {
     class FuncCounter: SyntaxVisitor {
       var funcCount = 0
-      override func visit(_ node: FunctionDeclSyntax) -> Bool {
+      override func visit(_ node: FunctionDeclSyntax) -> SyntaxVisitorContinueKind {
         funcCount += 1
-        return true
+        return .visitChildren
       }
     }
     XCTAssertNoThrow(try {
@@ -70,9 +70,9 @@ public class SyntaxVisitorTestCase: XCTestCase {
     class VisitCollections: SyntaxVisitor {
       var numberOfCodeBlockItems = 0
 
-      override func visit(_ items: CodeBlockItemListSyntax) -> Bool {
+      override func visit(_ items: CodeBlockItemListSyntax) -> SyntaxVisitorContinueKind {
         numberOfCodeBlockItems += items.count
-        return true
+        return .visitChildren
       }
     }