[Syntax] Add init(unsafeCasting: Syntax) to concrete node types

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

@@ -50,6 +50,15 @@ let syntaxCollectionsFile = SourceFileSyntax(leadingTrivia: copyrightHeader) {
         """
       )
 
+      DeclSyntax(
+        """
+        @_transparent
+        init(unsafeCasting node: Syntax) {
+          self._syntaxNode = node
+        }
+        """
+      )
+
       DeclSyntax("public static let syntaxKind = SyntaxKind.\(node.memberCallName)")
     }
   }

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

@@ -52,6 +52,15 @@ func syntaxNode(nodesStartingWith: [Character]) -> SourceFileSyntax {
           """
         )
 
+        DeclSyntax(
+          """
+          @_transparent
+          init(unsafeCasting node: Syntax) {
+            self._syntaxNode = node
+          }
+          """
+        )
+
         let initSignature = InitSignature(node)
 
         try! InitializerDeclSyntax(

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

@@ -72,8 +72,7 @@ let syntaxRewriterFile = SourceFileSyntax(leadingTrivia: copyrightHeader) {
       """
       /// Rewrite `node`, keeping its parent unless `detach` is `true`.
       public func rewrite(_ node: some SyntaxProtocol, detach: Bool = false) -> Syntax {
-        var rewritten = Syntax(node)
-        self.dispatchVisit(&rewritten)
+        let rewritten = self.visitImpl(Syntax(node))
         if detach {
           return rewritten
         }
@@ -87,11 +86,20 @@ let syntaxRewriterFile = SourceFileSyntax(leadingTrivia: copyrightHeader) {
 
     DeclSyntax(
       """
-      /// Visit a ``TokenSyntax``.
-      ///   - Parameter token: the token that is being visited
+      /// Visit any Syntax node.
+      ///   - Parameter node: the node that is being visited
       ///   - Returns: the rewritten node
-      open func visit(_ token: TokenSyntax) -> TokenSyntax {
-        return token
+      @available(*, deprecated, renamed: "rewrite(_:detach:)")
+      public func visit(_ node: Syntax) -> Syntax {
+        return visitImpl(node)
+      }
+      """
+    )
+
+    DeclSyntax(
+      """
+      public func visit<T: SyntaxChildChoices>(_ node: T) -> T {
+        visitImpl(Syntax(node)).cast(T.self)
       }
       """
     )
@@ -133,24 +141,11 @@ let syntaxRewriterFile = SourceFileSyntax(leadingTrivia: copyrightHeader) {
 
     DeclSyntax(
       """
-      /// Visit any Syntax node.
-      ///   - Parameter node: the node that is being visited
+      /// Visit a ``TokenSyntax``.
+      ///   - Parameter token: the token that is being visited
       ///   - Returns: the rewritten node
-      @available(*, deprecated, renamed: "rewrite(_:detach:)")
-      public func visit(_ node: Syntax) -> Syntax {
-        var rewritten = node
-        dispatchVisit(&rewritten)
-        return rewritten
-      }
-      """
-    )
-
-    DeclSyntax(
-      """
-      public func visit<T: SyntaxChildChoices>(_ node: T) -> T {
-        var rewritten = Syntax(node)
-        dispatchVisit(&rewritten)
-        return rewritten.cast(T.self)
+      open func visit(_ token: TokenSyntax) -> TokenSyntax {
+        return token
       }
       """
     )
@@ -164,7 +159,7 @@ let syntaxRewriterFile = SourceFileSyntax(leadingTrivia: copyrightHeader) {
           ///   - Returns: the rewritten node
           \(node.apiAttributes())\
           open func visit(_ node: \(node.kind.syntaxType)) -> \(node.kind.syntaxType) {
-            return visitChildren(node._syntaxNode).cast(\(node.kind.syntaxType).self)
+            return \(node.kind.syntaxType)(unsafeCasting: visitChildren(node._syntaxNode))
           }
           """
         )
@@ -176,7 +171,7 @@ let syntaxRewriterFile = SourceFileSyntax(leadingTrivia: copyrightHeader) {
           ///   - Returns: the rewritten node
           \(node.apiAttributes())\
           open func visit(_ node: \(node.kind.syntaxType)) -> \(node.baseType.syntaxBaseName) {
-            return \(node.baseType.syntaxBaseName)(visitChildren(node._syntaxNode).cast(\(node.kind.syntaxType).self))
+            return \(node.baseType.syntaxBaseName)(\(node.kind.syntaxType)(unsafeCasting: visitChildren(node._syntaxNode)))
           }
           """
         )
@@ -193,32 +188,35 @@ let syntaxRewriterFile = SourceFileSyntax(leadingTrivia: copyrightHeader) {
         ///   - Returns: the rewritten node
         \(baseNode.apiAttributes())\
         public func visit(_ node: \(baseKind.syntaxType)) -> \(baseKind.syntaxType) {
-          var node: Syntax = Syntax(node)
-          dispatchVisit(&node)
-          return node.cast(\(baseKind.syntaxType).self)
+          visitImpl(Syntax(node)).cast(\(baseKind.syntaxType).self)
         }
         """
       )
     }
 
+    // NOTE: '@inline(never)' because perf tests showed the best results.
+    // It keeps 'dispatchVisit(_:)' function small, and make all 'case' bodies exactly the same pattern.
+    // Which enables some optimizations.
     DeclSyntax(
       """
-      /// Interpret `node` as a node of type `nodeType`, visit it, calling
-      /// the `visit` to transform the node.
-      @inline(__always)
-      private func visitImpl<NodeType: SyntaxProtocol>(
-        _ node: inout Syntax,
-        _ nodeType: NodeType.Type,
-        _ visit: (NodeType) -> some SyntaxProtocol
-      ) {
-        let origNode = node
-        visitPre(origNode)
-        node = visitAny(origNode) ?? Syntax(visit(origNode.cast(NodeType.self)))
-        visitPost(origNode)
+      @inline(never)
+      private func visitTokenSyntaxImpl(_ node: Syntax) -> Syntax {
+        Syntax(visit(TokenSyntax(unsafeCasting: node)))
       }
       """
     )
 
+    for node in NON_BASE_SYNTAX_NODES {
+      DeclSyntax(
+        """
+        @inline(never)
+        private func visit\(node.kind.syntaxType)Impl(_ node: Syntax) -> Syntax {
+          Syntax(visit(\(node.kind.syntaxType)(unsafeCasting: node)))
+        }
+        """
+      )
+    }
+
     try IfConfigDeclSyntax(
       leadingTrivia:
         """
@@ -255,26 +253,26 @@ let syntaxRewriterFile = SourceFileSyntax(leadingTrivia: copyrightHeader) {
                 /// that determines the correct visitation function will be popped of the
                 /// stack before the function is being called, making the switch's stack
                 /// space transient instead of having it linger in the call stack.
-                private func visitationFunc(for node: Syntax) -> ((inout Syntax) -> Void)
+                private func visitationFunc(for node: Syntax) -> (Syntax) -> Syntax
                 """
               ) {
                 try SwitchExprSyntax("switch node.raw.kind") {
                   SwitchCaseSyntax("case .token:") {
-                    StmtSyntax("return { self.visitImpl(&$0, TokenSyntax.self, self.visit) }")
+                    StmtSyntax("return self.visitTokenSyntaxImpl(_:)")
                   }
 
                   for node in NON_BASE_SYNTAX_NODES {
                     SwitchCaseSyntax("case .\(node.enumCaseCallName):") {
-                      StmtSyntax("return { self.visitImpl(&$0, \(node.kind.syntaxType).self, self.visit) }")
+                      StmtSyntax("return self.visit\(node.kind.syntaxType)Impl(_:)")
                     }
                   }
                 }
               }
 
               DeclSyntax(
                 """
-                private func dispatchVisit(_ node: inout Syntax) {
-                  visitationFunc(for: node)(&node)
+                private func dispatchVisit(_ node: Syntax) -> Syntax {
+                  visitationFunc(for: node)(node)
                 }
                 """
               )
@@ -285,15 +283,15 @@ let syntaxRewriterFile = SourceFileSyntax(leadingTrivia: copyrightHeader) {
           poundKeyword: .poundElseToken(),
           elements: .statements(
             CodeBlockItemListSyntax {
-              try! FunctionDeclSyntax("private func dispatchVisit(_ node: inout Syntax)") {
+              try! FunctionDeclSyntax("private func dispatchVisit(_ node: Syntax) -> Syntax") {
                 try SwitchExprSyntax("switch node.raw.kind") {
                   SwitchCaseSyntax("case .token:") {
-                    StmtSyntax("return visitImpl(&node, TokenSyntax.self, visit)")
+                    StmtSyntax("return visitTokenSyntaxImpl(node)")
                   }
 
                   for node in NON_BASE_SYNTAX_NODES {
                     SwitchCaseSyntax("case .\(node.enumCaseCallName):") {
-                      StmtSyntax("return visitImpl(&node, \(node.kind.syntaxType).self, visit)")
+                      StmtSyntax("return visit\(node.kind.syntaxType)Impl(node)")
                     }
                   }
                 }
@@ -304,6 +302,16 @@ let syntaxRewriterFile = SourceFileSyntax(leadingTrivia: copyrightHeader) {
       }
     )
 
+    DeclSyntax(
+      """
+      private func visitImpl(_ node: Syntax) -> Syntax {
+        visitPre(node)
+        defer { visitPost(node) }
+        return visitAny(node) ?? dispatchVisit(node)
+      }
+      """
+    )
+
     DeclSyntax(
       """
       private func visitChildren(_ node: Syntax) -> Syntax {
@@ -325,9 +333,7 @@ let syntaxRewriterFile = SourceFileSyntax(leadingTrivia: copyrightHeader) {
         for case let (child?, info) in RawSyntaxChildren(node) where viewMode.shouldTraverse(node: child) {
 
           // Build the Syntax node to rewrite
-          var childNode = nodeFactory.create(parent: node, raw: child, absoluteInfo: info)
-
-          dispatchVisit(&childNode)
+          var childNode = visitImpl(nodeFactory.create(parent: node, raw: child, absoluteInfo: info))
           if childNode.raw.id != child.id {
             // The node was rewritten, let's handle it