[Syntax] Introduce SyntaxLayout

This replaces most use case of `keyPathInParent` and
`SyntaxNodeStructure.layout`. Since getting and comparing `KeyPath` is
not trivial, `keyPathInParent` were suffered from performance issue,

Newly introduced `SyntaxProtocol.propertyInParent` is trivial, and
comparing it with a SyntaxLayoutProperty is also trivial.

Author: rintaro

CodeGeneration/Sources/SyntaxSupport/SyntaxNodeKind.swift

@@ -376,19 +376,6 @@ public enum SyntaxNodeKind: String, CaseIterable, IdentifierConvertible, TypeCon
     return "\(syntaxType)Protocol"
   }
 
-  /// For base node types, generates the name of the protocol to which all
-  /// concrete leaf nodes that derive from this base kind should conform.
-  ///
-  /// - Warning: This property can only be accessed for base node kinds; attempting to
-  /// access it for a non-base kind will result in a runtime error.
-  public var leafProtocolType: TypeSyntax {
-    if isBase {
-      return "_Leaf\(syntaxType)NodeProtocol"
-    } else {
-      fatalError("Only base kind can define leaf protocol")
-    }
-  }
-
   /// If the syntax kind has been renamed, the previous raw value that is now
   /// deprecated.
   public var deprecatedRawValue: String? {

CodeGeneration/Sources/generate-swift-syntax/GenerateSwiftSyntax.swift

@@ -115,7 +115,7 @@ struct GenerateSwiftSyntax: AsyncParsableCommand {
       ),
 
       // SwiftSyntax
-      GeneratedFileSpec(swiftSyntaxGeneratedDir + ["ChildNameForKeyPath.swift"], childNameForKeyPathFile),
+      GeneratedFileSpec(swiftSyntaxGeneratedDir + ["ConcreteSyntaxProperty.swift"], concreteSyntaxPropertyFile),
       GeneratedFileSpec(swiftSyntaxGeneratedDir + ["Keyword.swift"], keywordFile),
       GeneratedFileSpec(swiftSyntaxGeneratedDir + ["raw", "RawSyntaxValidation.swift"], rawSyntaxValidationFile),
       GeneratedFileSpec(
@@ -128,6 +128,7 @@ struct GenerateSwiftSyntax: AsyncParsableCommand {
       GeneratedFileSpec(swiftSyntaxGeneratedDir + ["SyntaxCollections.swift"], syntaxCollectionsFile),
       GeneratedFileSpec(swiftSyntaxGeneratedDir + ["SyntaxEnum.swift"], syntaxEnumFile),
       GeneratedFileSpec(swiftSyntaxGeneratedDir + ["SyntaxKind.swift"], syntaxKindFile),
+      GeneratedFileSpec(swiftSyntaxGeneratedDir + ["SyntaxLayoutPropertyName.swift"], syntaxLayoutPropertyNameFile),
       GeneratedFileSpec(swiftSyntaxGeneratedDir + ["SyntaxRewriter.swift"], syntaxRewriterFile),
       GeneratedFileSpec(swiftSyntaxGeneratedDir + ["SyntaxTraits.swift"], syntaxTraitsFile),
       GeneratedFileSpec(

CodeGeneration/Sources/generate-swift-syntax/templates/swiftparserdiagnostics/ChildNameForDiagnosticsFile.swift

@@ -27,13 +27,13 @@ let childNameForDiagnosticFile = SourceFileSyntax(leadingTrivia: copyrightHeader
   )
 
   try! FunctionDeclSyntax(
-    "private func childNameForDiagnostics(_ keyPath: AnyKeyPath) -> String?"
+    "private func childNameForDiagnostics(_ property: SyntaxLayoutProperty) -> String?"
   ) {
-    try! SwitchExprSyntax("switch keyPath") {
+    try! SwitchExprSyntax("switch property") {
       for node in NON_BASE_SYNTAX_NODES.compactMap(\.layoutNode) {
         for child in node.children {
           if let nameForDiagnostics = child.nameForDiagnostics {
-            SwitchCaseSyntax("case \\\(node.type.syntaxBaseName).\(child.memberCallName):") {
+            SwitchCaseSyntax("case \(node.type.syntaxBaseName).layout[.\(child.memberCallName)]:") {
               StmtSyntax(#"return "\#(raw: nameForDiagnostics)""#)
             }
           }
@@ -52,10 +52,10 @@ let childNameForDiagnosticFile = SourceFileSyntax(leadingTrivia: copyrightHeader
     """
     extension SyntaxProtocol {
       var childNameInParent: String? {
-        guard let keyPath = self.keyPathInParent else {
+        guard let property = self.propertyInParent else {
           return nil
         }
-        return childNameForDiagnostics(keyPath)
+        return childNameForDiagnostics(property)
       }
     }
     """

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

@@ -0,0 +1,51 @@
+//===----------------------------------------------------------------------===//
+//
+// This source file is part of the Swift.org open source project
+//
+// Copyright (c) 2014 - 2023 Apple Inc. and the Swift project authors
+// Licensed under Apache License v2.0 with Runtime Library Exception
+//
+// See https://swift.org/LICENSE.txt for license information
+// See https://swift.org/CONTRIBUTORS.txt for the list of Swift project authors
+//
+//===----------------------------------------------------------------------===//
+
+import SwiftSyntax
+import SwiftSyntaxBuilder
+import SyntaxSupport
+import Utils
+
+let concreteSyntaxPropertyFile = SourceFileSyntax(leadingTrivia: copyrightHeader) {
+  DeclSyntax(
+    """
+    extension ConcreteSyntaxProperty {
+      fileprivate init(_ index: Int) {
+        self.index = .init(index)
+      }
+    }
+    """
+  )
+
+  for node in NON_BASE_SYNTAX_NODES {
+    if let layoutNode = node.layoutNode {
+      try! ExtensionDeclSyntax(
+        "\(node.apiAttributes())extension ConcreteSyntaxProperty where Base == \(node.kind.syntaxType)"
+      ) {
+        for (index, child) in layoutNode.children.enumerated() {
+          let childType: TypeSyntax =
+            child.kind.isNodeChoicesEmpty
+            ? child.syntaxNodeKind.syntaxType
+            : "\(node.kind.syntaxType).\(child.syntaxChoicesType)"
+          let type = child.isOptional ? TypeSyntax("\(childType)?") : TypeSyntax("\(childType)")
+          DeclSyntax(
+            """
+            public static var \(child.varDeclName): ConcreteSyntaxProperty<\(node.kind.syntaxType), \(type)> {
+              .init(\(raw: index))
+            }
+            """
+          )
+        }
+      }
+    }
+  }
+}

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

@@ -287,8 +287,7 @@ let syntaxBaseNodesFile = SourceFileSyntax(leadingTrivia: copyrightHeader) {
       }
     }
 
-    leafProtocolDecl(type: node.kind.leafProtocolType, inheritedType: node.kind.protocolType)
-    leafProtocolExtension(type: node.kind.leafProtocolType, inheritedType: node.kind.protocolType)
+    leafProtocolExtension(inheritedType: node.kind.protocolType)
   }
 
   try! ExtensionDeclSyntax(
@@ -317,27 +316,13 @@ let syntaxBaseNodesFile = SourceFileSyntax(leadingTrivia: copyrightHeader) {
     }
   }
 
-  leafProtocolDecl(type: "_LeafSyntaxNodeProtocol", inheritedType: "SyntaxProtocol")
-  leafProtocolExtension(type: "_LeafSyntaxNodeProtocol", inheritedType: "SyntaxProtocol")
+  leafProtocolExtension(inheritedType: "SyntaxProtocol")
 }
 
-private func leafProtocolDecl(type: TypeSyntax, inheritedType: TypeSyntax) -> DeclSyntax {
-  DeclSyntax(
-    """
-    /// Protocol that syntax nodes conform to if they don't have any semantic subtypes.
-    /// These are syntax nodes that are not considered base nodes for other syntax types.
-    ///
-    /// Syntax nodes conforming to this protocol have their inherited casting methods
-    /// deprecated to prevent incorrect casting.
-    public protocol \(type): \(inheritedType) {}
-    """
-  )
-}
-
-private func leafProtocolExtension(type: TypeSyntax, inheritedType: TypeSyntax) -> DeclSyntax {
-  DeclSyntax(
+private func leafProtocolExtension(inheritedType: TypeSyntax) -> DeclSyntax {
+  return DeclSyntax(
     #"""
-    extension \#(type) {
+    extension _LeafSyntaxNodeProtocol where Self: \#(inheritedType) {
       /// Checks if the current leaf syntax node can be cast to a different specified type.
       ///
       /// - Returns: `false` since the leaf node cannot be cast to a different specified type.

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

@@ -59,7 +59,7 @@ let syntaxCollectionsFile = SourceFileSyntax(leadingTrivia: copyrightHeader) {
         """
       )
 
-      DeclSyntax("public static let syntaxKind = SyntaxKind.\(node.memberCallName)")
+      DeclSyntax("public static var syntaxKind: SyntaxKind { .\(node.enumCaseCallName) }")
     }
   }
 }

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

@@ -46,6 +46,20 @@ let syntaxKindFile = SourceFileSyntax(leadingTrivia: copyrightHeader) {
       }
     }
 
+    try VariableDeclSyntax("public var isLayout: Bool") {
+      try SwitchExprSyntax("switch self") {
+        for node in SYNTAX_NODES where node.layoutNode != nil {
+          SwitchCaseSyntax("case .\(node.enumCaseCallName):") {
+            StmtSyntax("return true")
+          }
+        }
+
+        SwitchCaseSyntax("default:") {
+          StmtSyntax("return false")
+        }
+      }
+    }
+
     try VariableDeclSyntax("public var isMissing: Bool") {
       try SwitchExprSyntax("switch self") {
         for name in SyntaxNodeKind.allCases where name.isMissing {

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

@@ -0,0 +1,42 @@
+//===----------------------------------------------------------------------===//
+//
+// This source file is part of the Swift.org open source project
+//
+// Copyright (c) 2014 - 2023 Apple Inc. and the Swift project authors
+// Licensed under Apache License v2.0 with Runtime Library Exception
+//
+// See https://swift.org/LICENSE.txt for license information
+// See https://swift.org/CONTRIBUTORS.txt for the list of Swift project authors
+//
+//===----------------------------------------------------------------------===//
+
+import SwiftSyntax
+import SwiftSyntaxBuilder
+import SyntaxSupport
+import Utils
+
+let syntaxLayoutPropertyNameFile = try! SourceFileSyntax(leadingTrivia: copyrightHeader) {
+  try ExtensionDeclSyntax("extension SyntaxLayoutProperty") {
+    try VariableDeclSyntax(
+      """
+      /// Property name if this is a valid property.
+      /// 'nil' if the `syntaxKind` is not a layout syntax, or the index is out of range.
+      @_spi(RawSyntax)
+      public var name: String?
+      """
+    ) {
+      try SwitchExprSyntax("switch (self.syntaxKind, self.index.value)") {
+        for node in NON_BASE_SYNTAX_NODES {
+          if let layoutNode = node.layoutNode {
+            for (index, child) in layoutNode.children.enumerated() {
+              SwitchCaseSyntax("case (.\(node.enumCaseCallName), \(literal: index)):") {
+                StmtSyntax("return \(literal: child.identifier.description)")
+              }
+            }
+          }
+        }
+        SwitchCaseSyntax("default: return nil")
+      }
+    }
+  }
+}

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

@@ -30,7 +30,7 @@ func syntaxNode(nodesStartingWith: [Character]) -> SourceFileSyntax {
 
         \(SwiftSyntax.Trivia(joining: [node.documentation, node.experimentalDocNote, node.grammar, node.containedIn]))\
         \(node.node.apiAttributes())\
-        public struct \(node.kind.syntaxType): \(node.baseType.syntaxBaseName)Protocol, SyntaxHashable, \(node.base.leafProtocolType)
+        public struct \(node.kind.syntaxType): \(node.baseType.syntaxBaseName)Protocol, SyntaxHashable, _LayoutSyntaxNodeProtocol
         """
       ) {
         for childNodeChoices in node.node.childrenNodeChoices() {
@@ -208,6 +208,12 @@ func syntaxNode(nodesStartingWith: [Character]) -> SourceFileSyntax {
           }
         }
 
+        // ========
+        // Metadata
+        // ========
+
+        DeclSyntax("public static var syntaxKind: SyntaxKind { .\(node.enumCaseCallName) }")
+
         let layout = ArrayExprSyntax {
           for child in node.children {
             ArrayElementSyntax(