Add experimental flag and keyPathMethodComponent node.

Author: amritpan

CodeGeneration/Sources/SyntaxSupport/ExperimentalFeatures.swift

@@ -22,6 +22,7 @@ public enum ExperimentalFeature: String, CaseIterable {
   case valueGenerics
   case abiAttribute
   case unsafeExpression
+  case keypathWithMethodMembers
 
   /// The name of the feature as it is written in the compiler's `Features.def` file.
   public var featureName: String {
@@ -44,6 +45,8 @@ public enum ExperimentalFeature: String, CaseIterable {
       return "ABIAttribute"
     case .unsafeExpression:
       return "WarnUnsafe"
+    case .keypathWithMethodMembers:
+      return "KeypathWithMethodMembers"
     }
   }
 
@@ -68,6 +71,8 @@ public enum ExperimentalFeature: String, CaseIterable {
       return "@abi attribute"
     case .unsafeExpression:
       return "'unsafe' expression"
+    case .keypathWithMethodMembers:
+      return "keypaths with method members"
     }
   }
 

CodeGeneration/Sources/SyntaxSupport/ExprNodes.swift

@@ -1209,6 +1209,10 @@ public let EXPR_NODES: [Node] = [
             name: "property",
             kind: .node(kind: .keyPathPropertyComponent)
           ),
+          Child(
+            name: "method",
+            kind: .node(kind: .keyPathMethodComponent)
+          ),
           Child(
             name: "subscript",
             kind: .node(kind: .keyPathSubscriptComponent)
@@ -1313,6 +1317,35 @@ public let EXPR_NODES: [Node] = [
     ]
   ),
 
+  Node(
+    kind: .keyPathMethodComponent,
+    base: .syntax,
+    nameForDiagnostics: "key path method component",
+    documentation: "A key path component like `.method()`, `.method(10)`, or `.method(val: 10)`.",
+    traits: [
+      "Parenthesized"
+    ],
+    children: [
+      Child(
+        name: "declName",
+        kind: .node(kind: .declReferenceExpr)
+      ),
+      Child(
+        name: "leftParen",
+        kind: .token(choices: [.token(.leftParen)])
+      ),
+      Child(
+        name: "arguments",
+        kind: .collection(kind: .labeledExprList, collectionElementName: "Argument"),
+        nameForDiagnostics: "arguments"
+      ),
+      Child(
+        name: "rightParen",
+        kind: .token(choices: [.token(.rightParen)])
+      ),
+    ]
+  ),
+
   Node(
     kind: .macroExpansionExpr,
     base: .expr,

CodeGeneration/Sources/SyntaxSupport/SyntaxNodeKind.swift

@@ -178,6 +178,7 @@ public enum SyntaxNodeKind: String, CaseIterable, IdentifierConvertible, TypeCon
   case keyPathOptionalComponent
   case keyPathPropertyComponent
   case keyPathSubscriptComponent
+  case keyPathMethodComponent
   case labeledExpr
   case labeledExprList
   case labeledSpecializeArgument