Add a string-based initializer for ExperimentalFeatures.

Tools (like swift-format) can use this to let users enable
experimental features in the parser via interfaces like the
command line, without having to handle the translation from
string to option set themselves.

Author: allevato

CodeGeneration/Sources/generate-swift-syntax/templates/swiftparser/ExperimentalFeaturesFile.swift

@@ -39,5 +39,26 @@ let experimentalFeaturesFile = SourceFileSyntax(leadingTrivia: copyrightHeader)
         """
       )
     }
+    
+    try! InitializerDeclSyntax(
+      """
+      /// Creates a new value representing the experimental feature with the
+      /// given name, or returns nil if the name is not recognized.
+      public init?(name: String)
+      """
+    ) {
+      try! SwitchExprSyntax("switch name") {
+        SwitchCaseListSyntax {
+          for feature in ExperimentalFeature.allCases {
+            SwitchCaseSyntax(#"case "\#(raw: feature.rawValue)":"#) {
+              ExprSyntax("self = .\(feature.token)")
+            }
+          }
+          SwitchCaseSyntax("default:") {
+            StmtSyntax("return nil")
+          }
+        }
+      }
+    }
   }
 }

Sources/SwiftParser/generated/ExperimentalFeatures.swift

@@ -44,4 +44,27 @@ extension Parser.ExperimentalFeatures {
 
   /// Whether to enable the parsing of ValueGenerics.
   public static let valueGenerics = Self (rawValue: 1 << 6)
+
+  /// Creates a new value representing the experimental feature with the
+  /// given name, or returns nil if the name is not recognized.
+  public init?(name: String) {
+    switch name {
+    case "referenceBindings":
+      self = .referenceBindings
+    case "thenStatements":
+      self = .thenStatements
+    case "doExpressions":
+      self = .doExpressions
+    case "nonescapableTypes":
+      self = .nonescapableTypes
+    case "trailingComma":
+      self = .trailingComma
+    case "coroutineAccessors":
+      self = .coroutineAccessors
+    case "valueGenerics":
+      self = .valueGenerics
+    default:
+      return nil
+    }
+  }
 }