Document why things are @frozen.

Author: DougGregor

Sources/SwiftSyntax/Raw/RawSyntaxNodes.swift.gyb

@@ -39,7 +39,7 @@ public struct Raw${node.name}: Raw${node.name if node.is_base() else node.base_t
 %      enums.append(('Element', [(NODE_MAP[choice_name].swift_syntax_kind, NODE_MAP[choice_name].name) for choice_name in node.collection_element_choices]))
 %   end
 %   for (name, choices) in enums:
-  @frozen
+  @frozen // FIXME: Not actually stable, works around a miscompile
   public enum ${name}: RawSyntaxNodeProtocol {
 %     for (swift_name, type_name) in choices:
     case `${swift_name}`(Raw${type_name})

Sources/SwiftSyntax/SyntaxCollections.swift.gyb

@@ -45,7 +45,7 @@ public extension SyntaxCollection {
 % end
 public struct ${node.name}: SyntaxCollection, SyntaxHashable {
 % if node.collection_element_choices:
-  @frozen
+  @frozen // FIXME: Not actually stable, works around a miscompile
   public enum Element: SyntaxChildChoices {
 %   for choice_name in node.collection_element_choices:
 %     choice = NODE_MAP[choice_name]

Sources/SwiftSyntax/SyntaxEnum.swift.gyb

@@ -20,7 +20,7 @@
 //===----------------------------------------------------------------------===//
 
 /// Enum to exhaustively switch over all different syntax nodes.
-@frozen
+@frozen // FIXME: Not actually stable, works around a miscompile
 public enum SyntaxEnum {
   case unknown(UnknownSyntax)
   case token(TokenSyntax)

Sources/SwiftSyntax/SyntaxKind.swift.gyb

@@ -19,7 +19,7 @@
 //===----------------------------------------------------------------------===//
 
 /// Enumerates the known kinds of Syntax represented in the Syntax tree.
-@frozen
+@frozen // FIXME: Not actually stable, works around a miscompile
 public enum SyntaxKind {
   case token
   case unknown

Sources/SwiftSyntax/SyntaxNodes.swift.gyb.template

@@ -49,6 +49,7 @@ nodes whose base kind are that specified kind.
 public struct ${node.name}: ${base_type}Protocol, SyntaxHashable {
 %     for child in node.children:
 %       if child.node_choices:
+  // FIXME: Not actually stable, works around a miscompile
   public enum ${child.name}: SyntaxChildChoices {
 %         for choice in child.node_choices:
     case `${choice.swift_name}`(${choice.type_name})

Sources/SwiftSyntax/TokenKind.swift.gyb

@@ -18,7 +18,7 @@
 //===----------------------------------------------------------------------===//
 
 /// Enumerates the kinds of tokens in the Swift language.
-@frozen
+@frozen // FIXME: Not actually stable, works around a miscompile
 public enum TokenKind: Hashable {
   case eof
 % for token in SYNTAX_TOKENS:
@@ -144,7 +144,7 @@ extension TokenKind: Equatable {
 }
 
 /// Plain token kind value, without an associated `String` value.
-@frozen
+@frozen // FIXME: Not actually stable, works around a miscompile
 public enum RawTokenKind: Equatable, Hashable {
   case eof
 % for token in SYNTAX_TOKENS: