anchor.diff:  
     void pushForControlFlowInfo(Token? awaitToken, Token forToken,
         Token leftParenthesis, ForLoopPartsImpl forLoopParts, Object entry) {
  -    if (entry == _invalidCollectionElement) {
  -      push(_invalidCollectionElement);
  -    } else if (enableControlFlowCollections) {
  -      push(
  -        ForElementImpl(
  -          awaitKeyword: awaitToken,
  -          forKeyword: forToken,
  -          leftParenthesis: leftParenthesis,
  -          forLoopParts: forLoopParts,
  -          rightParenthesis: leftParenthesis.endGroup!,
  -          body: entry as CollectionElementImpl,
  -        ),
  -      );
  -    } else {
  -      _reportFeatureNotEnabled(
  -        feature: ExperimentalFeatures.control_flow_collections,
  -        startToken: forToken,
  -      );
  -      push(_invalidCollectionElement);
  -    }
  +    push(
  +      ForElementImpl(
  +        awaitKeyword: awaitToken,
  +        forKeyword: forToken,
  +        leftParenthesis: leftParenthesis,
  +        forLoopParts: forLoopParts,
  +        rightParenthesis: leftParenthesis.endGroup!,
  +        body: entry as CollectionElementImpl,
  +      ),
  +    );
     }
   
     void pushIfControlFlowInfo(
  
positive.code: import 'package:collection/collection.dart';
  import 'package:pub_semver/pub_semver.dart';
  
  const _invalidCollectionElement = _InvalidCollectionElement._();
  
  /// A parser listener that builds the analyzer's AST structure.
  class AstBuilder extends StackListener {
    final AstFactoryImpl ast = astFactory;
  
negative.code:   /// `true` if non-nullable behavior is enabled.
    final bool enableNonNullable;
  
    /// `true` if triple-shift behavior is enabled
    final bool enableTripleShift;
  
  