pkg/kernel/lib/transformations/track_widget_constructor_locations.dart

// Copyright (c) 2019, the Dart project authors.  Please see the AUTHORS file
// for details. All rights reserved. Use of this source code is governed by a
// BSD-style license that can be found in the LICENSE file.

library kernel.transformations.track_widget_constructor_locations;

import '../ast.dart';
import '../target/changed_structure_notifier.dart';

// Parameter name used to track where widget constructor calls were made from.
//
// The parameter name contains a randomly generated hex string to avoid
// collision with user generated parameters.
const String _creationLocationParameterName =
    r'$creationLocationd_0dea112b090073317d4';

/// Name of private field added to the Widget class and any other classes that
/// implement Widget.
///
/// Regardless of what library a class implementing Widget is defined in, the
/// private field will always be defined in the context of the widget_inspector
/// library ensuring no name conflicts with regular fields.
const String _locationFieldName = r'_location';

bool _hasNamedParameter(FunctionNode function, String name) {
  return function.namedParameters.any(
    (NamedParameter parameter) => parameter.parameterName == name,
  );
}

bool _hasNamedArgument(Arguments arguments, String argumentName) {
  return arguments.named.any(
    (NamedExpression argument) => argument.name == argumentName,
  );
}

Variable? _getNamedParameter(FunctionNode function, String parameterName) {
  for (NamedParameter parameter in function.namedParameters) {
    if (parameter.parameterName == parameterName) {
      return parameter;
    }
  }
  return null;
}

// TODO(jacobr): find a solution that supports optional positional parameters.
/// Add the creation location to the arguments list if possible.
///
/// Returns whether the creation location argument could be added. We cannot
/// currently add the named argument for functions with optional positional
/// parameters as the current scheme requires adding the creation location as a
/// named parameter. Fortunately that is not a significant issue in practice as
/// no Widget classes in package:flutter have optional positional parameters.
/// This code degrades gracefully for constructors with optional positional
/// parameters by skipping adding the creation location argument rather than
/// failing.
void _maybeAddCreationLocationArgument(
  Arguments arguments,
  FunctionNode function,
  Expression creationLocation,
) {
  if (_hasNamedArgument(arguments, _creationLocationParameterName)) {
    return;
  }
  if (!_hasNamedParameter(function, _creationLocationParameterName)) {
    // TODO(jakemac): We don't apply the transformation to dependencies kernel
    // outlines, so instead we just assume the named parameter exists.
    //
    // The only case in which it shouldn't exist is if the function has optional
    // positional parameters so it cannot have optional named parameters.
    if (function.requiredParameterCount !=
        function.positionalParameters.length) {
      return;
    }
  }

  final NamedExpression namedArgument = new NamedExpression(
    _creationLocationParameterName,
    creationLocation,
  );
  namedArgument.parent = arguments;
  arguments.named = NamedExpressionList.generate(
    arguments.named.length + 1,
    (i) => i < arguments.named.length ? arguments.named[i] : namedArgument,
  );
}

/// Adds a named parameter to a function if the function does not already have
/// a named parameter with the name or optional positional parameters.
bool _maybeAddNamedParameter(FunctionNode function, NamedParameter parameter) {
  if (_hasNamedParameter(function, _creationLocationParameterName)) {
    // Gracefully handle if this method is called on a function that has already
    // been transformed.
    return false;
  }
  // Function has optional positional parameters so cannot have optional named
  // parameters.
  if (function.requiredParameterCount != function.positionalParameters.length) {
    return false;
  }
  parameter.parent = function;
  final NamedParameterList existing = function.namedParameters;
  function.namedParameters = NamedParameterList.generate(
    existing.length + 1,
    (int i) => i < existing.length ? existing[i] : parameter,
  );
  return true;
}

/// Transformer that modifies all calls to Widget constructors and "Widget
/// factories" to include a _Location parameter specifying the location where
/// the constructor or widget factory call was made.
///
/// This transformer requires that all Widget constructors and Widget factories
/// have already been transformed to have a named parameter with the name
/// specified by `_locationParameterName`.
///
/// A "Widget factory" is an extension instance method annotated with the
/// `@widgetFactory` annotations. A _Location parameter is added to such methods
/// and this is used as the location value for all Widget constructor
/// invocations within the method.
class _WidgetCallSiteTransformer extends Transformer {
  final WidgetCreatorTracker _tracker;

  /// The creation location parameter of the extension factory method enclosing
  /// the node that is currently being transformed.
  ///
  /// Used to flow the creation location parameter to the call sites of widget
  /// constructors and extension factory methods within an enclosing extension
  /// factory method.
  Expression? _currentExtensionFactoryLocationParameter;

  /// Current factory constructor that node being transformed is inside.
  ///
  /// Used to flow the location passed in as an argument to the factory to the
  /// actual constructor call within the factory.
  Procedure? _currentFactory;

  /// Library that contains the transformed call sites.
  ///
  /// The transformation of the call sites is affected by the NNBD opt-in status
  /// of the library.
  Library? _currentLibrary;

  new({required WidgetCreatorTracker tracker}) : _tracker = tracker;

  /// Builds a call to the const constructor of the _Location
  /// object specifying the location where a constructor call was made and
  /// optionally the locations for all parameters passed in.
  ///
  /// Specifying the parameters passed in is an experimental feature. With
  /// access to the source code of an application you could determine the
  /// locations of the parameters passed in from the source location of the
  /// constructor call but it is convenient to bundle the location and names
  /// of the parameters passed in so that tools can show parameter locations
  /// without re-parsing the source code.
  ConstructorInvocation _constructLocation(
    Location location, {
    required Class locationClass,
    String? name,
  }) {
    final NamedExpressionList arguments = NamedExpressionList(
      new NamedExpression('file', new StringLiteral(location.file.toString())),
      new NamedExpression('line', new IntLiteral(location.line)),
      new NamedExpression('column', new IntLiteral(location.column)),
      name != null
          ? new NamedExpression('name', new StringLiteral(name))
          : null,
    );

    return new ConstructorInvocation(
      locationClass.constructors.first,
      new Arguments(ExpressionList.empty, named: arguments),
      isConst: true,
    );
  }

  @override
  Procedure visitProcedure(Procedure node) {
    if (_isWidgetFactory(node)) {
      final NamedParameter locationParameter = node.function.namedParameters
          .firstWhere(
            (parameter) =>
                parameter.parameterName == _creationLocationParameterName,
          );
      _currentExtensionFactoryLocationParameter = VariableGet(
        locationParameter,
      );
      node.transformChildren(this);
      _currentExtensionFactoryLocationParameter = null;
      return node;
    }
    if (node.isFactory) {
      _currentFactory = node;
      node.transformChildren(this);
      _currentFactory = null;
      return node;
    }
    node.transformChildren(this);
    return node;
  }

  bool _isWidgetFactory(Procedure node) {
    return node.isExtensionMember &&
        _hasNamedParameter(node.function, _creationLocationParameterName);
  }

  @override
  StaticInvocation visitStaticInvocation(StaticInvocation node) {
    node.transformChildren(this);
    final Procedure target = node.target;
    if (target.isFactory) {
      final Class constructedClass = target.enclosingClass!;
      final _TrackingClasses? tracking = _tracker._getTrackingClasses(
        constructedClass,
      );
      if (tracking == null) {
        return node;
      }

      _addLocationArgument(
        node,
        target.function,
        constructedClass: constructedClass,
        isConst: node.isConst,
        locationClass: tracking.locationClass,
      );
      return node;
    }
    if (_isWidgetFactory(target)) {
      final NamedParameter parameter = target.function.namedParameters
          .firstWhere((p) => p.parameterName == _creationLocationParameterName);
      final DartType type = parameter.type;
      if (type is InterfaceType) {
        _addLocationArgument(
          node,
          target.function,
          locationClass: type.classNode,
        );
        return node;
      }
    }
    return node;
  }

  void _addLocationArgument(
    InvocationExpression node,
    FunctionNode function, {
    Class? constructedClass,
    bool isConst = false,
    required Class locationClass,
  }) {
    Expression? location = _currentExtensionFactoryLocationParameter;
    if (location == null ||
        // We cannot pass the location parameter of the enclosing extension
        // factory method to a const constructor call, so we fallback to
        // passing the location of the constructor call.
        isConst) {
      location = _computeLocation(
        node,
        function,
        constructedClass,
        isConst: isConst,
        locationClass: locationClass,
      );
    }
    _maybeAddCreationLocationArgument(node.arguments, function, location);
  }

  @override
  ConstructorInvocation visitConstructorInvocation(ConstructorInvocation node) {
    node.transformChildren(this);

    final Constructor constructor = node.target;
    final Class constructedClass = constructor.enclosingClass;
    final _TrackingClasses? tracking = _tracker._getTrackingClasses(
      constructedClass,
    );
    if (tracking == null) {
      return node;
    }

    _addLocationArgument(
      node,
      constructor.function,
      constructedClass: constructedClass,
      isConst: node.isConst,
      locationClass: tracking.locationClass,
    );
    return node;
  }

  Expression _computeLocation(
    InvocationExpression node,
    FunctionNode function,
    Class? constructedClass, {
    bool isConst = false,
    required Class locationClass,
  }) {
    assert(constructedClass != null || !isConst);

    // For factory constructors we need to use the location specified as an
    // argument to the factory constructor rather than the location
    if (constructedClass != null &&
        _currentFactory != null &&
        _tracker._isSubclassWhere(
          constructedClass,
          (Class c) => c == _currentFactory!.enclosingClass!,
        ) &&
        // If the constructor invocation is constant we cannot refer to the
        // location parameter of the surrounding factory since it isn't a
        // constant expression.
        !isConst) {
      final Variable? creationLocationParameter = _getNamedParameter(
        _currentFactory!.function,
        _creationLocationParameterName,
      );
      if (creationLocationParameter != null) {
        return new VariableGet(creationLocationParameter);
      }
    }

    if (node.location == null) {
      return new NullLiteral();
    }

    return _constructLocation(
      node.location!,
      locationClass: locationClass,
      name:
          constructedClass?.name ??
          // For extension factory methods we use the name of the method.
          (function.parent! as Procedure).name.text,
    );
  }

  void enterLibrary(Library library) {
    assert(
      _currentLibrary == null,
      "Attempting to enter library '${library.fileUri}' "
      "without having exited library '${_currentLibrary!.fileUri}'.",
    );
    _currentLibrary = library;
  }

  void exitLibrary() {
    assert(
      _currentLibrary != null,
      "Attempting to exit a library without having entered one.",
    );
    _currentLibrary = null;
  }
}

/// Rewrites all Widget constructors, constructor invocations,
/// "Widget factories", and Widget factory invocations to add a
/// parameter specifying the location the constructor/factory was called from.
///
/// The creation location is stored as a private field named `_location`
/// on the base Widget class and flowed through the constructors using a named
/// parameter.
///
/// A "Widget factory" is an extension instance method annotated with the
/// `@widgetFactory` annotations. A _Location parameter is added to such methods
/// and this is used as the location value for all Widget constructor
/// invocations within the method.
class WidgetCreatorTracker {
  bool _foundClasses = false;

  /// The [Widget] class defined in the `package:flutter` library.
  ///
  /// Used to perform is-tests to determine whether Dart constructor calls are
  /// creating [Widget] objects.
  Class? _widgetClass;

  /// The _Location class defined in the `package:flutter` library.
  Class? _locationClass;

  /// The _HasCreationLocation class defined in the `package:flutter` library.
  ///
  /// Marker interface indicating that a private _location field is available.
  Class? _hasCreationLocationClass;

  /// Annotation class used to mark an extension method as a "Widget factory".
  ///
  /// Widgets created within the body of an extension factory method will have
  /// their creation location set to the call site of the extension factory
  /// method.
  Class? _widgetFactoryClass;

  /// The _HasCreationLocation class defined in the `dart:developer` library.
  Class? _developerHasCreationLocationClass;

  /// The CreationLocation class defined in the `dart:developer` library.
  Class? _developerCreationLocationClass;

  void _resolveWellKnownClasses(Iterable<Library> libraries) {
    // If the Widget or Debug location classes have been updated we need to get
    // the latest version
    for (Library library in libraries) {
      final Uri importUri = library.importUri;

      // Legacy Case: Search for hardcoded Flutter classes.
      // TODO(http://dartbug.com/63225): Remove this once Flutter is migrated
      // to the new API.
      if (importUri.isScheme('package')) {
        if (importUri.path == 'flutter/src/widgets/framework.dart') {
          for (Class class_ in library.classes) {
            if (class_.name == 'Widget') {
              _widgetClass = class_;
            }
          }
        } else {
          if (importUri.path == 'flutter/src/widgets/widget_inspector.dart') {
            for (Class class_ in library.classes) {
              if (class_.name == '_HasCreationLocation') {
                _hasCreationLocationClass = class_;
              } else if (class_.name == '_Location') {
                _locationClass = class_;
              } else if (class_.name == '_WidgetFactory') {
                _widgetFactoryClass = class_;
              }
            }
          }
        }
      }

      // New Case: Search for classes in `dart:developer`
      if (importUri.isScheme('dart') && importUri.path == 'developer') {
        for (Class class_ in library.classes) {
          if (class_.name == '_HasCreationLocation') {
            _developerHasCreationLocationClass = class_;
          } else if (class_.name == 'CreationLocation') {
            _developerCreationLocationClass = class_;
          }
        }
      }
    }
    // TODO(johnniwinther): Require the [_widgetFactoryClass] once the
    //  `widgetFactory` is stable in flutter.
    _foundClasses =
        (_widgetClass != null &&
            _hasCreationLocationClass != null &&
            _locationClass != null) ||
        (_developerHasCreationLocationClass != null &&
            _developerCreationLocationClass != null);
  }

  /// Modify [clazz] to add the location field that is
  /// the first parameter of all constructors of the class.
  ///
  /// This method should only be called for classes that implement but do not
  /// extend the tracking base class.
  void _transformClassImplementingTrackingClass(
    Class clazz,
    _TrackingClasses tracking,
    ChangedStructureNotifier? changedStructureNotifier,
  ) {
    if (clazz.fields.any(
      (Field field) => field.name.text == tracking.locationFieldName,
    )) {
      // This class has already been transformed. Skip
      return;
    }
    clazz.implementedTypes.add(
      new Supertype(tracking.hasCreationLocationClass, DartTypeList.empty),
    );
    changedStructureNotifier?.registerClassHierarchyChange(clazz);

    // We intentionally use the library context of the _HasCreationLocation
    // class for the private field even if [clazz] is in a different library
    // so that all classes implementing the tracking class behave consistently.
    final Name fieldName = new Name(
      tracking.locationFieldName,
      tracking.hasCreationLocationClass.enclosingLibrary,
    );
    final Field locationField = new Field.immutable(
      fieldName,
      type: new InterfaceType(
        tracking.locationClass,
        clazz.enclosingLibrary.nullable,
      ),
      isFinal: true,
      fieldReference: clazz.reference.canonicalName
          ?.getChildFromFieldWithName(fieldName)
          .reference,
      getterReference: clazz.reference.canonicalName
          ?.getChildFromFieldGetterWithName(fieldName)
          .reference,
      fileUri: clazz.fileUri,
    );
    clazz.addField(locationField);

    final Set<Constructor> _handledConstructors =
        new Set<Constructor>.identity();

    void handleConstructor(Constructor constructor) {
      if (!_handledConstructors.add(constructor)) {
        return;
      }
      assert(
        !_hasNamedParameter(
          constructor.function,
          _creationLocationParameterName,
        ),
      );
      final NamedParameter parameter = new NamedParameter(
        parameterName: _creationLocationParameterName,
        type: new InterfaceType(
          tracking.locationClass,
          clazz.enclosingLibrary.nullable,
        ),
        defaultValue: new NullLiteral(),
      );
      if (!_maybeAddNamedParameter(constructor.function, parameter)) {
        return;
      }

      bool hasRedirectingInitializer = false;
      for (Initializer initializer in constructor.initializers) {
        if (initializer is RedirectingInitializer) {
          if (initializer.target.enclosingClass == clazz) {
            // We need to handle this constructor first or the call to
            // addDebugLocationArgument below will fail due to the named
            // parameter not yet existing on the constructor.
            handleConstructor(initializer.target);
          }
          _maybeAddCreationLocationArgument(
            initializer.arguments,
            initializer.target.function,
            new VariableGet(parameter),
          );
          hasRedirectingInitializer = true;
          break;
        }
      }
      if (!hasRedirectingInitializer) {
        constructor.initializers.add(
          new FieldInitializer(locationField, new VariableGet(parameter)),
        );
        // TODO(jacobr): add an assert verifying the locationField is not
        // null. Currently, we cannot safely add this assert because we do not
        // handle Widget classes with optional positional arguments. There are
        // no Widget classes in the flutter repo with optional positional
        // arguments but it is possible users could add classes with optional
        // positional arguments.
        //
        // constructor.initializers.add(new AssertInitializer(
        //   new AssertStatement(
        //     new IsExpression(
        //         new VariableGet(variable), tracking.locationClass.thisType),
        //     conditionStartOffset: constructor.fileOffset,
        //     conditionEndOffset: constructor.fileOffset,
        // )));
      }
    }

    // Add named parameters to all constructors.
    clazz.constructors.forEach(handleConstructor);
  }

  /// Transform the given [libraries].
  ///
  /// The [moduleLibraries] are searched for the Widget class,
  /// the _Location class, the _HasCreationLocation class and the
  /// _WidgetFactory class.
  /// If the component does not contain them, the ones from a previous run is
  /// used (if any), otherwise no transformation is performed.
  ///
  /// Upon transformation the [changedStructureNotifier] (if provided) is used
  /// to notify the listener that  that class hierarchy of certain classes has
  /// changed. This is necessary for instance when doing an incremental
  /// compilation where the class hierarchy is kept between compiles and thus
  /// has to be kept up to date.
  void transform(
    List<Library> libraries,
    List<Library> moduleLibraries,
    ChangedStructureNotifier? changedStructureNotifier,
  ) {
    if (libraries.isEmpty) {
      return;
    }

    _resolveWellKnownClasses(moduleLibraries);

    if (!_foundClasses) {
      // Neither package:flutter nor dart:developer tracking classes found.
      return;
    }

    final Set<Class> transformedClasses = new Set<Class>.identity();
    final Set<Extension> transformedExtensions = new Set<Extension>.identity();
    final Set<Library> librariesToTransform = new Set<Library>.identity()
      ..addAll(libraries);

    for (Library library in libraries) {
      for (Class class_ in library.classes) {
        _transformWidgetConstructors(
          librariesToTransform,
          transformedClasses,
          class_,
          changedStructureNotifier,
        );
      }
      for (Extension extension in library.extensions) {
        _transformExtension(
          librariesToTransform,
          transformedExtensions,
          extension,
        );
      }
    }

    // Transform call sites to pass the location parameter.
    final _WidgetCallSiteTransformer callsiteTransformer =
        new _WidgetCallSiteTransformer(tracker: this);

    for (Library library in libraries) {
      callsiteTransformer.enterLibrary(library);
      library.transformChildren(callsiteTransformer);
      callsiteTransformer.exitLibrary();
    }
  }

  _TrackingClasses? _getTrackingClasses(Class clazz) {
    // New Case: Check for 'pragma('track-creation-locations')' annotation.
    if (_hasTrackCreationLocationsPragmaAnnotation(clazz)) {
      if (_developerHasCreationLocationClass != null &&
          _developerCreationLocationClass != null) {
        return new _TrackingClasses(
          hasCreationLocationClass: _developerHasCreationLocationClass!,
          locationClass: _developerCreationLocationClass!,
          locationFieldName: _locationFieldName,
        );
      }
    }

    // Legacy Case: Check for widget class.
    if (_isSubclassOfWidget(clazz)) {
      if (_hasCreationLocationClass != null && _locationClass != null) {
        return new _TrackingClasses(
          hasCreationLocationClass: _hasCreationLocationClass!,
          locationClass: _locationClass!,
          locationFieldName: _locationFieldName,
        );
      }
    }

    return null;
  }

  bool _isSubclassOfWidget(Class clazz) {
    if (_widgetClass == null) return false;
    return _isSubclassWhere(clazz, (Class c) => c == _widgetClass);
  }

  bool _hasTrackCreationLocationsPragmaAnnotation(Class clazz) {
    if (_developerHasCreationLocationClass == null) return false;
    return _isSubclassWhere(
      clazz,
      (Class c) => _hasPragmaAnnotation(c, 'track-creation-locations'),
    );
  }

  bool _hasPragmaAnnotation(Annotatable node, String pragmaName) {
    for (Expression annotation in node.annotations) {
      if (_getPragmaName(annotation) == pragmaName) {
        return true;
      }
    }
    return false;
  }

  String? _getPragmaName(Expression expression) {
    // Direct invocation, e.g. `@pragma('...')`.
    // Applies before constant evaluation (newly compiled modules).
    if (expression
        case RedirectingFactoryInvocation(
              expression: final ConstructorInvocation invocation,
            ) ||
            final ConstructorInvocation invocation) {
      final Class enclosingClass = invocation.target.enclosingClass;
      if (enclosingClass.name == 'pragma' &&
          enclosingClass.enclosingLibrary.importUri.toString() == 'dart:core') {
        if (invocation.arguments.positional.isNotEmpty) {
          final Expression firstArg = invocation.arguments.positional.first;
          if (firstArg is StringLiteral) {
            return firstArg.value;
          }
        }
      }
    }

    // Aliased constant, e.g. `@widgetFactory`
    // with `const widgetFactory = pragma('...');`.
    // Applies before constant evaluation (newly compiled modules).
    if (expression is StaticGet) {
      final Member target = expression.target;
      if (target is Field && target.isConst) {
        if (target.initializer != null) {
          return _getPragmaName(target.initializer!);
        }
      }
    }

    // Evaluated constant pragma.
    // Applies after constant evaluation (incremental or modular compilation).
    if (expression is ConstantExpression) {
      final Constant constant = expression.constant;
      if (constant is InstanceConstant) {
        final Class enclosingClass = constant.classNode;
        if (enclosingClass.name == 'pragma' &&
            enclosingClass.enclosingLibrary.importUri.toString() ==
                'dart:core') {
          for (final Constant value in constant.fieldValues.values) {
            if (value is StringConstant) {
              return value.value;
            }
          }
        }
      }
    }
    return null;
  }

  Class? _getFactoryLocationClass(Procedure method) {
    if (_hasPragmaAnnotation(method, 'track-creation-locations')) {
      return _developerCreationLocationClass;
    }
    if (_hasWidgetFactoryAnnotation(method)) {
      return _locationClass;
    }
    return null;
  }

  bool _isSubclassWhere(Class a, bool Function(Class b) predicate) {
    // TODO(askesc): Cache results.
    // TODO(askesc): Test for subtype rather than subclass.
    Class? current = a;
    while (current != null) {
      if (predicate(current)) return true;
      current = current.superclass;
    }
    return false;
  }

  bool _hasWidgetFactoryAnnotation(Procedure node) =>
      _isAnnotatedWithNamedValueOfType(
        node,
        _widgetFactoryClass,
        _widgetFactoryClass,
      );

  bool _isAnnotatedWithNamedValueOfType(
    Annotatable node,
    Class? annotationClass,
    Class? typeClass,
  ) {
    if (annotationClass == null || typeClass == null) return false;
    return node.annotations.any((annotation) {
      if (annotation is! StaticGet) {
        return false;
      }
      final Member target = annotation.target;
      if (target is! Field) {
        return false;
      }
      final DartType type = target.type;
      if (type is! InterfaceType) {
        return false;
      }
      if (type.nullability == Nullability.nullable) {
        return false;
      }
      return type.classNode == typeClass;
    });
  }

  void _transformWidgetConstructors(
    Set<Library> librariesToBeTransformed,
    Set<Class> transformedClasses,
    Class clazz,
    ChangedStructureNotifier? changedStructureNotifier,
  ) {
    final _TrackingClasses? tracking = _getTrackingClasses(clazz);
    if (tracking == null ||
        !librariesToBeTransformed.contains(clazz.enclosingLibrary) ||
        !transformedClasses.add(clazz)) {
      return;
    }

    // Ensure super classes have been transformed before this class.
    if (clazz.superclass != null &&
        !transformedClasses.contains(clazz.superclass)) {
      _transformWidgetConstructors(
        librariesToBeTransformed,
        transformedClasses,
        clazz.superclass!,
        changedStructureNotifier,
      );
    }

    for (Procedure procedure in clazz.procedures) {
      if (procedure.isFactory) {
        _maybeAddNamedParameter(
          procedure.function,
          new NamedParameter(
            parameterName: _creationLocationParameterName,
            type: new InterfaceType(
              tracking.locationClass,
              clazz.enclosingLibrary.nullable,
            ),
            defaultValue: new NullLiteral(),
          ),
        );
      }
    }

    // Handle the widget class and classes that implement but do not extend the
    // widget class.
    if (clazz.superclass == null ||
        _getTrackingClasses(clazz.superclass!)?.hasCreationLocationClass !=
            tracking.hasCreationLocationClass) {
      _transformClassImplementingTrackingClass(
        clazz,
        tracking,
        changedStructureNotifier,
      );
      return;
    }

    final Set<Constructor> _handledConstructors =
        new Set<Constructor>.identity();

    void handleConstructor(Constructor constructor) {
      if (!_handledConstructors.add(constructor)) {
        return;
      }

      final NamedParameter parameter = new NamedParameter(
        parameterName: _creationLocationParameterName,
        type: new InterfaceType(
          tracking.locationClass,
          clazz.enclosingLibrary.nullable,
        ),
        defaultValue: new NullLiteral(),
      );
      if (_hasNamedParameter(
        constructor.function,
        _creationLocationParameterName,
      )) {
        // Constructor was already rewritten.
        // TODO(jacobr): is this case actually hit?
        return;
      }
      if (!_maybeAddNamedParameter(constructor.function, parameter)) {
        return;
      }
      for (Initializer initializer in constructor.initializers) {
        if (initializer is RedirectingInitializer) {
          if (initializer.target.enclosingClass == clazz) {
            // We need to handle this constructor first or the call to
            // addDebugLocationArgument could fail due to the named parameter
            // not existing.
            handleConstructor(initializer.target);
          }

          _maybeAddCreationLocationArgument(
            initializer.arguments,
            initializer.target.function,
            new VariableGet(parameter),
          );
        } else if (initializer is SuperInitializer) {
          final Class superclass = initializer.target.enclosingClass;
          if (_getTrackingClasses(superclass)?.hasCreationLocationClass ==
              tracking.hasCreationLocationClass) {
            _maybeAddCreationLocationArgument(
              initializer.arguments,
              initializer.target.function,
              new VariableGet(parameter),
            );
          }
        }
      }
    }

    clazz.constructors.forEach(handleConstructor);
  }

  void _transformExtension(
    Set<Library> librariesToBeTransformed,
    Set<Extension> transformedExtensions,
    Extension extension,
  ) {
    // TODO(johnniwinther): We should have a lint for unsupported use of
    // `@widgetFactory`.

    if (!librariesToBeTransformed.contains(extension.enclosingLibrary) ||
        !transformedExtensions.add(extension)) {
      return;
    }

    for (ExtensionMemberDescriptor member in extension.memberDescriptors) {
      if (member.isStatic) {
        // We could support static extension methods but it is not clear that
        // there is a use case for this.
        continue;
      }
      final Procedure? method = member.memberReference?.asProcedure;
      if (method != null) {
        _transformExtensionProcedure(method, extension);
      }
      final Procedure? tearOff = member.tearOffReference?.asProcedure;
      if (tearOff != null) {
        _transformExtensionProcedure(tearOff, extension);
      }
    }
  }

  void _transformExtensionProcedure(Procedure method, Extension extension) {
    final Class? locationClass = _getFactoryLocationClass(method);
    if (locationClass == null) {
      return;
    }

    _maybeAddNamedParameter(
      method.function,
      new NamedParameter(
        parameterName: _creationLocationParameterName,
        type: new InterfaceType(
          locationClass,
          extension.enclosingLibrary.nullable,
        ),
        defaultValue: new NullLiteral(),
      ),
    );
  }
}

/// Holds the set of creation location classes, either
/// from `package:flutter` or `dart:developer`.
class _TrackingClasses {
  final Class hasCreationLocationClass;
  final Class locationClass;
  final String locationFieldName;

  new({
    required this.hasCreationLocationClass,
    required this.locationClass,
    required this.locationFieldName,
  });
}