pkg/nnbd_migration/lib/src/potential_modification.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.

import 'package:analyzer/dart/ast/ast.dart';
import 'package:analyzer_plugin/protocol/protocol_common.dart' show SourceEdit;
import 'package:nnbd_migration/src/conditional_discard.dart';
import 'package:nnbd_migration/src/nullability_node.dart';

/// Records information about how a conditional expression or statement might
/// need to be modified.
class ConditionalModification extends PotentialModification {
  final int offset;

  final int end;

  final bool isStatement;

  final ConditionalDiscard discard;

  final _KeepNode condition;

  final _KeepNode thenStatement;

  final _KeepNode elseStatement;

  factory ConditionalModification(AstNode node, ConditionalDiscard discard) {
    if (node is IfStatement) {
      return ConditionalModification._(
          node.offset,
          node.end,
          node is Statement,
          discard,
          _KeepNode(node.condition),
          _KeepNode(node.thenStatement),
          _KeepNode(node.elseStatement));
    } else {
      throw new UnimplementedError('TODO(paulberry)');
    }
  }

  ConditionalModification._(this.offset, this.end, this.isStatement,
      this.discard, this.condition, this.thenStatement, this.elseStatement);

  @override
  bool get isEmpty => discard.keepTrue && discard.keepFalse;

  @override
  Iterable<SourceEdit> get modifications {
    if (isEmpty) return const [];
    // TODO(paulberry): move the following logic into DartEditBuilder (see
    // dartbug.com/35872).
    var result = <SourceEdit>[];
    var keepNodes = <_KeepNode>[];
    if (!discard.pureCondition) {
      keepNodes.add(condition); // TODO(paulberry): test
    }
    if (discard.keepTrue) {
      keepNodes.add(thenStatement); // TODO(paulberry): test
    }
    if (discard.keepFalse) {
      keepNodes.add(elseStatement); // TODO(paulberry): test
    }
    // TODO(paulberry): test thoroughly
    for (int i = 0; i < keepNodes.length; i++) {
      var keepNode = keepNodes[i];
      if (i == 0 && keepNode.offset != offset) {
        result.add(SourceEdit(offset, 0, '/* '));
      }
      if (i != 0 || keepNode.offset != offset) {
        result.add(SourceEdit(keepNode.offset, 0, '*/ '));
      }
      if (i != keepNodes.length - 1 || keepNode.end != end) {
        result.add(SourceEdit(keepNode.end, 0,
            keepNode.isExpression && isStatement ? '; /*' : ' /*'));
      }
      if (i == keepNodes.length - 1 && keepNode.end != end) {
        result.add(SourceEdit(end, 0, ' */'));
      }
    }
    return result;
  }
}

/// Records information about the possible addition of an import
/// to the source code.
class PotentiallyAddImport extends PotentialModification {
  final _usages = <PotentialModification>[];

  final int _offset;
  final String _importPath;

  PotentiallyAddImport(
      AstNode beforeNode, this._importPath, PotentialModification usage)
      : _offset = beforeNode.offset {
    _usages.add(usage);
  }

  get importPath => _importPath;

  @override
  bool get isEmpty {
    for (PotentialModification usage in _usages) {
      if (!usage.isEmpty) {
        return false;
      }
    }
    return true;
  }

  // TODO(danrubel): change all of dartfix NNBD to use DartChangeBuilder
  @override
  Iterable<SourceEdit> get modifications =>
      isEmpty ? const [] : [SourceEdit(_offset, 0, "import '$_importPath';\n")];

  void addUsage(PotentialModification usage) {
    _usages.add(usage);
  }
}

/// Records information about the possible addition of a `@required` annotation
/// to the source code.
class PotentiallyAddRequired extends PotentialModification {
  final NullabilityNode _node;

  final int _offset;

  PotentiallyAddRequired(DefaultFormalParameter parameter, this._node)
      : _offset = parameter.offset;

  @override
  bool get isEmpty => _node.isNullable;

  @override
  Iterable<SourceEdit> get modifications =>
      isEmpty ? const [] : [SourceEdit(_offset, 0, '@required ')];
}

/// Interface used by data structures representing potential modifications to
/// the code being migrated.
abstract class PotentialModification {
  bool get isEmpty;

  /// Gets the individual migrations that need to be done, considering the
  /// solution to the constraint equations.
  Iterable<SourceEdit> get modifications;
}

/// Helper object used by [ConditionalModification] to keep track of AST nodes
/// within the conditional expression.
class _KeepNode {
  final int offset;

  final int end;

  final bool isExpression;

  factory _KeepNode(AstNode node) {
    int offset = node.offset;
    int end = node.end;
    if (node is Block && node.statements.isNotEmpty) {
      offset = node.statements.beginToken.offset;
      end = node.statements.endToken.end;
    }
    return _KeepNode._(offset, end, node is Expression);
  }

  _KeepNode._(this.offset, this.end, this.isExpression);
}