pkg/analysis_server/lib/src/services/correction/util.dart

// Copyright (c) 2014, 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 'dart:math';

import 'package:_fe_analyzer_shared/src/scanner/token.dart';
import 'package:analysis_server/src/protocol_server.dart'
    show doSourceChange_addElementEdit;
import 'package:analysis_server/src/services/linter/lint_names.dart';
import 'package:analysis_server/src/utilities/extensions/ast.dart';
import 'package:analysis_server/src/utilities/strings.dart';
import 'package:analyzer/dart/analysis/features.dart';
import 'package:analyzer/dart/analysis/results.dart';
import 'package:analyzer/dart/analysis/session.dart';
import 'package:analyzer/dart/ast/ast.dart';
import 'package:analyzer/dart/ast/precedence.dart';
import 'package:analyzer/dart/ast/visitor.dart';
import 'package:analyzer/dart/element/element.dart';
import 'package:analyzer/dart/element/nullability_suffix.dart';
import 'package:analyzer/dart/element/type.dart';
import 'package:analyzer/error/listener.dart';
import 'package:analyzer/src/dart/ast/extensions.dart';
import 'package:analyzer/src/dart/ast/utilities.dart';
import 'package:analyzer/src/dart/scanner/reader.dart';
import 'package:analyzer/src/dart/scanner/scanner.dart';
import 'package:analyzer/src/generated/source.dart';
import 'package:analyzer_plugin/protocol/protocol_common.dart'
    show SourceChange, SourceEdit;
import 'package:analyzer_plugin/src/utilities/string_utilities.dart';
import 'package:analyzer_plugin/utilities/range_factory.dart';
import 'package:collection/collection.dart';
import 'package:path/path.dart' as path;

/// Adds edits to the given [change] that ensure that all the [libraries] are
/// imported into the given [targetLibrary].
Future<void> addLibraryImports(AnalysisSession session, SourceChange change,
    LibraryElement targetLibrary, Set<Source> libraries) async {
  var libraryPath = targetLibrary.source.fullName;

  var resolveResult = await session.getResolvedUnit(libraryPath);
  if (resolveResult is! ResolvedUnitResult) {
    return;
  }

  var libUtils = CorrectionUtils(resolveResult);
  var eol = libUtils.endOfLine;
  // Prepare information about existing imports.
  LibraryDirective? libraryDirective;
  var importDirectives = <_ImportDirectiveInfo>[];
  for (var directive in libUtils.unit.directives) {
    if (directive is LibraryDirective) {
      libraryDirective = directive;
    } else if (directive is ImportDirective) {
      var uriStr = directive.uri.stringValue;
      if (uriStr != null) {
        importDirectives.add(
          _ImportDirectiveInfo(uriStr, directive.offset, directive.end),
        );
      }
    }
  }

  // Prepare all URIs to import.
  var uriList = libraries
      .map((library) => getLibrarySourceUri(
          session.resourceProvider.pathContext, targetLibrary, library.uri))
      .toList();
  uriList.sort((a, b) => a.compareTo(b));

  // Insert imports: between existing imports.
  if (importDirectives.isNotEmpty) {
    var isFirstPackage = true;
    for (var importUri in uriList) {
      var inserted = false;
      var isPackage = importUri.startsWith('package:');
      var isAfterDart = false;
      for (var existingImport in importDirectives) {
        if (existingImport.uri.startsWith('dart:')) {
          isAfterDart = true;
        }
        if (existingImport.uri.startsWith('package:')) {
          isFirstPackage = false;
        }
        if (importUri.compareTo(existingImport.uri) < 0) {
          var importCode = "import '$importUri';$eol";
          doSourceChange_addElementEdit(change, targetLibrary,
              SourceEdit(existingImport.offset, 0, importCode));
          inserted = true;
          break;
        }
      }
      if (!inserted) {
        var importCode = "${eol}import '$importUri';";
        if (isPackage && isFirstPackage && isAfterDart) {
          importCode = eol + importCode;
        }
        doSourceChange_addElementEdit(change, targetLibrary,
            SourceEdit(importDirectives.last.end, 0, importCode));
      }
      if (isPackage) {
        isFirstPackage = false;
      }
    }
    return;
  }

  // Insert imports: after the library directive.
  if (libraryDirective != null) {
    var prefix = eol + eol;
    for (var importUri in uriList) {
      var importCode = "${prefix}import '$importUri';";
      prefix = eol;
      doSourceChange_addElementEdit(change, targetLibrary,
          SourceEdit(libraryDirective.end, 0, importCode));
    }
    return;
  }

  // If still at the beginning of the file, skip shebang and line comments.
  {
    var desc = libUtils.getInsertDescTop();
    var offset = desc.offset;
    for (var i = 0; i < uriList.length; i++) {
      var importUri = uriList[i];
      var importCode = "import '$importUri';$eol";
      if (i == 0) {
        importCode = desc.prefix + importCode;
      }
      if (i == uriList.length - 1) {
        importCode = importCode + desc.suffix;
      }
      doSourceChange_addElementEdit(
          change, targetLibrary, SourceEdit(offset, 0, importCode));
    }
  }
}

/// Climbs up [PrefixedIdentifier] and [PropertyAccess] nodes that include
/// [node].
Expression climbPropertyAccess(Expression node) {
  while (true) {
    var parent = node.parent;
    if (parent is PrefixedIdentifier && parent.identifier == node) {
      node = parent;
      continue;
    }
    if (parent is PropertyAccess && parent.propertyName == node) {
      node = parent;
      continue;
    }
    return node;
  }
}

/// Return references to the [element] inside the [root] node.
List<SimpleIdentifier> findLocalElementReferences(
    AstNode root, LocalElement element) {
  var collector = _ElementReferenceCollector(element);
  root.accept(collector);
  return collector.references;
}

/// TODO(scheglov) replace with nodes once there will be
/// [CompilationUnit.getComments].
///
/// Returns [SourceRange]s of all comments in [unit].
List<SourceRange> getCommentRanges(CompilationUnit unit) {
  var ranges = <SourceRange>[];
  var token = unit.beginToken;
  while (token.type != TokenType.EOF) {
    var commentToken = token.precedingComments;
    while (commentToken != null) {
      ranges.add(range.token(commentToken));
      commentToken = commentToken.next as CommentToken?;
    }
    token = token.next!;
  }
  return ranges;
}

String getDefaultValueCode(DartType type) {
  if (type.isDartCoreBool) {
    return 'false';
  }
  if (type.isDartCoreInt) {
    return '0';
  }
  if (type.isDartCoreDouble) {
    return '0.0';
  }
  if (type.isDartCoreString) {
    return "''";
  }
  // no better guess
  return 'null';
}

/// Return all [LocalElement]s defined in the given [node].
List<LocalElement> getDefinedLocalElements(AstNode node) {
  var collector = _LocalElementsCollector();
  node.accept(collector);
  return collector.elements;
}

/// Return the name of the [Element] kind.
String getElementKindName(Element element) {
  return element.kind.displayName;
}

/// Returns the name to display in the UI for the given [Element].
String getElementQualifiedName(Element element) {
  var kind = element.kind;
  if (kind == ElementKind.FIELD || kind == ElementKind.METHOD) {
    return '${element.enclosingElement!.displayName}.${element.displayName}';
  } else if (kind == ElementKind.LIBRARY) {
    // Libraries may not have names, so use a path relative to the context root.
    final session = element.session!;
    final pathContext = session.resourceProvider.pathContext;
    final rootPath = session.analysisContext.contextRoot.root.path;
    final library = element as LibraryElement;

    return pathContext.relative(library.source.fullName, from: rootPath);
  } else {
    return element.displayName;
  }
}

/// If the given [node] is in a class, enum or mixin declaration, return the
/// declared [ClassElement]. Otherwise return `null`.
ClassElement? getEnclosingClassElement(AstNode node) =>
    node.thisOrAncestorOfType<ClassOrMixinDeclaration>()?.declaredElement;

/// Returns a class or an unit member enclosing the given [input].
AstNode? getEnclosingClassOrUnitMember(AstNode input) {
  var member = input;
  for (var node in input.withParents) {
    if (node is ClassDeclaration) {
      return member;
    }
    if (node is CompilationUnit) {
      return member;
    }
    member = node;
  }
  return null;
}

/// Return the [ExecutableElement] of the enclosing executable [AstNode].
ExecutableElement? getEnclosingExecutableElement(AstNode input) {
  for (var node in input.withParents) {
    if (node is FunctionDeclaration) {
      return node.declaredElement;
    }
    if (node is ConstructorDeclaration) {
      return node.declaredElement;
    }
    if (node is MethodDeclaration) {
      return node.declaredElement;
    }
  }
  return null;
}

/// Return the enclosing executable [AstNode].
AstNode? getEnclosingExecutableNode(AstNode input) {
  for (var node in input.withParents) {
    if (node is FunctionDeclaration) {
      return node;
    }
    if (node is ConstructorDeclaration) {
      return node;
    }
    if (node is MethodDeclaration) {
      return node;
    }
  }
  return null;
}

/// If the given [node] is in an extension, return the declared
/// [ExtensionElement]. Otherwise return `null`.
ExtensionElement? getEnclosingExtensionElement(AstNode node) =>
    node.thisOrAncestorOfType<ExtensionDeclaration>()?.declaredElement;

/// Returns [getExpressionPrecedence] for the parent of [node], or
/// ASSIGNMENT_PRECEDENCE if the parent node is a [ParenthesizedExpression].
///
/// The reason is that `(expr)` is always executed after `expr`.
Precedence getExpressionParentPrecedence(AstNode node) {
  var parent = node.parent!;
  if (parent is ParenthesizedExpression) {
    return Precedence.assignment;
  } else if (parent is IndexExpression && parent.index == node) {
    return Precedence.assignment;
  } else if (parent is AssignmentExpression &&
      node == parent.rightHandSide &&
      parent.parent is CascadeExpression) {
    // This is a hack to allow nesting of cascade expressions within other
    // cascade expressions. The problem is that if the precedence of two
    // expressions are equal it sometimes means that we don't need parentheses
    // (such as replacing the `b` in `a + b` with `c + d`) and sometimes do
    // (such as replacing the `v` in `..f = v` with `a..b`).
    return Precedence.conditional;
  }
  return getExpressionPrecedence(parent);
}

/// Returns the precedence of [node] it is an [Expression], NO_PRECEDENCE
/// otherwise.
Precedence getExpressionPrecedence(AstNode node) {
  if (node is Expression) {
    return node.precedence;
  }
  return Precedence.none;
}

/// Returns the namespace of the given [ImportElement].
Map<String, Element> getImportNamespace(ImportElement imp) {
  return imp.namespace.definedNames;
}

/// Computes the best URI to import [what] into [from].
String getLibrarySourceUri(
    path.Context pathContext, LibraryElement from, Uri what) {
  if (what.isScheme('file')) {
    var fromFolder = pathContext.dirname(from.source.fullName);
    var relativeFile = pathContext.relative(what.path, from: fromFolder);
    return pathContext.split(relativeFile).join('/');
  }
  return what.toString();
}

/// Returns the line prefix from the given source, i.e. basically just a
/// whitespace prefix of the given [String].
String getLinePrefix(String line) {
  var index = 0;
  while (index < line.length) {
    var c = line.codeUnitAt(index);
    if (!isWhitespace(c)) {
      break;
    }
    index++;
  }
  return line.substring(0, index);
}

/// Return the [LocalVariableElement] if given [node] is a reference to a local
/// variable, or `null` in the other case.
LocalVariableElement? getLocalVariableElement(SimpleIdentifier node) {
  var element = node.staticElement;
  if (element is LocalVariableElement) {
    return element;
  }
  return null;
}

/// Return the nearest common ancestor of the given [nodes].
AstNode? getNearestCommonAncestor(List<AstNode> nodes) {
  // may be no nodes
  if (nodes.isEmpty) {
    return null;
  }
  // prepare parents
  var parents = <List<AstNode>>[];
  for (var node in nodes) {
    parents.add(getParents(node));
  }
  // find min length
  var minLength = 1 << 20;
  for (var parentList in parents) {
    minLength = min(minLength, parentList.length);
  }
  // find deepest parent
  var i = 0;
  for (; i < minLength; i++) {
    if (!_allListsIdentical(parents, i)) {
      break;
    }
  }
  return parents[0][i - 1];
}

/// Returns the [Expression] qualifier if given [node] is the name part of a
/// [PropertyAccess] or a [PrefixedIdentifier]. Maybe `null`.
Expression? getNodeQualifier(SimpleIdentifier node) {
  var parent = node.parent;
  if (parent is MethodInvocation && identical(parent.methodName, node)) {
    return parent.target;
  }
  if (parent is PropertyAccess && identical(parent.propertyName, node)) {
    return parent.target;
  }
  if (parent is PrefixedIdentifier && identical(parent.identifier, node)) {
    return parent.prefix;
  }
  return null;
}

/// Returns the [ParameterElement] if the given [node] is a reference to a
/// parameter, or `null` in the other case.
ParameterElement? getParameterElement(SimpleIdentifier node) {
  var element = node.staticElement;
  if (element is ParameterElement) {
    return element;
  }
  return null;
}

/// Return parent [AstNode]s from compilation unit (at index "0") to the given
/// [node].
List<AstNode> getParents(AstNode node) {
  return node.withParents.toList().reversed.toList();
}

/// If given [node] is name of qualified property extraction, returns target
/// from which this property is extracted, otherwise `null`.
Expression? getQualifiedPropertyTarget(AstNode node) {
  var parent = node.parent;
  if (parent is PrefixedIdentifier) {
    var prefixed = parent;
    if (prefixed.identifier == node) {
      return parent.prefix;
    }
  }
  if (parent is PropertyAccess) {
    var access = parent;
    if (access.propertyName == node) {
      return access.realTarget;
    }
  }
  return null;
}

/// Returns the given [statement] if not a block, or the first child statement
/// if a block, or `null` if more than one child.
Statement? getSingleStatement(Statement? statement) {
  if (statement is Block) {
    List<Statement> blockStatements = statement.statements;
    if (blockStatements.length != 1) {
      return null;
    }
    return blockStatements[0];
  }
  return statement;
}

/// Returns the given [statement] if not a block, or all the children statements
/// if a block.
List<Statement> getStatements(Statement statement) {
  if (statement is Block) {
    return statement.statements;
  }
  return [statement];
}

/// Checks if the given [element]'s display name equals to the given [name].
bool hasDisplayName(Element? element, String name) {
  return element?.displayName == name;
}

/// Checks if given [DartNode] is the left hand side of an assignment, or a
/// declaration of a variable.
bool isLeftHandOfAssignment(SimpleIdentifier node) {
  if (node.inSetterContext()) {
    return true;
  }
  return node.parent is VariableDeclaration &&
      (node.parent as VariableDeclaration).name == node;
}

/// Return `true` if the given [node] is the name of a [NamedExpression].
bool isNamedExpressionName(SimpleIdentifier node) {
  var parent = node.parent;
  if (parent is Label) {
    var label = parent;
    if (identical(label.label, node)) {
      var parent2 = label.parent;
      if (parent2 is NamedExpression) {
        return identical(parent2.name, label);
      }
    }
  }
  return false;
}

/// If the given [expression] is the `expression` property of a
/// [NamedExpression] then returns this [NamedExpression], otherwise returns
/// [expression].
Expression stepUpNamedExpression(Expression expression) {
  var parent = expression.parent;
  return parent is NamedExpression ? parent : expression;
}

/// Return `true` if the given [lists] are identical at the given [position].
bool _allListsIdentical(List<List<Object>> lists, int position) {
  var element = lists[0][position];
  for (var list in lists) {
    if (list[position] != element) {
      return false;
    }
  }
  return true;
}

/// This exception is thrown to cancel the current correction operation,
/// such as quick assist or quick fix because an inconsistency was detected.
/// These inconsistencies may happen as a part of normal workflow, e.g. because
/// a resource was deleted, or an analysis result was invalidated.
class CancelCorrectionException {
  final Object? exception;

  CancelCorrectionException({this.exception});
}

/// Describes the location for a newly created [ClassMember].
class ClassMemberLocation {
  final String prefix;
  final int offset;
  final String suffix;

  ClassMemberLocation(this.prefix, this.offset, this.suffix);
}

class CorrectionUtils {
  final CompilationUnit unit;
  final LibraryElement _library;
  final String _buffer;

  /// The [ClassElement] the generated code is inserted to, so we can decide if
  /// a type parameter may or may not be used.
  ClassElement? targetClassElement;

  ExecutableElement? targetExecutableElement;

  String? _endOfLine;

  CorrectionUtils(ResolvedUnitResult result)
      : unit = result.unit,
        _library = result.libraryElement,
        _buffer = result.content;

  /// Returns the EOL to use for this [CompilationUnit].
  String get endOfLine {
    var endOfLine = _endOfLine;
    if (endOfLine != null) {
      return endOfLine;
    }

    if (_buffer.contains('\r\n')) {
      return _endOfLine = '\r\n';
    } else {
      return _endOfLine = '\n';
    }
  }

  /// Returns the [AstNode] that encloses the given offset.
  AstNode? findNode(int offset) => NodeLocator(offset).searchWithin(unit);

  /// Returns names of elements that might conflict with a new local variable
  /// declared at [offset].
  Set<String> findPossibleLocalVariableConflicts(int offset) {
    var conflicts = <String>{};
    var enclosingNode = findNode(offset)!;
    var enclosingBlock = enclosingNode.thisOrAncestorOfType<Block>();
    if (enclosingBlock != null) {
      var visitor = _CollectReferencedUnprefixedNames();
      enclosingBlock.accept(visitor);
      return visitor.names;
    }
    return conflicts;
  }

  /// Returns the indentation with the given level.
  String getIndent(int level) => repeat('  ', level);

  /// Returns a [InsertDesc] describing where to insert an ignore_for_file
  /// comment.
  ///
  /// When an existing ignore_for_file comment is found, this returns the start
  /// of the following line, although calling code may choose to fold into the
  /// previous line.
  CorrectionUtils_InsertDesc getInsertDescIgnoreForFile() {
    var offset = 0;
    var insertEmptyLineBefore = false;
    var insertEmptyLineAfter = false;
    var source = _buffer;

    // Look for the last blank line in any leading comments (to insert after all
    // header comments but not after any comment "attached" code). If an
    // existing ignore_for_file comment is found while looking, then insert
    // after that.

    int? lastBlankLineOffset;
    var insertOffset = 0;
    while (offset < source.length - 1) {
      var nextLineOffset = getLineNext(offset);
      var line = source.substring(offset, nextLineOffset).trim();

      if (line.startsWith('// ignore_for_file:')) {
        // Found existing ignore, insert after this.
        insertOffset = nextLineOffset;
        break;
      } else if (line.isEmpty) {
        // Track last blank line, as we will insert there.
        lastBlankLineOffset = offset;
        offset = nextLineOffset;
      } else if (line.startsWith('#!') || line.startsWith('//')) {
        // Skip comment/hash-bang.
        offset = nextLineOffset;
      } else {
        // We found some code.
        // If we found a blank line, insert it after that.
        if (lastBlankLineOffset != null) {
          insertOffset = lastBlankLineOffset;
          insertEmptyLineBefore = true;
        } else {
          // Otherwise, insert it before the first line of code.
          insertOffset = offset;
          insertEmptyLineAfter = true;
        }
        break;
      }
    }

    var desc = CorrectionUtils_InsertDesc();
    desc.offset = insertOffset;
    if (insertEmptyLineBefore) {
      desc.prefix = endOfLine;
    }
    if (insertEmptyLineAfter) {
      desc.suffix = endOfLine;
    }
    return desc;
  }

  /// Returns a [InsertDesc] describing where to insert a new directive or a
  /// top-level declaration at the top of the file.
  CorrectionUtils_InsertDesc getInsertDescTop() {
    // skip leading line comments
    var offset = 0;
    var insertEmptyLineBefore = false;
    var insertEmptyLineAfter = false;
    var source = _buffer;
    // skip hash-bang
    if (offset < source.length - 2) {
      var linePrefix = getText(offset, 2);
      if (linePrefix == '#!') {
        insertEmptyLineBefore = true;
        offset = getLineNext(offset);
        // skip empty lines to first line comment
        var emptyOffset = offset;
        while (emptyOffset < source.length - 2) {
          var nextLineOffset = getLineNext(emptyOffset);
          var line = source.substring(emptyOffset, nextLineOffset);
          if (line.trim().isEmpty) {
            emptyOffset = nextLineOffset;
            continue;
          } else if (line.startsWith('//')) {
            offset = emptyOffset;
            break;
          } else {
            break;
          }
        }
      }
    }
    // skip line comments
    while (offset < source.length - 2) {
      var linePrefix = getText(offset, 2);
      if (linePrefix == '//') {
        insertEmptyLineBefore = true;
        offset = getLineNext(offset);
      } else {
        break;
      }
    }
    // determine if empty line is required after
    var nextLineOffset = getLineNext(offset);
    var insertLine = source.substring(offset, nextLineOffset);
    if (insertLine.trim().isNotEmpty) {
      insertEmptyLineAfter = true;
    }
    // fill InsertDesc
    var desc = CorrectionUtils_InsertDesc();
    desc.offset = offset;
    if (insertEmptyLineBefore) {
      desc.prefix = endOfLine;
    }
    if (insertEmptyLineAfter) {
      desc.suffix = endOfLine;
    }
    return desc;
  }

  /// Skips whitespace characters and single EOL on the right from [index].
  ///
  /// If [index] the end of a statement or method, then in the most cases it is
  /// a start of the next line.
  int getLineContentEnd(int index) {
    var length = _buffer.length;
    // skip whitespace characters
    while (index < length) {
      var c = _buffer.codeUnitAt(index);
      if (!isWhitespace(c) || isEOL(c)) {
        break;
      }
      index++;
    }
    // skip single \r
    if (index < length && _buffer.codeUnitAt(index) == 0x0D) {
      index++;
    }
    // skip single \n
    if (index < length && _buffer.codeUnitAt(index) == 0x0A) {
      index++;
    }
    // done
    return index;
  }

  /// Skips spaces and tabs on the left from [index].
  ///
  /// If [index] is the start or a statement, then in the most cases it is a
  /// start on its line.
  int getLineContentStart(int index) {
    while (index > 0) {
      var c = _buffer.codeUnitAt(index - 1);
      if (!isSpace(c)) {
        break;
      }
      index--;
    }
    return index;
  }

  /// Returns a start index of the next line after the line which contains the
  /// given index.
  int getLineNext(int index) {
    var length = _buffer.length;
    // skip to the end of the line
    while (index < length) {
      var c = _buffer.codeUnitAt(index);
      if (c == 0xD || c == 0xA) {
        break;
      }
      index++;
    }
    // skip single \r
    if (index < length && _buffer.codeUnitAt(index) == 0xD) {
      index++;
    }
    // skip single \n
    if (index < length && _buffer.codeUnitAt(index) == 0xA) {
      index++;
    }
    // done
    return index;
  }

  /// Returns the whitespace prefix of the line which contains given offset.
  String getLinePrefix(int index) {
    var lineStart = getLineThis(index);
    var length = _buffer.length;
    var lineNonWhitespace = lineStart;
    while (lineNonWhitespace < length) {
      var c = _buffer.codeUnitAt(lineNonWhitespace);
      if (c == 0xD || c == 0xA) {
        break;
      }
      if (!isWhitespace(c)) {
        break;
      }
      lineNonWhitespace++;
    }
    return getText(lineStart, lineNonWhitespace - lineStart);
  }

  /// Returns a [SourceRange] that covers [sourceRange] and extends (if
  /// possible) to cover whole lines.
  SourceRange getLinesRange(SourceRange sourceRange,
      {bool skipLeadingEmptyLines = false}) {
    // start
    var startOffset = sourceRange.offset;
    var startLineOffset = getLineContentStart(startOffset);
    if (skipLeadingEmptyLines) {
      startLineOffset = skipEmptyLinesLeft(startLineOffset);
    }
    // end
    var endOffset = sourceRange.end;
    var afterEndLineOffset = endOffset;
    var lineInfo = unit.lineInfo!;
    var lineStart = lineInfo
        .getOffsetOfLine(lineInfo.getLocation(startLineOffset).lineNumber - 1);
    if (lineStart == startLineOffset) {
      // Only consume line ends after the end of the range if there is nothing
      // else on the line containing the beginning of the range. Otherwise this
      // will end up incorrectly merging two line.
      afterEndLineOffset = getLineContentEnd(endOffset);
    }
    // range
    return range.startOffsetEndOffset(startLineOffset, afterEndLineOffset);
  }

  /// Returns a [SourceRange] that covers all the given [Statement]s.
  SourceRange getLinesRangeStatements(List<Statement> statements) {
    return getLinesRange(range.nodes(statements));
  }

  /// Returns the start index of the line which contains given index.
  int getLineThis(int index) {
    while (index > 0) {
      var c = _buffer.codeUnitAt(index - 1);
      if (c == 0xD || c == 0xA) {
        break;
      }
      index--;
    }
    return index;
  }

  /// Returns the line prefix consisting of spaces and tabs on the left from the
  /// given [AstNode].
  String getNodePrefix(AstNode node) {
    var offset = node.offset;
    // function literal is special, it uses offset of enclosing line
    if (node is FunctionExpression) {
      return getLinePrefix(offset);
    }
    // use just prefix directly before node
    return getPrefix(offset);
  }

  /// Returns the text of the given [AstNode] in the unit.
  String getNodeText(AstNode node) {
    return getText(node.offset, node.length);
  }

  /// Returns the line prefix consisting of spaces and tabs on the left from the
  /// given offset.
  String getPrefix(int endIndex) {
    var startIndex = getLineContentStart(endIndex);
    return _buffer.substring(startIndex, endIndex);
  }

  /// Returns the text of the given range in the unit.
  String getRangeText(SourceRange range) {
    return getText(range.offset, range.length);
  }

  /// Returns the text of the given range in the unit.
  String getText(int offset, int length) {
    return _buffer.substring(offset, offset + length);
  }

  /// Returns the source to reference [type] in this [CompilationUnit].
  ///
  /// Fills [librariesToImport] with [LibraryElement]s whose elements are
  /// used by the generated source, but not imported.
  String? getTypeSource(DartType type, Set<Source> librariesToImport,
      {StringBuffer? parametersBuffer}) {
    var alias = type.alias;
    if (alias != null) {
      return _getTypeCodeElementArguments(
        librariesToImport: librariesToImport,
        element: alias.element,
        isNullable: type.nullabilitySuffix == NullabilitySuffix.question,
        typeArguments: alias.typeArguments,
      );
    }

    if (type is DynamicType) {
      return 'dynamic';
    }

    if (type is FunctionType) {
      if (parametersBuffer == null) {
        return 'Function';
      }
      parametersBuffer.write('(');
      for (var parameter in type.parameters) {
        var parameterType = getTypeSource(parameter.type, librariesToImport);
        if (parametersBuffer.length != 1) {
          parametersBuffer.write(', ');
        }
        parametersBuffer.write(parameterType);
        parametersBuffer.write(' ');
        parametersBuffer.write(parameter.name);
      }
      parametersBuffer.write(')');
      return getTypeSource(type.returnType, librariesToImport);
    }

    if (type is InterfaceType) {
      return _getTypeCodeElementArguments(
        librariesToImport: librariesToImport,
        element: type.element,
        isNullable: type.nullabilitySuffix == NullabilitySuffix.question,
        typeArguments: type.typeArguments,
      );
    }

    if (type is NeverType) {
      return 'Never';
    }

    if (type is TypeParameterType) {
      var element = type.element;
      if (_isTypeParameterVisible(element)) {
        return element.name;
      } else {
        return 'dynamic';
      }
    }

    if (type is VoidType) {
      return 'void';
    }

    throw UnimplementedError('(${type.runtimeType}) $type');
  }

  /// Indents given source left or right.
  String indentSourceLeftRight(String source, {bool indentLeft = true}) {
    var sb = StringBuffer();
    var indent = getIndent(1);
    var eol = endOfLine;
    var lines = source.split(eol);
    for (var i = 0; i < lines.length; i++) {
      var line = lines[i];
      // last line, stop if empty
      if (i == lines.length - 1 && isEmpty(line)) {
        break;
      }
      // update line
      if (indentLeft) {
        line = removeStart(line, indent)!;
      } else {
        line = '$indent$line';
      }
      // append line
      sb.write(line);
      sb.write(eol);
    }
    return sb.toString();
  }

  /// Return the source of the inverted condition for the given logical
  /// expression.
  String invertCondition(Expression expression) =>
      _invertCondition0(expression)._source;

  /// Return `true` if the given class, mixin, enum or extension [declaration]
  /// has open '{' and close '}' on the same line, e.g. `class X {}`.
  bool isClassWithEmptyBody(CompilationUnitMember declaration) {
    return getLineThis(_getLeftBracket(declaration)!.offset) ==
        getLineThis(_getRightBracket(declaration)!.offset);
  }

  /// Return <code>true</code> if [range] contains only whitespace or comments.
  bool isJustWhitespaceOrComment(SourceRange range) {
    var trimmedText = getRangeText(range).trim();
    // may be whitespace
    if (trimmedText.isEmpty) {
      return true;
    }
    // may be comment
    return TokenUtils.getTokens(trimmedText, unit.featureSet).isEmpty;
  }

  ClassMemberLocation newCaseClauseAtEndLocation(SwitchStatement statement) {
    var blockStartLine = getLineThis(statement.leftBracket.offset);
    var blockEndLine = getLineThis(statement.end);
    var offset = blockEndLine;
    var prefix = '';
    var suffix = '';
    if (blockStartLine == blockEndLine) {
      // The switch body is on a single line.
      prefix = endOfLine;
      offset = statement.leftBracket.end;
      suffix = getLinePrefix(statement.offset);
    }
    return ClassMemberLocation(prefix, offset, suffix);
  }

  ClassMemberLocation? prepareEnumNewConstructorLocation(
    EnumDeclaration enumDeclaration,
  ) {
    var indent = getIndent(1);

    var targetMember = enumDeclaration.members
        .where((e) => e is FieldDeclaration || e is ConstructorDeclaration)
        .lastOrNull;
    if (targetMember != null) {
      return ClassMemberLocation(
        endOfLine + endOfLine + indent,
        targetMember.end,
        '',
      );
    }

    var semicolon = enumDeclaration.semicolon;
    if (semicolon != null) {
      return ClassMemberLocation(
        endOfLine + endOfLine + indent,
        semicolon.end,
        '',
      );
    }

    var lastConstant = enumDeclaration.constants.last;
    return ClassMemberLocation(
      ';' + endOfLine + endOfLine + indent,
      lastConstant.end,
      '',
    );
  }

  ClassMemberLocation? prepareNewClassMemberLocation(
      CompilationUnitMember declaration,
      bool Function(ClassMember existingMember) shouldSkip) {
    var indent = getIndent(1);
    // Find the last target member.
    ClassMember? targetMember;
    var members = _getMembers(declaration);
    if (members == null) {
      return null;
    }
    for (var member in members) {
      if (shouldSkip(member)) {
        targetMember = member;
      } else {
        break;
      }
    }
    // After the last target member.
    if (targetMember != null) {
      return ClassMemberLocation(
          endOfLine + endOfLine + indent, targetMember.end, '');
    }
    // At the beginning of the class.
    var suffix = members.isNotEmpty || isClassWithEmptyBody(declaration)
        ? endOfLine
        : '';
    return ClassMemberLocation(
        endOfLine + indent, _getLeftBracket(declaration)!.end, suffix);
  }

  ClassMemberLocation? prepareNewConstructorLocation(
      AnalysisSession session, ClassDeclaration classDeclaration) {
    final sortConstructorsFirst = session.analysisContext.analysisOptions
        .isLintEnabled(LintNames.sort_constructors_first);
    // If sort_constructors_first is enabled, don't skip over the fields.
    final shouldSkip = sortConstructorsFirst
        ? (member) => member is ConstructorDeclaration
        : (member) =>
            member is FieldDeclaration || member is ConstructorDeclaration;

    return prepareNewClassMemberLocation(classDeclaration, shouldSkip);
  }

  ClassMemberLocation? prepareNewFieldLocation(
      CompilationUnitMember declaration) {
    return prepareNewClassMemberLocation(
        declaration, (member) => member is FieldDeclaration);
  }

  ClassMemberLocation? prepareNewGetterLocation(
      CompilationUnitMember declaration) {
    return prepareNewClassMemberLocation(
        declaration,
        (member) =>
            member is FieldDeclaration ||
            member is ConstructorDeclaration ||
            member is MethodDeclaration && member.isGetter);
  }

  ClassMemberLocation? prepareNewMethodLocation(
      CompilationUnitMember declaration) {
    return prepareNewClassMemberLocation(
        declaration,
        (member) =>
            member is FieldDeclaration ||
            member is ConstructorDeclaration ||
            member is MethodDeclaration);
  }

  /// Returns the source with indentation changed from [oldIndent] to
  /// [newIndent], keeping indentation of lines relative to each other.
  String replaceSourceIndent(
      String source, String oldIndent, String newIndent) {
    // prepare STRING token ranges
    var lineRanges = <SourceRange>[];
    {
      var tokens = TokenUtils.getTokens(source, unit.featureSet);
      for (var token in tokens) {
        if (token.type == TokenType.STRING) {
          lineRanges.add(range.token(token));
        }
      }
    }
    // re-indent lines
    var sb = StringBuffer();
    var eol = endOfLine;
    var lines = source.split(eol);
    var lineOffset = 0;
    for (var i = 0; i < lines.length; i++) {
      var line = lines[i];
      // last line, stop if empty
      if (i == lines.length - 1 && isEmpty(line)) {
        break;
      }
      // check if "offset" is in one of the String ranges
      var inString = false;
      for (var lineRange in lineRanges) {
        if (lineOffset > lineRange.offset && lineOffset < lineRange.end) {
          inString = true;
        }
        if (lineOffset > lineRange.end) {
          break;
        }
      }
      lineOffset += line.length + eol.length;
      // update line indent
      if (!inString) {
        line = '$newIndent${removeStart(line, oldIndent)}';
      }
      // append line
      sb.write(line);
      sb.write(eol);
    }
    return sb.toString();
  }

  /// Returns the source of the given [SourceRange] with indentation changed
  /// from [oldIndent] to [newIndent], keeping indentation of lines relative
  /// to each other.
  String replaceSourceRangeIndent(
      SourceRange range, String oldIndent, String newIndent) {
    var oldSource = getRangeText(range);
    return replaceSourceIndent(oldSource, oldIndent, newIndent);
  }

  /// Return `true` if [selection] covers [node] and there are any
  /// non-whitespace tokens between [selection] and [node] start/end.
  bool selectionIncludesNonWhitespaceOutsideNode(
      SourceRange selection, AstNode node) {
    return _selectionIncludesNonWhitespaceOutsideRange(
        selection, range.node(node));
  }

  /// Skip spaces, tabs and EOLs on the left from [index].
  ///
  /// If [index] is the start of a method, then in the most cases return the end
  /// of the previous not-whitespace line.
  int skipEmptyLinesLeft(int index) {
    var lastLine = index;
    while (index > 0) {
      var c = _buffer.codeUnitAt(index - 1);
      if (!isWhitespace(c)) {
        return lastLine;
      }
      if (isEOL(c)) {
        lastLine = index;
      }
      index--;
    }
    return 0;
  }

  /// Return the import element used to import given [element] into the library.
  /// May be `null` if was not imported, i.e. declared in the same library.
  ImportElement? _getImportElement(Element element) {
    for (var imp in _library.imports) {
      var definedNames = getImportNamespace(imp);
      if (definedNames.containsValue(element)) {
        return imp;
      }
    }
    return null;
  }

  Token? _getLeftBracket(CompilationUnitMember declaration) {
    if (declaration is ClassOrMixinDeclaration) {
      return declaration.leftBracket;
    } else if (declaration is ExtensionDeclaration) {
      return declaration.leftBracket;
    }
    return null;
  }

  List<ClassMember>? _getMembers(CompilationUnitMember declaration) {
    if (declaration is ClassOrMixinDeclaration) {
      return declaration.members;
    } else if (declaration is ExtensionDeclaration) {
      return declaration.members;
    }
    return null;
  }

  Token? _getRightBracket(CompilationUnitMember declaration) {
    if (declaration is ClassOrMixinDeclaration) {
      return declaration.rightBracket;
    } else if (declaration is ExtensionDeclaration) {
      return declaration.rightBracket;
    }
    return null;
  }

  String? _getTypeCodeElementArguments({
    required Set<Source> librariesToImport,
    required Element element,
    required bool isNullable,
    required List<DartType> typeArguments,
  }) {
    var sb = StringBuffer();

    // check if imported
    var library = element.library;
    if (library != null && library != _library) {
      // no source, if private
      if (element.isPrivate) {
        return null;
      }
      // ensure import
      var importElement = _getImportElement(element);
      if (importElement != null) {
        var prefix = importElement.prefix;
        if (prefix != null) {
          sb.write(prefix.displayName);
          sb.write('.');
        }
      } else {
        librariesToImport.add(library.source);
      }
    }

    // append simple name
    var name = element.displayName;
    sb.write(name);
    if (isNullable) {
      sb.write('?');
    }

    // append type arguments
    if (typeArguments.isNotEmpty) {
      sb.write('<');
      for (var i = 0; i < typeArguments.length; i++) {
        var argument = typeArguments[i];
        if (i != 0) {
          sb.write(', ');
        }
        var argumentSrc = getTypeSource(argument, librariesToImport);
        if (argumentSrc != null) {
          sb.write(argumentSrc);
        } else {
          return null;
        }
      }
      sb.write('>');
    }

    // done
    return sb.toString();
  }

  /// @return the [InvertedCondition] for the given logical expression.
  _InvertedCondition _invertCondition0(Expression expression) {
    if (expression is BooleanLiteral) {
      if (expression.value) {
        return _InvertedCondition._simple('false');
      } else {
        return _InvertedCondition._simple('true');
      }
    } else if (expression is BinaryExpression) {
      var operator = expression.operator.type;
      var le = expression.leftOperand;
      var re = expression.rightOperand;
      var ls = _InvertedCondition._simple(getNodeText(le));
      var rs = _InvertedCondition._simple(getNodeText(re));
      if (operator == TokenType.LT) {
        return _InvertedCondition._binary2(ls, ' >= ', rs);
      }
      if (operator == TokenType.GT) {
        return _InvertedCondition._binary2(ls, ' <= ', rs);
      }
      if (operator == TokenType.LT_EQ) {
        return _InvertedCondition._binary2(ls, ' > ', rs);
      }
      if (operator == TokenType.GT_EQ) {
        return _InvertedCondition._binary2(ls, ' < ', rs);
      }
      if (operator == TokenType.EQ_EQ) {
        return _InvertedCondition._binary2(ls, ' != ', rs);
      }
      if (operator == TokenType.BANG_EQ) {
        return _InvertedCondition._binary2(ls, ' == ', rs);
      }
      if (operator == TokenType.AMPERSAND_AMPERSAND) {
        ls = _invertCondition0(le);
        rs = _invertCondition0(re);
        return _InvertedCondition._binary(
            TokenType.BAR_BAR.precedence, ls, ' || ', rs);
      }
      if (operator == TokenType.BAR_BAR) {
        ls = _invertCondition0(le);
        rs = _invertCondition0(re);
        return _InvertedCondition._binary(
            TokenType.AMPERSAND_AMPERSAND.precedence, ls, ' && ', rs);
      }
    } else if (expression is IsExpression) {
      var expressionSource = getNodeText(expression.expression);
      var typeSource = getNodeText(expression.type);
      if (expression.notOperator == null) {
        return _InvertedCondition._simple('$expressionSource is! $typeSource');
      } else {
        return _InvertedCondition._simple('$expressionSource is $typeSource');
      }
    } else if (expression is PrefixExpression) {
      var operator = expression.operator.type;
      if (operator == TokenType.BANG) {
        var operand = expression.operand.unParenthesized;
        return _InvertedCondition._simple(getNodeText(operand));
      }
    } else if (expression is ParenthesizedExpression) {
      return _invertCondition0(expression.unParenthesized);
    }
    var type = expression.typeOrThrow;
    if (type.isDartCoreBool) {
      return _InvertedCondition._simple('!${getNodeText(expression)}');
    }
    return _InvertedCondition._simple(getNodeText(expression));
  }

  /// Checks if [element] is visible in [targetExecutableElement] or
  /// [targetClassElement].
  bool _isTypeParameterVisible(TypeParameterElement element) {
    var enclosing = element.enclosingElement;
    return identical(enclosing, targetExecutableElement) ||
        identical(enclosing, targetClassElement);
  }

  /// Return `true` if [selection] covers [range] and there are any
  /// non-whitespace tokens between [selection] and [range] start/end.
  bool _selectionIncludesNonWhitespaceOutsideRange(
      SourceRange selection, SourceRange sourceRange) {
    // selection should cover range
    if (!selection.covers(sourceRange)) {
      return false;
    }
    // non-whitespace between selection start and range start
    if (!isJustWhitespaceOrComment(
        range.startOffsetEndOffset(selection.offset, sourceRange.offset))) {
      return true;
    }
    // non-whitespace after range
    if (!isJustWhitespaceOrComment(
        range.startOffsetEndOffset(sourceRange.end, selection.end))) {
      return true;
    }
    // only whitespace in selection around range
    return false;
  }
}

/// Describes where to insert new directive or top-level declaration.
class CorrectionUtils_InsertDesc {
  int offset = 0;
  String prefix = '';
  String suffix = '';
}

/// Utilities to work with [Token]s.
class TokenUtils {
  static List<Token> getNodeTokens(AstNode node) {
    var result = <Token>[];
    for (var token = node.beginToken;; token = token.next!) {
      result.add(token);
      if (token == node.endToken) {
        break;
      }
    }
    return result;
  }

  /// Return the tokens of the given Dart source, not `null`, may be empty if no
  /// tokens or some exception happens.
  static List<Token> getTokens(String s, FeatureSet featureSet) {
    try {
      var tokens = <Token>[];
      var scanner = Scanner(
        _SourceMock(),
        CharSequenceReader(s),
        AnalysisErrorListener.NULL_LISTENER,
      )..configureFeatures(
          featureSetForOverriding: featureSet,
          featureSet: featureSet,
        );
      var token = scanner.tokenize();
      while (token.type != TokenType.EOF) {
        tokens.add(token);
        token = token.next!;
      }
      return tokens;
    } catch (e) {
      return [];
    }
  }
}

class _CollectReferencedUnprefixedNames extends RecursiveAstVisitor {
  final Set<String> names = <String>{};

  @override
  void visitSimpleIdentifier(SimpleIdentifier node) {
    if (!_isPrefixed(node)) {
      names.add(node.name);
    }
  }

  static bool _isPrefixed(SimpleIdentifier node) {
    var parent = node.parent;
    return parent is ConstructorName && parent.name == node ||
        parent is MethodInvocation &&
            parent.methodName == node &&
            parent.realTarget != null ||
        parent is PrefixedIdentifier && parent.identifier == node ||
        parent is PropertyAccess && parent.target == node;
  }
}

class _ElementReferenceCollector extends RecursiveAstVisitor<void> {
  final Element element;
  final List<SimpleIdentifier> references = [];

  _ElementReferenceCollector(this.element);

  @override
  void visitSimpleIdentifier(SimpleIdentifier node) {
    if (node.staticElement == element) {
      references.add(node);
    }
  }
}

class _ImportDirectiveInfo {
  final String uri;
  final int offset;
  final int end;

  _ImportDirectiveInfo(this.uri, this.offset, this.end);
}

/// A container with a source and its precedence.
class _InvertedCondition {
  final int _precedence;

  final String _source;

  _InvertedCondition(this._precedence, this._source);

  static _InvertedCondition _binary(int precedence, _InvertedCondition left,
      String operation, _InvertedCondition right) {
    var src = _parenthesizeIfRequired(left, precedence) +
        operation +
        _parenthesizeIfRequired(right, precedence);
    return _InvertedCondition(precedence, src);
  }

  static _InvertedCondition _binary2(
      _InvertedCondition left, String operation, _InvertedCondition right) {
    // TODO(scheglov) consider merging with "_binary()" after testing
    return _InvertedCondition(
        1 << 20, '${left._source}$operation${right._source}');
  }

  /// Adds enclosing parenthesis if the precedence of the [_InvertedCondition]
  /// if less than the precedence of the expression we are going it to use in.
  static String _parenthesizeIfRequired(
      _InvertedCondition expr, int newOperatorPrecedence) {
    if (expr._precedence < newOperatorPrecedence) {
      return '(${expr._source})';
    }
    return expr._source;
  }

  static _InvertedCondition _simple(String source) =>
      _InvertedCondition(2147483647, source);
}

/// Visitor that collects defined [LocalElement]s.
class _LocalElementsCollector extends RecursiveAstVisitor<void> {
  final elements = <LocalElement>[];

  @override
  void visitSimpleIdentifier(SimpleIdentifier node) {
    if (node.inDeclarationContext()) {
      var element = node.staticElement;
      if (element is LocalElement) {
        elements.add(element);
      }
    }
  }
}

class _SourceMock implements Source {
  @override
  dynamic noSuchMethod(Invocation invocation) => super.noSuchMethod(invocation);
}