Added prefer condtional expressions rule and fix (#59)

* Add prefer-conditional-expressions rule and fix

* Add tests for prefer-conditional-expressions rule

* fix nested test plugin path

* Fix tests after merge

* Update lint_test/prefer_conditional_expressions_ignore_nested_test/prefer_conditional_expressions_ignore_nested_test.dart

---------

Co-authored-by: Denis Bogatirov <denis.bohatyrov@computools.com>
Co-authored-by: Yurii Prykhodko <144313329+yurii-prykhodko-solid@users.noreply.github.com>

lib/lints/prefer_conditional_expressions/models/prefer_conditional_expressions_parameters.dart

@@ -0,0 +1,21 @@
+/// A data model class that represents the "prefer conditional expressions"
+/// input parameters.
+class PreferConditionalExpressionsParameters {
+  static const _ignoreNestedConfig = 'ignore-nested';
+
+  /// Should rule ignore nested if statements
+  final bool ignoreNested;
+
+  /// Constructor for [PreferConditionalExpressionsParameters] model
+  const PreferConditionalExpressionsParameters({
+    required this.ignoreNested,
+  });
+
+  /// Method for creating from json data
+  factory PreferConditionalExpressionsParameters.fromJson(
+    Map<String, Object?> json,
+  ) =>
+      PreferConditionalExpressionsParameters(
+        ignoreNested: json[_ignoreNestedConfig] as bool? ?? false,
+      );
+}

lib/lints/prefer_conditional_expressions/prefer_conditional_expressions_fix.dart

@@ -0,0 +1,117 @@
+import 'package:analyzer/dart/ast/ast.dart';
+import 'package:analyzer/dart/ast/token.dart';
+import 'package:analyzer/error/error.dart';
+import 'package:analyzer/source/source_range.dart';
+import 'package:custom_lint_builder/custom_lint_builder.dart';
+import 'package:solid_lints/lints/prefer_conditional_expressions/prefer_conditional_expressions_visitor.dart';
+
+/// A Quick fix for `avoid-unnecessary-type-assertions` rule
+/// Suggests to remove unnecessary assertions
+class PreferConditionalExpressionsFix extends DartFix {
+  @override
+  void run(
+    CustomLintResolver resolver,
+    ChangeReporter reporter,
+    CustomLintContext context,
+    AnalysisError analysisError,
+    List<AnalysisError> others,
+  ) {
+    context.registry.addIfStatement((node) {
+      if (analysisError.sourceRange.intersects(node.sourceRange)) {
+        final statementInfo = analysisError.data as StatementInfo?;
+        if (statementInfo == null) return;
+
+        final correction = _createCorrection(statementInfo);
+        if (correction == null) return;
+
+        _addReplacement(reporter, statementInfo.statement, correction);
+      }
+    });
+  }
+
+  void _addReplacement(
+    ChangeReporter reporter,
+    IfStatement node,
+    String correction,
+  ) {
+    final changeBuilder = reporter.createChangeBuilder(
+      message: "Convert to conditional expression.",
+      priority: 1,
+    );
+
+    changeBuilder.addDartFileEdit((builder) {
+      builder.addSimpleReplacement(
+        SourceRange(node.offset, node.length),
+        correction,
+      );
+    });
+  }
+
+  String? _createCorrection(StatementInfo info) {
+    final thenStatement = info.unwrappedThenStatement;
+    final elseStatement = info.unwrappedElseStatement;
+
+    final condition = info.statement.expression;
+
+    if (thenStatement is AssignmentExpression &&
+        elseStatement is AssignmentExpression) {
+      final target = thenStatement.leftHandSide;
+      final firstExpression = thenStatement.rightHandSide;
+      final secondExpression = elseStatement.rightHandSide;
+
+      final thenStatementOperator = thenStatement.operator.type;
+      final elseStatementOperator = elseStatement.operator.type;
+
+      if (_isAssignmentOperatorNotEq(thenStatementOperator) &&
+          _isAssignmentOperatorNotEq(elseStatementOperator)) {
+        final prefix = thenStatement.leftHandSide;
+        final thenPart =
+            '$prefix ${thenStatementOperator.stringValue} $firstExpression';
+        final elsePart =
+            '$prefix ${elseStatementOperator.stringValue} $secondExpression;';
+
+        return '$condition ? $thenPart : $elsePart';
+      }
+
+      final correctionForLiterals = _createCorrectionForLiterals(
+        condition,
+        firstExpression,
+        secondExpression,
+      );
+
+      return '$target = $correctionForLiterals';
+    }
+
+    if (thenStatement is ReturnStatement && elseStatement is ReturnStatement) {
+      final firstExpression = thenStatement.expression;
+      final secondExpression = elseStatement.expression;
+      final correction = _createCorrectionForLiterals(
+        condition,
+        firstExpression,
+        secondExpression,
+      );
+
+      return 'return $correction';
+    }
+
+    return null;
+  }
+
+  String _createCorrectionForLiterals(
+    Expression condition,
+    Expression? firstExpression,
+    Expression? secondExpression,
+  ) {
+    if (firstExpression is BooleanLiteral &&
+        secondExpression is BooleanLiteral) {
+      final isInverted = !firstExpression.value && secondExpression.value;
+
+      return '${isInverted ? "!" : ""}$condition;';
+    }
+
+    return '$condition ? $firstExpression : $secondExpression;';
+  }
+
+  bool _isAssignmentOperatorNotEq(TokenType token) =>
+      token.isAssignmentOperator && token != TokenType.EQ;
+}

lib/lints/prefer_conditional_expressions/prefer_conditional_expressions_rule.dart

@@ -0,0 +1,62 @@
+import 'package:analyzer/error/listener.dart';
+import 'package:custom_lint_builder/custom_lint_builder.dart';
+import 'package:solid_lints/lints/prefer_conditional_expressions/models/prefer_conditional_expressions_parameters.dart';
+import 'package:solid_lints/lints/prefer_conditional_expressions/prefer_conditional_expressions_fix.dart';
+import 'package:solid_lints/lints/prefer_conditional_expressions/prefer_conditional_expressions_visitor.dart';
+import 'package:solid_lints/models/rule_config.dart';
+import 'package:solid_lints/models/solid_lint_rule.dart';
+
+// Inspired by TSLint (https://palantir.github.io/tslint/rules/prefer-conditional-expression/)
+
+/// A `prefer-conditional-expressions` rule which warns about
+/// simple if statements that can be replaced with conditional expressions
+class PreferConditionalExpressionsRule
+    extends SolidLintRule<PreferConditionalExpressionsParameters> {
+  /// The [LintCode] of this lint rule that represents the error if number of
+  /// parameters reaches the maximum value.
+  static const lintName = 'prefer-conditional-expressions';
+
+  PreferConditionalExpressionsRule._(super.config);
+
+  /// Creates a new instance of [PreferConditionalExpressionsRule]
+  /// based on the lint configuration.
+  factory PreferConditionalExpressionsRule.createRule(
+    CustomLintConfigs configs,
+  ) {
+    final config = RuleConfig(
+      configs: configs,
+      name: lintName,
+      paramsParser: PreferConditionalExpressionsParameters.fromJson,
+      problemMessage: (value) => 'Prefer conditional expression.',
+    );
+
+    return PreferConditionalExpressionsRule._(config);
+  }
+
+  @override
+  void run(
+    CustomLintResolver resolver,
+    ErrorReporter reporter,
+    CustomLintContext context,
+  ) {
+    context.registry.addCompilationUnit((node) {
+      final visitor = PreferConditionalExpressionsVisitor(
+        ignoreNested: config.parameters.ignoreNested,
+      );
+      node.accept(visitor);
+
+      for (final element in visitor.statementsInfo) {
+        reporter.reportErrorForNode(
+          code,
+          element.statement,
+          null,
+          null,
+          element,
+        );
+      }
+    });
+  }
+
+  @override
+  List<Fix> getFixes() => [PreferConditionalExpressionsFix()];
+}

lib/lints/prefer_conditional_expressions/prefer_conditional_expressions_visitor.dart

@@ -0,0 +1,158 @@
+// MIT License
+//
+// Copyright (c) 2020-2021 Dart Code Checker team
+//
+// Permission is hereby granted, free of charge, to any person obtaining a copy
+// of this software and associated documentation files (the "Software"), to deal
+// in the Software without restriction, including without limitation the rights
+// to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
+// copies of the Software, and to permit persons to whom the Software is
+// furnished to do so, subject to the following conditions:
+//
+// The above copyright notice and this permission notice shall be included in
+// all
+// copies or substantial portions of the Software.
+//
+// THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+// IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+// FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
+// AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+// LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
+// OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
+// SOFTWARE.
+
+import 'package:analyzer/dart/ast/ast.dart';
+import 'package:analyzer/dart/ast/visitor.dart';
+
+/// The AST visitor that will collect all if statements that can be simplified
+/// into conditional expressions.
+class PreferConditionalExpressionsVisitor extends RecursiveAstVisitor<void> {
+  final _statementsInfo = <StatementInfo>[];
+
+  final bool _ignoreNested;
+
+  /// List of statement info that represents all simple if statements
+  Iterable<StatementInfo> get statementsInfo => _statementsInfo;
+
+  /// Creates instance of [PreferConditionalExpressionsVisitor]
+  PreferConditionalExpressionsVisitor({
+    required bool ignoreNested,
+  }) : _ignoreNested = ignoreNested;
+
+  @override
+  void visitIfStatement(IfStatement node) {
+    super.visitIfStatement(node);
+
+    if (_ignoreNested) {
+      final visitor = _ConditionalsVisitor();
+      node.visitChildren(visitor);
+
+      if (visitor.hasInnerConditionals) {
+        return;
+      }
+    }
+
+    if (node.parent is! IfStatement &&
+        node.elseStatement != null &&
+        node.elseStatement is! IfStatement) {
+      _checkBothAssignment(node);
+      _checkBothReturn(node);
+    }
+  }
+
+  void _checkBothAssignment(IfStatement statement) {
+    final thenAssignment = _getAssignmentExpression(statement.thenStatement);
+    final elseAssignment = _getAssignmentExpression(statement.elseStatement);
+
+    if (thenAssignment != null &&
+        elseAssignment != null &&
+        _haveEqualNames(thenAssignment, elseAssignment)) {
+      _statementsInfo.add(
+        StatementInfo(
+          statement: statement,
+          unwrappedThenStatement: thenAssignment,
+          unwrappedElseStatement: elseAssignment,
+        ),
+      );
+    }
+  }
+
+  AssignmentExpression? _getAssignmentExpression(Statement? statement) {
+    if (statement is ExpressionStatement &&
+        statement.expression is AssignmentExpression) {
+      return statement.expression as AssignmentExpression;
+    }
+
+    if (statement is Block && statement.statements.length == 1) {
+      return _getAssignmentExpression(statement.statements.first);
+    }
+
+    return null;
+  }
+
+  bool _haveEqualNames(
+    AssignmentExpression thenAssignment,
+    AssignmentExpression elseAssignment,
+  ) =>
+      thenAssignment.leftHandSide is Identifier &&
+      elseAssignment.leftHandSide is Identifier &&
+      (thenAssignment.leftHandSide as Identifier).name ==
+          (elseAssignment.leftHandSide as Identifier).name;
+
+  void _checkBothReturn(IfStatement statement) {
+    final thenReturn = _getReturnStatement(statement.thenStatement);
+    final elseReturn = _getReturnStatement(statement.elseStatement);
+
+    if (thenReturn != null && elseReturn != null) {
+      _statementsInfo.add(
+        StatementInfo(
+          statement: statement,
+          unwrappedThenStatement: thenReturn,
+          unwrappedElseStatement: elseReturn,
+        ),
+      );
+    }
+  }
+
+  ReturnStatement? _getReturnStatement(Statement? statement) {
+    if (statement is ReturnStatement) {
+      return statement;
+    }
+
+    if (statement is Block && statement.statements.length == 1) {
+      return _getReturnStatement(statement.statements.first);
+    }
+
+    return null;
+  }
+}
+
+class _ConditionalsVisitor extends RecursiveAstVisitor<void> {
+  bool hasInnerConditionals = false;
+
+  @override
+  void visitConditionalExpression(ConditionalExpression node) {
+    hasInnerConditionals = true;
+
+    super.visitConditionalExpression(node);
+  }
+}
+
+/// Data class contains info required for fix
+class StatementInfo {
+  /// If statement node
+  final IfStatement statement;
+
+  /// Contents of if block
+  final AstNode unwrappedThenStatement;
+
+  /// Contents of else block
+  final AstNode unwrappedElseStatement;
+
+  /// Creates instance of an [StatementInfo]
+  const StatementInfo({
+    required this.statement,
+    required this.unwrappedThenStatement,
+    required this.unwrappedElseStatement,
+  });
+}

lib/solid_lints.dart

@@ -19,6 +19,7 @@ import 'package:solid_lints/lints/no_empty_block/no_empty_block_rule.dart';
 import 'package:solid_lints/lints/no_equal_then_else/no_equal_then_else_rule.dart';
 import 'package:solid_lints/lints/no_magic_number/no_magic_number_rule.dart';
 import 'package:solid_lints/lints/number_of_parameters/number_of_parameters_metric.dart';
+import 'package:solid_lints/lints/prefer_conditional_expressions/prefer_conditional_expressions_rule.dart';
 import 'package:solid_lints/models/solid_lint_rule.dart';
 
 /// Creates a plugin for our custom linter
@@ -47,6 +48,7 @@ class _SolidLints extends PluginBase {
       NoEqualThenElseRule.createRule(configs),
       MemberOrderingRule.createRule(configs),
       NoMagicNumberRule.createRule(configs),
+      PreferConditionalExpressionsRule.createRule(configs),
     ];
 
     // Return only enabled rules

lint_test/analysis_options.yaml

@@ -49,3 +49,4 @@ custom_lint:
         - did-update-widget-method
         - dispose-method
     - no-magic-number
+    - prefer-conditional-expressions

lint_test/no_equal_then_else_test.dart

@@ -1,6 +1,7 @@
 // ignore_for_file: unused_local_variable
 // ignore_for_file: cyclomatic_complexity
 // ignore_for_file: no-magic-number
+// ignore_for_file: prefer-conditional-expressions
 
 /// Check the `no-equal-then-else` rule
 void fun() {

lint_test/prefer_conditional_expressions_ignore_nested_test/analysis_options.yaml

@@ -0,0 +1,8 @@
+analyzer:
+  plugins:
+    - ../custom_lint
+
+custom_lint:
+  rules:
+    - prefer-conditional-expressions:
+      ignore-nested: true