pattern assignment support for parameter_assignments (#4212)

Author: pq

lib/src/rules/parameter_assignments.dart

@@ -4,6 +4,7 @@
 
 import 'package:analyzer/dart/ast/ast.dart';
 import 'package:analyzer/dart/ast/visitor.dart';
+import 'package:analyzer/dart/element/element.dart';
 
 import '../analyzer.dart';
 
@@ -125,16 +126,48 @@ class _DeclarationVisitor extends RecursiveAstVisitor {
       {required this.paramIsNotNullByDefault,
       required this.paramDefaultsToNull});
 
+  Element? get parameterElement => parameter.declaredElement;
+
+  void checkPatternElements(DartPattern node) {
+    NodeList<PatternField>? fields;
+    if (node is RecordPattern) fields = node.fields;
+    if (node is ObjectPattern) fields = node.fields;
+    if (fields != null) {
+      for (var field in fields) {
+        if (field.pattern.element == parameterElement) {
+          reportLint(node);
+        }
+      }
+    } else {
+      List<AstNode>? elements;
+      if (node is ListPattern) elements = node.elements;
+      if (node is MapPattern) elements = node.elements;
+      if (elements == null) return;
+      for (var element in elements) {
+        if (element is MapPatternEntry) {
+          element = element.value;
+        }
+        if (element.element == parameterElement) {
+          reportLint(node);
+        }
+      }
+    }
+  }
+
+  void reportLint(AstNode node) {
+    rule.reportLint(node, arguments: [parameter.name!.lexeme]);
+  }
+
   @override
   visitAssignmentExpression(AssignmentExpression node) {
     if (paramIsNotNullByDefault) {
       if (_isFormalParameterReassigned(parameter, node)) {
-        rule.reportLint(node, arguments: [parameter.name!.lexeme]);
+        reportLint(node);
       }
     } else if (paramDefaultsToNull) {
       if (_isFormalParameterReassigned(parameter, node)) {
         if (hasBeenAssigned) {
-          rule.reportLint(node, arguments: [parameter.name!.lexeme]);
+          reportLint(node);
         }
         hasBeenAssigned = true;
       }
@@ -143,13 +176,20 @@ class _DeclarationVisitor extends RecursiveAstVisitor {
     super.visitAssignmentExpression(node);
   }
 
+  @override
+  visitPatternAssignment(PatternAssignment node) {
+    checkPatternElements(node.pattern);
+
+    super.visitPatternAssignment(node);
+  }
+
   @override
   visitPostfixExpression(PostfixExpression node) {
     if (paramIsNotNullByDefault) {
       var operand = node.operand;
       if (operand is SimpleIdentifier &&
-          operand.staticElement == parameter.declaredElement) {
-        rule.reportLint(node, arguments: [parameter.name!.lexeme]);
+          operand.staticElement == parameterElement) {
+        reportLint(node);
       }
     }
 
@@ -161,8 +201,8 @@ class _DeclarationVisitor extends RecursiveAstVisitor {
     if (paramIsNotNullByDefault) {
       var operand = node.operand;
       if (operand is SimpleIdentifier &&
-          operand.staticElement == parameter.declaredElement) {
-        rule.reportLint(node, arguments: [parameter.name!.lexeme]);
+          operand.staticElement == parameterElement) {
+        reportLint(node);
       }
     }
 
@@ -206,3 +246,11 @@ class _Visitor extends SimpleAstVisitor<void> {
     }
   }
 }
+
+extension on AstNode {
+  Element? get element {
+    var self = this;
+    if (self is AssignedVariablePattern) return self.element;
+    return null;
+  }
+}

test/rules/parameter_assignments_test.dart

@@ -9,6 +9,7 @@ import '../rule_test_support.dart';
 main() {
   defineReflectiveSuite(() {
     defineReflectiveTests(ParameterAssignmentsTest);
+    defineReflectiveTests(ParameterAssignmentsTestLanguage300);
   });
 }
 
@@ -177,3 +178,63 @@ class A {
     ]);
   }
 }
+
+@reflectiveTest
+class ParameterAssignmentsTestLanguage300 extends LintRuleTest
+    with LanguageVersion300Mixin {
+  @override
+  String get lintRule => 'parameter_assignments';
+
+  // If and switch cases don't need verification since params aren't valid
+  // constant pattern expressions.
+
+  test_listAssignment() async {
+    await assertDiagnostics(r'''
+f(var b) {
+  [b] = [1];
+  print('$b');
+}
+''', [
+      lint(13, 3),
+    ]);
+  }
+
+  test_mapAssignment() async {
+    await assertDiagnostics(r'''
+f(var a) {
+  {'a': a} = {'a': 1};
+  print('$a');
+}
+''', [
+      lint(13, 8),
+    ]);
+  }
+
+  test_objectAssignment() async {
+    await assertDiagnostics(r'''
+class A {
+  int a;
+  A(this.a);
+}
+
+f(var b) {
+  A(a: b) = A(1);
+  print('$b');
+}
+''', [
+      lint(48, 7),
+    ]);
+  }
+
+  test_recordAssignment() async {
+    await assertDiagnostics(r'''
+void f(var a) {
+  var b = 0;
+  (a, b) = (1, 2);
+  print(b);
+}
+''', [
+      lint(31, 6),
+    ]);
+  }
+}