Augment. Report DECLARATION_NAMED_AUGMENTED_INSIDE_AUGMENTATION for D…

…eclaredVariablePattern.

Change-Id: I819d03d0a8c58d1f54ec5637bce4d45ad2b91e83
Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/366065
Commit-Queue: Konstantin Shcheglov <scheglov@google.com>
Reviewed-by: Brian Wilkerson <brianwilkerson@google.com>

pkg/analyzer/lib/src/fasta/ast_builder.dart

@@ -4010,6 +4010,16 @@ class AstBuilder extends StackListener {
     assert(_featureSet.isEnabled(Feature.patterns));
     assert(variable.lexeme != '_');
     var type = pop() as TypeAnnotationImpl?;
+
+    if (_enclosingDeclarationAugmentToken != null) {
+      if (variable.lexeme == 'augmented') {
+        errorReporter.errorReporter?.atToken(
+          variable,
+          ParserErrorCode.DECLARATION_NAMED_AUGMENTED_INSIDE_AUGMENTATION,
+        );
+      }
+    }
+
     push(
       DeclaredVariablePatternImpl(
         keyword: keyword,

pkg/analyzer/test/src/diagnostics/declaration_named_augmented_inside_augmentation_test.dart

@@ -41,6 +41,46 @@ augment class A {
     ]);
   }
 
+  test_insideFunctionAugmentation_declaredVariablePattern_assignment() async {
+    newFile('$testPackageLibPath/a.dart', r'''
+import augment 'test.dart';
+
+void f() {}
+''');
+
+    await assertErrorsInCode('''
+augment library 'a.dart';
+
+augment void f() {
+  var (augmented,) = (0,);
+}
+''', [
+      error(ParserErrorCode.DECLARATION_NAMED_AUGMENTED_INSIDE_AUGMENTATION, 53,
+          9),
+      error(WarningCode.UNUSED_LOCAL_VARIABLE, 53, 9),
+    ]);
+  }
+
+  test_insideFunctionAugmentation_declaredVariablePattern_match() async {
+    newFile('$testPackageLibPath/a.dart', r'''
+import augment 'test.dart';
+
+void f() {}
+''');
+
+    await assertErrorsInCode('''
+augment library 'a.dart';
+
+augment void f() {
+  if ((0,) case (var augmented,)) {}
+}
+''', [
+      error(ParserErrorCode.DECLARATION_NAMED_AUGMENTED_INSIDE_AUGMENTATION, 67,
+          9),
+      error(WarningCode.UNUSED_LOCAL_VARIABLE, 67, 9),
+    ]);
+  }
+
   test_insideFunctionAugmentation_formalParameter() async {
     newFile('$testPackageLibPath/a.dart', r'''
 import augment 'test.dart';