Default trailing comma support to `true` (#26647).

pkg/analyzer/test/generated/parser_test.dart

Index: pkg/analyzer/test/generated/parser_test.dart
diff --git a/pkg/analyzer/test/generated/parser_test.dart b/pkg/analyzer/test/generated/parser_test.dart
index e74309d6d31aebada6826a5e0b61f9e19f8f06ea..ee61b20bcdc623663decf6fc9ec1bacccfa0da4e 100644
--- a/pkg/analyzer/test/generated/parser_test.dart
+++ b/pkg/analyzer/test/generated/parser_test.dart
@@ -1197,21 +1197,11 @@ class Foo {
   }
 
   void test_extraCommaInParameterList() {
-    parseTrailingCommas = true;
-    parse4("parseFormalParameterList", "(int a, , int b)",
-        [ParserErrorCode.MISSING_IDENTIFIER, ParserErrorCode.EXPECTED_TOKEN]);
-    parseTrailingCommas = false;
     parse4("parseFormalParameterList", "(int a, , int b)",
         [ParserErrorCode.MISSING_IDENTIFIER, ParserErrorCode.EXPECTED_TOKEN]);
   }
 
   void test_extraCommaTrailingNamedParameterGroup() {
-    parseTrailingCommas = true;
-    parse4("parseFormalParameterList", "({int b},)", [
-      ParserErrorCode.MISSING_IDENTIFIER,
-      ParserErrorCode.NORMAL_BEFORE_OPTIONAL_PARAMETERS
-    ]);
-    parseTrailingCommas = false;
     parse4("parseFormalParameterList", "({int b},)", [
       ParserErrorCode.MISSING_IDENTIFIER,
       ParserErrorCode.NORMAL_BEFORE_OPTIONAL_PARAMETERS
@@ -1219,12 +1209,6 @@ class Foo {
   }
 
   void test_extraCommaTrailingPositionalParameterGroup() {
-    parseTrailingCommas = true;
-    parse4("parseFormalParameterList", "([int b],)", [
-      ParserErrorCode.MISSING_IDENTIFIER,
-      ParserErrorCode.NORMAL_BEFORE_OPTIONAL_PARAMETERS
-    ]);
-    parseTrailingCommas = false;
     parse4("parseFormalParameterList", "([int b],)", [
       ParserErrorCode.MISSING_IDENTIFIER,
       ParserErrorCode.NORMAL_BEFORE_OPTIONAL_PARAMETERS
@@ -1232,12 +1216,8 @@ class Foo {
   }
 
   void test_extraTrailingCommaInParameterList() {
-    parseTrailingCommas = true;
     parse4("parseFormalParameterList", "(a,,)",
         [ParserErrorCode.MISSING_IDENTIFIER]);
-    parseTrailingCommas = false;
-    parse4("parseFormalParameterList", "(a,,)",
-        [ParserErrorCode.MISSING_IDENTIFIER, ParserErrorCode.EXPECTED_TOKEN]);
   }
 
   void test_factoryTopLevelDeclaration_class() {
@@ -1740,7 +1720,6 @@ class Foo {
   }
 
   void test_missingIdentifierForParameterGroup() {
-    parseTrailingCommas = true;
     parse4("parseFormalParameterList", "(,)",
         [ParserErrorCode.MISSING_IDENTIFIER]);
   }
@@ -2807,12 +2786,6 @@ class ParserTestCase extends EngineTestCase {
   bool enableGenericMethodComments = false;
 
   /**
-   * A flag indicating whether parsing trailing commas in parameter and argument
-   * lists should be enabled for this test.
-   */
-  bool parseTrailingCommas = false;
-
-  /**
    * Return a CommentAndMetadata object with the given values that can be used for testing.
    *
    * @param comment the comment to be wrapped in the object
@@ -2866,7 +2839,6 @@ class ParserTestCase extends EngineTestCase {
     parser.parseGenericMethods = enableGenericMethods;
     parser.parseGenericMethodComments = enableGenericMethodComments;
     parser.parseFunctionBodies = parseFunctionBodies;
-    parser.parseTrailingCommas = parseTrailingCommas;
     Object result =
         invokeParserMethodImpl(parser, methodName, objects, tokenStream);
     //
@@ -4793,7 +4765,6 @@ class SimpleParserTest extends ParserTestCase {
   }
 
   void test_parseArgumentList_trailing_comma() {
-    parseTrailingCommas = true;
     ArgumentList argumentList = parse4("parseArgumentList", "(x, y, z,)");
     NodeList<Expression> arguments = argumentList.arguments;
     expect(arguments, hasLength(3));
@@ -5982,7 +5953,6 @@ class SimpleParserTest extends ParserTestCase {
   }
 
   void test_parseClassMember_method_trailing_commas() {
-    parseTrailingCommas = true;
     MethodDeclaration method =
         parse("parseClassMember", <Object>["C"], "void f(int x, int y,) {}");
     expect(method.documentationComment, isNull);
@@ -7899,7 +7869,6 @@ void''');
   }
 
   void test_parseFormalParameterList_named_trailing_comma() {
-    parseTrailingCommas = true;
     FormalParameterList parameterList =
         parse4("parseFormalParameterList", "(A a, {B b,})");
     expect(parameterList.leftParenthesis, isNotNull);
@@ -7950,7 +7919,6 @@ void''');
   }
 
   void test_parseFormalParameterList_normal_single_trailing_comma() {
-    parseTrailingCommas = true;
     FormalParameterList parameterList =
         parse4("parseFormalParameterList", "(A a,)");
     expect(parameterList.leftParenthesis, isNotNull);
@@ -7981,7 +7949,6 @@ void''');
   }
 
   void test_parseFormalParameterList_positional_trailing_comma() {
-    parseTrailingCommas = true;
     FormalParameterList parameterList =
         parse4("parseFormalParameterList", "(A a, [B b,])");
     expect(parameterList.leftParenthesis, isNotNull);