even cleaner

json_serializable/lib/src/check_dependencies.dart

@@ -13,7 +13,7 @@ import 'constants.dart';
 const _productionDirectories = {'lib', 'bin'};
 const _annotationPkgName = 'json_annotation';
 final _supportLanguageRange =
-    VersionConstraint.parse(supportLanguageConstraint);
+    VersionConstraint.parse(supportedLanguageConstraint);
 final requiredJsonAnnotationMinVersion = Version.parse('4.9.0');
 
 Future<void> pubspecHasRightVersion(BuildStep buildStep) async {
@@ -52,23 +52,25 @@ Future<void> _validatePubspec(bool production, BuildStep buildStep) async {
   //
   // Ensure the current package language version is at least the minimum.
   //
-
   final currentPackageName = pubspec.name;
-
   final packageConfig = await buildStep.packageConfig;
-
   final thisPackage = packageConfig[currentPackageName]!;
 
-  // build_runner will error out without an SDK version - so this "should" be
-  // fine.
+  // build_runner will error out without an SDK version - so assuming
+  // `languageVersion` is not null.
   final thisPackageVersion = thisPackage.languageVersion!;
 
   final thisPackageVer = Version.parse('$thisPackageVersion.0');
   if (!_supportLanguageRange.allows(thisPackageVer)) {
     log.warning(
-      'The language version ($thisPackageVer) of this package '
-      '($currentPackageName) does not match the required range '
-      '`$supportLanguageConstraint`.',
+      '''
+The language version ($thisPackageVer) of this package ($currentPackageName) does not match the required range `$supportedLanguageConstraint`.
+
+Edit pubspec.yaml to include an SDK constraint of at least $supportedLanguageConstraint.
+
+environment:
+  sdk: $supportedLanguageConstraint
+''',
     );
   }
 }

json_serializable/lib/src/constants.dart

@@ -16,4 +16,4 @@ const converterOrKeyInstructions = r'''
 
 /// This package generates code that uses case statements, which were introduced
 /// in Dart 3.0.
-const supportLanguageConstraint = '^3.0.0';
+const supportedLanguageConstraint = '^3.0.0';

json_serializable/test/annotation_version_test.dart

@@ -36,13 +36,18 @@ void main() {
       await _structurePackage(
         environment: const {'sdk': '^$sdkLowerBound'},
         dependencies: {'json_annotation': _annotationLowerBound},
-        message: 'The language version ($sdkLowerBound) of this package '
-            '($_testPkgName) does not match the required range '
-            '`$supportLanguageConstraint`.',
+        message: '''
+The language version ($sdkLowerBound) of this package ($_testPkgName) does not match the required range `$supportedLanguageConstraint`.
+
+Edit pubspec.yaml to include an SDK constraint of at least $supportedLanguageConstraint.
+
+environment:
+  sdk: $supportedLanguageConstraint
+''',
       );
     });
 
-    test('is at least the required `$supportLanguageConstraint`', () async {
+    test('is at least the required `$supportedLanguageConstraint`', () async {
       await _structurePackage(
         dependencies: {'json_annotation': _annotationLowerBound},
         message: null,
@@ -135,7 +140,7 @@ const _testPkgName = '_test_pkg';
 Future<void> _structurePackage({
   String sourceDirectory = 'lib',
   required String? message,
-  Map<String, dynamic> environment = const {'sdk': supportLanguageConstraint},
+  Map<String, dynamic> environment = const {'sdk': supportedLanguageConstraint},
   Map<String, dynamic> dependencies = const {},
   Map<String, dynamic> devDependencies = const {},
 }) async {