Use correct language version for formatter

CHANGELOG.md

@@ -1,3 +1,7 @@
+## 5.4.6
+
+* Pass actual language version of generating package to formatter.
+
 ## 5.4.5
 
 * Ignore "must_be_immutable" warning in generated files. Mocks cannot be made

lib/src/builder.dart

@@ -44,7 +44,9 @@ import 'package:collection/collection.dart';
 import 'package:dart_style/dart_style.dart';
 import 'package:mockito/annotations.dart';
 import 'package:mockito/src/version.dart';
+import 'package:package_config/package_config_types.dart';
 import 'package:path/path.dart' as p;
+import 'package:pub_semver/pub_semver.dart';
 import 'package:source_gen/source_gen.dart';
 
 /// For a source Dart library, generate the mocks referenced therein.
@@ -141,12 +143,17 @@ class MockBuilder implements Builder {
         orderDirectives: true,
         useNullSafetySyntax: sourceLibIsNonNullable);
     final rawOutput = mockLibrary.accept(emitter).toString();
-    // The source lib may be pre-null-safety because of an explicit opt-out
-    // (`// @dart=2.9`), as opposed to living in a pre-null-safety package. To
-    // allow for this situation, we must also add an opt-out comment here.
+
+    final packageConfig = await buildStep.packageConfig;
+    var surroundingLanguageVersion = DartFormatter.latestLanguageVersion;
+    if (packageConfig[mockLibraryAsset.package]
+        case Package(:final languageVersion?)) {
+      surroundingLanguageVersion =
+          Version(languageVersion.major, languageVersion.minor, 0);
+    }
+
     final mockLibraryContent =
-        DartFormatter(languageVersion: DartFormatter.latestLanguageVersion)
-            .format('''
+        DartFormatter(languageVersion: surroundingLanguageVersion).format('''
 // Mocks generated by Mockito $packageVersion from annotations
 // in ${entryLib.definingCompilationUnit.source.uri.path}.
 // Do not manually edit this file.

pubspec.yaml

@@ -1,5 +1,5 @@
 name: mockito
-version: 5.4.5
+version: 5.4.6
 description: >-
   A mock framework inspired by Mockito with APIs for Fakes, Mocks,
   behavior verification, and stubbing.
@@ -20,7 +20,9 @@ dependencies:
   dart_style: '>=2.3.7 <4.0.0'
   matcher: ^0.12.16
   meta: ^1.15.0
+  package_config: ^2.1.1
   path: ^1.9.0
+  pub_semver: ^2.1.5
   source_gen: ">=1.4.0 <3.0.0"
   test_api: ">=0.6.1 <0.8.0"
 
@@ -30,5 +32,4 @@ dev_dependencies:
   build_web_compilers: ^4.0.11
   http: ^1.0.0
   lints: ^5.1.0
-  package_config: ^2.1.0
   test: ^1.24.4