[gen-l10n] Remove more ignores, conditionally generate some code (#78975)

packages/flutter_tools/lib/src/localizations/gen_l10n.dart

@@ -1169,6 +1169,7 @@ class LocalizationsGenerator {
       .replaceAll('@(supportedLanguageCodes)', supportedLanguageCodes.join(', '))
       .replaceAll('@(messageClassImports)', sortedClassImports.join('\n'))
       .replaceAll('@(delegateClass)', delegateClass)
+      .replaceAll('@(requiresFoundationImport)', _useDeferredLoading ? '' : "import 'package:flutter/foundation.dart';")
       .replaceAll('@(requiresIntlImport)', _containsPluralMessage() ? "import 'package:intl/intl.dart' as intl;" : '')
       .replaceAll('@(canBeNullable)', _usesNullableGetter ? '?' : '')
       .replaceAll('@(needsNullCheck)', _usesNullableGetter ? '' : '!');

packages/flutter_tools/lib/src/localizations/gen_l10n_templates.dart

@@ -12,8 +12,7 @@ const String fileTemplate = '''
 @(header)
 import 'dart:async';
 
-// ignore: unused_import
-import 'package:flutter/foundation.dart';
+@(requiresFoundationImport)
 import 'package:flutter/widgets.dart';
 import 'package:flutter_localizations/flutter_localizations.dart';
 import 'package:intl/intl.dart' as intl;
@@ -74,7 +73,6 @@ import 'package:intl/intl.dart' as intl;
 abstract class @(class) {
   @(class)(String locale) : localeName = intl.Intl.canonicalizedLocale(locale.toString());
 
-  // ignore: unused_field
   final String localeName;
 
   static @(class)@(canBeNullable) of(BuildContext context) {

packages/flutter_tools/test/general.shard/generate_localizations_test.dart

@@ -57,6 +57,9 @@ const String singleZhMessageArbFileString = '''
 const String intlImportDartCode = '''
 import 'package:intl/intl.dart' as intl;
 ''';
+const String foundationImportDartCode = '''
+import 'package:flutter/foundation.dart';
+''';
 
 void _standardFlutterDirectoryL10nSetup(FileSystem fs) {
   final Directory l10nDirectory = fs.currentDirectory.childDirectory('lib').childDirectory('l10n')
@@ -1882,6 +1885,60 @@ import 'output-localization-file_en.dart' deferred as output-localization-file_e
       expect(localizationsFile, contains(intlImportDartCode));
     });
 
+    testUsingContext('foundation package import should be omitted from file template when deferred loading = true', () {
+      fs.currentDirectory.childDirectory('lib').childDirectory('l10n')..createSync(recursive: true)
+        ..childFile(defaultTemplateArbFileName).writeAsStringSync(singleMessageArbFileString)
+        ..childFile('app_es.arb').writeAsStringSync(singleEsMessageArbFileString);
+
+      final LocalizationsGenerator generator = LocalizationsGenerator(fs);
+      try {
+        generator.initialize(
+          inputPathString: defaultL10nPathString,
+          outputPathString: defaultL10nPathString,
+          templateArbFileName: defaultTemplateArbFileName,
+          outputFileString: defaultOutputFileString,
+          classNameString: defaultClassNameString,
+          useDeferredLoading: true,
+        );
+        generator.loadResources();
+        generator.writeOutputFiles(BufferLogger.test());
+      } on Exception catch (e) {
+        fail('Generating output files should not fail: $e');
+      }
+
+      final String localizationsFile = fs.file(
+        fs.path.join(syntheticL10nPackagePath, 'output-localization-file.dart'),
+      ).readAsStringSync();
+      expect(localizationsFile, isNot(contains(foundationImportDartCode)));
+    });
+
+    testUsingContext('foundation package import should be kept in file template when deferred loading = false', () {
+      fs.currentDirectory.childDirectory('lib').childDirectory('l10n')..createSync(recursive: true)
+        ..childFile(defaultTemplateArbFileName).writeAsStringSync(singleMessageArbFileString)
+        ..childFile('app_es.arb').writeAsStringSync(singleEsMessageArbFileString);
+
+      final LocalizationsGenerator generator = LocalizationsGenerator(fs);
+      try {
+        generator.initialize(
+          inputPathString: defaultL10nPathString,
+          outputPathString: defaultL10nPathString,
+          templateArbFileName: defaultTemplateArbFileName,
+          outputFileString: defaultOutputFileString,
+          classNameString: defaultClassNameString,
+          useDeferredLoading: false,
+        );
+        generator.loadResources();
+        generator.writeOutputFiles(BufferLogger.test());
+      } on Exception catch (e) {
+        fail('Generating output files should not fail: $e');
+      }
+
+      final String localizationsFile = fs.file(
+        fs.path.join(syntheticL10nPackagePath, 'output-localization-file.dart'),
+      ).readAsStringSync();
+      expect(localizationsFile, contains(foundationImportDartCode));
+    });
+
     testUsingContext('check for string interpolation rules', () {
       const String enArbCheckList = '''
 {