Migrate flutter_localizations to null safety. (#68645)

Migrate flutter_localizations to null safety.

dev/tools/localization/bin/gen_localizations.dart

@@ -382,15 +382,20 @@ $factoryDeclaration
 ///
 /// Used by [generateGetter] below.
 String generateType(Map<String, dynamic> attributes) {
+  bool optional = false;
+  String type = 'String';
   if (attributes != null) {
+    optional = attributes.containsKey('optional');
     switch (attributes['x-flutter-type'] as String) {
       case 'icuShortTimePattern':
-        return 'TimeOfDayFormat';
+        type = 'TimeOfDayFormat';
+        break;
       case 'scriptCategory':
-        return 'ScriptCategory';
+        type = 'ScriptCategory';
+        break;
     }
   }
-  return 'String';
+  return type + (optional ? '?' : '');
 }
 
 /// Returns the appropriate name for getters with the given attributes.

dev/tools/localization/gen_cupertino_localizations.dart

@@ -16,7 +16,6 @@ HeaderGenerator generateCupertinoHeader = (String regenerateInstructions) {
 
 import 'dart:collection';
 
-import 'package:flutter/foundation.dart';
 import 'package:flutter/cupertino.dart';
 import 'package:intl/intl.dart' as intl;
 
@@ -40,14 +39,14 @@ ConstructorGenerator generateCupertinoConstructor = (LocaleInfo locale) {
   /// For details on the meaning of the arguments, see [GlobalCupertinoLocalizations].
   const CupertinoLocalization${locale.camelCase()}({
     String localeName = '$localeName',
-    @required intl.DateFormat fullYearFormat,
-    @required intl.DateFormat dayFormat,
-    @required intl.DateFormat mediumDateFormat,
-    @required intl.DateFormat singleDigitHourFormat,
-    @required intl.DateFormat singleDigitMinuteFormat,
-    @required intl.DateFormat doubleDigitMinuteFormat,
-    @required intl.DateFormat singleDigitSecondFormat,
-    @required intl.NumberFormat decimalFormat,
+    required intl.DateFormat fullYearFormat,
+    required intl.DateFormat dayFormat,
+    required intl.DateFormat mediumDateFormat,
+    required intl.DateFormat singleDigitHourFormat,
+    required intl.DateFormat singleDigitMinuteFormat,
+    required intl.DateFormat doubleDigitMinuteFormat,
+    required intl.DateFormat singleDigitSecondFormat,
+    required intl.NumberFormat decimalFormat,
   }) : super(
     localeName: localeName,
     fullYearFormat: fullYearFormat,
@@ -64,7 +63,7 @@ ConstructorGenerator generateCupertinoConstructor = (LocaleInfo locale) {
 const String cupertinoFactoryName = 'getCupertinoTranslation';
 
 const String cupertinoFactoryDeclaration = '''
-GlobalCupertinoLocalizations getCupertinoTranslation(
+GlobalCupertinoLocalizations? getCupertinoTranslation(
   Locale locale,
   intl.DateFormat fullYearFormat,
   intl.DateFormat dayFormat,

dev/tools/localization/gen_material_localizations.dart

@@ -16,7 +16,6 @@ HeaderGenerator generateMaterialHeader = (String regenerateInstructions) {
 
 import 'dart:collection';
 
-import 'package:flutter/foundation.dart';
 import 'package:flutter/material.dart';
 import 'package:intl/intl.dart' as intl;
 
@@ -40,15 +39,15 @@ ConstructorGenerator generateMaterialConstructor = (LocaleInfo locale) {
   /// For details on the meaning of the arguments, see [GlobalMaterialLocalizations].
   const MaterialLocalization${locale.camelCase()}({
     String localeName = '$localeName',
-    @required intl.DateFormat fullYearFormat,
-    @required intl.DateFormat compactDateFormat,
-    @required intl.DateFormat shortDateFormat,
-    @required intl.DateFormat mediumDateFormat,
-    @required intl.DateFormat longDateFormat,
-    @required intl.DateFormat yearMonthFormat,
-    @required intl.DateFormat shortMonthDayFormat,
-    @required intl.NumberFormat decimalFormat,
-    @required intl.NumberFormat twoDigitZeroPaddedFormat,
+    required intl.DateFormat fullYearFormat,
+    required intl.DateFormat compactDateFormat,
+    required intl.DateFormat shortDateFormat,
+    required intl.DateFormat mediumDateFormat,
+    required intl.DateFormat longDateFormat,
+    required intl.DateFormat yearMonthFormat,
+    required intl.DateFormat shortMonthDayFormat,
+    required intl.NumberFormat decimalFormat,
+    required intl.NumberFormat twoDigitZeroPaddedFormat,
   }) : super(
     localeName: localeName,
     fullYearFormat: fullYearFormat,
@@ -66,7 +65,7 @@ ConstructorGenerator generateMaterialConstructor = (LocaleInfo locale) {
 const String materialFactoryName = 'getMaterialTranslation';
 
 const String materialFactoryDeclaration = '''
-GlobalMaterialLocalizations getMaterialTranslation(
+GlobalMaterialLocalizations? getMaterialTranslation(
   Locale locale,
   intl.DateFormat fullYearFormat,
   intl.DateFormat compactDateFormat,

dev/tools/localization/localizations_validator.dart

@@ -67,8 +67,9 @@ void validateEnglishLocalizations(File file) {
       continue;
     }
 
+    final bool optional = atResource.containsKey('optional');
     final String description = atResource['description'] as String;
-    if (description == null)
+    if (description == null && !optional)
       errorMessages.writeln('No description specified for $atResourceId');
 
     final String plural = atResource['plural'] as String;
@@ -78,7 +79,7 @@ void validateEnglishLocalizations(File file) {
       if (!bundle.containsKey(resourceIdOther))
         errorMessages.writeln('Default plural resource $resourceIdOther undefined');
     } else {
-      if (!bundle.containsKey(resourceId))
+      if (!optional && !bundle.containsKey(resourceId))
         errorMessages.writeln('No matching $resourceId defined for $atResourceId');
     }
   }