Windows support

monarch/lib/src/builders/builder_helper.dart

@@ -2,13 +2,16 @@ import 'package:build/build.dart';
 // import 'package:build_runner_core/build_runner_core.dart';
 import 'package:path/path.dart' as p;
 
-const generatedOutputDirectory = '.dart_tool/build/generated';
+String generatedOutputDirectory = p.join('.dart_tool','build','generated');
 
 String getOuputPathInGeneratedOutputDirectory(AssetId inputId) {
-  return '$generatedOutputDirectory/${inputId.package}/${p.dirname(inputId.path)}';
+  return p.join(generatedOutputDirectory, inputId.package, p.dirname(inputId.path));
 }
 
 String getRelativePathFromOutputToInput(AssetId inputId) {
   final outputPath = getOuputPathInGeneratedOutputDirectory(inputId);
-  return p.relative(inputId.path, from: outputPath);
+  return normalizeAssetPath(p.relative(inputId.path, from: outputPath));
 }
+
+/// Asset paths always have forward slashes regardless of platform.
+String normalizeAssetPath(String path) => path.replaceAll(r'\', '/');

monarch/lib/src/builders/main_builder.dart

@@ -3,6 +3,9 @@ import 'dart:async';
 import 'package:build/build.dart';
 import 'package:glob/glob.dart';
 import 'package:dart_style/dart_style.dart';
+import 'package:path/path.dart' as p;
+
+import 'builder_helper.dart';
 
 class MainBuilder implements Builder {
   @override
@@ -60,7 +63,11 @@ class MainBuilder implements Builder {
   Iterable<String> _getImportStatements(Map<String, AssetId> map) {
     return map.entries.map((item) {
       final libraryPrefix = item.key;
-      return "import '../${item.value.path}' as $libraryPrefix;";
+      final targetPath = item.value.path;
+
+      final relativePath =
+          normalizeAssetPath(p.relative(targetPath, from: 'lib'));
+      return "import r'$relativePath' as $libraryPrefix;";
     });
   }
 

monarch/lib/src/builders/meta_stories_generator.dart

@@ -57,7 +57,7 @@ class MetaStoriesGenerator extends Generator {
       List<String> storiesNames, Map<String, String> storiesMap) {
     return '''
 import 'package:monarch/monarch.dart';
-import '$pathToStoriesFile';
+import r'$pathToStoriesFile';
 
 const metaStories = MetaStories('${storiesAssetId.package}', '${storiesAssetId.path}', [${storiesNames.join(', ')}], $storiesMap);
 

monarch/lib/src/builders/meta_themes_generator.dart

@@ -52,7 +52,7 @@ Element name: ${element.name}
       String pathToThemeFile, List<String> metaThemeExpressions) {
     return '''
 import 'package:monarch/monarch.dart';
-import '$pathToThemeFile';
+import r'$pathToThemeFile';
 
 final metaThemeItems = [
   ${metaThemeExpressions.join(', ')}

monarch/lib/src/monarch_app/active_locale.dart

@@ -39,6 +39,11 @@ class ActiveLocale with Log {
     }
   }
 
+  void resetActiveLocale() {
+    _activeLocale = null;
+    log.fine('active locale reset');
+  }
+
   void assertIsLoaded() {
     if (locale == null) {
       throw StateError('Expected activeLocale to be set');
@@ -54,16 +59,23 @@ class ActiveLocale with Log {
   }
 
   void setActiveLocaleTag(String localeTag) {
-    setActiveLocale(parseLocale(localeTag));
+    if (localeTag == 'System Locale') {
+      // As of 2020-10-08, the platform apps send 'System Locale' when there aren't
+      // any user-defined locales, in which case the StoryApp will create a MaterialApp
+      // without any localization data. In this case, Flutter's default behavior is to
+      // use the only supported locale which is en-US.
+      resetActiveLocale();
+    }
+    else {
+      setActiveLocale(parseLocale(localeTag));
+    }
   }
 
   void close() {
     _loadingStatusStreamController.close();
   }
 }
 
-const defaultLocale = Locale('en', 'US');
-
 Locale parseLocale(String localeTag) {
   ArgumentError.checkNotNull(localeTag, 'localeTag');
   if (localeTag.isEmpty) {

monarch/lib/src/monarch_app/stories_errors.dart

@@ -51,6 +51,9 @@ String _getActiveStoryErrorMessage() {
     return 'There was no active story selected.';
   } else {
     final metaStories = _monarchData.metaStoriesMap[activeStoryId.pathKey];
+    if (metaStories == null) {
+      return 'Unexpected - Could not find meta stories for ${activeStoryId.pathKey}';
+    }
     return '''
 The relevant story is:
   ${metaStories.path} > ${activeStoryId.name}''';