better error handling

Author: danylo-safonov-solid

tools/add_imports/bin/add_imports.dart

@@ -3,7 +3,9 @@ import 'dart:io';
 import 'package:add_imports/src/args.dart';
 import 'package:add_imports/src/config.dart';
 import 'package:add_imports/src/util.dart';
+import 'package:args/args.dart';
 import 'package:collection/collection.dart';
+import 'package:yaml/yaml.dart';
 
 void main(List<String> arguments) {
   try {
@@ -13,25 +15,19 @@ void main(List<String> arguments) {
     if (newSource == sourceString) return;
 
     sourceFile.writeAsStringSync(newSource);
-  } on String catch (e) {
-    print(e);
   } on FileSystemException catch (e) {
     print('Error while accessing ${e.path}');
+  } on YamlException {
+    print('Error while parsing config');
+  } on ArgParserException {
+    print(Args.usage);
   }
 }
 
 (File, Config) init(List<String> arguments) {
-  final Args(
-    :filename,
-    :configpath,
-  ) = mapException(() => Args.parse(arguments), (_) => Args.usage);
-
-  final config = mapException(
-    () => Config.fromYaml(
-      File(configpath).readAsStringSync(),
-    ),
-    (_) => 'Error while reading config from "$configpath"',
-  );
+  final Args(:filename, :configpath) = Args.parse(arguments);
+  final configString = File(configpath).readAsStringSync();
+  final config = Config.fromYaml(configString);
 
   return (File(filename), config);
 }

tools/add_imports/lib/src/args.dart

@@ -1,23 +1,27 @@
 import 'package:args/args.dart';
 
 class Args {
-  static final parser = ArgParser()
+  static final _parser = ArgParser()
     ..addOption('filename')
     ..addOption('configpath', defaultsTo: 'add_imports.yaml');
 
   final String filename;
   final String configpath;
 
-  static String get usage => parser.usage;
+  static String get usage => _parser.usage;
 
   Args({required this.filename, required this.configpath});
 
   factory Args.parse(List<String> arguments) {
-    final result = parser.parse(arguments);
+    try {
+      final result = _parser.parse(arguments);
 
-    return Args(
-      filename: result['filename'] as String,
-      configpath: result['configpath'] as String,
-    );
+      return Args(
+        filename: result['filename'] as String,
+        configpath: result['configpath'] as String,
+      );
+    } catch (_) {
+      throw ArgParserException('');
+    }
   }
 }

tools/add_imports/lib/src/config.dart

@@ -10,19 +10,23 @@ class Config {
   Config({required this.fileUrlPrefix, required this.classesMap});
 
   factory Config.fromYaml(String yamlString) {
-    final parsedYaml = loadYaml(yamlString) as YamlMap;
-
-    final classesMap = (parsedYaml['classes_map'] as YamlMap).map(
-      (key, value) => MapEntry(
-        key as String,
-        [...value as YamlList].cast<String>(),
-      ),
-    );
-
-    return Config(
-      classesMap: classesMap,
-      fileUrlPrefix: parsedYaml['file_url_prefix'] as String,
-    );
+    try {
+      final parsedYaml = loadYaml(yamlString) as YamlMap;
+
+      final classesMap = (parsedYaml['classes_map'] as YamlMap).map(
+        (key, value) => MapEntry(
+          key as String,
+          [...value as YamlList].cast<String>(),
+        ),
+      );
+
+      return Config(
+        classesMap: classesMap,
+        fileUrlPrefix: parsedYaml['file_url_prefix'] as String,
+      );
+    } catch (_) {
+      throw YamlException('', null);
+    }
   }
 
   String _filenameForClass(String classname) =>