support older gist formats

pkgs/sketch_pad/lib/editor/codemirror.dart

@@ -6,6 +6,7 @@
 library;
 
 import 'dart:js_interop';
+
 import 'package:web/web.dart';
 
 extension type CodeMirrorOptions._(JSObject _) implements JSObject {

pkgs/sketch_pad/lib/gists.dart

@@ -28,17 +28,22 @@ class GistLoader {
 }
 
 class Gist {
+  static const String defaultFileName = 'main.dart';
+
   final String id;
   final String? description;
   final String? owner;
   final List<GistFile> files;
+  final List<String> validationIssues = [];
 
   Gist({
     required this.id,
     required this.description,
     required this.owner,
     required this.files,
-  });
+  }) {
+    _validateGist();
+  }
 
   factory Gist.fromJson(Map<String, dynamic> json) {
 /* {
@@ -80,9 +85,28 @@ class Gist {
   }
 
   String? get mainDartSource {
-    return files
-        .firstWhereOrNull((file) => file.fileName == 'main.dart')
-        ?.content;
+    GistFile? file;
+
+    // First, try and load 'main.dart'.
+    file = files.firstWhereOrNull((file) => file.fileName == defaultFileName);
+
+    // Fall back on the older (unintentional) contention - loading from the
+    // single dart file in a gist.
+    file ??= files.singleWhereOrNull((file) => file.fileName.endsWith('.dart'));
+
+    return file?.content;
+  }
+
+  void _validateGist() {
+    final file =
+        files.singleWhereOrNull((file) => file.fileName.endsWith('.dart'));
+
+    if (file == null) {
+      validationIssues.add('Warning: no Dart file found in the gist');
+    } else if (file.fileName != defaultFileName) {
+      validationIssues.add('Warning: no gist content in $defaultFileName '
+          '(loading from ${file.fileName})');
+    }
   }
 }
 

pkgs/sketch_pad/lib/model.dart

@@ -262,6 +262,14 @@ class AppServices {
           appModel.sourceCodeController.text = fallbackSnippet;
         } else {
           appModel.sourceCodeController.text = source;
+
+          if (gist.validationIssues.isNotEmpty) {
+            final message = gist.validationIssues.join('\n');
+            appModel.editorStatus.showToast(
+              message,
+              duration: const Duration(seconds: 10),
+            );
+          }
         }
 
         appModel.appReady.value = true;

pkgs/sketch_pad/test/gists_test.dart

@@ -32,6 +32,20 @@ void main() {
 
       expect(gist.mainDartSource, isNull);
     });
+
+    test('validates main.dart missing', () {
+      final gist =
+          Gist.fromJson(jsonDecode(jsonSampleNoMain) as Map<String, dynamic>);
+
+      expect(gist.validationIssues, isNotEmpty);
+    });
+
+    test('validates unexpected dart content file', () {
+      final gist = Gist.fromJson(
+          jsonDecode(jsonSampleAlternativeFile) as Map<String, dynamic>);
+
+      expect(gist.validationIssues, isNotEmpty);
+    });
   });
 }
 
@@ -76,7 +90,7 @@ const String jsonSampleNoMain = '''
   "user": null,
   "truncated": false,
   "files": {
-    "main.dart": {
+    "main.html": {
       "filename": "main.html",
       "type": "application/vnd.dart",
       "language": "Dart",
@@ -88,3 +102,30 @@ const String jsonSampleNoMain = '''
   }
 }
 ''';
+
+const String jsonSampleAlternativeFile = '''
+{
+  "id": "d3bd83918d21b6d5f778bdc69c3d36d6",
+  "description": "Fibonacci",
+  "owner": {
+    "login": "flutterdevrelgists"
+  },
+  "public": false,
+  "created_at": "2021-08-23T23:27:20Z",
+  "updated_at": "2023-05-30T10:59:27Z",
+  "comments": 0,
+  "user": null,
+  "truncated": false,
+  "files": {
+    "sample_1.dart": {
+      "filename": "sample_1.dart",
+      "type": "application/vnd.dart",
+      "language": "Dart",
+      "raw_url": "https://gist.githubusercontent.com/flutterdevrelgists/d3bd83918d21b6d5f778bdc69c3d36d6/raw/5eaecf3519fe453298d077068194720c9729be62/main.dart",
+      "size": 369,
+      "truncated": false,
+      "content": "..."
+    }
+  }
+}
+''';