update rust_builder

rust_builder/cargokit/build_tool/lib/src/cargo.dart

@@ -0,0 +1,48 @@
+/// This is copied from Cargokit (which is the official way to use it currently)
+/// Details: https://fzyzcjy.github.io/flutter_rust_bridge/manual/integrate/builtin
+
+import 'dart:io';
+
+import 'package:path/path.dart' as path;
+import 'package:toml/toml.dart';
+
+class ManifestException {
+  ManifestException(this.message, {required this.fileName});
+
+  final String? fileName;
+  final String message;
+
+  @override
+  String toString() {
+    if (fileName != null) {
+      return 'Failed to parse package manifest at $fileName: $message';
+    } else {
+      return 'Failed to parse package manifest: $message';
+    }
+  }
+}
+
+class CrateInfo {
+  CrateInfo({required this.packageName});
+
+  final String packageName;
+
+  static CrateInfo parseManifest(String manifest, {final String? fileName}) {
+    final toml = TomlDocument.parse(manifest);
+    final package = toml.toMap()['package'];
+    if (package == null) {
+      throw ManifestException('Missing package section', fileName: fileName);
+    }
+    final name = package['name'];
+    if (name == null) {
+      throw ManifestException('Missing package name', fileName: fileName);
+    }
+    return CrateInfo(packageName: name);
+  }
+
+  static CrateInfo load(String manifestDir) {
+    final manifestFile = File(path.join(manifestDir, 'Cargo.toml'));
+    final manifest = manifestFile.readAsStringSync();
+    return parseManifest(manifest, fileName: manifestFile.path);
+  }
+}