fix(dynamite): Fix generating part directive and serializers conditionally

Signed-off-by: jld3103 <jld3103yt@gmail.com>

packages/dynamite/dynamite/lib/src/builder/imports.dart

@@ -1,8 +1,9 @@
 import 'package:build/build.dart';
 import 'package:code_builder/code_builder.dart';
+import 'package:dynamite/src/builder/state.dart';
 import 'package:path/path.dart' as p;
 
-List<Spec> generateImports(final AssetId outputId) => [
+List<Spec> generateImports(final AssetId outputId, final State state) => [
       const Code('// ignore_for_file: camel_case_types'),
       const Code('// ignore_for_file: discarded_futures'),
       const Code('// ignore_for_file: public_member_api_docs'),
@@ -23,6 +24,8 @@ List<Spec> generateImports(final AssetId outputId) => [
       Directive.import('package:meta/meta.dart'),
       Directive.import('package:universal_io/io.dart'),
       const Code(''),
-      Directive.part(p.basename(outputId.changeExtension('.g.dart').path)),
-      const Code(''),
+      if (state.resolvedTypes.isNotEmpty) ...[
+        Directive.part(p.basename(outputId.changeExtension('.g.dart').path)),
+        const Code(''),
+      ],
     ];

packages/dynamite/dynamite/lib/src/builder/serializer.dart

@@ -1,9 +1,7 @@
 import 'package:code_builder/code_builder.dart';
 import 'package:dynamite/src/builder/state.dart';
 
-List<Spec> buildSerializer(final State state) {
-  if (state.resolvedTypes.isNotEmpty) {
-    return [
+List<Spec> buildSerializer(final State state) => [
       const Code('// coverage:ignore-start'),
       const Code('final Serializers _serializers = (Serializers().toBuilder()'),
       ...state.resolvedTypes
@@ -18,7 +16,3 @@ List<Spec> buildSerializer(final State state) {
       ),
       const Code('// coverage:ignore-end'),
     ];
-  }
-
-  return [];
-}

packages/dynamite/dynamite/lib/src/openapi_builder.dart

@@ -51,9 +51,7 @@ class OpenAPIBuilder implements Builder {
 
       final state = State();
 
-      final output = ListBuilder<Spec>()
-        ..addAll(generateImports(outputId))
-        ..addAll(generateClients(spec, state));
+      final output = ListBuilder<Spec>();
 
       if (spec.components?.schemas != null) {
         for (final schema in spec.components!.schemas!.entries) {
@@ -86,9 +84,17 @@ class OpenAPIBuilder implements Builder {
         }
       }
 
+      // Imports need to be generated after everything else so we know if we need the local part directive,
+      // but they need to be added to the beginning of the output.
+      final clients = generateClients(spec, state);
+      final serializer = buildSerializer(state);
+      final imports = generateImports(outputId, state);
+
       output
+        ..addAll(imports)
+        ..addAll(clients)
         ..addAll(state.output)
-        ..addAll(buildSerializer(state));
+        ..addAll(serializer);
 
       final patterns = [
         RegExp(