Address review comments.

pkgs/_macro_host/lib/macro_host.dart

@@ -13,11 +13,12 @@ class MacroHost {
   final MacroRunner macroRunner = MacroRunner();
   late final HostEndpoint hostEndpoint;
 
-  MacroHost({required MacroHostService service})
-      : macroServer = MacroServer(service: service);
+  MacroHost._(this.macroServer, this.hostEndpoint);
 
-  Future<void> serve() async {
-    hostEndpoint = await macroServer.serve();
+  static Future<MacroHost> serve({required MacroHostService service}) async {
+    final server = MacroServer(service: service);
+    final endpoint = await server.serve();
+    return MacroHost._(server, endpoint);
   }
 
   // TODO(davidmorgan): methods for integration with analyzer+CFE go here:

pkgs/_test_macros/lib/declare_x_macro.dart

@@ -12,9 +12,7 @@ class DeclareX {
 // TODO(davidmorgan): this is a placeholder; make it do something, test it.
 class DeclareXImplementation implements Macro {
   @override
-  MacroDescription get description => MacroDescription(
-        runsInPhaseThree: true,
-      );
+  MacroDescription get description => MacroDescription(runsInPhases: [3]);
 
   @override
   Future<AugmentResponse> augment(Host host, AugmentRequest request) async {

pkgs/macro_service/lib/src/macro_service.g.dart

@@ -33,21 +33,11 @@ extension type HostEndpoint.fromJson(Map<String, Object?> node) {
 /// Information about a macro that the macro provides to the host.
 extension type MacroDescription.fromJson(Map<String, Object?> node) {
   MacroDescription({
-    bool? runsInPhaseOne,
-    bool? runsInPhaseTwo,
-    bool? runsInPhaseThree,
+    List<int>? runsInPhases,
   }) : this.fromJson({
-          if (runsInPhaseOne != null) 'runsInPhaseOne': runsInPhaseOne,
-          if (runsInPhaseTwo != null) 'runsInPhaseTwo': runsInPhaseTwo,
-          if (runsInPhaseThree != null) 'runsInPhaseThree': runsInPhaseThree,
+          if (runsInPhases != null) 'runsInPhases': runsInPhases,
         });
 
-  /// Whether the macro runs in phase one to produce types.
-  bool get runsInPhaseOne => node['runsInPhaseOne'] as bool;
-
-  /// Whether the macro runs in phase two to produce declarations.
-  bool get runsInPhaseTwo => node['runsInPhaseTwo'] as bool;
-
-  /// Whether the macro runs in phase three to produce definitions.
-  bool get runsInPhaseThree => node['runsInPhaseThree'] as bool;
+  /// Phases that the macro runs in: 1, 2 and/or 3.
+  List<int> get runsInPhases => (node['runsInPhases'] as List).cast();
 }

schemas/macro_service.schema.json

@@ -34,17 +34,12 @@
       "type": "object",
       "description": "Information about a macro that the macro provides to the host.",
       "properties": {
-        "runsInPhaseOne": {
-          "description": "Whether the macro runs in phase one to produce types.",
-          "type": "boolean"
-        },
-        "runsInPhaseTwo": {
-          "description": "Whether the macro runs in phase two to produce declarations.",
-          "type": "boolean"
-        },
-        "runsInPhaseThree": {
-          "description": "Whether the macro runs in phase three to produce definitions.",
-          "type": "boolean"
+        "runsInPhases": {
+          "description": "Phases that the macro runs in: 1, 2 and/or 3.",
+          "type": "array",
+          "items": {
+            "type": "integer"
+          }
         }
       }
     }

tool/dart_model_generator/lib/generate_dart_model.dart

@@ -156,22 +156,34 @@ PropertyMetadata _readPropertyMetadata(String name, JsonSchema schema) {
         description: schema.description,
         name: name,
         type: PropertyType.list,
-        // `items` should be a type specified with a `$ref`.
-        elementTypeName: _readRefName(schema, 'items')),
+        elementTypeName: _readRefNameOrType(schema, 'items')),
     SchemaType.object => PropertyMetadata(
         description: schema.description,
         name: name,
         type: PropertyType.map,
         // `additionalProperties` should be a type specified with a `$ref`.
-        elementTypeName: _readRefName(schema, 'additionalProperties')),
+        elementTypeName: _readRefNameOrType(schema, 'additionalProperties')),
     _ => throw UnsupportedError('Unsupported schema type: ${schema.type}'),
   };
 }
 
 /// Reads the type name of a `$ref` to a `$def`.
-String _readRefName(JsonSchema schema, String key) {
-  final ref = (schema.schemaMap![key] as Map)[r'$ref'] as String;
-  return ref.substring(r'#/$defs/'.length);
+///
+/// If it's not there, falls back to `type` mapped to a Dart type name.
+String _readRefNameOrType(JsonSchema schema, String key) {
+  final typeSchema = schema.schemaMap![key] as Map;
+  final ref = typeSchema[r'$ref'] as String?;
+  if (ref != null) {
+    return ref.substring(r'#/$defs/'.length);
+  } else {
+    final type = typeSchema['type'] as String;
+    switch (type) {
+      case 'integer':
+        return 'int';
+      default:
+        throw UnsupportedError(type);
+    }
+  }
 }
 
 /// The Dart types used in extension types to model JSON types.