feat: Added implements based on the type of the generated class.

packages/graphql_codegen/lib/src/config/config.dart

@@ -52,6 +52,23 @@ class GraphQLCodegenConfigEnum {
   Map<String, dynamic> toJson() => _$GraphQLCodegenConfigEnumToJson(this);
 }
 
+@JsonSerializable()
+class GraphQLCodegenConfigImplements {
+  final String parent;
+  final String? import;
+
+  const GraphQLCodegenConfigImplements({
+    required this.parent,
+    this.import,
+  });
+
+  @override
+  factory GraphQLCodegenConfigImplements.fromJson(Map<String, dynamic> json) =>
+      _$GraphQLCodegenConfigImplementsFromJson(json);
+
+  Map<String, dynamic> toJson() => _$GraphQLCodegenConfigImplementsToJson(this);
+}
+
 @JsonSerializable()
 class GraphQLCodegenConfig {
   final Set<GraphQLCodegenConfigClient> clients;
@@ -67,6 +84,7 @@ class GraphQLCodegenConfig {
   final String outputDirectory;
   final bool disableContextReplacement;
   final bool disableCopyWithGeneration;
+  final Map<String, List<GraphQLCodegenConfigImplements>> typeImplements;
 
   GraphQLCodegenConfig({
     this.clients = const {},
@@ -82,6 +100,7 @@ class GraphQLCodegenConfig {
     this.extraKeywords = const [],
     this.outputDirectory = '.',
     this.disableCopyWithGeneration = false,
+    this.typeImplements = const {},
   });
 
   @override

packages/graphql_codegen/lib/src/printer/base/document.dart

@@ -110,6 +110,17 @@ Class printContext(PrintContext c) {
     c.addDependency(extendContext.path);
   }
   final properties = c.context.properties;
+
+  final typeImplements =
+      context.config.typeImplements[c.namePrinter.printClassName(context.path)];
+  if (typeImplements != null) {
+    for (final t in typeImplements) {
+      if (t.import != null) {
+        c.addPackage(t.import!);
+      }
+    }
+  }
+
   return Class(
     (b) => b
       ..name = c.namePrinter.printClassName(context.path)
@@ -120,6 +131,8 @@ Class printContext(PrintContext c) {
             .map(refer),
         if (extendContext != null)
           refer(c.namePrinter.printClassName(extendContext.path)),
+        if (typeImplements != null)
+          ...typeImplements.map((e) => Reference(e.parent, e.import))
       ])
       ..constructors = ListBuilder([
         _printConstructor(c, properties),

packages/graphql_codegen/test/assets/fragments_implements/document.graphql

@@ -0,0 +1,19 @@
+type Query {
+  t: T
+}
+
+type T {
+  id: String!
+  name: String
+}
+
+fragment F on T {
+  id
+  name
+}
+
+query Q {
+  t {
+    ...F
+  }
+}