chore(smithy): Codegen improvements (#3439)

* chore(smithy): Codegen improvements

- Adds further override capabilities for shapes
- Aligns `@default` and `@required` behavior more closely to the spec
- Only generates `_init` if necessary

* chore(aft): Don't generate V1 models for `custom` service

Since this tests very specific V2 features, the V1 transformation doesn't provide any value and prevents certain usages.

* test(goldens): Add default value tests

* fix(aft): SDK models are V2

* chore(repo): Regenerate SDK

* chore(repo): Clean up

.github/dependabot.yaml

@@ -1033,20 +1033,6 @@ updates:
       - dependency-name: "amplify_lints"
       - dependency-name: "smithy_aws"
       - dependency-name: "aws_signature_v4"
-  - package-ecosystem: "pub"
-    directory: "packages/smithy/goldens/lib/custom"
-    schedule:
-      interval: "daily"
-    ignore:
-      # Ignore patch version bumps
-      - dependency-name: "*"
-        update-types:
-          - "version-update:semver-patch"
-      - dependency-name: "smithy"
-      - dependency-name: "aws_common"
-      - dependency-name: "amplify_lints"
-      - dependency-name: "smithy_aws"
-      - dependency-name: "aws_signature_v4"
   - package-ecosystem: "pub"
     directory: "packages/smithy/goldens/lib/restJson1"
     schedule:

packages/aft/lib/src/commands/generate/generate_goldens_command.dart

@@ -24,6 +24,10 @@ const awsProtocols = [
   'restXml',
   'restXmlWithNamespace',
 ];
+// Skip generating V1 since we use V2-specific traits and test descriptions.
+const skipV1 = [
+  'custom',
+];
 
 /// Command for generating the AWS SDK for a given package and `sdk.yaml` file.
 class GenerateGoldensCommand extends AmplifyCommand {
@@ -311,6 +315,9 @@ override_platforms:
         continue;
       }
       for (final version in SmithyVersion.values) {
+        if (version == SmithyVersion.v1 && skipV1.contains(protocolName)) {
+          continue;
+        }
         final ast = await _transform(
           version,
           modelPath,

packages/aft/lib/src/commands/generate/generate_sdk_command.dart

@@ -166,7 +166,9 @@ class GenerateSdkCommand extends AmplifyCommand with GlobOptions {
       await outputDir.create(recursive: true);
     }
 
-    final smithyModel = SmithyAstBuilder();
+    final smithyModel = SmithyAstBuilder()
+      ..version = SmithyVersion.v2
+      ..shapes = ShapeMap({});
 
     final modelsDir = await _modelsDirForRef(config.ref);
     final models = modelsDir.list().whereType<File>();
@@ -178,7 +180,6 @@ class GenerateSdkCommand extends AmplifyCommand with GlobOptions {
       final astJson = await model.readAsString();
       final ast = parseAstJson(astJson);
 
-      smithyModel.shapes ??= ShapeMap({});
       smithyModel.shapes!.addAll(ast.shapes);
     }