From eaa7f232622a41f8f502576ecc9014c3247ca06e Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Kehan=F0=9F=9A=80?= <kehanw@amazon.com>
Date: Tue, 17 Mar 2026 12:26:51 -0400
Subject: [PATCH 1/2] fix: skip OperationGenerator in types-only codegen mode
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In types-only mode, OperationGenerator is invoked for operations added
to the synthetic service by SyntheticServiceTransform. OperationGenerator
calls EventStreamIndex, which iterates all operation input/output members
via model.expectShape(). The synthetic model built by
SyntheticServiceTransform has an incomplete transitive closure — @mixin
shapes (e.g. BaseError, ComponentInstanceMixin) are flattened during
model assembly and not resolvable via expectShape() in the transformed
model, causing ExpectationNotMetException.

The old DirectedJavaTypeCodegen (removed in #1057) never implemented
generateOperation(), so this path was never hit. The unified
DirectedJavaCodegen runs OperationGenerator unconditionally, which is
unnecessary in types-only mode — operation input/output types are
generated through generateStructure(), not generateOperation().

This adds an isTypesOnly() guard to generateOperation() and refactors
generateService() to use the same helper.
---
 .../smithy/java/codegen/DirectedJavaCodegen.java | 16 ++++++++++++++--
 1 file changed, 14 insertions(+), 2 deletions(-)

diff --git a/codegen/codegen-plugin/src/main/java/software/amazon/smithy/java/codegen/DirectedJavaCodegen.java b/codegen/codegen-plugin/src/main/java/software/amazon/smithy/java/codegen/DirectedJavaCodegen.java
index d5b25b208..6061442a8 100644
--- a/codegen/codegen-plugin/src/main/java/software/amazon/smithy/java/codegen/DirectedJavaCodegen.java
+++ b/codegen/codegen-plugin/src/main/java/software/amazon/smithy/java/codegen/DirectedJavaCodegen.java
@@ -130,6 +130,13 @@ public void generateOperation(GenerateOperationDirective<CodeGenerationContext,
         if (isSynthetic(directive.shape())) {
             return;
         }
+        // In types-only mode, skip OperationGenerator. Operation input/output types are still
+        // generated via generateStructure(). OperationGenerator creates operation wiring classes
+        // and invokes EventStreamIndex, which fails on models built by SyntheticServiceTransform
+        // when @mixin shapes are present (incomplete transitive closure).
+        if (isTypesOnly()) {
+            return;
+        }
         if (modes.contains(CodegenMode.SERVER)) {
             new OperationInterfaceGenerator().accept(directive);
         }
@@ -139,8 +146,7 @@ public void generateOperation(GenerateOperationDirective<CodeGenerationContext,
     @Override
     public void generateService(GenerateServiceDirective<CodeGenerationContext, JavaCodegenSettings> directive) {
         // In TYPES-only mode, generateService is a no-op (the synthetic service has no real service shape)
-        if (modes.contains(CodegenMode.TYPES) && !modes.contains(CodegenMode.CLIENT)
-                && !modes.contains(CodegenMode.SERVER)) {
+        if (isTypesOnly()) {
             return;
         }
 
@@ -188,4 +194,10 @@ public void customizeAfterIntegrations(CustomizeDirective<CodeGenerationContext,
     private static boolean isSynthetic(Shape shape) {
         return shape.getId().getNamespace().equals(SyntheticServiceTransform.SYNTHETIC_NAMESPACE);
     }
+
+    private boolean isTypesOnly() {
+        return modes.contains(CodegenMode.TYPES)
+                && !modes.contains(CodegenMode.CLIENT)
+                && !modes.contains(CodegenMode.SERVER);
+    }
 }

From f56810f35ff3d2881e44166a8639c653cdf95f3c Mon Sep 17 00:00:00 2001
From: Kehan Wang <AgentKWang@users.noreply.github.com>
Date: Tue, 17 Mar 2026 16:46:30 -0400
Subject: [PATCH 2/2] Update
 codegen/codegen-plugin/src/main/java/software/amazon/smithy/java/codegen/DirectedJavaCodegen.java

Co-authored-by: Manuel Sugawara <sugmanue@amazon.com>
---
 .../amazon/smithy/java/codegen/DirectedJavaCodegen.java       | 4 ----
 1 file changed, 4 deletions(-)

diff --git a/codegen/codegen-plugin/src/main/java/software/amazon/smithy/java/codegen/DirectedJavaCodegen.java b/codegen/codegen-plugin/src/main/java/software/amazon/smithy/java/codegen/DirectedJavaCodegen.java
index 6061442a8..4170b142d 100644
--- a/codegen/codegen-plugin/src/main/java/software/amazon/smithy/java/codegen/DirectedJavaCodegen.java
+++ b/codegen/codegen-plugin/src/main/java/software/amazon/smithy/java/codegen/DirectedJavaCodegen.java
@@ -130,10 +130,6 @@ public void generateOperation(GenerateOperationDirective<CodeGenerationContext,
         if (isSynthetic(directive.shape())) {
             return;
         }
-        // In types-only mode, skip OperationGenerator. Operation input/output types are still
-        // generated via generateStructure(). OperationGenerator creates operation wiring classes
-        // and invokes EventStreamIndex, which fails on models built by SyntheticServiceTransform
-        // when @mixin shapes are present (incomplete transitive closure).
         if (isTypesOnly()) {
             return;
         }