Add new codgen processor to throw ModelInvalidException on naming case and type collisions instead of NPE

codegen/src/main/java/software/amazon/awssdk/codegen/customization/processors/DefaultCustomizationProcessor.java

@@ -42,6 +42,7 @@ public static CodegenCustomizationProcessor getProcessorFor(
                 new S3RemoveBucketFromUriProcessor(),
                 new S3ControlRemoveAccountIdHostPrefixProcessor(),
                 new ExplicitStringPayloadQueryProtocolProcessor(),
+                new ShapeNameCollisionValidatorProcessor(),
                 new LowercaseShapeValidatorProcessor(),
                 new LongPollingOperationProcessor()
                 );

codegen/src/main/java/software/amazon/awssdk/codegen/customization/processors/ShapeNameCollisionValidatorProcessor.java

@@ -0,0 +1,71 @@
+/*
+ * Copyright Amazon.com, Inc. or its affiliates. All Rights Reserved.
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License").
+ * You may not use this file except in compliance with the License.
+ * A copy of the License is located at
+ *
+ *  http://aws.amazon.com/apache2.0
+ *
+ * or in the "license" file accompanying this file. This file is distributed
+ * on an "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either
+ * express or implied. See the License for the specific language governing
+ * permissions and limitations under the License.
+ */
+
+package software.amazon.awssdk.codegen.customization.processors;
+
+import java.util.ArrayList;
+import java.util.LinkedHashMap;
+import java.util.List;
+import java.util.Map;
+import java.util.Objects;
+import software.amazon.awssdk.codegen.customization.CodegenCustomizationProcessor;
+import software.amazon.awssdk.codegen.internal.Utils;
+import software.amazon.awssdk.codegen.model.intermediate.IntermediateModel;
+import software.amazon.awssdk.codegen.model.service.ServiceModel;
+import software.amazon.awssdk.codegen.model.service.Shape;
+import software.amazon.awssdk.codegen.validation.ModelInvalidException;
+import software.amazon.awssdk.codegen.validation.ValidationEntry;
+import software.amazon.awssdk.codegen.validation.ValidationErrorId;
+import software.amazon.awssdk.codegen.validation.ValidationErrorSeverity;
+
+/**
+ * Rejects two shape names that map to the same generated Java class name (they differ only by the case of their first
+ * character) when the shapes are of different types, since one silently overwrites the other and the lost shape later fails
+ * codegen.
+ */
+public class ShapeNameCollisionValidatorProcessor implements CodegenCustomizationProcessor {
+
+    @Override
+    public void preprocess(ServiceModel serviceModel) {
+        Map<String, String> shapeByClassName = new LinkedHashMap<>();
+        List<ValidationEntry> collisions = new ArrayList<>();
+
+        serviceModel.getShapes().forEach((shapeName, shape) -> {
+            String className = Utils.capitalize(shapeName);
+            String existing = shapeByClassName.putIfAbsent(className, shapeName);
+            if (existing != null && !sameType(serviceModel.getShapes().get(existing), shape)) {
+                String errorMsg = String.format(
+                    "Shape names '%s' and '%s' collide because they map to the same generated class name '%s'. Please rename "
+                    + "one of them in your service model.",
+                    existing, shapeName, className);
+                collisions.add(ValidationEntry.create(ValidationErrorId.INVALID_IDENTIFIER_NAME,
+                                                      ValidationErrorSeverity.DANGER, errorMsg));
+            }
+        });
+
+        if (!collisions.isEmpty()) {
+            throw ModelInvalidException.builder().validationEntries(collisions).build();
+        }
+    }
+
+    private static boolean sameType(Shape a, Shape b) {
+        return Objects.equals(a.getType(), b.getType());
+    }
+
+    @Override
+    public void postprocess(IntermediateModel intermediateModel) {
+        // no-op
+    }
+}

codegen/src/test/java/software/amazon/awssdk/codegen/IntermediateModelBuilderTest.java

@@ -16,6 +16,7 @@
 package software.amazon.awssdk.codegen;
 
 import static org.assertj.core.api.Assertions.assertThat;
+import static org.assertj.core.api.Assertions.assertThatThrownBy;
 import static org.junit.jupiter.api.Assertions.assertEquals;
 import static org.junit.jupiter.api.Assertions.assertFalse;
 import static org.junit.jupiter.api.Assertions.assertTrue;
@@ -28,6 +29,10 @@
 import software.amazon.awssdk.codegen.model.intermediate.ShapeModel;
 import software.amazon.awssdk.codegen.model.service.ServiceModel;
 import software.amazon.awssdk.codegen.utils.ModelLoaderUtils;
+import software.amazon.awssdk.codegen.validation.ModelInvalidException;
+import software.amazon.awssdk.codegen.validation.ValidationEntry;
+import software.amazon.awssdk.codegen.validation.ValidationErrorId;
+import software.amazon.awssdk.codegen.validation.ValidationErrorSeverity;
 
 public class IntermediateModelBuilderTest {
 
@@ -47,6 +52,27 @@ public void testServiceAndShapeNameCollisions() throws Exception {
             .containsExactlyInAnyOrder("DefaultCollisionException", "DefaultCollisionRequest", "DefaultCollisionResponse");
     }
 
+    @Test
+    public void build_shapesCollideByCase_throwsModelInvalid() {
+        final File modelFile = new File(IntermediateModelBuilderTest.class
+                                            .getResource("poet/client/c2j/shape-name-collision-validator/case-insensitive-service-2.json").getFile());
+
+        assertThatThrownBy(() -> new IntermediateModelBuilder(
+            C2jModels.builder()
+                     .serviceModel(ModelLoaderUtils.loadModel(ServiceModel.class, modelFile))
+                     .customizationConfig(CustomizationConfig.create())
+                     .build())
+            .build())
+            .isInstanceOf(ModelInvalidException.class)
+            .hasMessageContaining("ReservationType")
+            .hasMessageContaining("reservationType")
+            .matches(e -> {
+                ValidationEntry entry = ((ModelInvalidException) e).validationEntries().get(0);
+                return entry.getErrorId() == ValidationErrorId.INVALID_IDENTIFIER_NAME
+                       && entry.getSeverity() == ValidationErrorSeverity.DANGER;
+            }, "validation entry is INVALID_IDENTIFIER_NAME / DANGER");
+    }
+
     @Test
     public void sharedOutputShapesLinkCorrectlyToOperationOutputs() {
         final File modelFile = new File(IntermediateModelBuilderTest.class

codegen/src/test/java/software/amazon/awssdk/codegen/customization/processors/ShapeNameCollisionValidatorProcessorTest.java

@@ -0,0 +1,69 @@
+/*
+ * Copyright Amazon.com, Inc. or its affiliates. All Rights Reserved.
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License").
+ * You may not use this file except in compliance with the License.
+ * A copy of the License is located at
+ *
+ *  http://aws.amazon.com/apache2.0
+ *
+ * or in the "license" file accompanying this file. This file is distributed
+ * on an "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either
+ * express or implied. See the License for the specific language governing
+ * permissions and limitations under the License.
+ */
+
+package software.amazon.awssdk.codegen.customization.processors;
+
+import static org.assertj.core.api.Assertions.assertThatCode;
+import static org.assertj.core.api.Assertions.assertThatThrownBy;
+
+import java.io.File;
+import java.io.IOException;
+import org.junit.jupiter.api.Test;
+import software.amazon.awssdk.codegen.model.service.ServiceModel;
+import software.amazon.awssdk.codegen.utils.ModelLoaderUtils;
+import software.amazon.awssdk.codegen.validation.ModelInvalidException;
+import software.amazon.awssdk.codegen.validation.ValidationEntry;
+import software.amazon.awssdk.codegen.validation.ValidationErrorId;
+import software.amazon.awssdk.codegen.validation.ValidationErrorSeverity;
+
+public class ShapeNameCollisionValidatorProcessorTest {
+
+    private final ShapeNameCollisionValidatorProcessor processor = new ShapeNameCollisionValidatorProcessor();
+
+    private static ServiceModel loadModel(String resource) throws IOException {
+        File file = new File(ShapeNameCollisionValidatorProcessorTest.class
+                                 .getResource("/software/amazon/awssdk/codegen/poet/client/c2j/" + resource).getFile());
+        return ModelLoaderUtils.loadModel(ServiceModel.class, file);
+    }
+
+    @Test
+    public void preprocess_shapesCollideByCase_throwsException() throws IOException {
+        ServiceModel serviceModel = loadModel("shape-name-collision-validator/case-insensitive-service-2.json");
+        assertThatThrownBy(() -> processor.preprocess(serviceModel))
+            .isInstanceOf(ModelInvalidException.class)
+            .hasMessageContaining("ReservationType")
+            .hasMessageContaining("reservationType")
+            .matches(e -> {
+                ModelInvalidException modelInvalid = (ModelInvalidException) e;
+                ValidationEntry entry = modelInvalid.validationEntries().get(0);
+                return entry.getErrorId() == ValidationErrorId.INVALID_IDENTIFIER_NAME &&
+                       entry.getSeverity() == ValidationErrorSeverity.DANGER;
+            }, "Validation entry details are correct");
+    }
+
+    @Test
+    public void preprocess_sameTypeShapesCollideByCase_doesNotThrow() throws IOException {
+        // Token/token both resolve to the same class but are both strings, so one harmlessly overwrites the other with
+        // equivalent output. Such pairs exist in shipping models (e.g. String/string) and must not be rejected.
+        ServiceModel serviceModel = loadModel("shape-name-collision-validator/same-type-service-2.json");
+        assertThatCode(() -> processor.preprocess(serviceModel)).doesNotThrowAnyException();
+    }
+
+    @Test
+    public void preprocess_noCaseCollision_doesNotThrow() throws IOException {
+        ServiceModel serviceModel = loadModel("shape-name-collision-validator/valid-service-2.json");
+        assertThatCode(() -> processor.preprocess(serviceModel)).doesNotThrowAnyException();
+    }
+}

codegen/src/test/resources/software/amazon/awssdk/codegen/poet/client/c2j/shape-name-collision-validator/case-insensitive-service-2.json

@@ -0,0 +1,56 @@
+{
+  "version": "2.0",
+  "metadata": {
+    "apiVersion": "2024-01-01",
+    "endpointPrefix": "collision",
+    "jsonVersion": "1.1",
+    "protocol": "json",
+    "serviceAbbreviation": "Collision",
+    "serviceFullName": "Shape Name Collision Build Test Service",
+    "serviceId": "Collision",
+    "signatureVersion": "v4",
+    "targetPrefix": "Collision",
+    "uid": "collision-2024-01-01"
+  },
+  "operations": {
+    "GetReservation": {
+      "name": "GetReservation",
+      "http": {
+        "method": "POST",
+        "requestUri": "/"
+      },
+      "input": {"shape": "GetReservationRequest"},
+      "output": {"shape": "GetReservationResponse"}
+    }
+  },
+  "shapes": {
+    "GetReservationRequest": {
+      "type": "structure",
+      "members": {
+        "Name": {"shape": "String"}
+      }
+    },
+    "GetReservationResponse": {
+      "type": "structure",
+      "members": {
+        "ReservationTypes": {"shape": "ReservationTypeList"}
+      }
+    },
+    "ReservationTypeList": {
+      "type": "list",
+      "member": {"shape": "reservationType"}
+    },
+    "ReservationType": {
+      "type": "structure",
+      "members": {
+        "Name": {"shape": "String"}
+      }
+    },
+    "reservationType": {
+      "type": "string"
+    },
+    "String": {
+      "type": "string"
+    }
+  }
+}

codegen/src/test/resources/software/amazon/awssdk/codegen/poet/client/c2j/shape-name-collision-validator/same-type-service-2.json

@@ -0,0 +1,32 @@
+{
+  "version": "2.0",
+  "metadata": {
+    "serviceId": "SameTypeCollision",
+    "serviceFullName": "Same Type Shape Name Collision Test Service"
+  },
+  "operations": {
+    "TestOperation": {
+      "name": "TestOperation",
+      "http": {
+        "method": "POST",
+        "requestUri": "/"
+      },
+      "input": {"shape": "TestOperationRequest"}
+    }
+  },
+  "shapes": {
+    "TestOperationRequest": {
+      "type": "structure",
+      "members": {
+        "Token": {"shape": "Token"},
+        "OtherToken": {"shape": "token"}
+      }
+    },
+    "Token": {
+      "type": "string"
+    },
+    "token": {
+      "type": "string"
+    }
+  }
+}

codegen/src/test/resources/software/amazon/awssdk/codegen/poet/client/c2j/shape-name-collision-validator/valid-service-2.json

@@ -0,0 +1,42 @@
+{
+  "version": "2.0",
+  "metadata": {
+    "serviceId": "ShapeNameNoCollision",
+    "serviceFullName": "Shape Name No Collision Validation Test Service"
+  },
+  "operations": {
+    "TestOperation": {
+      "name": "TestOperation",
+      "http": {
+        "method": "POST",
+        "requestUri": "/"
+      },
+      "input": {"shape": "TestOperationRequest"}
+    }
+  },
+  "shapes": {
+    "TestOperationRequest": {
+      "type": "structure",
+      "members": {
+        "IpAddress": {
+          "shape": "IpAddress"
+        },
+        "IpAddr": {
+          "shape": "IPAddress"
+        },
+        "Token": {
+          "shape": "nextToken"
+        }
+      }
+    },
+    "IpAddress": {
+      "type": "string"
+    },
+    "IPAddress": {
+      "type": "string"
+    },
+    "nextToken": {
+      "type": "string"
+    }
+  }
+}