fix: nest conflicting endpoint parameters

Author: smilkuri

smithy-typescript-codegen/src/main/java/software/amazon/smithy/typescript/codegen/endpointsV2/EndpointsV2Generator.java

@@ -17,6 +17,7 @@
 
 import java.nio.file.Paths;
 import java.util.Collections;
+import java.util.HashMap;
 import java.util.HashSet;
 import java.util.List;
 import java.util.Map;
@@ -117,15 +118,41 @@ private void generateEndpointParameters() {
                     "export interface ClientInputEndpointParameters {",
                     "}",
                     () -> {
-                        Map<String, String> clientInputParams = ruleSetParameterFinder.getClientContextParams();
-                        //Omit Endpoint params that should not be a part of the ClientInputEndpointParameters interface
+                        Map<String, String> clientContextParams = ruleSetParameterFinder.getClientContextParams();
                         Map<String, String> builtInParams = ruleSetParameterFinder.getBuiltInParams();
                         builtInParams.keySet().removeIf(OmitEndpointParams::isOmitted);
-                        clientInputParams.putAll(builtInParams);
-
+                        // Known config keys that could collide
+                        Set<String> knownConfigKeys = Set.of(
+                            "apiKey", "retryStrategy", "requestHandler");
+                        // Built-in params that should not be in clientContextParams
+                        Set<String> builtinParamNames = Set.of("region", "fips", "dualstack", "endpoint");
+                        // Separate conflicting params into clientContextParams
+                        Map<String, String> nestedParams = new HashMap<>();
+                        Map<String, String> directParams = new HashMap<>(builtInParams);
+                        for (Map.Entry<String, String> entry : clientContextParams.entrySet()) {
+                        // params that should go in clientContextParams, exclude builtins
+                            if (knownConfigKeys.contains(entry.getKey())
+                                && !builtinParamNames.contains(entry.getKey())) {
+                                    nestedParams.put(entry.getKey(), entry.getValue());
+                            } else {
+                                directParams.put(entry.getKey(), entry.getValue());
+                            }
+                        }
+                        // Add clientContextParams for conflicting params
+                        if (!nestedParams.isEmpty()) {
+                            writer.write("clientContextParams?: {");
+                            writer.indent();
+                            ObjectNode ruleSet = endpointRuleSetTrait.getRuleSet().expectObjectNode();
+                            ruleSet.getObjectMember("parameters").ifPresent(parameters -> {
+                                parameters.accept(new RuleSetParametersVisitor(writer, nestedParams, true));
+                            });
+                            writer.dedent();
+                            writer.write("};");
+                        }
+                        // Add direct params
                         ObjectNode ruleSet = endpointRuleSetTrait.getRuleSet().expectObjectNode();
                         ruleSet.getObjectMember("parameters").ifPresent(parameters -> {
-                            parameters.accept(new RuleSetParametersVisitor(writer, clientInputParams, true));
+                            parameters.accept(new RuleSetParametersVisitor(writer, directParams, true));
                         });
                     }
                 );
@@ -149,6 +176,21 @@ private void generateEndpointParameters() {
                     "}",
                     () -> {
                         writer.openBlock("return Object.assign(options, {", "});", () -> {
+                            // Add precedence logic for conflicting params
+                            Map<String, String> clientContextParams =
+                                ruleSetParameterFinder.getClientContextParams();
+                            Set<String> knownConfigKeys = Set.of(
+                                "apiKey", "retryStrategy", "requestHandler");
+                            Set<String> builtinParamNames = Set.of("region", "fips", "dualstack", "endpoint");
+                            for (Map.Entry<String, String> entry
+                                : clientContextParams.entrySet()) {
+                                // Only use clientContextParams precedence for customer-defined params, not builtins
+                                if (knownConfigKeys.contains(entry.getKey())
+                                    && !builtinParamNames.contains(entry.getKey())) {
+                                    writer.write("$L: options.clientContextParams?.$L ?? options.$L,",
+                                        entry.getKey(), entry.getKey(), entry.getKey());
+                                }
+                            }
                             ObjectNode ruleSet = endpointRuleSetTrait.getRuleSet().expectObjectNode();
                             ruleSet.getObjectMember("parameters").ifPresent(parameters -> {
                                 parameters.accept(new RuleSetParametersVisitor(writer, true));