Fix bug where queryParams was ignored if there were no other params

.changelog/1760126889.md

@@ -0,0 +1,12 @@
+---
+applies_to:
+  - client
+authors:
+  - rcoh
+references: [ "smithy-rs#4346" ]
+breaking: false
+new_feature: false
+bug_fix: true
+---
+
+Fix bug where httpQueryParams were silently dropped when no other query parameters were modeled.

AGENTS.md

@@ -10,6 +10,55 @@
 
 Protocol files: `codegen-{core,server}/.../protocols/`
 
+## Protocol Tests
+
+Protocol tests validate that generated code correctly implements Smithy protocols (like restJson1, awsJson1_1, etc.).
+
+### Adding Protocol Tests
+
+Protocol tests are defined in Smithy model files using `@httpRequestTests` and `@httpResponseTests` traits:
+
+```smithy
+@http(uri: "/my-operation", method: "GET")
+@httpRequestTests([
+    {
+        id: "MyOperationRequest",
+        documentation: "Test description",
+        protocol: "aws.protocols#restJson1",
+        method: "GET",
+        uri: "/my-operation",
+        queryParams: ["param1=value1", "param2=value2"],
+        params: {
+            queryMap: {
+                "param1": "value1",
+                "param2": "value2"
+            }
+        },
+        appliesTo: "client",
+    }
+])
+operation MyOperation {
+    input: MyOperationInput,
+}
+```
+
+### Key Protocol Test Locations
+
+- **`codegen-core/common-test-models/rest-json-extras.smithy`** - restJson1 protocol tests
+- **`codegen-core/common-test-models/constraints.smithy`** - Constraint validation tests with restJson1
+- **`codegen-client-test/model/main.smithy`** - awsJson1_1 protocol tests
+
+### httpQueryParams Bug Investigation
+
+When investigating the `@httpQueryParams` bug (where query parameters weren't appearing in requests), the issue was in `RequestBindingGenerator.kt` line 173. The bug occurred when:
+
+1. An operation had ONLY `@httpQueryParams` (no regular `@httpQuery` parameters)
+2. The condition `if (dynamicParams.isEmpty() && literalParams.isEmpty() && mapParams.isEmpty())` would skip generating the `uri_query` function
+
+The fix was to ensure `mapParams.isEmpty()` was included in the condition check. The current implementation correctly generates query parameters for `@httpQueryParams` even when no other query parameters exist.
+
+**Testing httpQueryParams**: Create operations with only `@httpQueryParams` to ensure they generate proper query strings in requests.
+
 ## preludeScope: Rust Prelude Types
 
 **Always use `preludeScope` for Rust prelude types:**

codegen-client/src/main/kotlin/software/amazon/smithy/rust/codegen/client/smithy/generators/http/RequestBindingGenerator.kt

@@ -170,7 +170,7 @@ class RequestBindingGenerator(
         val dynamicParams = index.getRequestBindings(operationShape, HttpBinding.Location.QUERY)
         val mapParams = index.getRequestBindings(operationShape, HttpBinding.Location.QUERY_PARAMS)
         val literalParams = httpTrait.uri.queryLiterals
-        if (dynamicParams.isEmpty() && literalParams.isEmpty()) {
+        if (dynamicParams.isEmpty() && literalParams.isEmpty() && mapParams.isEmpty()) {
             return false
         }
         val preloadedParams = literalParams.keys + dynamicParams.map { it.locationName }

codegen-core/common-test-models/rest-json-extras.smithy

@@ -66,6 +66,7 @@ service RestJsonExtras {
         CaseInsensitiveErrorOperation,
         EmptyStructWithContentOnWireOp,
         QueryPrecedence,
+        HttpQueryParamsOnlyOperation,
     ],
     errors: [ExtraError]
 }
@@ -350,3 +351,46 @@ structure EmptyStructWithContentOnWireOpOutput {
 operation EmptyStructWithContentOnWireOp {
     output: EmptyStructWithContentOnWireOpOutput,
 }
+
+@http(uri: "/http-query-params-only", method: "GET")
+@httpRequestTests([
+    {
+        id: "HttpQueryParamsOnlyRequest",
+        documentation: "Test that httpQueryParams are included in request when no other query parameters exist",
+        protocol: "aws.protocols#restJson1",
+        method: "GET",
+        uri: "/http-query-params-only",
+        queryParams: ["shouldExpandRoles=true", "shouldShowOnlyAuthForThisDocument=false"],
+        params: {
+            queryMap: {
+                "shouldExpandRoles": "true",
+                "shouldShowOnlyAuthForThisDocument": "false"
+            }
+        },
+        appliesTo: "client",
+    },
+    {
+        id: "HttpQueryParamsOnlyEmptyRequest",
+        documentation: "Test that empty httpQueryParams map results in no query parameters",
+        protocol: "aws.protocols#restJson1",
+        method: "GET",
+        uri: "/http-query-params-only",
+        params: {
+            queryMap: {}
+        },
+        appliesTo: "client",
+    }
+])
+operation HttpQueryParamsOnlyOperation {
+    input: HttpQueryParamsOnlyInput,
+}
+
+structure HttpQueryParamsOnlyInput {
+    @httpQueryParams
+    queryMap: QueryMap,
+}
+
+map QueryMap {
+    key: String,
+    value: String,
+}