[rust] fix: free-form object query parameters reference a nonexistent models::serde_json (#24866)

* fix: [rust] type free-form object parameters as serde_json::Value, not models::serde_json::Value

A free-form object parameter (type: object with no properties) maps to
serde_json::Value, but the api templates qualify every non-primitive,
non-container parameter type with models:: - and models re-exports no
serde_json, so the generated crate fails with E0433. Free-form body
parameters already avoid this because updateRequestBodyForObject marks
them primitive; give non-body free-form parameters the same treatment.
Free-form schemas with additionalProperties stay containers (HashMap)
and keep their JSON serialization.

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01CxDNCjqJycKTfzVWg2SeTJ

* ci: retrigger after ubuntu mirror outage

* [rust] tidy: shorten the free-form parameter comment

Co-Authored-By: Claude Opus 5.5 (1M context) <noreply@anthropic.com>

* [rust] test: cover free-form object parameters in all four libraries

Co-Authored-By: Claude Opus 5.5 (1M context) <noreply@anthropic.com>

* [rust] test: cover free-form object path and header parameters

The fix marks every free-form entry in allParams, so the fixture now
also carries a free-form path parameter and a free-form header
parameter, and the test asserts both are typed serde_json::Value.

Co-Authored-By: Claude Opus 5.5 (1M context) <noreply@anthropic.com>

---------

Co-authored-by: Claude Fable 5 <noreply@anthropic.com>

Author: wiebren

modules/openapi-generator/src/main/java/org/openapitools/codegen/languages/RustClientCodegen.java

@@ -795,6 +795,13 @@ public OperationsMap postProcessOperationsWithModels(OperationsMap objs, List<Mo
                     param.isPrimitiveType = true;
                     param.isString = true;
                 }
+
+                // Free-form objects are `serde_json::Value`, which is not in `models`: mark them primitive, as
+                // DefaultCodegen.updateRequestBodyForObject does for bodies, so no `models::` prefix is added.
+                // Free-form maps (`additionalProperties`) are containers and keep their handling.
+                if (param.isFreeFormObject && !param.isContainer) {
+                    param.isPrimitiveType = true;
+                }
             }
 
             if (operation.pathParams != null && operation.pathParams.size() > 0) {

modules/openapi-generator/src/test/java/org/openapitools/codegen/rust/RustClientCodegenTest.java

@@ -319,6 +319,37 @@ public void testIntegerPropertyEnum() throws IOException {
         TestUtils.assertFileNotContains(outputPath, linearize("#[serde(rename = \"0\")]"));
     }
 
+    @Test
+    public void testFreeFormObjectParams() throws IOException {
+        for (String library : List.of("reqwest", "hyper", "hyper0x", "reqwest-trait")) {
+            Path target = Files.createTempDirectory("test");
+            target.toFile().deleteOnExit();
+            final CodegenConfigurator configurator = new CodegenConfigurator()
+                    .setGeneratorName("rust")
+                    .setLibrary(library)
+                    .setInputSpec("src/test/resources/3_0/rust/free-form-object-params.yaml")
+                    .setSkipOverwrite(false)
+                    .setOutputDir(target.toAbsolutePath().toString().replace("\\", "/"));
+            List<File> files = new DefaultGenerator().opts(configurator.toClientOptInput()).generate();
+            files.forEach(File::deleteOnExit);
+            Path outputPath = Path.of(target.toString(), "/src/apis/default_api.rs");
+            TestUtils.assertFileExists(outputPath);
+            // A free-form object query, path or header parameter maps to `serde_json::Value`, which lives
+            // outside of the `models` module.
+            TestUtils.assertFileContains(outputPath, "filter: Option<serde_json::Value>");
+            TestUtils.assertFileContains(outputPath, "selector: serde_json::Value");
+            TestUtils.assertFileContains(outputPath, "x_filter: Option<serde_json::Value>");
+            TestUtils.assertFileNotContains(outputPath, "models::serde_json");
+            // A free-form object with additionalProperties stays a map.
+            TestUtils.assertFileContains(outputPath, "tags: Option<std::collections::HashMap<String, String>>");
+            TestUtils.assertFileContains(outputPath, "meta: Option<std::collections::HashMap<String, serde_json::Value>>");
+            if (library.equals("reqwest")) {
+                // Maps keep their JSON serialization (`HashMap` does not implement `Display`).
+                TestUtils.assertFileContains(outputPath, "req_builder.query(&[(\"meta\", &serde_json::to_string(param_value)?)])");
+            }
+        }
+    }
+
     @Test
     public void testArrayWithObjectEnumValues() throws IOException {
         Path target = Files.createTempDirectory("test");

modules/openapi-generator/src/test/resources/3_0/rust/free-form-object-params.yaml

@@ -0,0 +1,54 @@
+openapi: 3.0.0
+info:
+  title: Free-form object parameters
+  version: 1.0.0
+paths:
+  /things:
+    get:
+      operationId: listThings
+      parameters:
+        - name: filter
+          in: query
+          description: A free-form object query parameter.
+          schema:
+            type: object
+        - name: tags
+          in: query
+          description: A free-form object with typed additionalProperties (a map).
+          schema:
+            type: object
+            additionalProperties:
+              type: string
+        - name: meta
+          in: query
+          description: A free-form object with additionalProperties true (also a map).
+          schema:
+            type: object
+            additionalProperties: true
+      responses:
+        '200':
+          description: OK
+          content:
+            application/json:
+              schema:
+                type: array
+                items:
+                  type: string
+  /things/{selector}:
+    get:
+      operationId: getThing
+      parameters:
+        - name: selector
+          in: path
+          required: true
+          description: A free-form object path parameter.
+          schema:
+            type: object
+        - name: X-Filter
+          in: header
+          description: A free-form object header parameter.
+          schema:
+            type: object
+      responses:
+        '200':
+          description: OK