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

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

@@ -783,6 +783,16 @@ public OperationsMap postProcessOperationsWithModels(OperationsMap objs, List<Mo
                     param.isPrimitiveType = true;
                     param.isString = true;
                 }
+
+                // Free-form objects are typed `serde_json::Value`, which does not live in the
+                // generated `models` module. Mark them as primitive so the templates do not
+                // qualify the type with a `models::` prefix, mirroring what
+                // `DefaultCodegen.updateRequestBodyForObject` already does for free-form body
+                // parameters. Free-form schemas with `additionalProperties` map to a container
+                // type (`HashMap`) and must keep their existing 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

@@ -293,6 +293,30 @@ public void testIntegerPropertyEnum() throws IOException {
         TestUtils.assertFileNotContains(outputPath, linearize("#[serde(rename = \"0\")]"));
     }
 
+    @Test
+    public void testFreeFormObjectQueryParam() throws IOException {
+        Path target = Files.createTempDirectory("test");
+        target.toFile().deleteOnExit();
+        final CodegenConfigurator configurator = new CodegenConfigurator()
+                .setGeneratorName("rust")
+                .setInputSpec("src/test/resources/3_0/rust/free-form-object-query-param.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 parameter maps to `serde_json::Value`, which lives
+        // outside of the `models` module.
+        TestUtils.assertFileContains(outputPath, "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>>");
+        // 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-query-param.yaml

@@ -0,0 +1,36 @@
+openapi: 3.0.0
+info:
+  title: Free-form object query parameter
+  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