[Rust] Add support for shallow object query params

Author: whirm

modules/openapi-generator/src/main/resources/rust/reqwest/api.mustache

@@ -155,7 +155,13 @@ pub {{#supportAsync}}async {{/supportAsync}}fn {{{operationId}}}(configuration:
     {{/isArray}}
     {{^isArray}}
     {{^isNullable}}
+    {{#isModel}}
+    let params = crate::apis::parse_flat_object(&serde_json::to_value({{{vendorExtensions.x-rust-param-identifier}}})?);
+    req_builder = req_builder.query(&params);
+    {{/isModel}}
+    {{^isModel}}
     req_builder = req_builder.query(&[("{{{baseName}}}", &{{{vendorExtensions.x-rust-param-identifier}}}.to_string())]);
+    {{/isModel}}
     {{/isNullable}}
     {{#isNullable}}
     {{#isDeepObject}}
@@ -232,7 +238,8 @@ pub {{#supportAsync}}async {{/supportAsync}}fn {{{operationId}}}(configuration:
         req_builder = req_builder.query(&[("{{{baseName}}}", &serde_json::to_string(param_value)?)]);
         {{/isObject}}
         {{#isModel}}
-        req_builder = req_builder.query(&[("{{{baseName}}}", &serde_json::to_string(param_value)?)]);
+        let params = crate::apis::parse_flat_object(&serde_json::to_value(param_value)?);
+        req_builder = req_builder.query(&params);
         {{/isModel}}
         {{^isObject}}
         {{^isModel}}

modules/openapi-generator/src/main/resources/rust/reqwest/api_mod.mustache

@@ -105,6 +105,33 @@ pub fn urlencode<T: AsRef<str>>(s: T) -> String {
     ::url::form_urlencoded::byte_serialize(s.as_ref().as_bytes()).collect()
 }
 
+pub fn parse_flat_object(value: &serde_json::Value) -> Vec<(String, String)> {
+    if let serde_json::Value::Object(object) = value {
+        let mut params = vec![];
+
+        for (key, value) in object {
+            match value {
+                serde_json::Value::Object(_) => {
+                    unreachable!(
+                        "This should never be reached, there's a bug on the codegen or the templates"
+                    )
+                }
+                serde_json::Value::Array(array) => {
+                    for (i, value) in array.iter().enumerate() {
+                        params.push((format!("{key}[{i}]"), value.to_string()));
+                    }
+                }
+                serde_json::Value::String(s) => params.push((key.to_string(), s.clone())),
+                _ => params.push((key.to_string(), value.to_string())),
+            }
+        }
+
+        return params;
+    }
+
+    unimplemented!("Only objects are supported")
+}
+
 pub fn parse_deep_object(prefix: &str, value: &serde_json::Value) -> Vec<(String, String)> {
     if let serde_json::Value::Object(object) = value {
         let mut params = vec![];