Avoid cloning AppCode during response conversions

src/response/mapping.rs

@@ -2,7 +2,7 @@ use alloc::string::String;
 use core::fmt::{Display, Formatter, Result as FmtResult};
 
 use super::core::ErrorResponse;
-use crate::AppError;
+use crate::{AppCode, AppError};
 
 impl Display for ErrorResponse {
     fn fmt(&self, f: &mut Formatter<'_>) -> FmtResult {
@@ -14,7 +14,7 @@ impl Display for ErrorResponse {
 impl From<AppError> for ErrorResponse {
     fn from(mut err: AppError) -> Self {
         let kind = err.kind;
-        let code = err.code.clone();
+        let code = core::mem::replace(&mut err.code, AppCode::from(kind));
         let retry = err.retry.take();
         let www_authenticate = err.www_authenticate.take();
         let policy = err.edit_policy;

src/response/problem_json.rs

@@ -162,8 +162,8 @@ impl ProblemJson {
     pub fn from_app_error(mut error: AppError) -> Self {
         error.emit_telemetry();
 
-        let code = error.code.clone();
         let kind = error.kind;
+        let code = core::mem::replace(&mut error.code, AppCode::from(kind));
         let message = error.message.take();
         let metadata = core::mem::take(&mut error.metadata);
         let edit_policy = error.edit_policy;

tests/app_code_reuse.rs

@@ -0,0 +1,27 @@
+use masterror::{AppCode, AppError, ErrorResponse, ProblemJson};
+
+fn error_with_dynamic_code() -> AppError {
+    let code = AppCode::try_new("DYNAMIC_REGRESSION_CODE".to_owned())
+        .expect("valid SCREAMING_SNAKE_CASE code");
+    AppError::internal("boom").with_code(code)
+}
+
+#[test]
+fn problem_json_reuses_app_code_allocation() {
+    let error = error_with_dynamic_code();
+    let expected_ptr = error.code.as_str().as_ptr();
+
+    let problem = ProblemJson::from_app_error(error);
+
+    assert_eq!(problem.code.as_str().as_ptr(), expected_ptr);
+}
+
+#[test]
+fn error_response_reuses_app_code_allocation() {
+    let error = error_with_dynamic_code();
+    let expected_ptr = error.code.as_str().as_ptr();
+
+    let response = ErrorResponse::from(error);
+
+    assert_eq!(response.code.as_str().as_ptr(), expected_ptr);
+}