[derive_utils] Copy kwargs not to modify it

pyo3-derive-backend/src/pymethod.rs

@@ -475,12 +475,12 @@ pub fn impl_arg_params(spec: &FnSpec<'_>, body: TokenStream) -> TokenStream {
 
         // Workaround to use the question mark operator without rewriting everything
         let _result = (|| {
-            pyo3::derive_utils::parse_fn_args(
+            let (_args, _kwargs) = pyo3::derive_utils::parse_fn_args(
                 _py,
                 Some(_LOCATION),
                 PARAMS,
-                &mut _args,
-                &mut _kwargs,
+                _args,
+                _kwargs,
                 #accept_args,
                 #accept_kwargs,
                 &mut output

src/derive_utils.rs

@@ -36,12 +36,12 @@ pub fn parse_fn_args<'p>(
     py: Python<'p>,
     fname: Option<&str>,
     params: &[ParamDescription],
-    args: &mut &'p PyTuple,
-    kwargs: &mut Option<&'p PyDict>,
+    args: &'p PyTuple,
+    kwargs: Option<&'p PyDict>,
     accept_args: bool,
     accept_kwargs: bool,
     output: &mut [Option<&'p PyAny>],
-) -> PyResult<()> {
+) -> PyResult<(&'p PyTuple, Option<&'p PyDict>)> {
     let nargs = args.len();
     let mut used_args = 0;
     macro_rules! raise_error {
@@ -49,6 +49,11 @@ pub fn parse_fn_args<'p>(
             concat!("{} ", $s), fname.unwrap_or("function") $(,$arg)*
         ))))
     }
+    // Copy kwargs not to modify it
+    let kwargs = match kwargs {
+        Some(k) => Some(k.copy()?),
+        None => None,
+    };
     // Iterate through the parameters and assign values to output:
     for (i, (p, out)) in params.iter().zip(output).enumerate() {
         *out = match kwargs.and_then(|d| d.get_item(p.name)) {
@@ -93,16 +98,18 @@ pub fn parse_fn_args<'p>(
         )
     }
     // Adjust the remaining args
-    if accept_args {
-        let slice = args
-            .slice(used_args as isize, nargs as isize)
-            .into_object(py);
-        *args = py.checked_cast_as(slice).unwrap();
-    }
-    if accept_kwargs && is_kwargs_empty {
-        *kwargs = None;
-    }
-    Ok(())
+    let args = if accept_args {
+        let slice = args.slice(used_args as isize, nargs as isize).into_py(py);
+        py.checked_cast_as(slice).unwrap()
+    } else {
+        args
+    };
+    let kwargs = if accept_kwargs && is_kwargs_empty {
+        None
+    } else {
+        kwargs
+    };
+    Ok((args, kwargs))
 }
 
 /// Builds a module (or null) from a user given initializer. Used for `#[pymodule]`.