From f0c5dc713d094aa02216f24c37685e8330c7e7e2 Mon Sep 17 00:00:00 2001
From: Askaholic <askaholic907@gmail.com>
Date: Sat, 3 Oct 2020 14:36:40 -0800
Subject: [PATCH] Add argument name to error messages in conversion errors

---
 pyo3-derive-backend/src/pymethod.rs | 17 ++++++++++++++---
 1 file changed, 14 insertions(+), 3 deletions(-)

diff --git a/pyo3-derive-backend/src/pymethod.rs b/pyo3-derive-backend/src/pymethod.rs
index 62ced447077..7d8afb29fad 100644
--- a/pyo3-derive-backend/src/pymethod.rs
+++ b/pyo3-derive-backend/src/pymethod.rs
@@ -475,10 +475,21 @@ fn impl_arg_param(
 
     let ty = arg.ty;
     let name = arg.name;
+    let transform_error = quote! {
+        |e| {
+            let reason = e.instance(_py).str()
+                .unwrap_or_else(|_| pyo3::types::PyString::new(_py, ""));
+            pyo3::PyErr::from_type(
+                e.ptype(_py),
+                format!("argument '{}': {}", stringify!(#name), reason)
+            )
+        }
+    };
 
     if spec.is_args(&name) {
         return quote! {
-            let #arg_name = <#ty as pyo3::FromPyObject>::extract(_args.as_ref())?;
+            let #arg_name = <#ty as pyo3::FromPyObject>::extract(_args.as_ref())
+                .map_err(#transform_error)?;
         };
     } else if spec.is_kwargs(&name) {
         return quote! {
@@ -518,7 +529,7 @@ fn impl_arg_param(
 
         quote! {
             let #mut_ _tmp: #target_ty = match #arg_value {
-                Some(_obj) => _obj.extract()?,
+                Some(_obj) => _obj.extract().map_err(#transform_error)?,
                 None => #default,
             };
             let #arg_name = #borrow_tmp;
@@ -526,7 +537,7 @@ fn impl_arg_param(
     } else {
         quote! {
             let #arg_name = match #arg_value {
-                Some(_obj) => _obj.extract()?,
+                Some(_obj) => _obj.extract().map_err(#transform_error)?,
                 None => #default,
             };
         }