Implement `From<Bound<'py, T>>` for PyErr (#3881)

* Implement `From<Bound<'py, T>>` for PyErr

* Replace PyErr::from_value_bound calls with .into

* Fix From<MyError> expected error message

* Add a trait bound to From<Bound<'py, T>> for PyErr

src/err/mod.rs

@@ -982,6 +982,24 @@ impl PyErrArguments for PyDowncastErrorArguments {
     }
 }
 
+/// Python exceptions that can be converted to [`PyErr`].
+///
+/// This is used to implement [`From<Bound<'_, T>> for PyErr`].
+///
+/// Users should not need to implement this trait directly. It is implemented automatically in the
+/// [`crate::import_exception!`] and [`crate::create_exception!`] macros.
+pub trait ToPyErr {}
+
+impl<'py, T> std::convert::From<Bound<'py, T>> for PyErr
+where
+    T: ToPyErr,
+{
+    #[inline]
+    fn from(err: Bound<'py, T>) -> PyErr {
+        PyErr::from_value_bound(err.into_any())
+    }
+}
+
 /// Convert `PyDowncastError` to Python `TypeError`.
 impl<'a> std::convert::From<PyDowncastError<'a>> for PyErr {
     fn from(err: PyDowncastError<'_>) -> PyErr {

src/exceptions.rs

@@ -54,6 +54,8 @@ macro_rules! impl_exception_boilerplate {
                 }
             }
         }
+
+        impl $crate::ToPyErr for $name {}
     };
 }
 
@@ -1074,7 +1076,7 @@ mod tests {
             );
 
             // Restoring should preserve the same error
-            let e = PyErr::from_value_bound(decode_err.into_any());
+            let e: PyErr = decode_err.into();
             e.restore(py);
 
             assert_eq!(

src/lib.rs

@@ -308,7 +308,7 @@ pub use crate::conversion::{AsPyPointer, FromPyObject, FromPyPointer, IntoPy, To
 #[allow(deprecated)]
 pub use crate::conversion::{PyTryFrom, PyTryInto};
 pub use crate::err::{
-    DowncastError, DowncastIntoError, PyDowncastError, PyErr, PyErrArguments, PyResult,
+    DowncastError, DowncastIntoError, PyDowncastError, PyErr, PyErrArguments, PyResult, ToPyErr,
 };
 pub use crate::gil::GILPool;
 #[cfg(not(PyPy))]

src/types/string.rs

@@ -73,9 +73,7 @@ impl<'a> PyStringData<'a> {
         match self {
             Self::Ucs1(data) => match str::from_utf8(data) {
                 Ok(s) => Ok(Cow::Borrowed(s)),
-                Err(e) => Err(crate::PyErr::from_value_bound(
+                Err(e) => Err(PyUnicodeDecodeError::new_utf8_bound(py, data, e)?.into()),
-                    PyUnicodeDecodeError::new_utf8_bound(py, data, e)?.into_any(),
-                )),
             },
             Self::Ucs2(data) => match String::from_utf16(data) {
                 Ok(s) => Ok(Cow::Owned(s)),
@@ -83,30 +81,26 @@ impl<'a> PyStringData<'a> {
                     let mut message = e.to_string().as_bytes().to_vec();
                     message.push(0);
 
-                    Err(crate::PyErr::from_value_bound(
+                    Err(PyUnicodeDecodeError::new_bound(
-                        PyUnicodeDecodeError::new_bound(
+                        py,
-                            py,
+                        CStr::from_bytes_with_nul(b"utf-16\0").unwrap(),
-                            CStr::from_bytes_with_nul(b"utf-16\0").unwrap(),
+                        self.as_bytes(),
-                            self.as_bytes(),
+                        0..self.as_bytes().len(),
-                            0..self.as_bytes().len(),
+                        CStr::from_bytes_with_nul(&message).unwrap(),
-                            CStr::from_bytes_with_nul(&message).unwrap(),
+                    )?
-                        )?
+                    .into())
-                        .into_any(),
-                    ))
                 }
             },
             Self::Ucs4(data) => match data.iter().map(|&c| std::char::from_u32(c)).collect() {
                 Some(s) => Ok(Cow::Owned(s)),
-                None => Err(crate::PyErr::from_value_bound(
+                None => Err(PyUnicodeDecodeError::new_bound(
-                    PyUnicodeDecodeError::new_bound(
+                    py,
-                        py,
+                    CStr::from_bytes_with_nul(b"utf-32\0").unwrap(),
-                        CStr::from_bytes_with_nul(b"utf-32\0").unwrap(),
+                    self.as_bytes(),
-                        self.as_bytes(),
+                    0..self.as_bytes().len(),
-                        0..self.as_bytes().len(),
+                    CStr::from_bytes_with_nul(b"error converting utf-32\0").unwrap(),
-                        CStr::from_bytes_with_nul(b"error converting utf-32\0").unwrap(),
+                )?
-                    )?
+                .into()),
-                    .into_any(),
-                )),
             },
         }
     }

tests/ui/invalid_result_conversion.stderr

@@ -5,6 +5,7 @@ error[E0277]: the trait bound `PyErr: From<MyError>` is not satisfied
    | ^^^^^^^^^^^^^ the trait `From<MyError>` is not implemented for `PyErr`
    |
    = help: the following other types implement trait `From<T>`:
+             <PyErr as From<pyo3::Bound<'py, T>>>
              <PyErr as From<std::io::Error>>
              <PyErr as From<PyBorrowError>>
              <PyErr as From<PyBorrowMutError>>
@@ -12,7 +13,6 @@ error[E0277]: the trait bound `PyErr: From<MyError>` is not satisfied
              <PyErr as From<DowncastError<'_, '_>>>
              <PyErr as From<DowncastIntoError<'_>>>
              <PyErr as From<NulError>>
-             <PyErr as From<IntoStringError>>
            and $N others
    = note: required for `MyError` to implement `Into<PyErr>`
    = note: this error originates in the attribute macro `pyfunction` (in Nightly builds, run with -Z macro-backtrace for more info)