rust/hg-cpython/src/ref_sharing.rs

// ref_sharing.rs
//
// Copyright 2019 Raphaël Gomès <[e-mail]>
//
// Permission is hereby granted, free of charge, to any person obtaining a copy
// of this software and associated documentation files (the "Software"), to
// deal in the Software without restriction, including without limitation the
// rights to use, copy, modify, merge, publish, distribute, sublicense, and/or
// sell copies of the Software, and to permit persons to whom the Software is
// furnished to do so, subject to the following conditions:
//
// The above copyright notice and this permission notice shall be included in
// all copies or substantial portions of the Software.
//
// THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
// IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
// FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
// AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
// LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING
// FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS
// IN THE SOFTWARE.

//! Macros for use in the `hg-cpython` bridge library.

/// Defines a `py_class!` that acts as a Python iterator over a Rust iterator.
///
/// TODO: this is a bit awkward to use, and a better (more complicated)
///     procedural macro would simplify the interface a lot.
///
/// # Parameters
///
/// * `$name` is the identifier to give to the resulting Rust struct.
/// * `$leaked` corresponds to `UnsafePyLeaked` in the matching `@shared data`
///   declaration.
/// * `$iterator_type` is the type of the Rust iterator.
/// * `$success_func` is a function for processing the Rust `(key, value)`
///   tuple on iteration success, turning it into something Python understands.
/// * `$success_func` is the return type of `$success_func`
///
/// # Safety
///
/// `$success_func` may take a reference, but it's lifetime may be cheated.
/// Do not copy it out of the function call.
///
/// # Example
///
/// ```
/// struct MyStruct {
///     inner: HashMap<Vec<u8>, Vec<u8>>;
/// }
///
/// py_class!(pub class MyType |py| {
///     @shared data inner: MyStruct;
///
///     def __iter__(&self) -> PyResult<MyTypeItemsIterator> {
///         let leaked_ref = self.inner_shared(py).leak_immutable();
///         MyTypeItemsIterator::from_inner(
///             py,
///             unsafe { leaked_ref.map(py, |o| o.iter()) },
///         )
///     }
/// });
///
/// impl MyType {
///     fn translate_key_value(
///         py: Python,
///         res: (&Vec<u8>, &Vec<u8>),
///     ) -> PyResult<Option<(PyBytes, PyBytes)>> {
///         let (f, entry) = res;
///         Ok(Some((
///             PyBytes::new(py, f),
///             PyBytes::new(py, entry),
///         )))
///     }
/// }
///
/// py_shared_iterator!(
///     MyTypeItemsIterator,
///     UnsafePyLeaked<HashMap<'static, Vec<u8>, Vec<u8>>>,
///     MyType::translate_key_value,
///     Option<(PyBytes, PyBytes)>
/// );
/// ```
macro_rules! py_shared_iterator {
    (
        $name: ident,
        $leaked: ty,
        $success_func: expr,
        $success_type: ty
    ) => {
        py_class!(pub class $name |py| {
            data inner: RefCell<$leaked>;

            def __next__(&self) -> PyResult<$success_type> {
                let mut leaked = self.inner(py).borrow_mut();
                let mut iter = unsafe { leaked.try_borrow_mut(py)? };
                match iter.next() {
                    None => Ok(None),
                    // res may be a reference of cheated 'static lifetime
                    Some(res) => $success_func(py, res),
                }
            }

            def __iter__(&self) -> PyResult<Self> {
                Ok(self.clone_ref(py))
            }
        });

        impl $name {
            pub fn from_inner(
                py: Python,
                leaked: $leaked,
            ) -> PyResult<Self> {
                Self::create_instance(
                    py,
                    RefCell::new(leaked),
                )
            }
        }
    };
}