rust/hg-cpython/src/ref_sharing.rs

cmdutil: rewrite walkchangerevs() by using logcmdutil functions

cmdutil.walkchangerevs() now takes (revs, makefilematcher) in place of
(match, opts), and only provides the "windowing" functionality. Unused
classes and functions will be removed by the next patch.

"hg grep --follow" (--all-files) is still broken since there is no logic
to follow copies while traversing changelog, but at least, it does follow
the DAG.

// 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),
                )
            }
        }
    };
}