hg-cpython: implement vcsgraph::Graph for our Index

Differential Revision: https://phab.mercurial-scm.org/D11946

rust/hg-cpython/src/cindex.rs

@@ -1,183 +1,201 b''
 // cindex.rs
 //
 // Copyright 2018 Georges Racinet <[e-mail]>
 //
 // This software may be used and distributed according to the terms of the
 // GNU General Public License version 2 or any later version.
 
 //! Bindings to use the Index defined by the parsers C extension
 //!
 //! Ideally, we should use an Index entirely implemented in Rust,
 //! but this will take some time to get there.
 
 use cpython::{
     exc::ImportError, exc::TypeError, ObjectProtocol, PyClone, PyErr,
     PyObject, PyResult, PyTuple, Python, PythonObject,
 };
 use hg::revlog::{Node, RevlogIndex};
 use hg::{Graph, GraphError, Revision, WORKING_DIRECTORY_REVISION};
 use libc::{c_int, ssize_t};
 
 const REVLOG_CABI_VERSION: c_int = 2;
 
 #[repr(C)]
 pub struct Revlog_CAPI {
     abi_version: c_int,
     index_length:
         unsafe extern "C" fn(index: *mut revlog_capi::RawPyObject) -> ssize_t,
     index_node: unsafe extern "C" fn(
         index: *mut revlog_capi::RawPyObject,
         rev: ssize_t,
     ) -> *const Node,
     index_parents: unsafe extern "C" fn(
         index: *mut revlog_capi::RawPyObject,
         rev: c_int,
         ps: *mut [c_int; 2],
     ) -> c_int,
 }
 
 py_capsule!(
     from mercurial.cext.parsers import revlog_CAPI
         as revlog_capi for Revlog_CAPI);
 
 /// A `Graph` backed up by objects and functions from revlog.c
 ///
 /// This implementation of the `Graph` trait, relies on (pointers to)
 /// - the C index object (`index` member)
 /// - the `index_get_parents()` function (`parents` member)
 ///
 /// # Safety
 ///
 /// The C index itself is mutable, and this Rust exposition is **not
 /// protected by the GIL**, meaning that this construct isn't safe with respect
 /// to Python threads.
 ///
 /// All callers of this `Index` must acquire the GIL and must not release it
 /// while working.
 ///
 /// # TODO find a solution to make it GIL safe again.
 ///
 /// This is non trivial, and can wait until we have a clearer picture with
 /// more Rust Mercurial constructs.
 ///
 /// One possibility would be to a `GILProtectedIndex` wrapper enclosing
 /// a `Python<'p>` marker and have it be the one implementing the
 /// `Graph` trait, but this would mean the `Graph` implementor would become
 /// likely to change between subsequent method invocations of the `hg-core`
 /// objects (a serious change of the `hg-core` API):
 /// either exposing ways to mutate the `Graph`, or making it a non persistent
 /// parameter in the relevant methods that need one.
 ///
 /// Another possibility would be to introduce an abstract lock handle into
 /// the core API, that would be tied to `GILGuard` / `Python<'p>`
 /// in the case of the `cpython` crate bindings yet could leave room for other
 /// mechanisms in other contexts.
 pub struct Index {
     index: PyObject,
     capi: &'static Revlog_CAPI,
 }
 
 impl Index {
     pub fn new(py: Python, index: PyObject) -> PyResult<Self> {
         let capi = unsafe { revlog_capi::retrieve(py)? };
         if capi.abi_version != REVLOG_CABI_VERSION {
             return Err(PyErr::new::<ImportError, _>(
                 py,
                 format!(
                     "ABI version mismatch: the C ABI revlog version {} \
                      does not match the {} expected by Rust hg-cpython",
                     capi.abi_version, REVLOG_CABI_VERSION
                 ),
             ));
         }
         let compat: u64 = index.getattr(py, "rust_ext_compat")?.extract(py)?;
         if compat == 0 {
             return Err(PyErr::new::<TypeError, _>(
                 py,
                 "index object not compatible with Rust",
             ));
         }
         Ok(Index { index, capi })
     }
 
     /// return a reference to the CPython Index object in this Struct
     pub fn inner(&self) -> &PyObject {
         &self.index
     }
 
     pub fn append(&mut self, py: Python, tup: PyTuple) -> PyResult<PyObject> {
         self.index.call_method(
             py,
             "append",
             PyTuple::new(py, &[tup.into_object()]),
             None,
         )
     }
 }
 
 impl Clone for Index {
     fn clone(&self) -> Self {
         let guard = Python::acquire_gil();
         Index {
             index: self.index.clone_ref(guard.python()),
             capi: self.capi,
         }
     }
 }
 
 impl PyClone for Index {
     fn clone_ref(&self, py: Python) -> Self {
         Index {
             index: self.index.clone_ref(py),
             capi: self.capi,
         }
     }
 }
 
 impl Graph for Index {
     /// wrap a call to the C extern parents function
     fn parents(&self, rev: Revision) -> Result<[Revision; 2], GraphError> {
         if rev == WORKING_DIRECTORY_REVISION {
             return Err(GraphError::WorkingDirectoryUnsupported);
         }
         let mut res: [c_int; 2] = [0; 2];
         let code = unsafe {
             (self.capi.index_parents)(
                 self.index.as_ptr(),
                 rev as c_int,
                 &mut res as *mut [c_int; 2],
             )
         };
         match code {
             0 => Ok(res),
             _ => Err(GraphError::ParentOutOfRange(rev)),
         }
     }
 }
 
+impl vcsgraph::graph::Graph for Index {
+    fn parents(
+        &self,
+        rev: Revision,
+    ) -> Result<vcsgraph::graph::Parents, vcsgraph::graph::GraphReadError>
+    {
+        match Graph::parents(self, rev) {
+            Ok(parents) => Ok(vcsgraph::graph::Parents(parents)),
+            Err(GraphError::ParentOutOfRange(rev)) => {
+                Err(vcsgraph::graph::GraphReadError::KeyedInvalidKey(rev))
+            }
+            Err(GraphError::WorkingDirectoryUnsupported) => Err(
+                vcsgraph::graph::GraphReadError::WorkingDirectoryUnsupported,
+            ),
+        }
+    }
+}
+
 impl RevlogIndex for Index {
     /// Note C return type is Py_ssize_t (hence signed), but we shall
     /// force it to unsigned, because it's a length
     fn len(&self) -> usize {
         unsafe { (self.capi.index_length)(self.index.as_ptr()) as usize }
     }
 
     fn node(&self, rev: Revision) -> Option<&Node> {
         let raw = unsafe {
             (self.capi.index_node)(self.index.as_ptr(), rev as ssize_t)
         };
         if raw.is_null() {
             None
         } else {
             // TODO it would be much better for the C layer to give us
             // a length, since the hash length will change in the near
             // future, but that's probably out of scope for the nodemap
             // patch series.
             //
             // The root of that unsafety relies in the signature of
             // `capi.index_node()` itself: returning a `Node` pointer
             // whereas it's a `char *` in the C counterpart.
             Some(unsafe { &*raw })
         }
     }
 }