diff rust/hg-core/src/revlog.rs @ 44005:6b332c1fc7fe

rust-core: extracted a revlog submodule

This moves fundamental definitions from the top of the crate
to the newly created `revlog` submodule and reexports them for
easy compatibility.

As we are about to add new features to this crate, we felt it
will improve clarity, and moreso if `ancestors` and `dagops`
would become submodules of `revlog`.

Differential Revision: https://phab.mercurial-scm.org/D7782

--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/rust/hg-core/src/revlog.rs	Wed Dec 25 15:17:55 2019 +0100
@@ -0,0 +1,38 @@
+// Copyright 2018-2020 Georges Racinet <[e-mail]>
+//           and Mercurial contributors
+//
+// This software may be used and distributed according to the terms of the
+// GNU General Public License version 2 or any later version.
+//! Mercurial concepts for handling revision history
+
+/// Mercurial revision numbers
+///
+/// As noted in revlog.c, revision numbers are actually encoded in
+/// 4 bytes, and are liberally converted to ints, whence the i32
+pub type Revision = i32;
+
+/// Marker expressing the absence of a parent
+///
+/// Independently of the actual representation, `NULL_REVISION` is guaranteed
+/// to be smaller that all existing revisions.
+pub const NULL_REVISION: Revision = -1;
+
+/// Same as `mercurial.node.wdirrev`
+///
+/// This is also equal to `i32::max_value()`, but it's better to spell
+/// it out explicitely, same as in `mercurial.node`
+pub const WORKING_DIRECTORY_REVISION: Revision = 0x7fffffff;
+
+/// The simplest expression of what we need of Mercurial DAGs.
+pub trait Graph {
+    /// Return the two parents of the given `Revision`.
+    ///
+    /// Each of the parents can be independently `NULL_REVISION`
+    fn parents(&self, rev: Revision) -> Result<[Revision; 2], GraphError>;
+}
+
+#[derive(Clone, Debug, PartialEq)]
+pub enum GraphError {
+    ParentOutOfRange(Revision),
+    WorkingDirectoryUnsupported,
+}