rust: working directory revision number constant

This introduces the constant, but does not use it anywhere yet.

rust/hg-core/src/lib.rs

@@ -1,30 +1,36 b''
 // 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.
 mod ancestors;
 pub mod dagops;
 pub use ancestors::{AncestorsIterator, LazyAncestors, MissingAncestors};
 #[cfg(test)]
 pub mod testing;
 
 /// 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;
 
 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, Revision) -> Result<[Revision; 2], GraphError>;
 }
 
 #[derive(Clone, Debug, PartialEq)]
 pub enum GraphError {
     ParentOutOfRange(Revision),
 }