comparison rust/hg-core/src/dirstate_tree/dirstate_map.rs @ 47334:18b3060fe598

dirstate-v2: Add a zero-size error type for dirstate v2 parse errors

This error should only happen if Mercurial is buggy or the file is corrupted.
It indicates for example that:

* A part of the file refers to another part, and the byte offset or item count
  would cause reading out of bounds, beyond the end of the file.
* The byte for an entry state has an invalid value

When parsing becomes lazy, many more functions will return a `Result` with
this error. Making it zero-size reduces the work that the `?` operator needs
to do to pass around the error value.

Differential Revision: https://phab.mercurial-scm.org/D10748

47333:69530e5d4fe5

    #[timed]
    pub fn new_v2(
        on_disk: &'on_disk [u8],
    ) -> Result<(Self, Option<DirstateParents>), DirstateError> {
        on_disk::read(on_disk)
    }

    #[timed]
    pub fn new_v1(
        on_disk: &'on_disk [u8],

47334:18b3060fe598

    #[timed]
    pub fn new_v2(
        on_disk: &'on_disk [u8],
    ) -> Result<(Self, Option<DirstateParents>), DirstateError> {
        Ok(on_disk::read(on_disk)?)
    }

    #[timed]
    pub fn new_v1(
        on_disk: &'on_disk [u8],