annotate rust/hg-core/src/dirstate_tree/on_disk.rs @ 47280:1766130fe9ba

dirstate-v2: Change the on-disk format when the requirement is enabled

For now, the format is the same except with an additional marker at the start.

This marker is redundant: for existing repositories it is `.hg/requires` that
determines which format to use. For new repositories, it is the new
`format.exp-dirstate-v2` config. There is no upgrade or downgrade so far.

Most of the changes are about plumbing a boolean through layers of APIs to
indicate which format should be used.

Differential Revision: https://phab.mercurial-scm.org/D10719

/// Added at the start of `.hg/dirstate` when the "v2" format is used.
/// Acts like a "magic number". This is a sanity check, not strictly necessary
/// since `.hg/requires` already governs which format should be used.
pub const V2_FORMAT_MARKER: &[u8; 12] = b"dirstate-v2\n";