rust: update the rust-cpython crate to 0.7.0 This notably brings support for Python 3.10, and includes the panic message when propagating a Rust panic as a Python exception. https://github.com/dgrunwald/rust-cpython/blob/master/CHANGELOG.md#070---2021-10-09 Differential Revision: https://phab.mercurial-scm.org/D11630

dirstate-v2: Name a constant in the Rust implementation We are about to introduce a Python version of this code that will also need this constant. Differential Revision: https://phab.mercurial-scm.org/D11547

dirstate-v2: Replace the 32-bit `mode` field with two bits Previously we stored the entire value from `stat_result.st_mode`, like dirstate-v1 does. However only the executable permission and type of file (only symbolic links and normal files are supported) are relevant to Mecurial. So replace this field with two bits in the existing bitfield byte. For now the unused space is left as padding, as it will be used for something else soon. Differential Revision: https://phab.mercurial-scm.org/D11635

dirstate-v2: Store unsigned integers inside DirstateEntry The negative marker values are not used anymore. Differential Revision: https://phab.mercurial-scm.org/D11634

dirstate-v2: Truncate directory mtimes to 31 bits of seconds … instead of 64 bits, while keeping the sub-second presision. This brings the size of one timestamp from 12 bytes to 8 bytes. 31 bits is chosen instead of 32 because that’s already what happens for the mtime of files and symlinks, because dirstate-v1 uses negative i32 values as markers. Later we’ll add sub-second precision for file/symlink mtimes, making their dirstate-v2 representation the same as for directories. Differential Revision: https://phab.mercurial-scm.org/D11633

dirstate-v2: Separate Rust structs for Timestamp and PackedTimestamp PackedTimestamp is now exclusively for dirstate-v2 serialization purpose. It contains unaligned big-endian integers. Timestamp is used everywhere else and contains native Rust integers. Differential Revision: https://phab.mercurial-scm.org/D11632

dirstate-v2: Change the representation of negative directory mtime Change it from how I previously thought C’s `timespec` works to how it actually works. The previous behavior was also buggy for timestamps strictly before the epoch but less than one second away from it, because two’s complement does not distinguish negative zero from positive zero. Differential Revision: https://phab.mercurial-scm.org/D11629