( )⚙ D11101 dirstate-v2: Reserve a few bytes of space for future extensions

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Differential D11101

dirstate-v2: Reserve a few bytes of space for future extensions
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Authored by SimonSapin on Jul 16 2021, 11:17 AM.

Details

Reviewers
Alphare
Group Reviewers
hg-reviewers
Commits
rHG852262e2e7d9: dirstate-v2: Reserve a few bytes of space for future extensions
Summary

See doc-comment

Diff Detail

Repository
rHG Mercurial
Branch
default
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Unit
No Unit Test Coverage

Event Timeline

SimonSapin created this revision.Jul 16 2021, 11:17 AM
baymax updated this revision to Diff 29357.Jul 16 2021, 5:45 PM

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Alphare accepted this revision.Jul 19 2021, 5:51 AM
This revision is now accepted and ready to land.Jul 19 2021, 5:51 AM
baymax updated this revision to Diff 29616.Jul 20 2021, 3:42 PM

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Revision Contents
Changeset List

Diff 29616

mercurial/dirstateutils/docket.py

from ..revlogutils import docket as docket_mod from ..revlogutils import docket as docket_mod
V2_FORMAT_MARKER = b"dirstate-v2\n" V2_FORMAT_MARKER = b"dirstate-v2\n"
# Must match the constant of the same name in # Must match the constant of the same name in
# `rust/hg-core/src/dirstate_tree/on_disk.rs` # `rust/hg-core/src/dirstate_tree/on_disk.rs`
TREE_METADATA_SIZE = 40 TREE_METADATA_SIZE = 44
# * 12 bytes: format marker # * 12 bytes: format marker
# * 32 bytes: node ID of the working directory's first parent # * 32 bytes: node ID of the working directory's first parent
# * 32 bytes: node ID of the working directory's second parent # * 32 bytes: node ID of the working directory's second parent
# * 4 bytes: big-endian used size of the data file # * 4 bytes: big-endian used size of the data file
# * {TREE_METADATA_SIZE} bytes: tree metadata, parsed separately # * {TREE_METADATA_SIZE} bytes: tree metadata, parsed separately
# * 1 byte: length of the data file's UUID # * 1 byte: length of the data file's UUID
# * variable: data file's UUID # * variable: data file's UUID

rust/hg-core/src/dirstate_tree/on_disk.rs

/// … even though only 160 bits are used for now, with SHA-1 /// … even though only 160 bits are used for now, with SHA-1
const USED_NODE_ID_BYTES: usize = 20; const USED_NODE_ID_BYTES: usize = 20;
pub(super) const IGNORE_PATTERNS_HASH_LEN: usize = 20; pub(super) const IGNORE_PATTERNS_HASH_LEN: usize = 20;
pub(super) type IgnorePatternsHash = [u8; IGNORE_PATTERNS_HASH_LEN]; pub(super) type IgnorePatternsHash = [u8; IGNORE_PATTERNS_HASH_LEN];
/// Must match the constant of the same name in /// Must match the constant of the same name in
/// `mercurial/dirstateutils/docket.py` /// `mercurial/dirstateutils/docket.py`
const TREE_METADATA_SIZE: usize = 40; const TREE_METADATA_SIZE: usize = 44;
/// Make sure that size-affecting changes are made knowingly /// Make sure that size-affecting changes are made knowingly
#[allow(unused)] #[allow(unused)]
fn static_assert_size_of() { fn static_assert_size_of() {
let _ = std::mem::transmute::<DocketHeader, [u8; 121]>;
let _ = std::mem::transmute::<TreeMetadata, [u8; TREE_METADATA_SIZE]>; let _ = std::mem::transmute::<TreeMetadata, [u8; TREE_METADATA_SIZE]>;
let _ = std::mem::transmute::<DocketHeader, [u8; TREE_METADATA_SIZE + 81]>;
let _ = std::mem::transmute::<Node, [u8; 43]>; let _ = std::mem::transmute::<Node, [u8; 43]>;
} }
// Must match `HEADER` in `mercurial/dirstateutils/docket.py` // Must match `HEADER` in `mercurial/dirstateutils/docket.py`
#[derive(BytesCast)] #[derive(BytesCast)]
#[repr(C)] #[repr(C)]
struct DocketHeader { struct DocketHeader {
marker: [u8; V2_FORMAT_MARKER.len()], marker: [u8; V2_FORMAT_MARKER.len()],
struct TreeMetadata { struct TreeMetadata {
root_nodes: ChildNodes, root_nodes: ChildNodes,
nodes_with_entry_count: Size, nodes_with_entry_count: Size,
nodes_with_copy_source_count: Size, nodes_with_copy_source_count: Size,
/// How many bytes of this data file are not used anymore /// How many bytes of this data file are not used anymore
unreachable_bytes: Size, unreachable_bytes: Size,
/// Current version always sets these bytes to zero when creating or
/// updating a dirstate. Future versions could assign some bits to signal
/// for example "the version that last wrote/updated this dirstate did so
/// in such and such way that can be relied on by versions that know to."
unused: [u8; 4],
/// If non-zero, a hash of ignore files that were used for some previous /// If non-zero, a hash of ignore files that were used for some previous
/// run of the `status` algorithm. /// run of the `status` algorithm.
/// ///
/// We define: /// We define:
/// ///
/// * "Root" ignore files are `.hgignore` at the root of the repository if /// * "Root" ignore files are `.hgignore` at the root of the repository if
/// it exists, and files from `ui.ignore.*` config. This set of files is /// it exists, and files from `ui.ignore.*` config. This set of files is
/// then sorted by the string representation of their path. /// then sorted by the string representation of their path.
let meta = TreeMetadata { let meta = TreeMetadata {
root_nodes, root_nodes,
nodes_with_entry_count: dirstate_map.nodes_with_entry_count.into(), nodes_with_entry_count: dirstate_map.nodes_with_entry_count.into(),
nodes_with_copy_source_count: dirstate_map nodes_with_copy_source_count: dirstate_map
.nodes_with_copy_source_count .nodes_with_copy_source_count
.into(), .into(),
unreachable_bytes: dirstate_map.unreachable_bytes.into(), unreachable_bytes: dirstate_map.unreachable_bytes.into(),
unused: [0; 4],
ignore_patterns_hash: dirstate_map.ignore_patterns_hash, ignore_patterns_hash: dirstate_map.ignore_patterns_hash,
}; };
Ok((writer.out, meta.as_bytes().to_vec(), append)) Ok((writer.out, meta.as_bytes().to_vec(), append))
} }
struct Writer<'dmap, 'on_disk> { struct Writer<'dmap, 'on_disk> {
dirstate_map: &'dmap DirstateMap<'on_disk>, dirstate_map: &'dmap DirstateMap<'on_disk>,
append: bool, append: bool,