annotate rust/hg-core/src/requirements.rs @ 48295:bf11ff22a9af

dirstate-v2: freeze the on-disk format

It seems the format as reached a good balance. With a core of new capabilities
that motivated it initially and enough new feature and room for future
improvement to be a clear progress we can set a milestone for.

Having the format frozen will help the feature to get real life testing, outside
of the test suite.

The feature itself stay experimental but the config gains a new name to avoid
people enable non-frozen version by default.

If too many bugs are reported during the RC we might move the format back to
experimental and drop its support in future version (in favor of a new one)

Differential Revision: https://phab.mercurial-scm.org/D11709

use crate::errors::{HgError, HgResultExt};
use crate::repo::Repo;
use crate::utils::join_display;
use crate::vfs::Vfs;
use std::collections::HashSet;

fn parse(bytes: &[u8]) -> Result<HashSet<String>, HgError> {
    // The Python code reading this file uses `str.splitlines`
    // which looks for a number of line separators (even including a couple of
    // non-ASCII ones), but Python code writing it always uses `\n`.
    let lines = bytes.split(|&byte| byte == b'\n');

    lines
        .filter(|line| !line.is_empty())
        .map(|line| {
            // Python uses Unicode `str.isalnum` but feature names are all
            // ASCII
            if line[0].is_ascii_alphanumeric() && line.is_ascii() {
                Ok(String::from_utf8(line.into()).unwrap())
            } else {
                Err(HgError::corrupted("parse error in 'requires' file"))
            }
        })
        .collect()
}

pub(crate) fn load(hg_vfs: Vfs) -> Result<HashSet<String>, HgError> {
    parse(&hg_vfs.read("requires")?)
}

pub(crate) fn load_if_exists(hg_vfs: Vfs) -> Result<HashSet<String>, HgError> {
    if let Some(bytes) = hg_vfs.read("requires").io_not_found_as_none()? {
        parse(&bytes)
    } else {
        // Treat a missing file the same as an empty file.
        // From `mercurial/localrepo.py`:
        // > requires file contains a newline-delimited list of
        // > features/capabilities the opener (us) must have in order to use
        // > the repository. This file was introduced in Mercurial 0.9.2,
        // > which means very old repositories may not have one. We assume
        // > a missing file translates to no requirements.
        Ok(HashSet::new())
    }
}

pub(crate) fn check(repo: &Repo) -> Result<(), HgError> {
    let unknown: Vec<_> = repo
        .requirements()
        .iter()
        .map(String::as_str)
        // .filter(|feature| !ALL_SUPPORTED.contains(feature.as_str()))
        .filter(|feature| {
            !REQUIRED.contains(feature) && !SUPPORTED.contains(feature)
        })
        .collect();
    if !unknown.is_empty() {
        return Err(HgError::unsupported(format!(
            "repository requires feature unknown to this Mercurial: {}",
            join_display(&unknown, ", ")
        )));
    }
    let missing: Vec<_> = REQUIRED
        .iter()
        .filter(|&&feature| !repo.requirements().contains(feature))
        .collect();
    if !missing.is_empty() {
        return Err(HgError::unsupported(format!(
            "repository is missing feature required by this Mercurial: {}",
            join_display(&missing, ", ")
        )));
    }
    Ok(())
}

/// rhg does not support repositories that are *missing* any of these features
const REQUIRED: &[&str] = &["revlogv1", "store", "fncache", "dotencode"];

/// rhg supports repository with or without these
const SUPPORTED: &[&str] = &[
    "generaldelta",
    SHARED_REQUIREMENT,
    SHARESAFE_REQUIREMENT,
    SPARSEREVLOG_REQUIREMENT,
    RELATIVE_SHARED_REQUIREMENT,
    REVLOG_COMPRESSION_ZSTD,
    DIRSTATE_V2_REQUIREMENT,
    // As of this writing everything rhg does is read-only.
    // When it starts writing to the repository, it’ll need to either keep the
    // persistent nodemap up to date or remove this entry:
    NODEMAP_REQUIREMENT,
];

// Copied from mercurial/requirements.py:

pub(crate) const DIRSTATE_V2_REQUIREMENT: &str = "dirstate-v2";

/// When narrowing is finalized and no longer subject to format changes,
/// we should move this to just "narrow" or similar.
#[allow(unused)]
pub(crate) const NARROW_REQUIREMENT: &str = "narrowhg-experimental";

/// Enables sparse working directory usage
#[allow(unused)]
pub(crate) const SPARSE_REQUIREMENT: &str = "exp-sparse";

/// Enables the internal phase which is used to hide changesets instead
/// of stripping them
#[allow(unused)]
pub(crate) const INTERNAL_PHASE_REQUIREMENT: &str = "internal-phase";

/// Stores manifest in Tree structure
#[allow(unused)]
pub(crate) const TREEMANIFEST_REQUIREMENT: &str = "treemanifest";

/// Increment the sub-version when the revlog v2 format changes to lock out old
/// clients.
#[allow(unused)]
pub(crate) const REVLOGV2_REQUIREMENT: &str = "exp-revlogv2.1";

/// A repository with the sparserevlog feature will have delta chains that
/// can spread over a larger span. Sparse reading cuts these large spans into
/// pieces, so that each piece isn't too big.
/// Without the sparserevlog capability, reading from the repository could use
/// huge amounts of memory, because the whole span would be read at once,
/// including all the intermediate revisions that aren't pertinent for the
/// chain. This is why once a repository has enabled sparse-read, it becomes
/// required.
#[allow(unused)]
pub(crate) const SPARSEREVLOG_REQUIREMENT: &str = "sparserevlog";

/// A repository with the the copies-sidedata-changeset requirement will store
/// copies related information in changeset's sidedata.
#[allow(unused)]
pub(crate) const COPIESSDC_REQUIREMENT: &str = "exp-copies-sidedata-changeset";

/// The repository use persistent nodemap for the changelog and the manifest.
#[allow(unused)]
pub(crate) const NODEMAP_REQUIREMENT: &str = "persistent-nodemap";

/// Denotes that the current repository is a share
#[allow(unused)]
pub(crate) const SHARED_REQUIREMENT: &str = "shared";

/// Denotes that current repository is a share and the shared source path is
/// relative to the current repository root path
#[allow(unused)]
pub(crate) const RELATIVE_SHARED_REQUIREMENT: &str = "relshared";

/// A repository with share implemented safely. The repository has different
/// store and working copy requirements i.e. both `.hg/requires` and
/// `.hg/store/requires` are present.
#[allow(unused)]
pub(crate) const SHARESAFE_REQUIREMENT: &str = "share-safe";

/// A repository that use zstd compression inside its revlog
#[allow(unused)]
pub(crate) const REVLOG_COMPRESSION_ZSTD: &str = "revlog-compression-zstd";