rust/hg-core/src/requirements.rs

use crate::errors::{HgError, HgResultExt};
use crate::repo::{Repo, 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> {
    for feature in repo.requirements() {
        if !SUPPORTED.contains(&feature.as_str()) {
            // TODO: collect and all unknown features and include them in the
            // error message?
            return Err(HgError::UnsupportedFeature(format!(
                "repository requires feature unknown to this Mercurial: {}",
                feature
            )));
        }
    }
    Ok(())
}

// TODO: set this to actually-supported features
const SUPPORTED: &[&str] = &[
    "dotencode",
    "fncache",
    "generaldelta",
    "revlogv1",
    SHARED_REQUIREMENT,
    SHARESAFE_REQUIREMENT,
    SPARSEREVLOG_REQUIREMENT,
    RELATIVE_SHARED_REQUIREMENT,
    "store",
    // 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:
    "persistent-nodemap",
];

// Copied from mercurial/requirements.py:

/// 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 sidedataflag requirement will allow to store extra
/// information for revision without altering their original hashes.
#[allow(unused)]
pub(crate) const SIDEDATA_REQUIREMENT: &str = "exp-sidedata-flag";

/// 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";