rust/hg-core/src/requirements.rs

rust: add Vfs trait

This will allow for the use of multiple vfs like in the Python implementation,
as well as hiding the details of the upcoming Python vfs wrapper to hg-core.

use crate::errors::{HgError, HgResultExt};
use crate::repo::Repo;
use crate::utils::join_display;
use crate::vfs::VfsImpl;
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: VfsImpl) -> Result<HashSet<String>, HgError> {
    parse(&hg_vfs.read("requires")?)
}

pub(crate) fn load_if_exists(
    hg_vfs: &VfsImpl,
) -> 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_REQUIREMENT,
    SHARED_REQUIREMENT,
    SHARESAFE_REQUIREMENT,
    SPARSEREVLOG_REQUIREMENT,
    RELATIVE_SHARED_REQUIREMENT,
    REVLOG_COMPRESSION_ZSTD,
    DIRSTATE_V2_REQUIREMENT,
    DIRSTATE_TRACKED_HINT_V1,
    // 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,
    // Not all commands support `sparse` and `narrow`. The commands that do
    // not should opt out by checking `has_sparse` and `has_narrow`.
    SPARSE_REQUIREMENT,
    NARROW_REQUIREMENT,
    // rhg doesn't care about bookmarks at all yet
    BOOKMARKS_IN_STORE_REQUIREMENT,
];

// Copied from mercurial/requirements.py:

pub const DIRSTATE_V2_REQUIREMENT: &str = "dirstate-v2";
pub const GENERALDELTA_REQUIREMENT: &str = "generaldelta";

/// A repository that uses the tracked hint dirstate file
#[allow(unused)]
pub const DIRSTATE_TRACKED_HINT_V1: &str = "dirstate-tracked-key-v1";

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

/// Bookmarks must be stored in the `store` part of the repository and will be
/// share accross shares
#[allow(unused)]
pub const BOOKMARKS_IN_STORE_REQUIREMENT: &str = "bookmarksinstore";

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

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

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

/// Whether to use the "RevlogNG" or V1 of the revlog format
#[allow(unused)]
pub const REVLOGV1_REQUIREMENT: &str = "revlogv1";

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

/// Increment the sub-version when the revlog v2 format changes to lock out old
/// clients.
#[allow(unused)]
pub const CHANGELOGV2_REQUIREMENT: &str = "exp-changelog-v2";

/// 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 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 const COPIESSDC_REQUIREMENT: &str = "exp-copies-sidedata-changeset";

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

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

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