rhg: make rhg recognise it supports zstd compression for revlogs

It already did, but was not aware of it.

Differential Revision: https://phab.mercurial-scm.org/D10324

rust/hg-core/src/requirements.rs

@@ -1,153 +1,158 b''
 use crate::errors::{HgError, HgResultExt};
 use crate::repo::{Repo, Vfs};
 use crate::utils::join_display;
 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,
     // 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:
 
 /// 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";
+
+/// A repository that use zstd compression inside its revlog
+#[allow(unused)]
+pub(crate) const REVLOG_COMPRESSION_ZSTD: &str = "revlog-compression-zstd";