--- a/rust/hg-core/src/requirements.rs	Mon Feb 01 19:30:28 2021 +0100
+++ b/rust/hg-core/src/requirements.rs	Thu Jan 14 13:04:12 2021 +0100
@@ -1,7 +1,8 @@
 use crate::errors::{HgError, HgResultExt};
-use crate::repo::Repo;
+use crate::repo::{Repo, Vfs};
+use std::collections::HashSet;
 
-fn parse(bytes: &[u8]) -> Result<Vec<String>, HgError> {
+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`.
@@ -21,10 +22,8 @@
         .collect()
 }
 
-pub fn load(repo: &Repo) -> Result<Vec<String>, HgError> {
-    if let Some(bytes) =
-        repo.hg_vfs().read("requires").io_not_found_as_none()?
-    {
+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.
@@ -34,13 +33,13 @@
         // > 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(Vec::new())
+        Ok(HashSet::new())
     }
 }
 
-pub fn check(repo: &Repo) -> Result<(), HgError> {
-    for feature in load(repo)? {
-        if !SUPPORTED.contains(&&*feature) {
+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!(
@@ -58,10 +57,77 @@
     "fncache",
     "generaldelta",
     "revlogv1",
-    "sparserevlog",
+    SHARED_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 = "exp-sharesafe";