diff -r f77e4daaf612 -r 005ae1a343f8 rust/rhg/src/commands/files.rs
--- a/rust/rhg/src/commands/files.rs	Fri Dec 03 14:36:40 2021 +0100
+++ b/rust/rhg/src/commands/files.rs	Tue Nov 16 11:53:58 2021 +0000
@@ -40,10 +40,38 @@
     let rev = invocation.subcommand_args.value_of("rev");
 
     let repo = invocation.repo?;
+
+    // It seems better if this check is removed: this would correspond to
+    // automatically enabling the extension if the repo requires it.
+    // However we need this check to be in sync with vanilla hg so hg tests
+    // pass.
+    if repo.has_sparse()
+        && invocation.config.get(b"extensions", b"sparse").is_none()
+    {
+        return Err(CommandError::unsupported(
+            "repo is using sparse, but sparse extension is not enabled",
+        ));
+    }
+
     if let Some(rev) = rev {
+        if repo.has_narrow() {
+            return Err(CommandError::unsupported(
+                "rhg files -r <rev> is not supported in narrow clones",
+            ));
+        }
         let files = list_rev_tracked_files(repo, rev).map_err(|e| (e, rev))?;
         display_files(invocation.ui, repo, files.iter())
     } else {
+        // The dirstate always reflects the sparse narrowspec, so if
+        // we only have sparse without narrow all is fine.
+        // If we have narrow, then [hg files] needs to check if
+        // the store narrowspec is in sync with the one of the dirstate,
+        // so we can't support that without explicit code.
+        if repo.has_narrow() {
+            return Err(CommandError::unsupported(
+                "rhg files is not supported in narrow clones",
+            ));
+        }
         let distate = Dirstate::new(repo)?;
         let files = distate.tracked_files()?;
         display_files(invocation.ui, repo, files.into_iter().map(Ok))