diff --git a/mercurial/debugcommands.py b/mercurial/debugcommands.py
--- a/mercurial/debugcommands.py
+++ b/mercurial/debugcommands.py
@@ -1497,6 +1497,18 @@
         pythonlib or _(b"unknown"),
     )
 
+    try:
+        from mercurial import rustext
+        rustext.__doc__  # trigger lazy import
+    except ImportError:
+        rustext = None
+
+    fm.write(
+        b'',
+        _(b"checking Rust extensions (%s)\n"),
+        b'missing' if rustext is None else 'installed',
+    )
+
     security = set(sslutil.supportedprotocols)
     if sslutil.hassni:
         security.add(b'sni')
diff --git a/rust/hg-cpython/src/lib.rs b/rust/hg-cpython/src/lib.rs
--- a/rust/hg-cpython/src/lib.rs
+++ b/rust/hg-cpython/src/lib.rs
@@ -72,6 +72,12 @@
         "PatternError",
         py.get_type::<exceptions::PatternError>(),
     )?;
+    /// Change this version whenever the API is changed
+    m.add(
+        py,
+        "version",
+        0,
+    )?;
     Ok(())
 });