diff -r 184e46550dc8 -r 1ecaf09d9964 rust/rhg/src/commands/files.rs
--- a/rust/rhg/src/commands/files.rs	Mon Feb 08 20:33:04 2021 +0100
+++ b/rust/rhg/src/commands/files.rs	Mon Feb 08 21:05:36 2021 +0100
@@ -1,5 +1,6 @@
 use crate::error::CommandError;
 use crate::ui::Ui;
+use clap::Arg;
 use clap::ArgMatches;
 use hg::config::Config;
 use hg::operations::list_rev_tracked_files;
@@ -14,6 +15,19 @@
 Returns 0 on success.
 ";
 
+pub fn args() -> clap::App<'static, 'static> {
+    clap::SubCommand::with_name("files")
+        .arg(
+            Arg::with_name("rev")
+                .help("search the repository as it is in REV")
+                .short("-r")
+                .long("--revision")
+                .value_name("REV")
+                .takes_value(true),
+        )
+        .about(HELP_TEXT)
+}
+
 pub fn run(
     ui: &Ui,
     config: &Config,