set up structure for multiple cli commands

The previous cli is now behind the 'serve' subcommand.

nix/modules/default/default.nix

@@ -79,7 +79,7 @@ in
       # Keep sorted
       serviceConfig = {
         DynamicUser = true;
-        ExecStart = "${lib.getExe cfg.package} --config ${configFile}";
+        ExecStart = "${lib.getExe cfg.package} serve --config ${configFile}";
         LockPersonality = true;
         MemoryDenyWriteExecute = true;
         PrivateDevices = true;

src/args.rs

@@ -1,35 +0,0 @@
-//! Integration with `clap`
-
-use std::path::PathBuf;
-
-use clap::{CommandFactory as _, FromArgMatches as _, Parser};
-
-/// Command line arguments
-#[derive(Parser)]
-#[clap(about, version = crate::version())]
-pub(crate) struct Args {
-    /// Path to the configuration file
-    #[clap(long, short)]
-    pub(crate) config: Option<PathBuf>,
-}
-
-/// Parse command line arguments into structured data
-pub(crate) fn parse() -> Args {
-    let mut command = Args::command().mut_arg("config", |x| {
-        let help = "Set the path to the configuration file";
-        x.help(help).long_help(format!(
-            "{}\n\nIf this option is specified, the provided value is used \
-             as-is.\n\nIf this option is not specified, then the XDG Base \
-             Directory Specification is followed, searching for the path `{}` \
-             in the configuration directories.
-            ",
-            help,
-            crate::config::DEFAULT_PATH.display(),
-        ))
-    });
-
-    match Args::from_arg_matches(&command.get_matches_mut()) {
-        Ok(x) => x,
-        Err(e) => e.format(&mut command).exit(),
-    }
-}

src/cli.rs

@@ -0,0 +1,51 @@
+//! Integration with `clap`
+
+use std::path::PathBuf;
+
+use clap::{Parser, Subcommand};
+
+/// Command line arguments
+#[derive(Parser)]
+#[clap(
+    about,
+    version = crate::version(),
+)]
+pub(crate) struct Args {
+    #[clap(subcommand)]
+    pub(crate) command: Command,
+}
+
+#[derive(Subcommand)]
+pub(crate) enum Command {
+    /// Run the server.
+    Serve(ServeArgs),
+}
+
+/// Wrapper for the `--config` arg.
+///
+/// This exists to centralize the `mut_arg` code that sets the help value based
+/// on runtime information.
+#[derive(clap::Args)]
+#[clap(mut_arg("config", |x| {
+    let help = "Set the path to the configuration file";
+    x.help(help).long_help(format!(
+        "{}\n\nIf this option is specified, the provided value is used \
+         as-is.\n\nIf this option is not specified, then the XDG Base \
+         Directory Specification is followed, searching for the path `{}` \
+         in the configuration directories.
+        ",
+        help,
+        crate::config::DEFAULT_PATH.display(),
+    ))
+}))]
+pub(crate) struct ConfigArg {
+    /// Path to the configuration file
+    #[clap(long, short)]
+    pub(crate) config: Option<PathBuf>,
+}
+
+#[derive(clap::Args)]
+pub(crate) struct ServeArgs {
+    #[clap(flatten)]
+    pub(crate) config: ConfigArg,
+}

src/main.rs

@@ -19,6 +19,7 @@ use axum::{
 use axum_server::{
     bind, bind_rustls, tls_rustls::RustlsConfig, Handle as ServerHandle,
 };
+use clap::Parser;
 use futures_util::FutureExt;
 use http::{
     header::{self, HeaderName},
@@ -41,7 +42,7 @@ use tower_http::{
 use tracing::{debug, error, info, info_span, warn, Instrument};
 
 mod api;
-mod args;
+mod cli;
 mod config;
 mod database;
 mod error;
@@ -51,6 +52,7 @@ mod utils;
 
 pub(crate) use api::ruma_wrapper::{Ar, Ra};
 use api::{client_server, server_server, well_known};
+use cli::{Args, Command};
 pub(crate) use config::{Config, ListenConfig};
 pub(crate) use database::KeyValueDatabase;
 pub(crate) use service::{pdu::PduEvent, Services};
@@ -108,9 +110,12 @@ async fn main() -> ExitCode {
 async fn try_main() -> Result<(), error::Main> {
     use error::Main as Error;
 
-    let args = args::parse();
+    let args = Args::parse();
+    // This is a placeholder, the logic specific to the 'serve' command will be
+    // moved to another file in a later commit
+    let Command::Serve(args) = args.command;
 
-    let config = config::load(args.config.as_ref()).await?;
+    let config = config::load(args.config.config.as_ref()).await?;
 
     let (_guard, reload_handles) = observability::init(&config)?;