feat: add --help command line argument

src/config.rs

@@ -52,6 +52,18 @@ pub struct CliArgs {
     pub zoom_level: Option<f32>,
 }
 
+/// Reason to abort running Verso.
+#[non_exhaustive]
+#[derive(thiserror::Error, Debug)]
+pub enum ArgError {
+    /// Failed to parse command line arguments
+    #[error("Failed to parse command line arguments: {0}\n  try \"--help\"")]
+    ParseError(#[from] getopts::Fail),
+    /// `--help` was used. Print help and exit.
+    #[error("{0}")]
+    Help(String),
+}
+
 /// Configuration of Verso instance.
 #[derive(Clone, Debug)]
 pub struct Config {
@@ -64,7 +76,7 @@ pub struct Config {
     pub resource_dir: PathBuf,
 }
 
-fn parse_cli_args() -> Result<CliArgs, getopts::Fail> {
+fn parse_cli_args() -> Result<CliArgs, ArgError> {
     let args: Vec<String> = std::env::args().collect();
 
     let mut opts = getopts::Options::new();
@@ -153,7 +165,12 @@ fn parse_cli_args() -> Result<CliArgs, getopts::Fail> {
 
     opts.optopt("", "zoom", "Initial window's zoom level", "1.5");
 
+    opts.optflag("", "help", "Display this help message");
+
     let matches: getopts::Matches = opts.parse(&args[1..])?;
+    if matches.opt_present("help") {
+        return Err(ArgError::Help(opts.usage(&opts.short_usage(&args[0]))));
+    }
     let url = matches
         .opt_str("url")
         .and_then(|url| match url::Url::parse(&url) {
@@ -273,9 +290,9 @@ fn parse_cli_args() -> Result<CliArgs, getopts::Fail> {
 
 impl Config {
     /// Create a new configuration for creating Verso instance.
-    pub fn new() -> Self {
+    pub fn new() -> Result<Self, ArgError> {
+        let args = parse_cli_args()?;
         let mut opts = Opts::default();
-        let args = parse_cli_args().unwrap_or_default();
 
         let (devtools_server_enabled, devtools_port) =
             if let Some(devtools_port) = args.devtools_port {
@@ -301,11 +318,11 @@ impl Config {
 
         let resource_dir = args.resource_dir.clone().unwrap_or(resources_dir_path());
 
-        Self {
+        Ok(Self {
             opts,
             args,
             resource_dir,
-        }
+        })
     }
 
     /// Register URL scheme protocols

src/errors.rs

@@ -17,4 +17,7 @@ pub enum Error {
     /// IPC errors.
     #[error(transparent)]
     IpcError(#[from] ipc_channel::ipc::IpcError),
+    /// Error parsing arguments (or `--help` was invoked).
+    #[error(transparent)]
+    ArgError(#[from] crate::config::ArgError),
 }

src/main.rs

@@ -1,20 +1,28 @@
 // Prevent console window from appearing on Windows
 #![cfg_attr(not(debug_assertions), windows_subsystem = "windows")]
 
+use std::process::ExitCode;
+
+use versoview::config::{ArgError, Config};
 use versoview::verso::EventLoopProxyMessage;
-use versoview::{Result, Verso};
+use versoview::Verso;
 use winit::application::ApplicationHandler;
 use winit::event_loop::{self, DeviceEvents};
 use winit::event_loop::{EventLoop, EventLoopProxy};
 
 struct App {
+    /// Config parsed from the command line. `config` XOR `verso` must be `Some`.
+    config: Option<Config>,
+    /// The verso browser handle (possibly uninitialized).
     verso: Option<Verso>,
     proxy: EventLoopProxy<EventLoopProxyMessage>,
 }
 
 impl ApplicationHandler<EventLoopProxyMessage> for App {
     fn resumed(&mut self, event_loop: &winit::event_loop::ActiveEventLoop) {
-        self.verso = Some(Verso::new(event_loop, self.proxy.clone()));
+        if let Some(config) = self.config.take() {
+            self.verso = Some(Verso::new(config, event_loop, self.proxy.clone()));
+        }
     }
 
     fn window_event(
@@ -46,18 +54,39 @@ impl ApplicationHandler<EventLoopProxyMessage> for App {
     }
 }
 
-fn main() -> Result<()> {
+fn run() -> versoview::errors::Result<()> {
+    let config = Some(versoview::config::Config::new()?);
     init_crypto();
 
     let event_loop = EventLoop::<EventLoopProxyMessage>::with_user_event().build()?;
     event_loop.listen_device_events(DeviceEvents::Never);
     let proxy = event_loop.create_proxy();
-    let mut app = App { verso: None, proxy };
+    let mut app = App {
+        config,
+        verso: None,
+        proxy,
+    };
     event_loop.run_app(&mut app)?;
 
     Ok(())
 }
 
+fn main() -> ExitCode {
+    run().map_or_else(
+        |e| match e {
+            versoview::Error::ArgError(ArgError::Help(message)) => {
+                println!("{message}");
+                ExitCode::SUCCESS
+            }
+            e => {
+                eprintln!("{e}");
+                ExitCode::FAILURE
+            }
+        },
+        |()| ExitCode::SUCCESS,
+    )
+}
+
 fn init_crypto() {
     rustls::crypto::aws_lc_rs::default_provider()
         .install_default()

src/verso.rs

@@ -80,8 +80,11 @@ impl Verso {
     /// - Canvas: Enabled
     /// - Constellation: Enabled
     /// - Image Cache: Enabled
-    pub fn new(evl: &ActiveEventLoop, proxy: EventLoopProxy<EventLoopProxyMessage>) -> Self {
-        let config = Config::new();
+    pub fn new(
+        config: Config,
+        evl: &ActiveEventLoop,
+        proxy: EventLoopProxy<EventLoopProxyMessage>,
+    ) -> Self {
         let to_controller_sender = if let Some(ipc_channel) = &config.args.ipc_channel {
             let sender =
                 IpcSender::<ToControllerMessage>::connect(ipc_channel.to_string()).unwrap();