style: report errors during CLI handling

src/cli.rs

@@ -2,13 +2,23 @@
 use bevy::prelude::{App, Entity, FileDragAndDrop};
 use bevy::window::PrimaryWindow;
 use std::env;
+use std::io;
 use std::path::PathBuf;
+use thiserror::Error;
 
 pub struct CliArgs {
     pub map_path: Option<PathBuf>,
     pub data_path: Option<PathBuf>,
 }
 
+#[derive(Error, Debug)]
+pub enum InitCliError {
+    #[error("supplied path is invalid.")]
+    InvalidPathError(#[from] io::Error),
+    #[error("window not initialized.")]
+    UninitWindow,
+}
+
 pub fn parse_args() -> CliArgs {
     let args: Vec<String> = env::args().collect();
     // the last args take priority
@@ -29,28 +39,27 @@ pub fn parse_args() -> CliArgs {
 
 /// Generate `FileDragAndDrop` such that the map and/or data
 /// if supplied as CLI args are later loaded.
-pub fn handle_cli_args(app: &mut App, cli_args: CliArgs) {
-    let Some((win, _)) = app
+pub fn handle_cli_args(app: &mut App, cli_args: CliArgs) -> Result<(), InitCliError> {
+    let (win, _) = app
         .world_mut()
         .query::<(Entity, &PrimaryWindow)>()
         .iter(app.world())
         .next()
-    else {
-        return;
-    };
+        .ok_or(InitCliError::UninitWindow)?;
     // paths are canonicalized so that they are not interpreted
     // to be in the assets directory by bevy's `AssetLoader`.
     if let Some(map_path) = cli_args.map_path {
         app.world_mut().send_event(FileDragAndDrop::DroppedFile {
             window: win,
-            path_buf: map_path.canonicalize().unwrap(),
+            path_buf: map_path.canonicalize()?,
         });
     }
 
     if let Some(data_path) = cli_args.data_path {
         app.world_mut().send_event(FileDragAndDrop::DroppedFile {
             window: win,
-            path_buf: data_path.canonicalize().unwrap(),
+            path_buf: data_path.canonicalize()?,
         });
     }
+    Ok(())
 }

src/main.rs

@@ -53,7 +53,13 @@ fn main() {
         .add_plugins(legend::LegendPlugin);
 
     let cli_args = cli::parse_args();
-    cli::handle_cli_args(app, cli_args);
+    if let Err(e) = cli::handle_cli_args(app, cli_args) {
+        use cli::InitCliError::*;
+        match e {
+            InvalidPathError(error) => error!("Supplied path as arg is invalid: {error}"),
+            UninitWindow => error!("Window was not initialized!"),
+        }
+    }
 
     app.run();
 }