[Merged by Bors] - bevy_dynamic_plugin: make it possible to handle loading errors

crates/bevy_dynamic_plugin/Cargo.toml

@@ -16,3 +16,4 @@ bevy_app = { path = "../bevy_app", version = "0.9.0-dev" }
 
 # other
 libloading = { version = "0.7" }
+thiserror = "1.0"

crates/bevy_dynamic_plugin/src/loader.rs

@@ -1,7 +1,17 @@
 use libloading::{Library, Symbol};
+use thiserror::Error;
 
 use bevy_app::{App, CreatePlugin, Plugin};
 
+/// Errors that can occur when loading a dynamic plugin
+#[derive(Debug, Error)]
+pub enum DynamicPluginLoadError {
+    #[error("cannot load library for dynamic plugin: {0}")]
+    Library(libloading::Error),
+    #[error("dynamic library does not contain a valid Bevy dynamic plugin")]
+    Plugin(libloading::Error),
+}
+
 /// Dynamically links a plugin at the given path. The plugin must export a function with the
 /// [`CreatePlugin`] signature named `_bevy_create_plugin`.
 ///
@@ -10,11 +20,15 @@ use bevy_app::{App, CreatePlugin, Plugin};
 /// The specified plugin must be linked against the exact same libbevy.so as this program.
 /// In addition the `_bevy_create_plugin` symbol must not be manually created, but instead created
 /// by deriving `DynamicPlugin` on a unit struct implementing [`Plugin`].
-pub unsafe fn dynamically_load_plugin(path: &str) -> (Library, Box<dyn Plugin>) {
-    let lib = Library::new(path).unwrap();
-    let func: Symbol<CreatePlugin> = lib.get(b"_bevy_create_plugin").unwrap();
+pub unsafe fn dynamically_load_plugin(
+    path: &str,
+) -> Result<(Library, Box<dyn Plugin>), DynamicPluginLoadError> {
+    let lib = Library::new(path).map_err(DynamicPluginLoadError::Library)?;
+    let func: Symbol<CreatePlugin> = lib
+        .get(b"_bevy_create_plugin")
+        .map_err(DynamicPluginLoadError::Plugin)?;
     let plugin = Box::from_raw(func());
-    (lib, plugin)
+    Ok((lib, plugin))
 }
 
 pub trait DynamicPluginExt {
@@ -26,7 +40,7 @@ pub trait DynamicPluginExt {
 
 impl DynamicPluginExt for App {
     unsafe fn load_plugin(&mut self, path: &str) -> &mut Self {
-        let (lib, plugin) = dynamically_load_plugin(path);
+        let (lib, plugin) = dynamically_load_plugin(path).unwrap();
         std::mem::forget(lib); // Ensure that the library is not automatically unloaded
         plugin.build(self);
         self