Add convenience methods to `ModuleLoader` (#3007)

* Add convenience methods to `ModuleLoader`

* Document special behaviour of `SimpleModuleLoader`

boa_engine/src/module/mod.rs

@@ -108,6 +108,26 @@ pub trait ModuleLoader {
         context: &mut Context<'_>,
     );
 
+    /// Registers a new module into the module loader.
+    ///
+    /// This is a convenience method for module loaders caching already parsed modules, since it
+    /// allows registering a new module through the `&dyn ModuleLoader` provided by
+    /// [`Context::module_loader`].
+    ///
+    /// Does nothing by default.
+    fn register_module(&self, _specifier: JsString, _module: Module) {}
+
+    /// Gets the module associated with the provided specifier.
+    ///
+    /// This is a convenience method for module loaders caching already parsed modules, since it
+    /// allows getting a cached module through the `&dyn ModuleLoader` provided by
+    /// [`Context::module_loader`].
+    ///
+    /// Returns `None` by default.
+    fn get_module(&self, _specifier: JsString) -> Option<Module> {
+        None
+    }
+
     /// Host hooks [`HostGetImportMetaProperties ( moduleRecord )`][meta] and
     /// [`HostFinalizeImportMeta ( importMeta, moduleRecord )`][final].
     ///
@@ -153,6 +173,12 @@ impl ModuleLoader for IdleModuleLoader {
 }
 
 /// A simple module loader that loads modules relative to a root path.
+///
+/// # Note
+///
+/// This loader only works by using the type methods [`SimpleModuleLoader::insert`] and
+/// [`SimpleModuleLoader::get`]. The utility methods on [`ModuleLoader`] don't work at the moment,
+/// but we'll unify both APIs in the future.
 #[derive(Debug)]
 pub struct SimpleModuleLoader {
     root: PathBuf,

boa_examples/src/bin/modules.rs

@@ -44,8 +44,9 @@ fn main() -> Result<(), Box<dyn Error>> {
         module.clone(),
     );
 
-    // The lifecycle of the module is tracked using promises, which can be a bit cumbersome
-    // for simple uses but that use case is better suited by the `Module::load_link_evaluate` method.
+    // The lifecycle of the module is tracked using promises which can be a bit cumbersome to use.
+    // If you just want to directly execute a module, you can use the `Module::load_link_evaluate`
+    // method to skip all the boilerplate.
     // This does the full version for demonstration purposes.
     //
     // parse -> load -> link -> evaluate