context: AppIfConfigured returns error; consider not-yet-provisioned modules (#6292)

* context: Add new `AppStrict()` method to avoid instantiating empty apps

* Rename AppStrict -> AppIfConfigured

---------

Co-authored-by: Matthew Holt <mholt@users.noreply.github.com>

context.go

@@ -453,23 +453,20 @@ func (ctx Context) App(name string) (any, error) {
 	return modVal, nil
 }
 
-// AppIfConfigured returns an app by its name if it has been
-// configured. Can be called instead of App() to avoid
-// instantiating an empty app when that's not desirable. If
-// the app has not been loaded, nil is returned.
-//
-// We return any type instead of the App type because it is not
-// intended for the caller of this method to be the one to start
-// or stop App modules. The caller is expected to assert to the
-// concrete type.
-func (ctx Context) AppIfConfigured(name string) any {
-	if ctx.cfg == nil {
-		// this can happen if the currently-active context
-		// is being accessed, but no config has successfully
-		// been loaded yet
-		return nil
+// AppIfConfigured is like App, but it returns an error if the
+// app has not been configured. This is useful when the app is
+// required and its absence is a configuration error, or when
+// the app is optional and you don't want to instantiate a
+// new one that hasn't been explicitly configured.
+func (ctx Context) AppIfConfigured(name string) (any, error) {
+	if app, ok := ctx.cfg.apps[name]; ok {
+		return app, nil
 	}
-	return ctx.cfg.apps[name]
+	appRaw := ctx.cfg.AppsRaw[name]
+	if appRaw == nil {
+		return nil, fmt.Errorf("app module %s is not configured", name)
+	}
+	return ctx.App(name)
 }
 
 // Storage returns the configured Caddy storage implementation.