feat: define sugar decorators for extensions

examples/greeter-extension/src/greeter-extension-point.ts

@@ -3,9 +3,9 @@
 // This file is licensed under the MIT License.
 // License text available at https://opensource.org/licenses/MIT
 
-import {inject, filterByTag, Getter} from '@loopback/context';
-import {Greeter} from './types';
+import {Getter} from '@loopback/context';
 import chalk from 'chalk';
+import {configuration, extensions, Greeter} from './types';
 
 /**
  * Options for the greeter extension point
@@ -23,16 +23,13 @@ export class GreeterExtensionPoint {
      * Inject a getter function to fetch greeters (bindings tagged with
      * 'greeter')
      */
-    @inject.getter(filterByTag({extensionPoint: 'greeter'}))
+    @extensions('greeter') // Sugar for @inject.getter(filterByTag({extensionPoint: 'greeter'}))
     private greeters: Getter<Greeter[]>,
     /**
      * An extension point should be able to receive its options via dependency
      * injection.
-     *
-     * FIXME (rfeng): A shortcut such as `@inject.config` is desired to avoid
-     * the hard-coded binding key
      */
-    @inject('greeter-extension-point.options', {optional: true})
+    @configuration() // Sugar for @inject('greeter-extension-point.options', {optional: true})
     private options?: GreeterExtensionPointOptions,
   ) {}
 

examples/greeter-extension/src/types.ts

@@ -3,7 +3,12 @@
 // This file is licensed under the MIT License.
 // License text available at https://opensource.org/licenses/MIT
 
-import {BindingTemplate, BindingScope} from '@loopback/context';
+import {
+  BindingScope,
+  BindingTemplate,
+  filterByTag,
+  inject,
+} from '@loopback/context';
 
 /**
  * Typically an extension point defines an interface as the contract for
@@ -14,9 +19,48 @@ export interface Greeter {
   greet(name: string): string;
 }
 
+/**
+ * A factory function to create binding template for extensions of the given
+ * extension point
+ * @param extensionPoint Name/id of the extension point
+ */
+export function extensionFor(extensionPoint: string): BindingTemplate {
+  return binding =>
+    binding.inScope(BindingScope.SINGLETON).tag({extensionPoint});
+}
+
 /**
  * A binding template for greeter extensions
- * @param binding
  */
-export const asGreeter: BindingTemplate = binding =>
-  binding.inScope(BindingScope.SINGLETON).tag({extensionPoint: 'greeter'});
+export const asGreeter: BindingTemplate = extensionFor('greeter');
+
+/**
+ * Shortcut to inject extensions for the given extension point. To be promoted
+ * as `@extensions` in `@loopback/core` module.
+ *
+ * @param extensionPoint Name/id of the extension point
+ */
+export function extensions(extensionPoint: string) {
+  return inject.getter(filterByTag({extensionPoint}));
+}
+
+/**
+ * Shortcut to inject configuration for the target binding. To be promoted
+ * as `@inject.config` in `@loopback/context` module.
+ */
+export function configuration() {
+  return inject(
+    '',
+    {decorator: '@inject.config', optional: true},
+    (ctx, injection, session?) => {
+      if (!session) return undefined;
+      // Find the key of the target binding
+      if (!session.currentBinding) return undefined;
+      const key = session.currentBinding!.key;
+      return ctx.get(`${key}.options`, {
+        session,
+        optional: injection.metadata && injection.metadata.optional,
+      });
+    },
+  );
+}