feat(context): fix generic typing for BindingFilter

packages/context/src/binding-filter.ts

@@ -10,16 +10,28 @@ import {BindingAddress} from './binding-key';
  * A function that filters bindings. It returns `true` to select a given
  * binding.
  */
-export type BindingFilter<ValueType = unknown> = (
-  binding: Readonly<Binding<ValueType>>,
-) => boolean;
+export type BindingFilter = (binding: Readonly<Binding<unknown>>) => boolean;
+
+export type BindingFilterGuard<T = unknown> = (
+  binding: Readonly<Binding<unknown>>,
+) => binding is Readonly<Binding<T>>;
+
+/**
+ * A helper function to cast a `BindingFilter` to a type guard
+ * @param filter A filter function
+ */
+export function asBindingFilterGuard<T = unknown>(
+  filter: BindingFilter,
+): BindingFilterGuard<T> {
+  return filter as BindingFilterGuard<T>;
+}
 
 /**
  * Select binding(s) by key or a filter function
  */
 export type BindingSelector<ValueType = unknown> =
   | BindingAddress<ValueType>
-  | BindingFilter<ValueType>;
+  | BindingFilter;
 
 /**
  * Type guard for binding address
@@ -35,7 +47,9 @@ export function isBindingAddress(
  * Create a binding filter for the tag pattern
  * @param tagPattern Binding tag name, regexp, or object
  */
-export function filterByTag(tagPattern: BindingTag | RegExp): BindingFilter {
+export function filterByTag<T = unknown>(
+  tagPattern: BindingTag | RegExp,
+): BindingFilter {
   if (typeof tagPattern === 'string' || tagPattern instanceof RegExp) {
     const regexp =
       typeof tagPattern === 'string'
@@ -58,7 +72,7 @@ export function filterByTag(tagPattern: BindingTag | RegExp): BindingFilter {
  * Create a binding filter from key pattern
  * @param keyPattern Binding key/wildcard, regexp, or a filter function
  */
-export function filterByKey(
+export function filterByKey<T = unknown>(
   keyPattern?: string | RegExp | BindingFilter,
 ): BindingFilter {
   if (typeof keyPattern === 'string') {

packages/context/src/context-view.ts

@@ -42,7 +42,7 @@ export class ContextView<T = unknown> extends EventEmitter
 
   constructor(
     protected readonly context: Context,
-    public readonly filter: BindingFilter<T>,
+    public readonly filter: BindingFilter,
   ) {
     super();
   }
@@ -161,10 +161,10 @@ export class ContextView<T = unknown> extends EventEmitter
  */
 export function createViewGetter<T = unknown>(
   ctx: Context,
-  bindingFilter: BindingFilter<T>,
+  bindingFilter: BindingFilter,
   session?: ResolutionSession,
 ): Getter<T[]> {
-  const view = new ContextView(ctx, bindingFilter);
+  const view = new ContextView<T>(ctx, bindingFilter);
   view.open();
   return view.asGetter(session);
 }

packages/context/src/context.ts

@@ -7,7 +7,12 @@ import * as debugFactory from 'debug';
 import {EventEmitter} from 'events';
 import {v1 as uuidv1} from 'uuid';
 import {Binding, BindingTag} from './binding';
-import {BindingFilter, filterByKey, filterByTag} from './binding-filter';
+import {
+  asBindingFilterGuard,
+  BindingFilter,
+  filterByKey,
+  filterByTag,
+} from './binding-filter';
 import {BindingAddress, BindingKey} from './binding-key';
 import {
   ContextEventObserver,
@@ -38,7 +43,11 @@ if (!Symbol.asyncIterator) {
   // tslint:disable-next-line:no-any
   (Symbol as any).asyncIterator = Symbol.for('Symbol.asyncIterator');
 }
-// This import must happen after the polyfill
+/**
+ * This following import must happen after the polyfill. The `auto-import` by
+ * an IDE such as VSCode may move the import before the polyfill. It must be
+ * fixed manually.
+ */
 import {iterator, multiple} from 'p-event';
 
 const debug = debugFactory('loopback:context');
@@ -518,8 +527,8 @@ export class Context extends EventEmitter {
   find<ValueType = BoundValue>(
     pattern?: string | RegExp | BindingFilter,
   ): Readonly<Binding<ValueType>>[] {
-    const bindings: Readonly<Binding>[] = [];
-    const filter = filterByKey(pattern);
+    const bindings: Readonly<Binding<ValueType>>[] = [];
+    const filter = asBindingFilterGuard<ValueType>(filterByKey(pattern));
 
     for (const b of this.registry.values()) {
       if (filter(b)) bindings.push(b);