DEV: Make `modifyClass` native class-aware, add tests (#16111)

app/assets/javascripts/discourse/app/lib/plugin-api.js

@@ -225,7 +225,15 @@ class PluginApi {
 
     if (canModify(klass, "member", resolverName, changes)) {
       delete changes.pluginId;
-      klass.class.reopen(changes);
+
+      if (klass.class.reopen) {
+        klass.class.reopen(changes);
+      } else {
+        Object.defineProperties(
+          klass.class.prototype || klass.class,
+          Object.getOwnPropertyDescriptors(changes)
+        );
+      }
     }
 
     return klass;

app/assets/javascripts/discourse/tests/unit/lib/plugin-api-test.js

@@ -0,0 +1,87 @@
+import { discourseModule } from "discourse/tests/helpers/qunit-helpers";
+import { test } from "qunit";
+import EmberObject from "@ember/object";
+import discourseComputed from "discourse-common/utils/decorators";
+import { withPluginApi } from "discourse/lib/plugin-api";
+
+discourseModule("Unit | Utility | plugin-api", function () {
+  test("modifyClass works with classic Ember objects", function (assert) {
+    const TestThingy = EmberObject.extend({
+      @discourseComputed
+      prop() {
+        return "hello";
+      },
+    });
+
+    this.registry.register("test-thingy:main", TestThingy);
+
+    withPluginApi("1.1.0", (api) => {
+      api.modifyClass("test-thingy:main", {
+        pluginId: "plugin-api-test",
+
+        @discourseComputed
+        prop() {
+          return `${this._super(...arguments)} there`;
+        },
+      });
+    });
+
+    const thingy = this.container.lookup("test-thingy:main");
+    assert.strictEqual(thingy.prop, "hello there");
+  });
+
+  test("modifyClass works with native class Ember objects", function (assert) {
+    class NativeTestThingy extends EmberObject {
+      @discourseComputed
+      prop() {
+        return "howdy";
+      }
+    }
+
+    this.registry.register("native-test-thingy:main", NativeTestThingy);
+
+    withPluginApi("1.1.0", (api) => {
+      api.modifyClass("native-test-thingy:main", {
+        pluginId: "plugin-api-test",
+
+        @discourseComputed
+        prop() {
+          return `${this._super(...arguments)} partner`;
+        },
+      });
+    });
+
+    const thingy = this.container.lookup("native-test-thingy:main");
+    assert.strictEqual(thingy.prop, "howdy partner");
+  });
+
+  test("modifyClass works with native classes", function (assert) {
+    class ClassTestThingy {
+      get keep() {
+        return "hey!";
+      }
+
+      get prop() {
+        return "top of the morning";
+      }
+    }
+
+    this.registry.register("class-test-thingy:main", new ClassTestThingy(), {
+      instantiate: false,
+    });
+
+    withPluginApi("1.1.0", (api) => {
+      api.modifyClass("class-test-thingy:main", {
+        pluginId: "plugin-api-test",
+
+        get prop() {
+          return "g'day";
+        },
+      });
+    });
+
+    const thingy = this.container.lookup("class-test-thingy:main");
+    assert.strictEqual(thingy.keep, "hey!");
+    assert.strictEqual(thingy.prop, "g'day");
+  });
+});