DEV: Add composer-service-cannot-submit-post transformer (#30903)

- Add `composer-service-cannot-submit-post` transformer to allow for disabling submit based on custom conditions
- Add tests for transformer
- Add a couple helpful appEvents, that plugins can use add custom error popups to plugin-defined fields.

app/assets/javascripts/discourse/app/lib/transformer/registry.js

@@ -9,6 +9,7 @@ export const VALUE_TRANSFORMERS = Object.freeze([
   // use only lowercase names
   "category-description-text",
   "category-display-name",
+  "composer-service-cannot-submit-post",
   "header-notifications-avatar-size",
   "home-logo-href",
   "home-logo-image-url",

app/assets/javascripts/discourse/app/services/composer.js

@@ -29,6 +29,7 @@ import getURL from "discourse/lib/get-url";
 import { disableImplicitInjections } from "discourse/lib/implicit-injections";
 import { wantsNewWindow } from "discourse/lib/intercept-click";
 import { emojiUnescape } from "discourse/lib/text";
+import { applyValueTransformer } from "discourse/lib/transformer";
 import {
   authorizesOneOrMoreExtensions,
   uploadIcon,
@@ -1008,13 +1009,21 @@ export default class ComposerService extends Service {
     }
 
     const composer = this.model;
+    const cantSubmitPost = applyValueTransformer(
+      "composer-service-cannot-submit-post",
+      composer?.cantSubmitPost,
+      { model: composer }
+    );
 
-    if (composer?.cantSubmitPost) {
+    if (cantSubmitPost) {
       if (composer?.viewFullscreen) {
         this.toggleFullscreen();
       }
 
       this.set("lastValidatedAt", Date.now());
+      this.appEvents.trigger("composer-service:last-validated-at-updated", {
+        model: composer,
+      });
       return;
     }
 
@@ -1752,6 +1761,7 @@ export default class ComposerService extends Service {
 
   clearLastValidatedAt() {
     this.set("lastValidatedAt", null);
+    this.appEvents.trigger("composer-service:last-validated-at-cleared");
   }
 }
 

app/assets/javascripts/discourse/tests/acceptance/transformers/composer-service-cant-submit-post-test.js

@@ -0,0 +1,49 @@
+import { click, fillIn, visit } from "@ember/test-helpers";
+import { test } from "qunit";
+import { withPluginApi } from "discourse/lib/plugin-api";
+import { acceptance } from "discourse/tests/helpers/qunit-helpers";
+
+acceptance("composer-service-cannot-submit-post transformer", function (needs) {
+  needs.user();
+  needs.settings({
+    allow_uncategorized_topics: true,
+  });
+
+  test("applying a value transformation - disable submit", async function (assert) {
+    withPluginApi("1.34.0", (api) => {
+      api.registerValueTransformer(
+        "composer-service-cannot-submit-post",
+        () => {
+          // Return true -- explicitly block submission!
+          return true;
+        }
+      );
+    });
+
+    await visit("/new-topic?title=topic title that is pretty long");
+    await fillIn(".d-editor-input", "this is the *content* of a post");
+    await click(".submit-panel .create");
+
+    assert.dom(".d-editor-input").exists("composer is still open");
+  });
+
+  test("applying a value transformation - allow submission", async function (assert) {
+    withPluginApi("1.34.0", (api) => {
+      api.registerValueTransformer(
+        "composer-service-cannot-submit-post",
+        ({ value }) => {
+          // Return value (which should be `false`, as we have a valid new topic to create)
+          return value;
+        }
+      );
+    });
+
+    await visit("/new-topic?title=topic title that is pretty long");
+    await fillIn(".d-editor-input", "this is the *content* of a post");
+    await click(".submit-panel .create");
+
+    assert
+      .dom(".d-editor-input")
+      .doesNotExist("closes the composer on successful creation");
+  });
+});