FIX: Do not offer to save draft if invalid (#13863)

An invalid draft is the draft of a topic with a short title or body.
The client does not save these, but it will ask the client if they want
to save it. Even if the answer is 'yes', the draft is discarded. This
commit skips Save button for small drafts.

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

@@ -1189,9 +1189,6 @@ export default Controller.extend({
           },
           onSaveDraft: () => {
             this._saveDraft();
-            if (this.model.draftKey === Composer.NEW_TOPIC_KEY) {
-              this.currentUser.set("has_topic_draft", true);
-            }
             this.model.clearState();
             this.close();
             resolve();
@@ -1242,7 +1239,9 @@ export default Controller.extend({
           );
         }
       } else {
-        this._saveDraftPromise = model.saveDraft().finally(() => {
+        this._saveDraftPromise = model
+          .saveDraft(this.currentUser)
+          .finally(() => {
             this._lastDraftSaved = Date.now();
             this._saveDraftPromise = null;
           });

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

@@ -1165,38 +1165,56 @@ const Composer = RestModel.extend({
     return "";
   },
 
-  saveDraft() {
+  @discourseComputed(
+    "draftSaving",
+    "disableDrafts",
+    "canEditTitle",
+    "title",
+    "reply",
+    "titleLengthValid",
+    "replyLength",
+    "minimumPostLength"
+  )
+  canSaveDraft() {
     if (this.draftSaving) {
-      return Promise.resolve();
+      return false;
     }
 
     // Do not save when drafts are disabled
     if (this.disableDrafts) {
-      return Promise.resolve();
+      return false;
     }
 
     if (this.canEditTitle) {
       // Save title and/or post body
       if (isEmpty(this.title) && isEmpty(this.reply)) {
-        return Promise.resolve();
+        return false;
       }
 
       // Do not save when both title and reply's length are too small
       if (!this.titleLengthValid && this.replyLength < this.minimumPostLength) {
-        return Promise.resolve();
+        return false;
       }
     } else {
       // Do not save when there is no reply
       if (isEmpty(this.reply)) {
-        return Promise.resolve();
+        return false;
       }
 
       // Do not save when the reply's length is too small
       if (this.replyLength < this.minimumPostLength) {
-        return Promise.resolve();
+        return false;
       }
     }
 
+    return true;
+  },
+
+  saveDraft(user) {
+    if (!this.canSaveDraft) {
+      return Promise.resolve();
+    }
+
     this.setProperties({
       draftSaving: true,
       draftConflictUser: null,
@@ -1225,6 +1243,10 @@ const Composer = RestModel.extend({
             draftConflictUser: result.conflict_user,
           });
         } else {
+          if (this.draftKey === NEW_TOPIC_KEY && user) {
+            user.set("has_topic_draft", true);
+          }
+
           this.setProperties({
             draftStatus: null,
             draftConflictUser: null,

app/assets/javascripts/discourse/app/templates/modal/discard-draft.hbs

@@ -6,6 +6,8 @@
 
 <div class="modal-footer">
   {{d-button icon="far-trash-alt" label="post.cancel_composer.discard" class="btn-danger discard-draft" action=(action "destroyDraft")}}
+  {{#if model.canSaveDraft}}
     {{d-button label="post.cancel_composer.save_draft" class="save-draft" action=(action "saveDraftAndClose")}}
+  {{/if}}
   {{d-button label="post.cancel_composer.keep_editing" class="keep-editing" action=(action "dismissModal")}}
 </div>

app/assets/javascripts/discourse/tests/acceptance/composer-test.js

@@ -999,4 +999,15 @@ acceptance("Composer", function (needs) {
     await fillIn(".d-editor-input", "@staff");
     assert.ok(exists(".composer-popup"), "Shows the 'group_mentioned' notice");
   });
+
+  test("Does not save invalid draft", async function (assert) {
+    this.siteSettings.min_first_post_length = 20;
+
+    await visit("/");
+    await click("#create-topic");
+    await fillIn("#reply-title", "Something");
+    await fillIn(".d-editor-input", "Something");
+    await click(".save-or-cancel .cancel");
+    assert.notOk(exists(".discard-draft-modal .save-draft"));
+  });
 });