Show error when submitting empty post rather than failing silently (#36650)

app/javascript/mastodon/actions/compose.js

@@ -5,6 +5,7 @@ import { throttle } from 'lodash';
 
 import api from 'mastodon/api';
 import { browserHistory } from 'mastodon/components/router';
+import { countableText } from 'mastodon/features/compose/util/counter';
 import { search as emojiSearch } from 'mastodon/features/emoji/emoji_mart_search_light';
 import { tagHistory } from 'mastodon/settings';
 
@@ -88,6 +89,7 @@ const messages = defineMessages({
   open: { id: 'compose.published.open', defaultMessage: 'Open' },
   published: { id: 'compose.published.body', defaultMessage: 'Post published.' },
   saved: { id: 'compose.saved.body', defaultMessage: 'Post saved.' },
+  blankPostError: { id: 'compose.error.blank_post', defaultMessage: 'Post can\'t be blank.' },
 });
 
 export const ensureComposeIsVisible = (getState) => {
@@ -197,7 +199,15 @@ export function submitCompose(successCallback) {
     const hasQuote = !!getState().getIn(['compose', 'quoted_status_id']);
     const spoiler_text = getState().getIn(['compose', 'spoiler']) ? getState().getIn(['compose', 'spoiler_text'], '') : '';
 
-    if (!(status?.length || media.size !== 0 || (hasQuote && spoiler_text?.length))) {
+    const fulltext = `${spoiler_text ?? ''}${countableText(status ?? '')}`;
+    const hasText = fulltext.trim().length > 0;
+
+    if (!(hasText || media.size !== 0 || (hasQuote && spoiler_text?.length))) {
+      dispatch(showAlert({
+        message: messages.blankPostError,
+      }));
+      dispatch(focusCompose());
+
       return;
     }
 

app/javascript/mastodon/features/compose/components/compose_form.jsx

@@ -123,11 +123,10 @@ class ComposeForm extends ImmutablePureComponent {
   };
 
   canSubmit = () => {
-    const { isSubmitting, isChangingUpload, isUploading, anyMedia, maxChars } = this.props;
+    const { isSubmitting, isChangingUpload, isUploading, maxChars } = this.props;
     const fulltext = this.getFulltextForCharacterCounting();
-    const isOnlyWhitespace = fulltext.length !== 0 && fulltext.trim().length === 0;
 
-    return !(isSubmitting || isUploading || isChangingUpload || length(fulltext) > maxChars || (isOnlyWhitespace && !anyMedia));
+    return !(isSubmitting || isUploading || isChangingUpload || length(fulltext) > maxChars);
   };
 
   handleSubmit = (e) => {

app/javascript/mastodon/locales/en.json

@@ -196,6 +196,7 @@
   "community.column_settings.local_only": "Local only",
   "community.column_settings.media_only": "Media Only",
   "community.column_settings.remote_only": "Remote only",
+  "compose.error.blank_post": "Post can't be blank.",
   "compose.language.change": "Change language",
   "compose.language.search": "Search languages...",
   "compose.published.body": "Post published.",