Change hashtag suggestion to prefer personal history capitalization (#34070)

app/javascript/mastodon/reducers/compose.js

@@ -242,12 +242,26 @@ const expiresInFromExpiresAt = expires_at => {
 
 const mergeLocalHashtagResults = (suggestions, prefix, tagHistory) => {
   prefix = prefix.toLowerCase();
+
   if (suggestions.length < 4) {
     const localTags = tagHistory.filter(tag => tag.toLowerCase().startsWith(prefix) && !suggestions.some(suggestion => suggestion.type === 'hashtag' && suggestion.name.toLowerCase() === tag.toLowerCase()));
-    return suggestions.concat(localTags.slice(0, 4 - suggestions.length).toJS().map(tag => ({ type: 'hashtag', name: tag })));
-  } else {
-    return suggestions;
+    suggestions = suggestions.concat(localTags.slice(0, 4 - suggestions.length).toJS().map(tag => ({ type: 'hashtag', name: tag })));
   }
+
+  // Prefer capitalization from personal history, unless personal history is all lower-case
+  const fixSuggestionCapitalization = (suggestion) => {
+    if (suggestion.type !== 'hashtag')
+      return suggestion;
+
+    const tagFromHistory = tagHistory.find((tag) => tag.localeCompare(suggestion.name, undefined, { sensitivity: 'accent' }) === 0);
+
+    if (!tagFromHistory || tagFromHistory.toLowerCase() === tagFromHistory)
+      return suggestion;
+
+    return { ...suggestion, name: tagFromHistory };
+  };
+
+  return suggestions.map(fixSuggestionCapitalization);
 };
 
 const normalizeSuggestions = (state, { accounts, emojis, tags, token }) => {