Preserve hashtag casing in web UI hashtag history (#8394)

Fix #8241

app/javascript/mastodon/actions/compose.js

@@ -130,7 +130,7 @@ export function submitCompose() {
         'Idempotency-Key': getState().getIn(['compose', 'idempotencyKey']),
       },
     }).then(function (response) {
-      dispatch(insertIntoTagHistory(response.data.tags));
+      dispatch(insertIntoTagHistory(response.data.tags, status));
       dispatch(submitComposeSuccess({ ...response.data }));
 
       // To make the app more responsive, immediately get the status into the columns
@@ -390,13 +390,13 @@ export function hydrateCompose() {
   };
 }
 
-function insertIntoTagHistory(tags) {
+function insertIntoTagHistory(recognizedTags, text) {
   return (dispatch, getState) => {
     const state = getState();
     const oldHistory = state.getIn(['compose', 'tagHistory']);
     const me = state.getIn(['meta', 'me']);
-    const names = tags.map(({ name }) => name);
-    const intersectedOldHistory = oldHistory.filter(name => !names.includes(name));
+    const names = recognizedTags.map(tag => text.match(new RegExp(`#${tag.name}`, 'i'))[0].slice(1));
+    const intersectedOldHistory = oldHistory.filter(name => names.findIndex(newName => newName.toLowerCase() === name.toLowerCase()) === -1);
 
     names.push(...intersectedOldHistory.toJS());
 

app/javascript/mastodon/reducers/compose.js

@@ -131,7 +131,7 @@ const updateSuggestionTags = (state, token) => {
 
   return state.merge({
     suggestions: state.get('tagHistory')
-      .filter(tag => tag.startsWith(prefix))
+      .filter(tag => tag.toLowerCase().startsWith(prefix.toLowerCase()))
       .slice(0, 4)
       .map(tag => '#' + tag),
     suggestion_token: token,