Uppercase letters in username break reachable mention check in composer

zogstrip · April 23, 2026, 8:34am

The correct fix is

github.com/discourse/discourse

DEV: Use ActiveRecord normalizes for username lookups (#37177)

main ← fix/unicode-username-lookups

closed 02:15AM - 14 Apr 26 UTC

ZogStriP

+159 -164

Leverages Rails' built-in `normalizes` feature to handle username normalization …consistently throughout the codebase. When you call `User.where(username_lower: value)` or `find_by(username_lower: value)`, ActiveRecord now automatically normalizes the input value. Key changes: - Adds `normalizes :username` (unicode normalize) and `normalizes :username_lower` (unicode normalize + downcase) to User - Adds `normalizes :email` (strip + downcase) to UserEmail - Removes manual `.downcase` and `.map(&:downcase)` calls before AR queries - Adds `User#matches_username?` method for comparing usernames - Simplifies `filter_by_username` and `filter_by_username_or_email` scopes to use `ILIKE ANY(ARRAY[?])` instead of branching on array vs single value - Updates `filter_by_username` to normalize input for ILIKE patterns - Updates `find_by_username` to rely on AR normalization - Fixes a SQL injection vulnerability in search user ordering - Uses before_save callback for username_lower assignment to ensure it runs even when validation is skipped (e.g., finish installation flow) - Adds shoulda matcher tests for username normalizations The `normalize_username` class method is kept for cases where AR can't help: raw SQL queries, ILIKE patterns, and direct comparisons. Ref - https://meta.discourse.org/t/393646

but it’s too big a change than I’m confortable merging at this point

Instead, I’m going to fix each “endpoints” one by one to make it simpler to review and less risky.

Here’s first step

github.com/discourse/discourse

FIX: Make composer mention reachability checks case-insensitive (#39482)

main ← fix-composer-mention-case-sensitivity

opened 08:30AM - 23 Apr 26 UTC

ZogStriP

+200 -190

Mentioning `@SomeUser` in a topic the mentioned user can't see (restricted categ…ory, PM they aren't invited to, topic they've muted) silently skipped the "cannot see this mention" warning popup whenever the typed name contained any uppercase letter. Same for mixed-case group names. Mention validation itself worked because of an existing client-side `.toLowerCase()` workaround, so the bug was easy to miss — mentions stayed `<a class="mention">` but the user got no signal that the mentioned account wouldn't actually be notified. Server side, `ComposerController#mentions` builds its `users` lookup keyed by `username_lower` and `groups` keyed by the case-preserved DB `name`, then iterated `@names.each { |n| users[n] || groups[n] }` without normalizing — so any uppercase character missed both hashes and `user_reasons`/`group_reasons` came back empty. Four downstream group helpers (`mentionable_group_ids`, `members_visible_group_ids`, `topic_allowed_group_ids`, `visible_group_ids_for_allowed_check`) used `where(name: @names)` which is case-sensitive in PostgreSQL, and the `SiteSetting.here_mention` membership test compared raw strings. Client side, `link-mentions.js` cached `foundUsers` / `userReasons` / `foundGroups` / `groupReasons` by the case as typed, and the prosemirror `mention.js` warning lookup did `response.users.includes(name)` plus `response.user_reasons[name]` with the original case — both of which the server only ever returned in the casing it had on hand. Normalize the controller's `@names` and `@allowed_names` once at the top of the action, switch all four group helpers to `LOWER(name) IN (?)`, lower-case the response keys, and lower-case client caches and lookups end to end. Also extract the inline notified-member query into `already_notified_member_count` and tighten the request specs to cover users, mentionable groups, group reasons in PMs, and `allowed_names` (both user and group branches) with mixed-case input. https://meta.discourse.org/t/401292

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Uppercase letters in username break reachable mention check in composer

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