Fix reactive display name disambiguation by aditya-cherukuru · Pull Request #5135 · matrix-org/matrix-js-sdk

aditya-cherukuru · 2026-01-12T06:20:21Z

Problem

Display name disambiguation (showing user ID suffix like Alice (@alice:server)) was not updating reactively when room members changed their display names.

Steps to reproduce:

Alice, Bob, Charlie are in a room
Bob changes display name to "Alice"
Expected: Disambiguation flags should update for all members sharing the name
Actual: Disambiguation flags only update after a page refresh

Root Cause:
updateDisplayNameCache() in room-state.ts correctly updates the display name → userId mapping, but did NOT recalculate the disambiguate flag for other members who share (or previously shared) that display name.

Solution

Track which display names are affected by a change (both old name and new name)
After updating the cache, call new method recalculateDisambiguationForDisplayNames()
This recalculates disambiguation for all members with those affected names
Emit RoomState.Members event so UI updates immediately

Testing

Added 3 unit tests covering the fix:

✅ should disambiguate existing member when another member changes to the same name
✅ should un-disambiguate member when conflicting member changes to different name
✅ should emit RoomState.members for affected members when disambiguation changes

Run with: yarn test -- --testPathPattern=room-state.spec.ts -t "reactive"

What this fixes

Scenario	Before	After
Bob changes name to "Alice"	Disambiguation not updated reactively ❌	Updates immediately ✅
Bob changes name from "Alice" to "Bob"	Original Alice stays disambiguated ❌	Gets un-disambiguated ✅

Remaining work (separate PR)

This PR addresses reactive updates for name changes. A separate issue exists for parted users (element-hq/element-meta#2850):

When a user with a clashing name leaves the room, the remaining user should be un-disambiguated
Will be addressed in a follow-up PR

Related to element-hq/element-web#31551

Related issues:

Disambiguated names only dis-disambiguate after a refresh Disambiguated names only dis-disambiguate after a refresh element-hq/element-web#468
MXID disambiguation stays visible indefinitely long MXID disambiguation stays visible indefinitely long element-hq/element-web#4795

Checklist

Tests written for new code
Linter and other CI checks pass
Sign-off given on the changes

Signed-off-by: @aditya-cherukuru cherukuru.aditya01@gmail.com

When a room member changes their display name, recalculate the disambiguation flag for all other members who share (or previously shared) that display name. This ensures that the 'disambiguate' flag is updated reactively when display name conflicts appear or are resolved. Fixes element-hq/element-web#468 Fixes element-hq/element-web#4795 Fixes element-hq/element-web#31551 Signed-off-by: aditya-cherukuru <cherukuru.aditya01@gmail.com>

dbkr · 2026-01-12T12:13:41Z

If you believe this is a security fix, this should have been submitted privately as per https://github.com/matrix-org/matrix-js-sdk?tab=security-ov-file - had this been a real security issue, you would have just disclosed it publicly, potentially causing a major security incident (even though the original bug was public, you gave specific steps on how to exploit the bug).

However, your repro steps describe Alice (the real Alice) sending a message and her display name not showing with disambiguation. This might be a little confusing but Charlie (the imposter Alice) would still be shown with the disambiguation showing he wasn't really Alice. So, if I understand correctly I think your AI might have got a little confused.

You've also marked this as fixing 31551 but then said that it's only a partial fix and there's follow-up work coming. This special syntax will cause the bug to be closed when the PR is merged so if it doesn't completely fix it, please just say "For" or something instead of "Fixes", or create a sub-issue and mark it as fixing that.

aditya-cherukuru · 2026-01-12T12:36:11Z

Thanks for the review @dbkr!

apologies for the confusion. I was echoing the "security implications" mention from the original issue but yeah, framing it as a full security bug here definitely sends the wrong signal about disclosure. Still learning the ropes with OSS contributions, so I appreciate the heads up. I'll tone it down to a UX/confusion issue which is what it really is.
I'll switch to Relates to since the parted users edge case still needs separate work.

Updating the description now. Let me know if the actual logic in room-state.ts looks reasonable to you!

dbkr · 2026-01-12T13:43:29Z

changelog.d/5135.bugfix

@@ -0,0 +1 @@
+Fix reactive display name disambiguation to update immediately when room members change their display names.


We don't use towncrier so you don't need this file.

dbkr · 2026-01-12T14:01:43Z

src/models/room-state.ts

    private updateDisplayNameCache(userId: string, displayName: string): void {
        const oldName = this.userIdsToDisplayNames[userId];
+
+        // Track which display names are affected by this change so we can


I think doing this in a function called, updateDisplayNameCache is confusing as this function is now doing more than just what its name implies. It might make more sense to do it a level above, perhaps? This might also allow it be be done differently as I'm finding the recalculateDisambiguationForDisplayNames to be quite specific and more like just a chunk of one large function moved out to a separate function rather than a reusable unit of functionality.

dbkr · 2026-01-12T14:06:56Z

src/models/room-state.ts

+                    // Recalculate disambiguation by re-setting the membership event.
+                    // This will call shouldDisambiguate() with the updated room state.
+                    const oldName = member.name;
+                    member.setMembershipEvent(member.events.member, this);


I don't love doing this by setting the same membership event again. Feels like if we want to update the disambiguation at other times, we should restructure to call it directly rather than faking things changing on that member.

- Added updateDisambiguation() method to RoomMember for direct disambiguation recalculation - Moved affected display name tracking to setStateEvents() instead of updateDisplayNameCache() - Removed setMembershipEvent() hack, now calls updateDisambiguation() directly Signed-off-by: aditya-cherukuru <cherukuru.aditya01@gmail.com>

aditya-cherukuru · 2026-01-13T05:49:04Z

Thanks for the guidance @dbkr. Your comments really made me see the code structure in a different way, I learnt a lot from this review. I've addressed the feedback and cleaned up the architecture as suggested. Will continue to get better!

dbkr · 2026-01-13T15:31:53Z

src/models/room-state.ts

+                    }
+                }
+            }
+        }


This is looking much nicer, thanks. One thing though: your previous logic excluded the user whose name was being changed. Do we need to do that here too to avoid duplicate events?

aditya-cherukuru · 2026-01-15T04:50:13Z

you're right! since the main loop already processes the user changing their name, my disambiguation loop would be doing redundant work for them.

I'll add a check to track which userIds were processed in the main batch and exclude them from the disambiguation pass. This ensures we only emit extra events for the other affected members, not duplicates.

Pushing the fix now.

Signed-off-by: aditya-cherukuru <cherukuru.aditya01@gmail.com>

Copilot

Pull request overview

This PR fixes a bug where display name disambiguation (showing user ID suffix like Alice (@alice:server)) did not update reactively when room members changed their display names. The fix ensures that when one member changes their name to match (or stop matching) another member's name, all affected members' disambiguation flags are recalculated and UI events are emitted immediately.

Changes:

Added tracking of affected display names during membership event processing
Implemented recalculation of disambiguation flags for all members with affected display names
Added new recalculateDisambiguatedName method to RoomMember class for on-demand disambiguation updates

Reviewed changes

Copilot reviewed 3 out of 3 changed files in this pull request and generated no comments.

File	Description
src/models/room-state.ts	Added logic to track display name changes and recalculate disambiguation for affected members after processing membership events
src/models/room-member.ts	Added new `recalculateDisambiguatedName` method to recalculate disambiguation flag and emit Name event when needed
spec/unit/room-state.spec.ts	Added three comprehensive tests covering disambiguation addition, removal, and event emission

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dbkr · 2026-02-05T11:23:36Z

Ah, the test failure here is legitimate and is this exact change being reflected in a screenshot of the member list in Element Web. You'll need to make a corresponding element-web PR to update the screenshot. If you use the same branch name it might pick up your fixed js-sdk so the tests pass there, although I'm not sure this will work from a fork. If not, we'll have to override the checks.

This PR updates the Playwright screenshot tests to reflect the changes from matrix-js-sdk PR element-hq#5135, which fixes reactive display name disambiguation. The screenshot will be updated based on CI test results to show the correct disambiguation behavior when multiple room members share the same display name. Related: matrix-org/matrix-js-sdk#5135

aditya-cherukuru · 2026-02-10T09:22:00Z

Hi @dbkr,

I've opened the companion Element Web PR to update the visual snapshots: element-hq/element-web#32431

I used the same branch name (fix/reactive-display-name-disambiguation) so the CI should pick up the SDK changes automatically. Currently waiting for the CI to run so I can grab the Linux-generated snapshots and push them to that branch.

aditya-cherukuru · 2026-02-12T10:10:27Z

hi @dbkr
Just a heads up, the companion Element Web PR (element-hq/element-web#32431) is now passing all tests (visual regression and unit tests).

The screenshot updates there confirm the fix is working as expected. This should be ready to merge whenever you are!

* Update screenshot for reactive display name disambiguation This PR updates the Playwright screenshot tests to reflect the changes from matrix-js-sdk PR #5135, which fixes reactive display name disambiguation. The screenshot will be updated based on CI test results to show the correct disambiguation behavior when multiple room members share the same display name. Related: matrix-org/matrix-js-sdk#5135 * Update member list screenshot for reactive disambiguation * Retry CI for flaky MatrixChat timeout

dbkr · 2026-02-12T14:22:48Z

Bypassing checks as the complement crypto tests are broken with pnpm and CI is broken without this.

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Exclude processed members from disambiguation loop

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Signed-off-by: aditya-cherukuru <cherukuru.aditya01@gmail.com>

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Update screenshot for reactive display name disambiguation element-hq/element-web#32431

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