The highlighted mention does not change with the cursor movement

[kbecciv]

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Version Number: 1.3.86.0
Reproducible in staging?: y
Reproducible in production?: n
If this was caught during regression testing, add the test name, ID and link from TestRail:
Email or phone of affected tester (no customers):
Logs: https://stackoverflow.com/c/expensify/questions/4856
Expensify/Expensify Issue URL:
Issue reported by: @daveSeife
Slack conversation: https://expensify.slack.com/archives/C049HHMV9SM/p1697640197267559

Action Performed:

1. Go to any chat
2. Write @ and the first few letters of any user(Eg: @dave)
3. Move the cursor through the name.

Expected Result:

The highlighted mention changes with the cursor movement

Actual Result:

The highlighted mention does not change with the cursor movement

Workaround:

Unknown

Platforms:

Which of our officially supported platforms is this issue occurring on?

• Android: Native
• Android: mWeb Chrome
• iOS: Native
• iOS: mWeb Safari
• MacOS: Chrome / Safari
• MacOS: Desktop

Screenshots/Videos

Android: Native

Screen_Recording_20231018_124932_New.Expensify.mp4

Android: mWeb Chrome

Screen_Recording_20231018_125037_Chrome.mp4

iOS: Native

RPReplay_Final1697647945.MP4

iOS: mWeb Safari

RPReplay_Final1697640399.MP4

MacOS: Chrome / Safari

T162macchrome-1.mention.mp4

MacOS: Desktop

requested QA team to verify

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[OSBotify]

👋 Friendly reminder that deploy blockers are time-sensitive ⏱ issues! Check out the open StagingDeployCash deploy checklist to see the list of PRs included in this release, then work quickly to do one of the following:

1. Identify the pull request that introduced this issue and revert it.
2. Find someone who can quickly fix the issue.
3. Fix the issue yourself.

[melvin-bot]

Triggered auto assignment to @stitesExpensify (Engineering), see https://stackoverflow.com/c/expensify/questions/4319 for more details.

[Pujan92]

Proposal

Please re-state the problem that we are trying to solve in this issue.

Highlighted mention doesn't change on selection change

What is the root cause of that problem?

Seems the regex is given a bad const from long NEW_LINE_OR_WHITE_SPACE_OR_EMOJI which was undefined, so the search func on string gives 0 and not -1. When this PR is updated with the available regex the issue persists due to old incorrect implementation.

What changes do you think we should make in order to solve the problem?

As prefix is used for calculating the suggestions, we can use selectionEnd for the leftString here.

App/src/pages/home/report/ReportActionCompose/SuggestionMention.js

Line 201 in 4a1e2b3

const leftString = value.substring(0, suggestionEndIndex);

const leftString = value.substring(0, selectionEnd);

[dummy-1111]

This is a regression from this PR #29239

[paultsimura]

This is not a bug. As discussed here, the behavior described in the issue is expected.
It was also stated in the PR description here: #29239