@Shizhao: Please copy the text in the yellow area also as text into this ticket. Thanks.

This might be a problem with live preview only (Preferences → Editing → Show previews without reloading the page).

Before rMW7e9cac27d115: LivePreview: Show parse warnings and preview header/warning, it used to not show that message at all, unlike normal preview.

在T266311#6574191中，@Aklapper写道：

@Shizhao: Please copy the text in the yellow area also as text into this ticket. Thanks.

[[File:Start hand.svg|65px|left|预览|link=]]
<div style="padding-left:80px">
<b><span style="font-size:115%;color:green">请注意</span></b>，这只是'''预览'''！内容还未保存。
<hr />
*您可以在编辑或修正内容后再次预览。 
*若您对当前的修改感觉满意，请点击'''提交编辑'''按钮以發佈文章。
*若是测试，请改用[[WP:SB|沙盒]]。
</div>

在T266311#6576223中，@matmarex写道：

This might be a problem with live preview only (Preferences → Editing → Show previews without reloading the page).

right! If this option is not checked, there will be no such bug.

Change 636780 had a related patch set uploaded (by Bartosz Dziewoński; owner: Bartosz Dziewoński):
[mediawiki/core@master] mediawiki.action.edit.preview: Parse 'previewnote' message on the server

https://gerrit.wikimedia.org/r/636780

Change 636780 merged by jenkins-bot:
[mediawiki/core@master] mediawiki.action.edit.preview: Parse 'previewnote' message on the server

https://gerrit.wikimedia.org/r/636780

@Shizhao: No User-notice; please read its project description

I will work on that today, but can't do it right now. I don't think this is a train blocker.

In T266311#6601647, @Krinkle wrote:

Re-opening as blocker per performance fixme in CR. If not easy to fix, the I'd recommend a temporary revert.

Fine to revert this patch for the time being to unblock train? We can backport the fix as necessary.

Change 639251 had a related patch set uploaded (by Bartosz Dziewoński; owner: Bartosz Dziewoński):
[mediawiki/core@master] mediawiki.action.edit.preview: Add versionCallback to improve startup perf

https://gerrit.wikimedia.org/r/639251

In T266311#6604084, @thcipriani wrote:

In T266311#6601647, @Krinkle wrote:

Re-opening as blocker per performance fixme in CR. If not easy to fix, the I'd recommend a temporary revert.

Fine to revert this patch for the time being to unblock train? We can backport the fix as necessary.

I'll repeat that I don't think this is a train blocker. We've had very similar code in production for years and it's not bringing the site down. It's a minor performance issue at worst, and I think my proposed fix can be reviewed whenever someone has the time. I shouldn't even have worked on this today.

If you do want to revert regardless, then it's fine, but please also revert https://gerrit.wikimedia.org/r/c/mediawiki/core/+/597262 to avoid regressing this issue (and reopen the issues associated with that).

Change 639495 had a related patch set uploaded (by Krinkle; owner: Bartosz Dziewoński):
[mediawiki/core@wmf/1.36.0-wmf.16] mediawiki.action.edit.preview: Add versionCallback to improve startup perf

https://gerrit.wikimedia.org/r/639495

Change 639251 merged by jenkins-bot:
[mediawiki/core@master] mediawiki.action.edit.preview: Add versionCallback to improve startup perf

https://gerrit.wikimedia.org/r/639251

Change 639495 merged by jenkins-bot:
[mediawiki/core@wmf/1.36.0-wmf.16] mediawiki.action.edit.preview: Add versionCallback to improve startup perf

https://gerrit.wikimedia.org/r/639495

Mentioned in SAL (#wikimedia-operations) [2020-11-05T17:21:21Z] <brennen@deploy1001> Synchronized php-1.36.0-wmf.16/resources/Resources.php: Backport: [[gerrit:639495|mediawiki.action.edit.preview: Add versionCallback to improve startup perf (T266311)]] (duration: 01m 10s)

Patch deployed; removing as train blocker.