Is this task for writing the code that makes the extension a beta feature or for making the deployment patches?

@kaldari - are we doing something like this for the NWE version too?
Assuming this ticket is only for the old wikitext editor.

This is also for the NWE version. Both editors should get the feature when you turn on the beta feature. Note that currently, enabling CodeMirror (via global config) enables syntax highlighting for both editors.

Change 358494 had a related patch set uploaded (by Niharika29; owner: Niharika29):
[mediawiki/extensions/CodeMirror@master] Add syntax highlight as a beta feature

https://gerrit.wikimedia.org/r/358494

The patch is complete except for missing illustrations which is tracked in T165541: Illustration for Syntax Highlighting beta feature.

Change 358494 merged by jenkins-bot:
[mediawiki/extensions/CodeMirror@master] Add syntax highlight as a beta feature

https://gerrit.wikimedia.org/r/358494

Change 366034 had a related patch set uploaded (by Niharika29; owner: Niharika29):
[mediawiki/extensions/CodeMirror@master] Make the discussion link point to the meta page for the feature and update description string

https://gerrit.wikimedia.org/r/366034

@Jdforrester-WMF : okay, I can't argue against using a Flow board. :) We'll link to the MW page.

Change 366034 abandoned by Jforrester:
Make the discussion link point to the meta page for the feature and update description string

Reason:
Per Danny on Phab.

https://gerrit.wikimedia.org/r/366034

In stalled you mean there will not be highlighting until 2019?

@IKhitron No, it's just temporary while we fix T172458: CodeMirror must not embed 5KB of config on every page view

Thank you. I know that, @DannyH, but if it could be fixed in a week there would be no stalled, I think.

And it' resolved now.