[icebraining]

No, if Mattermost and Gitlab were linked, the AGPL restrictions would apply to the Gitlab code, even if it's MIT licensed. Otherwise, anyone would just be able to make a MIT-licensed wrapper around an AGPL project, allowing indirect linking between proprietary code and AGPL.

What Mattermost apparently did was compile their own code (under the name "Gitlab Mattermost"), and distribute that compiled version under MIT, so there's no AGPL in the Gitlab distribution.