BitBucket change announcement: "Pull requests are now immutable" - what does this mean?

[Dan Bonachea]

The Atlassian Change Blog provides details about new and pending changes being rolled out to customers of their products.

The BitBucket Cloud section of this week's blog (Jan 16 to Jan 23, 2023) linked above contains this cryptic new entry:

Text version:

---

Pull requests are now immutable
ROLLING OUT / NEW THIS WEEK
Bitbucket Cloud pull requests are now immutable. Note: You might come across pull requests that were merged before this change was implemented, so you may see some changes that are not relevant anymore.

---

Can anyone explain what this entry means and what functionality was actually changed?

I've played around with several test pull requests, but so far have not noticed any difference in capabilities or features.

[Ulrich Kuhnhardt [IzymesCo]]

Thanks for posting this question. I would love an explanation too.

[Ulrich Kuhnhardt [IzymesCo]]

I poked about a bit and what I think is different is that 

Merged pull requests are now immutable :=)

•  you cant change the title or description
• you can't Un-approve or approve post merge

Looks like you can still leave comments.

[Dan Bonachea]

@Ulrich Kuhnhardt [IzymesCo] Thanks for your observations, I suspect you are correct.

I've also noticed that modifying or deleting the source branch of a merged PR no longer appears to alter the code diff displayed in the interface for that merged PR (an unintuitive display defect that I recall noticing in the past, although I cannot say with certainty when it changed because our team quickly learned to avoid that behavior).

It would be nice to get some clarity from Atlassian regarding whether we've correctly divined the extent of the recent changes.