[llvm-dev] [cfe-dev] Phabricator Maintenance

Thu Jun 25 08:05:02 PDT 2020

From: cfe-dev <cfe-dev-bounces at lists.llvm.org> On Behalf Of Hubert Tong via cfe-dev
Sent: Thursday, June 25, 2020 7:51 AM
To: Zachary Turner <zturner at roblox.com>
Cc: LLVM Dev <llvm-dev at lists.llvm.org>; Nikita Popov <nikita.ppv at gmail.com>; Clang Dev <cfe-dev at lists.llvm.org>
Subject: Re: [cfe-dev] [llvm-dev] Phabricator Maintenance

On Thu, Jun 25, 2020 at 6:04 AM Zachary Turner via cfe-dev <cfe-dev at lists.llvm.org<mailto:cfe-dev at lists.llvm.org>> wrote:

On Thu, Jun 25, 2020 at 2:43 AM Nikita Popov <nikita.ppv at gmail.com<mailto:nikita.ppv at gmail.com>> wrote:
On Thu, Jun 25, 2020 at 11:22 AM Zachary Turner via llvm-dev <llvm-dev at lists.llvm.org<mailto:llvm-dev at lists.llvm.org>> wrote:
I can’t really provide a doc, but i can describe what I believe to be the biggest problem.

In a GH PR, comments are associated with commit hashes.  If a commit hash ceases to exist, so do all comments associated with it.  The comments are quite literally destroyed and irretrievable.

Either I'm misunderstand something, or this is just blatantly incorrect. Assuming we're talking about pull request reviews here, review comments do not get lost, regardless of how you rebase the pull request branch.
Try this experiment:

1. Create a PR
2. Have someone leave a comment on a line of code.  You should get an email.
3. Make another change locally and squash it
4. git push -f
5. Go to your email and click the link for the comment that was made in step 2.

GH should tell you that the comment does not exist.

Now that i think about it, the comment is probably still visible in the web ui by clicking “Show Outdated”.  But you cannot see the code that was requested to be changed.  That comment has a link associated with it, and if you click that link you just get “the commit does not exist”
In other words, the context is gone. The state that the reviewer saw is no longer necessarily retrievable (via GitHub).
Perhaps that is mitigated by the e-mail archive, which could make it possible to reconstruct that context.
[Keane, Erich] Well, you get a preview of the line commented on/surrounding lines, but yes, the history disappears.  That said, we explicitly discourage force-push on my downstream for exactly this reason.  I don’t know if there is a way to, but it would be wonderful if we could just prevent force-pushes from happening on reviews.

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