From: Duy Nguyen <pclouds@gmail.com>
Date: Tue, 17 Jul 2018 16:39:58 GMT
Subject: Re: [PATCH 2/2] repack -ad: prune the list of shallow commits
Message-ID: <CACsJy8Ce0kXTCzLf6jFq1QjY4Q4QePfk1JbgGUr-kQqQDCc7mA@mail.gmail.com>
In-Reply-To: <b4e01a963fd16f50d12c1f67c6e64bec8b1e9673.1531513093.git.gitgitgadget@gmail.com>

On Fri, Jul 13, 2018 at 10:19 PM Johannes Schindelin via GitGitGadget
<gitgitgadget@gmail.com> wrote:
>
> From: Johannes Schindelin <johannes.schindelin@gmx.de>
>
> While it is true that we never add unreachable commits into pack files
> intentionally (as `git repack`'s documentation states), we must not
> forget that a `git fetch --prune` (or even a `git fetch` when a ref was
> force-pushed in the meantime) can make a commit unreachable that was
> reachable before.
>
> Therefore it is not safe to assume that a `git repack -adlf` will keep
> unreachable commits alone (under the assumption that they had not been
> packed in the first place).
>
> This is particularly important to keep in mind when looking at the
> `.git/shallow` file: if any commits listed in that file become
> unreachable, it is not a problem, but if they go missing, it *is* a
> problem. One symptom of this problem is that a deepening fetch may now
> fail with
>
>         fatal: error in object: unshallow <commit-hash>
>

Could you elaborate a bit more? I don't quite see the connection
between the reachability in the first two paragraphs and .git/shallow
in the third one. I'm guessing we drop objects in between because
"they go missing"? Where? How does prune_shallow() in prune.c play any
role in this (if it does)?
-- 
Duy