[PATCH STABLE] repoview: fix corrupted hiddencache crash Mercurial (issue5042)

[Laurent Charignon]

> On Jan 20, 2016, at 12:59 PM, Matt Mackall <mpm at selenic.com> wrote:
> 
> On Wed, 2016-01-20 at 20:46 +0000, Laurent Charignon wrote:
>>> On Jan 20, 2016, at 10:18 AM, Gregory Szorc <gregory.szorc at gmail.com> wrote:
>>> 
>>> 
>>> 
>>>> On Jan 20, 2016, at 10:09, Laurent Charignon <lcharignon at fb.com> wrote:
>>>> 
>>>> # HG changeset patch
>>>> # User Laurent Charignon <lcharignon at fb.com>
>>>> # Date 1453313317 28800
>>>> #      Wed Jan 20 10:08:37 2016 -0800
>>>> # Branch stable
>>>> # Node ID 688f61fa0e0a8cc9139a533cb3fe6cb411b1dc8f
>>>> # Parent  3203dfe341f962e33256d6475fc3585563db78ad
>>>> repoview: fix corrupted hiddencache crash Mercurial (issue5042)
>>>> 
>>>> Before this patch if the hiddencache existed but was empty, it would crash
>>>> mercurial. This patch adds exception handling when reading the hiddencache
>>>> to
>>>> avoid the issue.
>>>> When encountering a corrupted cache file we print a devel warning. There
>>>> would
>>>> be no point in issuing a normal warning as the user wouldn't be able to do
>>>> anything about the situation.
>>>> 
>>>> The warning looks like:
>>>> 
>>>> devel-warn: corrupted hidden cache, removing it at: /path/to/repoview.py
>>>> 
>>>> diff --git a/mercurial/repoview.py b/mercurial/repoview.py
>>>> --- a/mercurial/repoview.py
>>>> +++ b/mercurial/repoview.py
>>>> @@ -150,6 +150,12 @@
>>>>                count = len(data) / 4
>>>>                hidden = frozenset(struct.unpack('>%ii' % count, data))
>>>>        return hidden
>>>> +    except struct.error:
>>>> +        repo.ui.develwarn('corrupted hidden cache, removing it')
>>>> +        if fh:
>>>> +            fh.close()
>>>> +        repo.vfs.unlink(cachefile)
>>>> +        return hidden
>>> 
>>> I don't have the full source in front of me. Do we handle read errors the
>>> same way? Do we have test coverage for e.g. permissions failure on file
>>> reading? If not, we should add it.
> 
> I think deleting the file is not the right policy. We should overwrite it (if we
> have permission) when refreshing the cache, but otherwise silently ignore it.

The file gets rewritten correctly right after we compute "hidden" in that case as we return None.
Let's silently ignore it, I will send a V2.

> 
>> What you mention is already handled at a lower level and we should probably
>> add test for it in another patch.
>> 
>> $ chmod 000 .hg/cache/hidden
>> $ hg st
>> abort: Permission denied: /home/lcharignon/hg/.hg/cache/hidden
> 
> This should also be silently ignored.

Sure, I will add code to silence the error and print it only in debug mode.

Thanks,

Laurent

> 
> -- 
> Mathematics is the supreme nostalgia of our time.