[PATCH 2 of 3 STABLE] changegroup: call 'prechangegroup' hook before setting up write delay

[Durham Goode]

On 11/6/15 10:07 AM, Pierre-Yves David wrote:
> # HG changeset patch
> # User Pierre-Yves David <pierre-yves.david at fb.com>
> # Date 1446832749 18000
> #      Fri Nov 06 12:59:09 2015 -0500
> # Branch stable
> # Node ID b720bb662a3e17cdfac3cc5c90fdd895673ec864
> # Parent  03916de16fe8f511a48b860bf8b7956d79ea8ef9
> # Available At https://urldefense.proofpoint.com/v2/url?u=http-3A__hg.netv6.net_marmoute-2Dwip_mercurial_&d=CwIGaQ&c=5VD0RTtNlTh3ycd41b3MUw&r=nuarHzhP1wi1T9iURRCj1A&m=rnYZCBGjsYVaHYznTww8TS18sR-RU_3WQT5S-Y9gSzU&s=Od6nMDVqvebNfgQ5PgZF3Ns5ryRRfpZIGbSJOM3sQxU&e=
> #              hg pull https://urldefense.proofpoint.com/v2/url?u=http-3A__hg.netv6.net_marmoute-2Dwip_mercurial_&d=CwIGaQ&c=5VD0RTtNlTh3ycd41b3MUw&r=nuarHzhP1wi1T9iURRCj1A&m=rnYZCBGjsYVaHYznTww8TS18sR-RU_3WQT5S-Y9gSzU&s=Od6nMDVqvebNfgQ5PgZF3Ns5ryRRfpZIGbSJOM3sQxU&e=  -r b720bb662a3e
> changegroup: call 'prechangegroup' hook before setting up write delay
>
> The 'prechangegroup' interfere with 'delayupdate' logic because it trigger the
> one time call of 'changelog._writepending' (see issure4934). There is no reason
> not to call that hook before setting up 'delayupdate' so we move the call a bit
> earlier to avoid interference.
>
> diff --git a/mercurial/changegroup.py b/mercurial/changegroup.py
> --- a/mercurial/changegroup.py
> +++ b/mercurial/changegroup.py
> @@ -327,17 +327,17 @@ class cg1unpacker(object):
>               # carries source information. In this case we use the top
>               # level data. We overwrite the argument because we need to use
>               # the top level value (if they exist) in this function.
>               srctype = tr.hookargs.setdefault('source', srctype)
>               url = tr.hookargs.setdefault('url', url)
> +            repo.hook('prechangegroup', throw=True, **tr.hookargs)
>   
> -            # write changelog data to temp files so concurrent readers will not see
> -            # inconsistent view
> +            # write changelog data to temp files so concurrent readers will not
> +            # see inconsistent view
>               cl = repo.changelog
>               cl.delayupdate(tr)
>               oldheads = cl.heads()
> -            repo.hook('prechangegroup', throw=True, **tr.hookargs)
>   
I think relying on no hooks being called between delayupdate and the 
actual changelog writes is subtle, brittle, and not a good fix for this. 
If you want a better fix than what I had, I think we should break the 
writepending subscription logic out of delayupdate and put it after the 
changelog write.