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random [computer [science]] notes...

Restore commit dates lost by Mercurial MQ extension

tl;dr

The Mercurial MQ extension does not store the creation date of a patch by default. This behavior can be changed but what about existing patches? If the patch queue is under version control it might be possible to restore at least some information.

Intro

In course of working on the CACAO VM I was forced to use mercurial for the first time. Being a self-confessed git enthusiast it was hard to give away most of the power over the history. After messing up the repository meta data several times using extensions like rebase and histedit I finally gave the MQ Extension a try.

Issue

I really like(d) the fact that its all about plain patches with only minimal meta data. Unfortunately the creation date is also excluded by default. This can be changed by adding the command line flag -D/--currentdate to the hg qnew and hg qrecord commands (or even create an alias). There is still another problem with qrefresh as it refreshes not only the patch but the also the date. This FAQ entry on the MQ Extension page provides a solution to the issue.

But it those not bring back date information for old patches. In my case a few months and ~230 patches worth of date information.

Solution

Fortunately not everything was lost. I put my patches under version control right from the beginning (the hg commit -mq command makes it really convenient.). I to commit my changes at least once a day. Therefor, the creation date of each patch file is stored in the queue repository. The hg log command together with some revset magic reveals the information:

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hg log -r "sort(all(),date)" --template "{date|date}\n" patch_file

Sat Jun 08 14:57:22 2013 +0200
Wed Jun 26 11:51:34 2013 +0200

It returns the modification dates in chronological ascending order.

To get the date format desired for the patch meta data the template filter hgdate can be used:

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hg log -r "sort(all(),date)" --template "{date|hgdate}\n" patch_file

1370696242 -7200
1372240294 -7200

Remark: for some strange reason the min(), limit(), etc. revsets functions did not work, so I use good old head(1) to select the first result.

The following script is intended to be run inside the patch directory (e.g. .hg/patch/). It greps for all patches without a # Date, fetches the creation time from the patch repository and insert it into the patch file.

Please always do a hg commit --mq and hg push --mq to backup you patches before touching anything.

(fix-patch-dates.sh) download
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#! /bin/bash

set -e
set -u

FILES_WITHOUT_DATE=$(grep --exclude=series --exclude=.* -L "^# Date" $(hg locate))

for file in $FILES_WITHOUT_DATE ; do
    # hg revset limit() did not work so head is used in place
    DATE=$(hg log -r "sort(all(),date)" --template "{date|hgdate}\n" $file | head -n1)
    sed -i.orig "2a\\# Date $DATE" $file
done

Known Problems

The date is always inserted on the 3rd line. This might be a problem in some scenarios. If the commit frequency in the patch repository low, you don’t get much useful data. Renamed and folded patches do not work.

Disclaimer

As always, this information is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY. Kittens may die if you don’t read the manual and know what you are doing.

Retrospective

It seems that the MQ Extension does not really fit my needs after all. The mercurial community has its own way of dealing with safe history editing, called ChangesetEvolution which centers around phases, histedit, evolve, rebase and other extensions. This is probably the right way of doing history editing things with mercurial.

References

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