Understanding and modifying the default diff for commits

[Andres Sommerhoff]

Thank you Pierre-Yves, my comments in red below.

Regards, Andres

On Wed, Jun 10, 2020 at 6:04 AM Pierre-Yves David <
pierre-yves.david at ens-lyon.org> wrote:

> Your use case is a bit unclear to me. I'll ask some silly questions to
> try to clarify that.
>
> As far as I understand, you are using KNIME to efit a "project" KNIME
> itself generate a bunch of XML file. Whenever anything happens, KNIME
> rewrite all files to update the author and last update file, regardless
> of them being affected by the update or not. Right ?
>
Yes, that is right.

>
> I assume these xml file contains actual data, right ? They are not
> generate by product you could exclude, right ?
>
The XML contains information on how to deal with scientific data
(information like mathematical formulas, conditions, filters, code, etc). I
could also save the model including the scientific data in place, but if
I'm going to commit to Mercurial, I reset the model in order to leave only
the structure and formulas of the model without any further data.


> The simplest option would probably to run a small script that revert
> these before commit, or that simply delete these field as another user
> suggested. You could configure it as a pre-status and pre-commit hook.


>
An interesting feature Mercurial has, is fileset `hg help fileset`. It
> would probably be simple to create a fileset that detect your case and
> use it in situation where it helps.
>

I will follow your suggestion and test the pre-status and pre-commit hook.
The fileset feature looks promising, maybe the option "grep(regex)" and
"modified()" can do the magic. However, I believe I will need to use the
regex over the diff report and not over the whole file in order to handle
my issue (I will investigate a bit further anyway)


> The best solution for your would probably to teach KNIME to not do this,
> but I guess you have tried that already.
>
I haven't tried to teach Knime as it is a huge software and I prefer to
learn how to adapt Mercurial. That way I can reuse my learning for other
general purposes in the future beyond the Knime world (and I think that
adapting Mercurial will be simpler than adapting Knime to my needs)


>
> Cheers,
>
> On 6/8/20 7:32 PM, Andres Sommerhoff wrote:
> > Hi all, I want to intervene the diff operation used by the mercurial
> > commit. I want to collect only the meaningful changes a heavy directory
> > tree full of XML files (this to make easier to audit what really has
> > changed, but also saving some disk space by doing so doesn’t hurt). I
> > was looking in internet and some mercurial add that could help, put I
> > was unsuccessfully, so thinking to make my own extension (or maybe some
> > scripting in pre-commit hook).
> >
> > I will appreciate any advice where to start my intervention of the diff
> > process during the commit of mercurial if I go to make my own extension?
> > Any help for locating the diff code that is used by mercurial (to look
> > and learn how is the interaction with it)?
> >
> > If you are curious about the problem I’m trying to deal with it, it is
> > the software KNIME that the projects (scientific models) developed in
> > that software is saved in several XML files, where each XML represent a
> > small portion of the model (“nodes” as called in KNIME). One project can
> > easily have more than 500 nodes (-> XML files). If I change a single
> > node and save the project, then not only the single related file is
> > changes but all the 500 XML files are also updated. Inside each XML file
> > the “last modification date” and “last author” is changed.
> >
> > I’m looking to skip all the files that the single change was updating
> > “last modification date” and “last author” but nothing else. By doing
> > so, I can focus in the important changes, making easy to audit the
> > manful modifications, merges can be far less cumbersome, and the history
> > much cleaner when making a log on a specific file.
> >
> > Maybe a simple command line option for the commit is the solution, but I
> > see no official option in the commit command in order to use an
> > alternative diff tool for calculating the patches. On the other hand, as
> > far I read, the “extdiff” option only affect the comparison of the
> > revisions, but not for commit process (maybe I’m wrong on this last
> > sentence). Or maybe a commit command line using the function
> > “diff([includepattern [, excludepattern]]):” in conjunction with
> > “--exclude “ will make the magic I’m looking for, but I couldn’t figure
> > it out yet.
> >
> > I’m on Windows 10, using Mercurial and TortoiseHg 5.0.2.
> >
> > Regards, Andres
> >
> > _______________________________________________
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> >
>
> --
> Pierre-Yves David
>
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