3-way merge with OURS strategy

[markus2330]

No description provided.

[FelixResch]

I added an implementation of the three-way merge based on Elektra Tools in the branch elektra-backend-threeway-merge.

I will add a few more tests and then create a PR.

[markus2330]

Thank you, but please use the new merging API from @Chemin1: src/libs/merge

Please ask if you have any questions.

[markus2330]

We got an answer from David Faure:

(IIRC) what KConfig does in such a case, at step 3, is to reload the file from
disk but without touching the entries marked as dirty (i.e. modified by the
configuration dialog), and then save the result.
I.e. this will overwrite entries modified by both, but preserve entries
modified externally and not modified by the application.
The comment at the top of KConfigIniBackend::parseConfig (and near the call to
that method) confirms this.
I can't pinpoint the actual logic in the code itself though (I don't know it
in full details).

@FelixResch did you spot such a code? Does the code do what it should do? Can you try if manually edited changes are really not lost?

@Chemin1 is this equivalent to 3-way merging or in which cases is 3-way merging better?

[FelixResch]

did you spot such a code? Does the code do what it should do? Can you try if manually edited changes are really not lost?

In KConfig.sync() the configuration is simply written to the backing storage.

In KConfig.reparseConfiguration() the changes are written to the backing storage by calling sync() and then the file is reread.

Hence the merging is actually done in reparseConfiguration() and not in sync(). The current implementation of the Elektra backend already reloads the changes during the call to sync(), but this can be removed.

[markus2330]

My question was about the unmodified code with the INI backend (the kconfig repo before we did anything), what is this code doing? And please also try if it actually works (manually edit a file and then press the save button in the configure dialog).

[FelixResch]

My question was about the unmodified code with the INI backend (the kconfig repo before we did anything), what is this code doing?

This is the first part of my answer (We haven't changed the implementation of these methods)

And please also try if it actually works (manually edit a file and then press the save button in the configure dialog).

Yes, this works

[markus2330]

Thank you for looking into it!

@Chemin1 can you please analyze if your algorithm will perform the same or better than this marking-dirty-configuration approach? The dirty approach sounds much simpler than a 3-way merge with our strategy.

[dominicjaeger]

is to reload the file from
disk but without touching the entries marked as dirty (i.e. modified by the
configuration dialog), and then save the result.

File was loaded once (base) and modified (our), then reloaded (their)

I.e. this will overwrite entries modified by both, but preserve entries
modified externally and not modified by the application

overwrite = use the marked version (our) and not the reloaded one (their)

@Chemin1 is this equivalent to 3-way merging or in which cases is 3-way merging better?

=> I think equivalent.

@Chemin1 can you please analyze if your algorithm will perform the same or better than this marking-dirty-configuration approach? The dirty approach sounds much simpler than a 3-way merge with our strategy.

As both seem to use three-way merging, the difference should be how good Elektra's and KConfig's Backends handle the properties of INI. I can analyze this, but I can't promise that I'll be able to finish it very quickly as I'll be participating in a tournament this weekend.

[markus2330]

This is not needed, thank you for looking into it!