pre-commit: Use qmlformat by default

[Holzhaus]

@poelzi pointed out that it's easy to forget to use the manual hook stage to run qmlformat manually, and I agree.

The hook will only run if you changed QML files anyway. Therefore, I think we can just enable the hook by default. If qmlformat is not installed, the user may skip the hook manually.

For contributors without experience with pre-commit, I added a wrapper script that displays an error description and a way to work around it if qmlformat is missing:

$ git commit
<snip>
qmlformat................................................................Failed
- hook id: qmlformat
- exit code: 1

qmlformat is not installed. It is included in Qt 5.15 and later. If that Qt
version is not available on your system, please use the SKIP environment
variable when committing:

    $ SKIP=qmlformat git commit

[uklotzde]

I agree. The number of developers that are affected will decline over time.

[Holzhaus]

Here we return exit code 1 so that the user is prompted to either install qmlformat or skip the hook manually.

We could also return exit code 0. Thdi would be even more convenient, but then the hook shows up as "passed" and the user has no way of knowing if qmlformat actually ran or not. This is an issue, especially on CI. Therefore, I prefer the "skip manually" approach.

[daschuer]

I can imagine that it can leads to extra hassle when resolving conflicts, because it does not run on diffs only.

So I would prefer exit code 0 version, since it will be visible in our CI anyway.
That follows the approach that the whole pre-commit is optional anyway. Compared to that. this is one only a side issue, where we should not annoy a contributor that has just decided to install pre-commit.

[Holzhaus]

So I would prefer exit code 0 version, since it will be visible in our CI anyway.

We cannot be sure about that. It will display as passed on CI in any case, even if your CI image does not actually have qmlformat.

I think the extra hassle is manageable. Just run this once:

$ echo SKIP=qmlformat >> ~/.profile

And don't forget remove it after upgrading to Qt 5.15 ;-).

[daschuer]

Yes ok. Ready to merge IMHO.

Just an idea, considering that we should not forget this .profile value.
How about use:
qmake --version
To exit 0 if qmlformat cannot be installed.

[uklotzde]

@daschuer Merge?

[daschuer]

Yes.