pkg: Implement message type "before" to display a pre-(install|upgrade) message.

[jurajlutter]

Implement a pkg-message type before that will be displayed before install and/or upgrade of package. For now, also sleep(10) is performed (although the time could be parametrized, with 0 being no sleep() at all).

[bapt]

I do like what I see, thanks a lot, would it be possible to add tests in the test suite ?

[bapt]

I like the idea of a "before" notion for packages, it should be tight to the same notions as install, upgrade etc.

We should be able to show a before/pre upgrade message only if upgrading from a given version to a given version, or only when about to remove a package etc. I think we should work toward that.

As for the way it is coded right now, I do like the patch I am seeing ;)

[jurajlutter]

I will merge my changes for pre-install, pre-upgrade, pre-remove.

[bapt]

Hello sorry it took time to get back to you. I really like this, how ever printing a message before the upgrade or install is happening is actually only useful if it is being done before the user actually proceed to the transaction.

the proposed implementation will print something and proceed anyway which is not really useful for the end user.
I think the proper semantic would be for the to print it at the time the user will be asked to proceed, for example:

Just before the "Proceed with this action? [y/N]: " there should be a loop on the job looking at all package to be installed, upgrade or removed, extracting the message from them and printing it.

[woodsb02]

Hello sorry it took time to get back to you. I really like this, how ever printing a message before the upgrade or install is happening is actually only useful if it is being done before the user actually proceed to the transaction.

the proposed implementation will print something and proceed anyway which is not really useful for the end user. I think the proper semantic would be for the to print it at the time the user will be asked to proceed, for example:

Just before the "Proceed with this action? [y/N]: " there should be a loop on the job looking at all package to be installed, upgrade or removed, extracting the message from them and printing it.

Agree with this proposed design, rather than a timer and proceed anyway. I think the porters handbook documentation should advise port maintainers to only use pre-upgrade messages if they really want to prompt users before proceeding - and steer them to use upgrade (renamed to post-upgrade?) otherwise?