[system_setup] Allow skipping locale-gen command

[CarlosNihelton]

Language packs post-install hook executes locale-gen.
For certain languages a matrix of locales is generated.
Re-running locale-gen regenerates not only the locale we wanted, but the whole matrix, causing further delays. One example of such locale matrix generation happening after installing a language pack can be seen below:

We can save up to 40s (tested on my laptop) by skipping locale-gen if apt succeeded.
Still useful to run it unconditionally in dry-run since apt won't execute any post-install hook.

[didrocks]

Still useful to run it unconditionally in dry-run since apt won't execute any post-install hook.
Sorry, I don’t understand this one. Basically, what‘s the point of running it in dry-run as we haven’t installed any new packages? Is the base system not self-sufficient? (and it’s dry-run anyway, so shouldn’t touch the system).

Also, this contradicts this comment you added as part of the PR, which implies the reverse (skipping it only in live run):

   # langpacks post-install hooks run locale-gen.
   # It makes sense to skip it in live run.

Sorry, I didn't express well what I intended to convey. The post install hook of various language-packs I looked into the sources invoke the script /usr/share/locales/install-language-pack:

#!/bin/sh -e

if [ -z "$1" ]; then
    echo "Usage: $0 <language code> <class> [<version>]"
    exit 0
fi

# install locales for base packages (not for gnome/kde)
if [ -z "$2" ]; then
    # Update requested locales if locales-all is not installed
    if dpkg-query -s locales-all >/dev/null 2>&1 ; then
        echo "locales-all installed, skipping locales generation"
    else
        /usr/sbin/locale-gen --keep-existing "$1"
    fi
fi

# ensure that .desktop caches are up to date
dpkg-trigger gmenucache || true

As you can see, unless locales-all is installed, it invokes locale-gen. If apt suceed running, we don't need to invoke locale-gen a second time. Yet, it's useful to preserve this controller ability to run locale-gen for the cases when apt fails.
In dry-run we don't install language packs, so apt will not run post-install hooks and there we use a 'mocked' environment to generate locales into and verify that we generated what was intended. Thus it's useful to run locale-gen in this controller in that situation.

[didrocks]

Sorry, it seems there is some formatting failure, I wrote above:

Sorry, I don’t understand this one. Basically, what‘s the point of running it in dry-run as we haven’t installed any new packages? Is the base system not self-sufficient? (and it’s dry-run anyway, so shouldn’t touch the system).

[CarlosNihelton]

Sorry, it seems there is some formatting failure, I wrote above:

Sorry, I don’t understand this one. Basically, what‘s the point of running it in dry-run as we haven’t installed any new packages? Is the base system not self-sufficient? (and it’s dry-run anyway, so shouldn’t touch the system).

The point would be asserting that locale would be installed either way. Nothing is written to the system, but to .subiquity directory tree. But I realized that we won't check the locale definition files that were generated, so I'm dropping those lines.

[didrocks]

But you still have the option on the function call itself, (using =ok btw?), it’s not needed anymore, correct?

[CarlosNihelton]

But you still have the option on the function call itself, (using =ok btw?), it’s not needed anymore, correct?

My take on that is: if apt fails to install language packs we still want to generate locale for the language user selected, to ensure date-time formatting, currency and other stuff works as she expects, even though the LC_MESSAGES come in English. Would you say those should be all or nothing?

[didrocks]

Hum, I see your point and I don’t have any arguments against it, so ok, that’s good enough to me :) Mind adding a small comment about this then and then, we can merge it, thanks!

[CarlosNihelton]

Hum, I see your point and I don’t have any arguments against it, so ok, that’s good enough to me :) Mind adding a small comment about this then and then, we can merge it, thanks!

There you go!