Ensure no broken symlinks in stage

[sergio-costas]

This PR adds a tool to ensure that there are no broken symlinks in stage, showing which packages must be added if needed.

[aleasto]

Uhh I think what you really want here is:

• apt-file find /path/to/link to find which package provides the link, and/or
• apt-file find $(realpath /path/to/link) to find which package provides the target

[3v1n0]

Uhh I think what you really want here is:

* `apt-file find /path/to/link` to find which package provides the link, and/or

* `apt-file find $(realpath /path/to/link)` to find which package provides the target

Yeah, but that implies filling a database, can it go using a different root prefix?

[aleasto]

Uhh I think what you really want here is:

* `apt-file find /path/to/link` to find which package provides the link, and/or

* `apt-file find $(realpath /path/to/link)` to find which package provides the target

Yeah, but that implies filling a database, can it go using a different root prefix?

If the plan is to run this during the snapcraft build, just call apt-file update in override-pull.

[sergio-costas]

Uhh I think what you really want here is:

* `apt-file find /path/to/link` to find which package provides the link, and/or

* `apt-file find $(realpath /path/to/link)` to find which package provides the target

I'm already doing that, but with dpkg...

Also, using apt-file requires to install the package and refresh the cache, something that dpkg doesn't require.

[aleasto]

Uhh I think what you really want here is:

* `apt-file find /path/to/link` to find which package provides the link, and/or

* `apt-file find $(realpath /path/to/link)` to find which package provides the target

I'm already doing that, but with dpkg...

But that implies that you need to install (and then remove) packages, which we should really avoid.
You also shouldn't assume to have network access at this point of the build.

[sergio-costas]

But that implies that you need to install (and then remove) packages, which we should really avoid. You also shouldn't assume to have network access at this point of the build.

Without network access I can't refresh the package list...

[aleasto]

But that implies that you need to install (and then remove) packages, which we should really avoid. You also shouldn't assume to have network access at this point of the build.

Without network access I can't refresh the package list...

You can in override-pull

[sergio-costas]

Without network access I can't refresh the package list...

You can in override-pull

Good point... Let me first debug other parts, and then I'll change that.

[sergio-costas]

@aleasto It builds armhf, arm64 and amd64. Still waiting for riscv64.

[aleasto]

Some comments in-line.
Please split the commits into one fixing the build and one adding the assertions

[aleasto]

awesome, LGTM if CI is green

[aleasto]

Ouch, yes

[sergio-costas]

Finally!!!! (tested locally. The trick was that environment variable).