Changing default snapcraft behavior and erroring on missing libraries

[Bill Filler]

On Tue, Jan 31, 2017 at 12:02 PM, Kyle Fazzari <kyle.fazzari at canonical.com>
wrote:

>
>
> On 01/31/2017 08:40 AM, Didier Roche wrote:
> > Le 31/01/2017 à 17:18, Sergio Schvezov a écrit :
> >> On Tue, 31 Jan 2017 16:21:41 +0100, Olivier Tilloy wrote:
> >>> On Tue, Jan 31, 2017 at 2:12 PM, Timo Jyrinki
> >>> <timo.jyrinki at gmail.com> wrote:
> >>>>> Do we have a clear understanding of why this happens? Qt apps are
> >>>>> supposed to be binary compatible against newer releases.
> >>>>> One exception could be if the app itself is shipping some plugins,
> >>>>> because in that case I believe that these plugins are somehow bound
> to a
> >>>>> specific Qt version.
> >>>> Yes, it seems snaps like ubuntu-terminal-app and dekko ship their on
> >>>> Qt version which should not be the case when the platform snap is
> >>>> used.
> >>> This is a bit tricky: when packaging a Qt application that uses the
> >>> platform snap, snapcraft will use ldd to crawl the app’s binaries and
> >>> will automagically add the libraries that it depends on to the
> >>> resulting snap (those libs are taken from the host system).
> >> This will be disabled by default and snapcraft will error on missing
> libraries
> >> unless you tell it is ok.
> >>
> > (first, sorry for the bad control+enter on my previous email)
> >
> > I'm a little bit uncomfortable with that statement for mainly 2 reasons:
> > * Changing default behavior is always cumbersome to developers who just
> > wants to work on their app. Here, we are introducing a breaking change
> > (snaps that used to build won't build anymore, especially those on
> > core). It's annoying also for people who did hook up their CI to
> > autopublish a snap.
> >
> > This is why we need to justify and carefully explain the change, in a
> > clear, defined way. I would suggest coordinating with David for a blog
> > post that we promote here and on the developer website:
> >   1. Why are we changing this? -> we are not doing this just to bother
> > you, developer, here is the technical reason why we are doing it.
> >   2. A small and minimal snippet of code of before/after so that people
> > aren't lost and know what to do
> >   3. When is it going to be released. Version, date, upgrade process.
> >
> > As this default behavior changes a lot of things, we need to ensure as
> > well that all our code snippet and tutorials are updated. So
> > coordinating all the way, please!
>
> I completely agree.
>
> > * The second one is that it seems there is a disable mechanism, mainly
> > telling "I know what I'm doing". I think this isn't what we want to
> > achieve and it's not fine-grained enough.
>
> Without knowing much about this change, I figure something like this
> would fit into build-attributes, which is per-part at least.
>
> > A common use-case I can see is an app depending on a platform snap and
> > embedding additional libraries for some functionality. If we have to
> > disable the check for not erroring out on the platform snap libs, we may
> > miss, on snap creation, or upgrade or more… additional library checks.
> > It seems we shouldn't use a big hammer like this (if it's really what
> > I'm understanding from this statement), but rather trying to get a way
> > more fine-grained and precise approach.
>
> You mean like asking the snap developer to provide an explicit list of
> libraries to error on? Or an explicit list of libraries to pull from the
> system if missing? Anything more fine-grained sounds messy to maintain
> from a snap developer perspective. And this applies to either direction:
> automatically pulling in dependencies from the system, or erroring on
> missing libraries.
>
> Note that, in your example, the consumer app should likely be built with
> the providing snap unpacked into the staging area. This guarantees that
> the consumer is build with the libraries etc. actually contained in the
> providing snap. Using this workflow, snapcraft doesn't do anything
> special with the libs contained in the staging area, even if they're
> filtered out of the final snap via the `prime` keyword. Where "anything
> special" is defined as trying to pull them in from the system, etc. I
> figure the "error on missing libs" would follow the same logic, and not
> error if the libs are satisfied in stage.
>

>From a developers perspective, it would be great if a workflow like the
following could happen:
 - if my snap uses other snaps via content-sharing, the providing snaps
would be automatically unpacked during the build and used to satisfy
depends so the libs are not copied into my snap
- if missing lib errors occur, give me the option to ignore and use system
libs, or error-out with the list of missing deps

This would satisfy use cases where the providing snap contains all the libs
my snap needs or just a portion of them. Sounds like we have most of this
already in some form but not exactly..


>
> --
> Kyle Fazzari (kyrofa)
> Software Engineer
> Canonical Ltd.
> kyle at canonical.com
>
>
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