[swift-build-dev] [Discussion Starter] Package post-clone script

[Honza Dvorsky]

I personally don't like the idea of an arbitrary script either, it was just
the first obvious solution to a problem I believe needs solving. The
advantage of building from source even of these base dependencies is that
the exact version of system dependencies
- can be ensured to be the same version across platforms
- their version is part of the explicit dependency graph

Currently, AFAIR, installing Redis with homebrew and apt-get each produce a
different version, which IMO defeats the point of having a dependency
manager in the first place. But I guess if your proposal could ensure that
the same version is installed on all platforms, this particular problem
would be solved.

> So the question becomes, is this sufficient? To have `brew install
openssl` run, or do you really need to install from source?

I'm still not sure. Now I think your proposal will probably help with most
cases (which is a very good way to approach things), but definitely not
all. Imagine you yourself having a cross-platform C project which needs
platform configuring before compilation. Even when you're completely in
control, the fact that you still can't get this working is troubling. But
maybe I'm just inflating extremely uncommon usecases.

One more thing - consider two Swift packages each needing a different
version of OpenSSL. Does your proposal handle that case?

Anyway, I'd love to read your proposal and then re-evaluate whether I still
feel like there's a large enough benefit in introducing such customization
to SwiftPM :)

Honza

On Mon, Mar 21, 2016 at 6:19 PM Max Howell <max.howell at apple.com> wrote:

>
> On Mar 19, 2016, at 10:55 AM, Honza Dvorsky via swift-build-dev <
> swift-build-dev at swift.org> wrote:
>
> Hi All,
>
> today I was trying to investigate how to build a proper cross-platform
> server-side Swift project and only use SwiftPM to do it. In particular, I
> was interested in getting OpenSSL/libcurl working as a dependency (built
> from source). The main reason is that currently the big Swift server
> frameworks all require manual steps during deployment (running apt-get/brew
> to install libcurl/openssl/others) and I am trying to get rid of these
> manual steps, eventually only requiring a `swift build` and run.
>
> With the great initial work
> <https://github.com/apple/swift-package-manager/pull/183> to support
> building C-family packages in SwiftPM done by Ankit, I was able to have a
> simple C package as a dependency, as advertised. However, the reality of
> big cross-platform open source projects like OpenSSL and libcurl is that in
> order to actually build it from source, a configure (or similar) script has
> to be run to get the source code ready for compilation. And this is where I
> got stuck.
>
> Thus I wanted to kick off a discussion of what approach of solving this
> problem with SwiftPM should be. The simple solution, which I'm tentatively
> proposing, is to have an optional "post-clone" script in the package's
> repository. Then, the Package.swift would optionally contain a field for
> the path to this script - and if present, it'd get run after SwiftPM clones
> this package. Note that this would be a "post-clone" script, not a
> "prebuild" script - I imagine it'd only run once when cloning and then only
> after each clean.
>
> In order to get users to stop having to run manual script to install all
> dependencies, I believe that we need to allow packages to declare what work
> needs to be done on its source before compilation can begin.
>
>
> I have a proposal I’d like to push today that adds knowledge to SwiftPM
> about how to install system dependencies for System Module Packages.
>
> We are not keen to add arbitrary script execution to SwiftPM, because: 1)
> Arbitrary scripts cannot be controlled and this leads to dependency hell
> and 2) arbitrary scripts mean your package graph may do anything, which
> nobody wants.
>
> Now I’m fine with the “root package” ie. the package the user has control
> over doing more, but this would be a different discussion.
>
> So the question becomes, is this sufficient? To have `brew install
> openssl` run, or do you really need to install from source?
>
> Max
>
>
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