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

[Chris Bailey]

To add one more question on the installation of system dependencies - does 
that then drive a need to install as root/sudo? If so, I can see that 
being a challenge for any cloud based application deployments, where your 
both unlikely to be able to run as root/sudo, or indeed be able to install 
into /usr/lib


Chris



From:   Honza Dvorsky via swift-build-dev <swift-build-dev at swift.org>
To:     Max Howell <max.howell at apple.com>
Cc:     "swift-build-dev at swift.org" <swift-build-dev at swift.org>
Date:   21/03/2016 18:38
Subject:        Re: [swift-build-dev] [Discussion Starter] Package 
post-clone script
Sent by:        swift-build-dev-bounces at swift.org



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 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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