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

[Max Howell]

> 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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