Structure and Interpretation of Computer Programmers

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Tuesday, November 27, 2018

Packaging software

I’ve been learning about Debian Packaging. I’ve built OS X packages, RPMs, Dockerfiles, JARs, and others, but never dpkgs, so I thought I’d give it a go.

My goal is to make a suite of GNUstep packages for Debian. There already are some in the base distribution, and while they’re pretty up to date they are based on a lot of “default” choices. So they use gcc and the GNU Objective-C runtime, which means no blocks and no modern objc features. The packages I’m making are, mostly thanks to overriding some choices in building gnustep-make, built using clang, the next-generation objc runtime, libdispatch etc.

The Debian packaging tools are very powerful, very well documented, and somewhat easy to use. But what really impressed me along this journey was CPack. I’ve used cmake before, on a team building a pretty big C++/Qt project. It’s great. It’s easier to understand than autoconf, easier to build correct build rules over a large tree than make, and can generate fast builds using ninja or IDE-compatible projects for Xcode, IntelliJ and (to some extent) Eclipse.

What cpack adds is the ability to generate packages, of various flavours (Darwin bundles, disk images, RPMs, DEBs, NullSoft installers, and more) from the information about the build targets. That’s really powerful.

Packaging software is a really important part of the customer experience: what is an “App Store” other than a package selection and distribution mechanism? It irks me that packaging systems are frequently either coupled to the target environment (Debian packages and OpenBSD ports are great, but only work in those systems), or baroque (indeed autoconf may have gone full-on rococo). Package builder-builders give distributors a useful respite, using a single tool to build packages that work for any of their customers.

It’s important that a CD pipeline produces the same artefacts that your customers use, and also that it consumes them: you can’t make a binary, test it, see that it works, then bundle it and ship it. You have to make a binary, bundle it, ship it, install it, then test it and see that it works. (Obviously the tests I’m talking about here are the “end-to-end”, or “customer environment” tests. You don’t wait until your thing is built to see whether your micro-tests pass, you wait until your micro-tests pass to decide whether it’s worth building the thing.)

I know that there are other build tools that also include packaging capabilities. The point is, using one makes things easier for you and for your customers. And, it turns out, CMake is quite a good choice for one.

posted by Graham at 12:45  

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