WEBVTT 00:00.000 --> 00:10.960 So we're going to really start now this time about Opam's Nick system dependency mechanism. 00:10.960 --> 00:12.440 Ryan, give us going to talk about that. 00:12.440 --> 00:18.960 We already saw a talk by Ryan, and we're curious to see this one, so go ahead, Ryan. 00:18.960 --> 00:21.200 Thank you very much, everyone. 00:21.200 --> 00:26.360 So I'm going to give you a quick talk on Opam's Nick system dependency mechanism. 00:26.360 --> 00:31.680 So if you don't know Opam is the Oklahoma language package manager, and as with many other 00:31.680 --> 00:36.440 languages, you can use Oklahoma packages from Nick's packages or specialized overlay, 00:36.440 --> 00:41.000 but sometimes the packages or package versions you might need might not be included in 00:41.000 --> 00:43.720 that repository or overlay. 00:43.720 --> 00:47.480 You can use a project like Twigs or PAM Nick's to programatically generate Nick's 00:47.480 --> 00:53.560 derivations from an Opam solve for your project and its dependencies. 00:53.560 --> 00:59.360 This is great for deploying a project developed with Opam to a Nick's our system, but it isn't 00:59.360 --> 01:02.120 a great experience for development. 01:02.120 --> 01:06.280 It's quite slow and you need to do an expensive Nick's rebuild every time a dependency 01:06.280 --> 01:10.120 is added or updated. 01:10.120 --> 01:12.160 Can we just use Opam on Nick's systems? 01:12.160 --> 01:17.560 Well, yes, for Oklahoma dependencies, but not trivially for non-Ochemical dependencies. 01:17.560 --> 01:22.680 If you depend on, for example, C libraries, you need to set up a Nick's development environment 01:22.680 --> 01:28.600 using something like Nick's shell or Nick's develop with the system dependencies. 01:28.600 --> 01:33.480 This requires a manual resolution of those dependencies, and the resulting binary will 01:33.480 --> 01:38.760 contain a path in the next store, which isn't part of a garbage collection route. 01:38.760 --> 01:45.960 So the built artifacts will stop working on the next next GC. 01:45.960 --> 01:50.160 I'm saying system dependencies a lot, and what I mean by that is Opam is rather unique for 01:50.160 --> 01:56.280 a language package manager in that supports providing non-Ochemical dependencies as external 01:56.280 --> 02:00.400 dependencies, they're called DepX, DepX. 02:00.400 --> 02:05.080 You can declare, parameterize, by things like an operating system, packages to be installed 02:05.080 --> 02:07.560 by your system package manager. 02:07.560 --> 02:12.120 So this is an example for the GNP project. 02:12.120 --> 02:16.200 This is like a C library for numerical computation. 02:16.200 --> 02:24.160 You can see here, on Nick's sauce, we depend upon the GNP package, but in DepX, for example, 02:24.160 --> 02:27.720 it's named LibGempDev. 02:27.720 --> 02:33.880 So when using a project that depends upon GNP in Oklahoma on a DepX system, Opam will invoke 02:33.880 --> 02:40.640 up-get install LibGempDev, the equivalent in a Nick's system would be a Nick's and 02:40.680 --> 02:46.160 the equivalent in the GNP, but this will only add binaries to the path. 02:46.160 --> 02:53.120 It won't set up flags that we need for development such as linking flags. 02:53.120 --> 03:02.680 So to provide Nick's system dependencies with Opam, we overhauled its system dependency mechanism 03:02.680 --> 03:04.520 in order to support this. 03:04.560 --> 03:12.200 So Opam gets the lists of DepX for the current switch, which is like a virtual environment, 03:12.200 --> 03:18.200 and creates a Nick's derivation file, they'll look something like this. 03:18.200 --> 03:27.320 You can see here we have the inputs to the derivation, which are the DepX from the Opam repository. 03:27.320 --> 03:33.960 And then the build phase, which is the only phase, builds an environment file that Opam 03:33.960 --> 03:40.520 can read, which sets up the environment variables, used inside the derivation. 03:40.520 --> 03:45.320 And you can see there's a list of variables which are excluded or appended to, instead 03:45.320 --> 03:55.520 of a normal export, and this is from the Nick's developer source code actually. 03:55.520 --> 03:59.720 This is basically how Nick's shell next to help work under the hood, but we're using the 03:59.720 --> 04:07.640 Okamil Package Manager to manage the environment. 04:07.640 --> 04:12.040 Can I get rid of that little, yeah, it's all right. 04:12.040 --> 04:21.800 So basically the resultant environment file is actually a RIT in the Nick's store, the 04:21.800 --> 04:27.080 Nick's GC thing, so it won't be garbage collected as long as that file exists. 04:27.080 --> 04:31.160 So that means your build artifacts will continue to work until you actually remove the switch, 04:31.160 --> 04:32.360 which is quite neat. 04:32.360 --> 04:38.520 Another neat aspect is it won't interact with your system environment, like the Opam, 04:38.520 --> 04:42.480 DepX mechanism with on another system, such as Debian, when you do that app install, 04:42.480 --> 04:45.040 blah, that changes your whole system. 04:45.040 --> 04:48.720 So this could be useful even on the next system. 04:48.720 --> 04:54.200 So before if you return install packages that depended upon ConfGMP, like the Let's Encrypts 04:54.200 --> 05:00.560 Library for provisioning till last year to forgets, you would get this linking error. 05:00.560 --> 05:08.400 But now you get prompted, do you want to run the Nick's build, and it will run a Nick's build 05:08.400 --> 05:14.040 upon this m.nix file, which is what I showed you earlier, and it will generate a Nick's 05:14.040 --> 05:15.040 own file. 05:15.040 --> 05:18.760 Those are different names, it's a little confusing, but that's actually the environment 05:18.760 --> 05:25.320 file, the Opam will read, and then you can see the subsequent install works seamlessly. 05:25.320 --> 05:29.480 And without this mechanism, you would have to manually get all the system dependencies 05:29.480 --> 05:31.480 you might need. 05:31.480 --> 05:32.480 Thank you. 05:32.480 --> 05:43.520 Let me know if you have any questions, grab me at the end, or something. 05:43.520 --> 05:44.520 Thank you very much.