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NixOS / Nix announcements / 19 Dec 2022
NixOS / Nix announcements / 19 Dec 2022
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From YouTube: What's new in Nix 2.8.0 - 2.12.0?

Description

0:10 Intro
0:41 Format Nix code with: nix fmt
1:19 Impure derivations (experimental feature)
4:20 Trace verbose
4:51 Debugger (experimental fetature)
6:43 Nix search exclude flag
7:39 Towards more portable nix
9:06 Outro

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Hi,, I'm daniel baker. welcome to the next installment of the nix release videos.. This.

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Is a summary of several releases from 2.8 through 2.12.

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And my name is tom breckney. I'm excited to provide an introduction to the new features.

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And progress for the nix project overall., I hope you will find these visual walkthroughs.

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Informative. sadly,, we were only covering the highlights of the mentioned releases.

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If we've missed anything,, please let us know in the comments: below. there's a lot to cover,.

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So let's get started. as of nix version 2.8,, there is a new experimental.

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Command, nix format,, which applies a formatter defined by the formatter.system lake output,.

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To the expressions in your nix files., you can format a file or a folder by passing it.

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As an argument or format all files by passing no argument. here, we have our flake file that.

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Defines the formatter and a file with a simple expression.: if you run nix format,, it will.

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Tell us how many files and which files have been formatted., and if we look at our example.

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File, we can see that it has been formatted. next,. We have impure derivations.. These are.

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Derivations that can produce a different result. Every time they're run,, as well as have additional.

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Things like be able to access the network during builds,, and they also don't have to.

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Have a known output produced or known output hash available at the time of build., so it's.

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Kind of a mix of several other kinds of derivations that already exist in nix.. This is just a recombination.

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Of some of those features., let's take a look at how this works. so first off, we have to.

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Enable a few things. we have to make sure we have at least impure derivations and ca.

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Derivations in existence. the rest of these,, I do these for usage and convenience., so we.

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Turn on impure derivations and ca derivations.. Now, let's take a look at what this looks: like.

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We bring in our standard nix packages as necessary,, and we make a derivation. name is going to be.

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My keys, and we're going to have this thing be impure. Equals set equals to true.. This is what.

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Tells the machinery to use this impure derivation. next,, we give it a command. in this particular.

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Case,, we'll just curl something. we'll go grab my ssh keys off of github for whatever reason,.

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Because we want those public keys., all right,, let's build it. and now that I've built it,.

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What happened is during the build,, this impure derivation can access the network and fetch our.

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Keys, and perhaps we could do something interesting with these., because this is an external resource,.

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This is considered impure, and because we don't know the result up, front. so technically,. If I.

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Go change my keys and rerun this build,. We might have a different result. notice. How, even though.

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I ran the same thing again, we did a rebuild without even asking for one.. This is because.

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Impure derivations are always going to be rebuilt, and their results are not cached. in that sense,.

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They will always run. and other interesting things that come out of. This is that, if you have,.

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You could have now chains of impure derivations that depend on each other.. They will continue.

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To be impure, derivations, and no pure derivation can depend on them. unless you have a hash at.

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Some point,, a known upfront hash that allows you to then convert it back into the pure world.

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For use in a pure derivation., some of the use cases we're thinking about for this is something like.

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Very complex transformations of something that has to be fetched from the network,.

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And then transform several times, and maybe we're going to break apart these transformations.

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Before we finally know what the output result is going to be,, because it's deterministic,.

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And then we use this elsewhere.. Some examples of this would be to process a git repository,.

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Or to process some binaries into some final form before we're going to use it elsewhere,.

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In our next expressions. so again,, this is right now an experimental feature., please play with it.

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Tell us what you think. as the next version. 2.10, a new built-in function, trace, verbose, is available.

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It is similar to the trace function,, but must be enabled explicitly. otherwise,.

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It behaves as a no op. here we have a command that uses the trace, verbose, function.

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If we run it,, it will simply return one., and here we have another command. That.

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Enables the trace, verbose, option. if we run this,, it will also print our message.

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The next feature we're excited about is debugging.. This allows us to take a look.

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At an environment when some sort of an error occurred or took place., so let's give this a shot.

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By running an evaluation on a file with this new flag of tac tac debugger,, we're able to.

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Run it, and then we see that we have dropped into some sort of an environment.

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Let's take a look at it., a breakpoint has been reached., it tells us where it's located,.

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And it gives us a little bit of a hint of the context above and below the line where this took.

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Place, and kind of explore what values are available. by typing colon env,. We can see we.

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Have a few variables available.: let's take a look at a and b. okay,. These are exactly what we expect.

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There are additional commands available under help to go. Look at the stack trace,. The current.

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Trace, to jump between stack traces, and to continue to the rest of the program.

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So, let's take a look at the backtrace. we're now at this level.. Let's say this is giving us all.

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The information we want, that is correct, and we can continue on to the next breakpoint,.

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And then now we can explore this environment as well. we've reached,. It looks like, line 10s and 11.

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We have some different expression inside of this.. We have a different environment, different variables.

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Available to us., so we've got to look at c and d, and there we go. that's pretty simple.

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This is pretty useful when you're evaluating a large expression, or there's something where.

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It's hard to follow the flow of events, and doing a bunch of trace statements is not feasible or.

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Hard to keep track of. nice thing is, you can kind of run this without the debugger active, and it.

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Just bypasses all of those break statements. so give this feature a shot,, and let us know what.

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You think., as of nix version 2.10, nix search, has a new flag, exclude, to filter out packages.

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Here we have a command to search nix packages for 0mq.

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If we run it,, we get a list of all packages that have 0mq in the name or the description.

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Here we add the exclude flag to our command to filter out any packages that mention python.

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And if we run it,, we can see that nix search has excluded those packages.

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We can also exclude multiple things by wrapping. The arguments to exclude in single quotes.

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And using the pipe operator. by wrapping the arguments to exclude in single quotes and using the pipe operator.

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Here you can see we're excluding python,, ocaml,, octave, and lisp.

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And if we run this,, the list is now much shorter.. This next feature makes it easy to try nix without.

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Having root permissions or going through a normal, install and only uses, some directories in your.

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Home., so let's give this a shot. first thing we need to do is we need to grab a static binary of.

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Nix itself. and that should be fairly quick here.. Once we have this,, we are going to give it executable.

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Permissions. and then we are ready to use., it looks like we can go, grab its help pages and start to.

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Actually use it. to make it a little bit access some additional experimental features,, I'm going.

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To turn those on by exporting a nix, config variable. and let's see if now we could run something.

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We get a little bit of warning that says that slash var, nix, nix, var nix does not exist. instead,.

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It's going to use something in my home directory as a true root store, because I have those features.

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Turned on in this particular kernel., this should be able to work. cool.. We now have a hello world.

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Able to run., let's go, take a look at what exists here., so in the local share nix root nix,. I have.

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All the things I would normally expect to happen at my root file system., but instead,. It now lives.

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Somewhere different, a little bit isolated., and this should make it easier to try out nix in this.

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Sort of situation. give it a shot. and that's the last feature for now. yesterday was the release.

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For 2.12 and is the last release scheduled for the year.. This contains a large number of documentation.

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Stability fixes. nixos 22.11 release that just happened will have 2.11 at the very least.. The.

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Nix repo itself will always have the latest releases available. as always,. Let us know if.

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There are additional changes: you're excited about., please thumbs up any issues or prs in the nix repo.

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Itself to bring it to the attention of the nix maintenance team. thank you.

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These releases will not be possible without the hard work done by the contributors.. We also want.

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To thank the users for bug reports, example usages, ideas,, and for making the nix community a better.

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Place. thank you.