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* fix up language in the packaging tutorial - make many sentences shorter - add links - expand on finding things - use more domain-specific headings - add next steps Co-authored-by: Henrik <i97henka@gmail.com> Co-authored-by: Olivia Crain <olivia@olivia.dev> Co-authored-by: Silvan Mosberger <github@infinisil.com>
673 lines
24 KiB
Markdown
673 lines
24 KiB
Markdown
---
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myst:
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html_meta:
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"description lang=en": "Packaging Existing Software With Nix"
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"keywords": "Nix, packaging"
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---
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(packaging-existing-software)=
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# Packaging existing software with Nix
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One of Nix's primary use-cases is in addressing common difficulties encountered with packaging software, such as specifying and obtaining dependencies.
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In the long term, Nix helps tremendously with alleviating such problems.
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But when *first* packaging existing software with Nix, it's common to encounter errors that seem inscrutable.
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## Introduction
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In this tutorial, you'll create your first [Nix derivations](https://nix.dev/manual/nix/2.18/language/derivations) to package C/C++ software, taking advantage of the [Nixpkgs Standard Environment](https://nixos.org/manual/nixpkgs/stable/#part-stdenv) (`stdenv`), which automates much of the work involved.
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### What will you learn?
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The tutorial begins with `hello`, an implementation of "hello world" which only requires dependencies already provided by `stdenv`.
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Next, you will build more complex packages with their own dependencies, leading you to use additional derivation features.
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You'll encounter and address Nix error messages, build failures, and a host of other issues, developing your iterative debugging techniques along the way.
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### What do you need?
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- Familiarity with the Unix shell and plain text editors
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- You should be confident with [reading the Nix language](reading-nix-language). Feel free to go back and work through the tutorial first.
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### How long does it take?
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Going through all the steps carefully will take around 60 minutes.
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## Your first package
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:::{note}
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<!--
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TODO: link to the Nix manual glossary entry once it's in a released build:
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https://hydra.nixos.org/job/nix/master/build.x86_64-linux/latest/download/manual/glossary.html#package
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-->
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A _package_ is a loosely defined concept that refers to either a collection of files and other data, or a {term}`Nix expression` representing such a collection before it comes into being.
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Packages in Nixpkgs have a conventional structure, allowing them to be discovered in searches and composed in environments alongside other packages.
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For the purposes of this tutorial, a "package" is a Nix language function that will evaluate to a derivation.
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It will enable you or others to produce an artifact for practical use, as a consequence of having "packaged existing software with Nix".
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:::
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To start, consider this skeleton derivation:
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```nix
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{ stdenv }:
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stdenv.mkDerivation { };
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```
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This is a function which takes an attribute set containing `stdenv`, and produces a derivation (which currently does nothing).
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### A package function
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GNU Hello is an implementation of the "hello world" program, with source code accessible [from the GNU Project's FTP server](https://ftp.gnu.org/gnu/hello/).
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To begin, add a `name` attribute to the set passed to `mkDerivation`.
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Every package needs a name and a version, and Nix will throw `error: derivation name missing` without.
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```diff
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stdenv.mkDerivation {
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+ pname = "hello";
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+ version = "2.12.1";
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```
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Next, you will declare a dependency on the latest version of `hello`, and instruct Nix to use `fetchzip` to download the [source code archive](https://ftp.gnu.org/gnu/hello/hello-2.12.1.tar.gz).
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:::{note}
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`fetchzip` can fetch [more archives](https://nixos.org/manual/nixpkgs/stable/#fetchurl) than just] zip files!
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:::
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The hash cannot be known until after the archive has been downloaded and unpacked.
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Nix will complain if the hash supplied to `fetchzip` is incorrect.
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It is common practice to supply a fake one with `lib.fakeSha256` and change the derivation definition after Nix reports the correct hash:
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```nix
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# hello.nix
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{
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lib,
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stdenv,
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fetchzip,
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}:
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stdenv.mkDerivation {
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pname = "hello";
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version = "2.12.1";
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src = fetchzip {
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url = "https://ftp.gnu.org/gnu/hello/hello-2.12.1.tar.gz";
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sha256 = lib.fakeSha256;
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};
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}
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```
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Save this file to `hello.nix` and run `nix-build` to observe your first build failure:
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```console
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$ nix-build hello.nix
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error: cannot evaluate a function that has an argument without a value ('lib')
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Nix attempted to evaluate a function as a top level expression; in
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this case it must have its arguments supplied either by default
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values, or passed explicitly with '--arg' or '--argstr'. See
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https://nix.dev/manual/nix/2.18/language/constructs.html#functions.
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at /home/nix-user/hello.nix:2:3:
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1| # hello.nix
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2| { lib
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| ^
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3| , stdenv
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```
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Problem: the expression in `hello.nix` is a *function*, which only produces its intended output if it is passed the correct *arguments*.
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### Building with `nix-build`
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`lib` is available from [`nixpkgs`](https://github.com/NixOS/nixpkgs/), which must be imported with another Nix expression in order to pass it as an argument to this derivation.
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The recommended way to do this is to create a `default.nix` file in the same directory as `hello.nix`, with the following contents:
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```nix
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# default.nix
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let
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nixpkgs = fetchTarball "https://github.com/NixOS/nixpkgs/tarball/nixos-22.11";
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pkgs = import nixpkgs { config = {}; overlays = []; };
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in
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{
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hello = pkgs.callPackage ./hello.nix { };
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}
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```
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This allows you to run `nix-build -A hello` to realize the derivation in `hello.nix`, similar to the current convention used in Nixpkgs.
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:::{note}
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[`callPackage`] automatically passes attributes from `pkgs` to the given function, if they match attributes required by that function's argument attrset.
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In this case, `callPackage` will supply `lib`, `stdenv`, and `fetchzip` to the function defined in `hello.nix`.
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:::
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Now run the `nix-build` command with the new argument:
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```console
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$ nix-build -A hello
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error:
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...
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… while evaluating attribute 'src' of derivation 'hello'
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at /home/nix-user/hello.nix:9:3:
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8|
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9| src = fetchzip {
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| ^
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10| url = "https://ftp.gnu.org/gnu/hello/hello-2.12.1.tar.gz";
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error: hash mismatch in file downloaded from 'https://ftp.gnu.org/gnu/hello/hello-2.12.1.tar.gz':
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specified: sha256:0000000000000000000000000000000000000000000000000000
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got: sha256:0xw6cr5jgi1ir13q6apvrivwmmpr5j8vbymp0x6ll0kcv6366hnn
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```
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### Finding the file hash
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As expected, the incorrect file hash caused an error, and Nix helpfully provided the correct one.
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In `hello.nix`, replace `lib.fakeSha256` with the correct hash:
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```nix
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# hello.nix
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{
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lib,
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stdenv,
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fetchzip,
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}:
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stdenv.mkDerivation {
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pname = "hello";
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version = "2.12.1";
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src = fetchzip {
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url = "https://ftp.gnu.org/gnu/hello/hello-2.12.1.tar.gz";
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sha256 = "0xw6cr5jgi1ir13q6apvrivwmmpr5j8vbymp0x6ll0kcv6366hnn";
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};
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}
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```
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Now run the previous command again:
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```console
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$ nix-build -A hello
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this derivation will be built:
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/nix/store/rbq37s3r76rr77c7d8x8px7z04kw2mk7-hello.drv
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building '/nix/store/rbq37s3r76rr77c7d8x8px7z04kw2mk7-hello.drv'...
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...
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configuring
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...
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configure: creating ./config.status
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config.status: creating Makefile
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...
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building
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... <many more lines omitted>
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```
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Great news: the derivation built successfully!
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The console output shows that `configure` was called, which produced a `Makefile` that was then used to build the project.
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It wasn't necessary to write any build instructions in this case because the `stdenv` build system is based on [GNU Autoconf](https://www.gnu.org/software/autoconf/), which automatically detected the structure of the project directory.
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### Build result
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Check your working directory for the result:
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```console
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$ ls
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default.nix hello.nix result
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```
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This `result` is a [symbolic link](https://en.wikipedia.org/wiki/Symbolic_link) to a Nix store location containing the built binary; you can call `./result/bin/hello` to execute this program:
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```console
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$ ./result/bin/hello
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Hello, world!
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```
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Congratulations, you have successfully packaged your first program with Nix!
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Next, you'll package another piece of software with external-to-`stdenv` dependencies that present new challenges, requiring you to make use of more `mkDerivation` features.
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## A package with dependencies
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Now you will package a somewhat more complicated program, [`icat`](https://github.com/atextor/icat), which allows you to render images in your terminal.
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Change the `default.nix` from the previous section by adding a new attribute for `icat`:
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```nix
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# default.nix
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let
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nixpkgs = fetchTarball "https://github.com/NixOS/nixpkgs/tarball/nixos-22.11";
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pkgs = import nixpkgs { config = {}; overlays = []; };
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in
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{
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hello = pkgs.callPackage ./hello.nix { };
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icat = pkgs.callPackage ./icat.nix { };
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}
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```
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Copy `hello.nix` to a new file `icat.nix`, and update the `pname` and `version` attributes in that file:
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```nix
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# icat.nix
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{
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lib,
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stdenv,
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fetchzip,
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}:
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stdenv.mkDerivation {
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pname = "icat";
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version = "v0.5";
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src = fetchzip {
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# ...
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};
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}
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```
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Now to download the source code.
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`icat`'s upstream repository is hosted on [GitHub](https://github.com/atextor/icat), so you should replace the previous [source fetcher](https://nixos.org/manual/nixpkgs/stable/#chap-pkgs-fetchers).
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This time you will use [`fetchFromGitHub`](https://nixos.org/manual/nixpkgs/stable/#fetchfromgithub) instead of `fetchzip`, by updating the argument attribute set to the function accordingly:
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```nix
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# icat.nix
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{
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lib,
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stdenv,
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fetchFromGitHub,
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}:
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stdenv.mkDerivation {
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pname = "icat";
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version = "v0.5";
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src = fetchFromGitHub {
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# ...
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};
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}
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```
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### Fetching source from GitHub
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While `fetchzip` required `url` and `sha256` arguments, more are needed for [`fetchFromGitHub`](https://nixos.org/manual/nixpkgs/stable/#fetchfromgithub).
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The source is URL is `https://github.com/atextor/icat`, which already gives the first two arguments:
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- `owner`: the name of the account controlling the repository
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```
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owner = "atextor";
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```
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- `repo`: the name of the repository to fetch
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```
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repo = "icat";
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``````
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Navigate to the project's [Tags page](https://github.com/atextor/icat/tags) to find a suitable [Git revision](https://git-scm.com/docs/revisions) (`rev`), such as the Git commit hash or tag (e.g. `v1.0`) corresponding to the release you want to fetch.
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In this case, the latest release tag is `v0.5`.
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As in the `hello` example, a hash must also be supplied.
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This time, instead of using `lib.fakeSha256` and letting `nix-build` report the correct one in an error, you can fetch the correct hash in the first place with the `nix-prefetch-url` command.
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You need the SHA256 hash of the *contents* of the tarball (as opposed to the hash of the tarball file itself).
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Therefore pass the `--unpack` and `--type sha256` arguments:
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```console
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$ nix-prefetch-url --unpack https://github.com/atextor/icat/archive/refs/tags/v0.5.tar.gz --type sha256
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path is '/nix/store/p8jl1jlqxcsc7ryiazbpm7c1mqb6848b-v0.5.tar.gz'
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0wyy2ksxp95vnh71ybj1bbmqd5ggp13x3mk37pzr99ljs9awy8ka
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```
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Set the correct hash for `fetchFromGitHub`:
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```nix
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# icat.nix
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{
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lib,
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stdenv,
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fetchFromGitHub,
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}:
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stdenv.mkDerivation {
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pname = "icat";
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version = "v0.5";
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src = fetchFromGitHub {
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owner = "atextor";
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repo = "icat";
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rev = "v0.5";
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sha256 = "0wyy2ksxp95vnh71ybj1bbmqd5ggp13x3mk37pzr99ljs9awy8ka";
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};
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}
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```
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### Missing dependencies
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Running `nix-build` with the new `icat` attribute, an entirely new issue is reported:
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```console
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$ nix-build -A icat
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these 2 derivations will be built:
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/nix/store/86q9x927hsyyzfr4lcqirmsbimysi6mb-source.drv
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/nix/store/l5wz9inkvkf0qhl8kpl39vpg2xfm2qpy-icat.drv
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...
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error: builder for '/nix/store/l5wz9inkvkf0qhl8kpl39vpg2xfm2qpy-icat.drv' failed with exit code 2;
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last 10 log lines:
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> from /nix/store/hkj250rjsvxcbr31fr1v81cv88cdfp4l-glibc-2.37-8-dev/include/stdio.h:27,
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> from icat.c:31:
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> /nix/store/hkj250rjsvxcbr31fr1v81cv88cdfp4l-glibc-2.37-8-dev/include/features.h:195:3: warning: #warning "_BSD_SOURCE and _SVID_SOURCE are deprecated, use _DEFAULT_SOURCE" [8;;https://gcc.gnu.org/onlinedocs/gcc/Warning-Options.html#index-Wcpp-Wcpp8;;]
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> 195 | # warning "_BSD_SOURCE and _SVID_SOURCE are deprecated, use _DEFAULT_SOURCE"
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> | ^~~~~~~
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> icat.c:39:10: fatal error: Imlib2.h: No such file or directory
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> 39 | #include <Imlib2.h>
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> | ^~~~~~~~~~
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> compilation terminated.
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> make: *** [Makefile:16: icat.o] Error 1
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For full logs, run 'nix log /nix/store/l5wz9inkvkf0qhl8kpl39vpg2xfm2qpy-icat.drv'.
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```
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A compiler error!
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The `icat` source was pulled from GitHub, and Nix tried to build what it found, but compilation failed due to a missing dependency: the `imlib2` header.
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If you [search for `imlib2` on search.nixos.org](https://search.nixos.org/packages?query=imlib2), you'll find that `imlib2` is already in Nixpkgs.
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Add this package to your build environment by adding `imlib2` to the arguments of the function in `icat.nix`.
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Then add the argument's value `imlib2` to the list of `buildInputs` in `stdenv.mkDerivation`:
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```nix
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# icat.nix
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{
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lib,
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stdenv,
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fetchFromGitHub,
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imlib2,
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}:
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stdenv.mkDerivation {
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pname = "icat";
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version = "v0.5";
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src = fetchFromGitHub {
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owner = "atextor";
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repo = "icat";
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rev = "v0.5";
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sha256 = "0wyy2ksxp95vnh71ybj1bbmqd5ggp13x3mk37pzr99ljs9awy8ka";
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};
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buildInputs = [ imlib2 ];
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}
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```
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Run `nix-build -A icat` again and you'll encounter another error, but compilation proceeds further this time:
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```console
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$ nix-build -A icat
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this derivation will be built:
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/nix/store/bw2d4rp2k1l5rg49hds199ma2mz36x47-icat.drv
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...
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error: builder for '/nix/store/bw2d4rp2k1l5rg49hds199ma2mz36x47-icat.drv' failed with exit code 2;
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last 10 log lines:
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> from icat.c:31:
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> /nix/store/hkj250rjsvxcbr31fr1v81cv88cdfp4l-glibc-2.37-8-dev/include/features.h:195:3: warning: #warning "_BSD_SOURCE and _SVID_SOURCE are deprecated, use _DEFAULT_SOURCE" [8;;https://gcc.gnu.org/onlinedocs/gcc/Warning-Options.html#index-Wcpp-Wcpp8;;]
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> 195 | # warning "_BSD_SOURCE and _SVID_SOURCE are deprecated, use _DEFAULT_SOURCE"
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> | ^~~~~~~
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> In file included from icat.c:39:
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> /nix/store/4fvrh0sjc8sbkbqda7dfsh7q0gxmnh9p-imlib2-1.11.1-dev/include/Imlib2.h:45:10: fatal error: X11/Xlib.h: No such file or directory
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> 45 | #include <X11/Xlib.h>
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> | ^~~~~~~~~~~~
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> compilation terminated.
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> make: *** [Makefile:16: icat.o] Error 1
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For full logs, run 'nix log /nix/store/bw2d4rp2k1l5rg49hds199ma2mz36x47-icat.drv'.
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```
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You can see a few warnings which should be corrected in the upstream code.
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But the important bit for this tutorial is `fatal error: X11/Xlib.h: No such file or directory`: another dependency is missing.
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## Finding packages
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Determining from where to source a dependency is currently a somewhat involved, because package names don't always correspond to library or program names.
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You will need the `Xlib.h` headers from the `X11` C package, the Nixpkgs derivation for which is `libX11`, available in the `xorg` package set.
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There are multiple ways to figure this out:
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### `search.nixos.org`
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:::{tip}
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The easiest way to find what you need is on search.nixos.org/packages.
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:::
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Unfortunately in this case, [searching for `x11`](https://search.nixos.org/packages?query=x11) produces too many irrelevant results because X11 is ubiquitous.
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On the left side bar there is a list package sets, and [selecting `xorg`](https://search.nixos.org/packages?channel=23.11&buckets={%22package_attr_set%22%3A[%22xorg%22]%2C%22package_license_set%22%3A[]%2C%22package_maintainers_set%22%3A[]%2C%22package_platforms%22%3A[]}&query=x11) shows something promising.
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In case all else fails, it helps to become familiar with searching the [Nixpkgs source code](https://github.com/nixos/nixpkgs) for keywords.
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### Git and `rg`
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To find name assignments in the source, search for `"<keyword> ="`.
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For example, these are the search results for [`"x11 = "`](https://github.com/search?q=repo%3ANixOS%2Fnixpkgs+%22x11+%3D%22&type=code) or [`"libx11 ="`](https://github.com/search?q=repo%3ANixOS%2Fnixpkgs+%22libx11+%3D%22&type=code) on Github .
|
|
|
|
Or fetch a local clone of the repository and use `rg`.
|
|
Nixpkgs is huge.
|
|
Only clone the latest revision if you don't want to wait a long time:
|
|
|
|
```console
|
|
$ nix-shell -p git ripgrep
|
|
[nix-shell:~]$ git glone https://github.com/NixOS/nixpkgs --depth 1
|
|
```
|
|
|
|
To narrow down results, specify which subdirectory you want to search:
|
|
|
|
```console
|
|
[nix-shell:~]$ rg "x11 =" pkgs
|
|
pkgs/tools/X11/primus/default.nix
|
|
21: primus = if useNvidia then primusLib_ else primusLib_.override { nvidia_x11 = null; };
|
|
22: primus_i686 = if useNvidia then primusLib_i686_ else primusLib_i686_.override { nvidia_x11 = null; };
|
|
|
|
pkgs/applications/graphics/imv/default.nix
|
|
38: x11 = [ libGLU xorg.libxcb xorg.libX11 ];
|
|
|
|
pkgs/tools/X11/primus/lib.nix
|
|
14: if nvidia_x11 == null then libGL
|
|
|
|
pkgs/top-level/linux-kernels.nix
|
|
573: ati_drivers_x11 = throw "ati drivers are no longer supported by any kernel >=4.1"; # added 2021-05-18;
|
|
... <a lot more results>
|
|
```
|
|
|
|
Since `rg` is case sensitive by default,
|
|
Add `-i` to make sure you don't miss anything:
|
|
|
|
```
|
|
[nix-shell:~]$ rg -i "libx11 =" pkgs
|
|
pkgs/applications/version-management/monotone-viz/graphviz-2.0.nix
|
|
55: ++ lib.optional (libX11 == null) "--without-x";
|
|
|
|
pkgs/top-level/all-packages.nix
|
|
14191: libX11 = xorg.libX11;
|
|
|
|
pkgs/servers/x11/xorg/default.nix
|
|
1119: libX11 = callPackage ({ stdenv, pkg-config, fetchurl, xorgproto, libpthreadstubs, libxcb, xtrans, testers }: stdenv.mkDerivation (finalAttrs: {
|
|
|
|
pkgs/servers/x11/xorg/overrides.nix
|
|
147: libX11 = super.libX11.overrideAttrs (attrs: {
|
|
```
|
|
|
|
### `nix-locate`
|
|
|
|
Consider using `nix-locate` from the [`nix-index`](https://github.com/nix-community/nix-index) tool to find derivations that provide what you need.
|
|
|
|
### Adding package sets as dependencies
|
|
|
|
Add this to your derivation's input attribute set and to `buildInputs`:
|
|
|
|
```nix
|
|
# icat.nix
|
|
{
|
|
lib,
|
|
stdenv,
|
|
fetchFromGitHub,
|
|
imlib2,
|
|
xorg,
|
|
}:
|
|
|
|
stdenv.mkDerivation {
|
|
pname = "icat";
|
|
version = "v0.5";
|
|
|
|
src = fetchFromGitHub {
|
|
owner = "atextor";
|
|
repo = "icat";
|
|
rev = "v0.5";
|
|
sha256 = "0wyy2ksxp95vnh71ybj1bbmqd5ggp13x3mk37pzr99ljs9awy8ka";
|
|
};
|
|
|
|
buildInputs = [ imlib2 xorg.libX11 ];
|
|
}
|
|
```
|
|
|
|
:::{note}
|
|
Only add the top-level `xorg` derivation to the input attrset, rather than the full `xorg.libX11`, as the latter would cause a syntax error.
|
|
|
|
Because Nix is lazily-evaluated, using `xorg.libX11` means that we only include the `libX11` attribute and the derivation doesn't actually include all of `xorg` into the build context.
|
|
:::
|
|
|
|
## Fixing build failures
|
|
|
|
Run the last command again:
|
|
|
|
```console
|
|
$ nix-build -A icat
|
|
this derivation will be built:
|
|
/nix/store/x1d79ld8jxqdla5zw2b47d2sl87mf56k-icat.drv
|
|
...
|
|
error: builder for '/nix/store/x1d79ld8jxqdla5zw2b47d2sl87mf56k-icat.drv' failed with exit code 2;
|
|
last 10 log lines:
|
|
> 195 | # warning "_BSD_SOURCE and _SVID_SOURCE are deprecated, use _DEFAULT_SOURCE"
|
|
> | ^~~~~~~
|
|
> icat.c: In function 'main':
|
|
> icat.c:319:33: warning: ignoring return value of 'write' declared with attribute 'warn_unused_result' [8;;https://gcc.gnu.org/onlinedocs/gcc/Warning-Options.html#index-Wunused-result-Wunused-result8;;]
|
|
> 319 | write(tempfile, &buf, 1);
|
|
> | ^~~~~~~~~~~~~~~~~~~~~~~~
|
|
> gcc -o icat icat.o -lImlib2
|
|
> installing
|
|
> install flags: SHELL=/nix/store/8fv91097mbh5049i9rglc73dx6kjg3qk-bash-5.2-p15/bin/bash install
|
|
> make: *** No rule to make target 'install'. Stop.
|
|
For full logs, run 'nix log /nix/store/x1d79ld8jxqdla5zw2b47d2sl87mf56k-icat.drv'.
|
|
```
|
|
|
|
The missing dependency error is solved, but there is now another problem: `make: *** No rule to make target 'install'. Stop.`
|
|
|
|
### `installPhase`
|
|
`stdenv` is automatically working with the `Makefile` that comes with `icat`.
|
|
The console output showas that `configure` and `make` are executed without issue, so the `icat` binary is compiling successfully.
|
|
|
|
The failure occurs when the `stdenv` attempts to run `make install`.
|
|
The `Makefile` included in the project happens to lack an `install` target.
|
|
The `README` in the `icat` repository only mentions using `make` to build the tool, leaving the installation step up to users.
|
|
|
|
To add this step to your derivation, use the [`installPhase` attribute](https://nixos.org/manual/nixpkgs/stable/#ssec-install-phase).
|
|
It contains a list of command strings that are executed to perform the installation.
|
|
|
|
Because `make` finishes successfully, the `icat` executable is available in the build directory.
|
|
You only need to copy it from there to the output directory.
|
|
|
|
In Nix, the output directory is stored in the `$out` variable.
|
|
That variable is accessible in the derivation's [`builder` execution environment](https://nix.dev/manual/nix/2.19/language/derivations#builder-execution).
|
|
Create a `bin` directory within the `$out` directory and copy the `icat` binary there:
|
|
|
|
```nix
|
|
# icat.nix
|
|
{
|
|
lib,
|
|
stdenv,
|
|
fetchFromGitHub,
|
|
imlib2,
|
|
xorg,
|
|
}:
|
|
|
|
stdenv.mkDerivation {
|
|
pname = "icat";
|
|
version = "v0.5";
|
|
|
|
src = fetchFromGitHub {
|
|
owner = "atextor";
|
|
repo = "icat";
|
|
rev = "v0.5";
|
|
sha256 = "0wyy2ksxp95vnh71ybj1bbmqd5ggp13x3mk37pzr99ljs9awy8ka";
|
|
};
|
|
|
|
buildInputs = [ imlib2 xorg.libX11.dev ];
|
|
|
|
installPhase = ''
|
|
mkdir -p $out/bin
|
|
cp icat $out/bin
|
|
'';
|
|
}
|
|
```
|
|
|
|
### Phases and hooks
|
|
|
|
Nixpkgs `stdenv.mkDerivation` derivations are separated into [phases](https://nixos.org/manual/nixpkgs/stable/#sec-stdenv-phases).
|
|
Each is intended to control some aspect of the build process.
|
|
|
|
Earlier you observed how `stdenv.mkDerivation` expected the project's `Makefile` to have an `install` target, and failed when it didn't.
|
|
To fix this, you defined a custom `installPhase` containing instructions for copying the `icat` binary to the correct output location, in effect installing it.
|
|
Up to that point, the `stdenv.mkDerivation` automatically determined the `buildPhase` information for the `icat` package.
|
|
|
|
During derivation realisation, there are a number of shell functions ("hooks", in Nixpkgs) which may execute in each derivation phase.
|
|
Hooks do things like set variables, source files, create directories, and so on.
|
|
|
|
These are specific to each phase, and run both before and after that phase's execution.
|
|
They modify the build environment for common operations during the build.
|
|
|
|
It's good practice when packaging software with Nix to include calls to these hooks in the derivation phases you define, even when you don't make direct use of them.
|
|
This facilitates easy [overriding](https://nixos.org/manual/nixpkgs/stable/#chap-overrides) of specific parts of the derivation later.
|
|
And it keeps the code tidy and makes it easier to read.
|
|
|
|
Adjust your `installPhase` to call the appropriate hooks:
|
|
|
|
```nix
|
|
# icat.nix
|
|
|
|
# ...
|
|
|
|
installPhase = ''
|
|
runHook preInstall
|
|
mkdir -p $out/bin
|
|
cp icat $out/bin
|
|
runHook postInstall
|
|
'';
|
|
|
|
# ...
|
|
|
|
```
|
|
## A successful build
|
|
|
|
Running the `nix-build` command once more will finally do what you want, repeatably.
|
|
Call `ls` in the local directory to find a `result` symlink to a location in the Nix store:
|
|
|
|
```console
|
|
$ ls
|
|
default.nix hello.nix icat.nix result
|
|
```
|
|
|
|
`result/bin/icat` is the executable built previously. Success!
|
|
|
|
## References
|
|
|
|
- [Nixpkgs Manual - Standard Environment](https://nixos.org/manual/nixpkgs/unstable/#part-stdenv)
|
|
- [Nix Pills - `callPackage` Design Pattern][`callPackage`]
|
|
|
|
[`callPackage`]: https://nixos.org/guides/nix-pills/callpackage-design-pattern.html
|
|
|
|
## Next steps
|
|
|
|
- [Add your own new packages to Nixpkgs](https://github.com/NixOS/nixpkgs/blob/master/CONTRIBUTING.md)
|
|
- [](../contributing/how-to-contribute.md)
|
|
- [](../contributing/how-to-get-help.md)
|
|
- [](sharing-dependencies)
|
|
- [](automatic-direnv)
|
|
- [](python-dev-environment)
|