depot/doc/languages-frameworks/dart.section.md

Dart

Dart applications

The function buildDartApplication builds Dart applications managed with pub.

It fetches its Dart dependencies automatically through pub2nix, and (through a series of hooks) builds and installs the executables specified in the pubspec file. The hooks can be used in other derivations, if needed. The phases can also be overridden to do something different from installing binaries.

If you are packaging a Flutter desktop application, use buildFlutterApplication instead.

pubspecLock is the parsed pubspec.lock file. pub2nix uses this to download required packages. This can be converted to JSON from YAML with something like yq . pubspec.lock, and then read by Nix.

Alternatively, autoPubspecLock can be used instead, and set to a path to a regular pubspec.lock file. This relies on import-from-derivation, and is not permitted in Nixpkgs, but can be useful at other times.

::: {.warning} When using autoPubspecLock with a local source directory, make sure to use a concatenation operator (e.g. autoPubspecLock = src + "/pubspec.lock";), and not string interpolation.

String interpolation will copy your entire source directory to the Nix store and use its store path, meaning that unrelated changes to your source tree will cause the generated pubspec.lock derivation to rebuild! :::

If the package has Git package dependencies, the hashes must be provided in the gitHashes set. If a hash is missing, an error message prompting you to add it will be shown.

The dart commands run can be overridden through pubGetScript and dartCompileCommand, you can also add flags using dartCompileFlags or dartJitFlags.

Dart supports multiple outputs types, you can choose between them using dartOutputType (defaults to exe). If you want to override the binaries path or the source path they come from, you can use dartEntryPoints. Outputs that require a runtime will automatically be wrapped with the relevant runtime (dartaotruntime for aot-snapshot, dart run for jit-snapshot and kernel, node for js), this can be overridden through dartRuntimeCommand.

{ lib, buildDartApplication, fetchFromGitHub }:

buildDartApplication rec {
  pname = "dart-sass";
  version = "1.62.1";

  src = fetchFromGitHub {
    owner = "sass";
    repo = pname;
    rev = version;
    hash = "sha256-U6enz8yJcc4Wf8m54eYIAnVg/jsGi247Wy8lp1r1wg4=";
  };

  pubspecLock = lib.importJSON ./pubspec.lock.json;
}

Patching dependencies

Some Dart packages require patches or build environment changes. Package derivations can be customised with the customSourceBuilders argument.

A collection of such customisations can be found in Nixpkgs, in the development/compilers/dart/package-source-builders directory.

This allows fixes for packages to be shared between all applications that use them. It is strongly recommended to add to this collection instead of including fixes in your application derivation itself.

Running executables from dev_dependencies

Many Dart applications require executables from the dev_dependencies section in pubspec.yaml to be run before building them.

This can be done in preBuild, in one of two ways:

1. Packaging the tool with buildDartApplication, adding it to Nixpkgs, and running it like any other application
2. Running the tool from the package cache

Of these methods, the first is recommended when using a tool that does not need to be of a specific version.

For the second method, the packageRun function from the dartConfigHook can be used. This is an alternative to dart run that does not rely on Pub.

e.g., for build_runner:

packageRun build_runner build

Do not use dart run <package_name>, as this will attempt to download dependencies with Pub.

Usage with nix-shell

Using dependencies from the Nix store

As buildDartApplication provides dependencies instead of pub get, Dart needs to be explicitly told where to find them.

Run the following commands in the source directory to configure Dart appropriately. Do not use pub after doing so; it will download the dependencies itself and overwrite these changes.

cp --no-preserve=all "$pubspecLockFilePath" pubspec.lock
mkdir -p .dart_tool && cp --no-preserve=all "$packageConfig" .dart_tool/package_config.json

Flutter applications

The function buildFlutterApplication builds Flutter applications.

See the Dart documentation for more details on required files and arguments.

flutter in Nixpkgs always points to flutterPackages.stable, which is the latest packaged version. To avoid unforeseen breakage during upgrade, packages in Nixpkgs should use a specific flutter version, such as flutter319 and flutter322, instead of using flutter directly.

{  flutter322, fetchFromGitHub }:

flutter322.buildFlutterApplication {
  pname = "firmware-updater";
  version = "0-unstable-2023-04-30";

  # To build for the Web, use the targetFlutterPlatform argument.
  # targetFlutterPlatform = "web";

  src = fetchFromGitHub {
    owner = "canonical";
    repo = "firmware-updater";
    rev = "6e7dbdb64e344633ea62874b54ff3990bd3b8440";
    hash = "sha256-s5mwtr5MSPqLMN+k851+pFIFFPa0N1hqz97ys050tFA=";
    fetchSubmodules = true;
  };

  pubspecLock = lib.importJSON ./pubspec.lock.json;
}

Usage with nix-shell

Flutter-specific nix-shell usage notes are included here. See the Dart documentation for general nix-shell instructions.

Entering the shell

By default, dependencies for only the targetFlutterPlatform are available in the build environment. This is useful for keeping closures small, but be problematic during development. It's common, for example, to build Web apps for Linux during development to take advantage of native features such as stateful hot reload.

To enter a shell with all the usual target platforms available, use the multiShell attribute.

e.g. nix-shell '<nixpkgs>' -A fluffychat-web.multiShell.