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1# Dart {#sec-language-dart}
2
3## Dart applications {#ssec-dart-applications}
4
5The function `buildDartApplication` builds Dart applications managed with pub.
6
7It 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.
8
9If you are packaging a Flutter desktop application, use [`buildFlutterApplication`](#ssec-dart-flutter) instead.
10
11`pubspecLock` is the parsed pubspec.lock file. pub2nix uses this to download required packages.
12This can be converted to JSON from YAML with something like `yq . pubspec.lock`, and then read by Nix.
13
14Alternatively, `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.
15
16::: {.warning}
17When using `autoPubspecLock` with a local source directory, make sure to use a
18concatenation operator (e.g. `autoPubspecLock = src + "/pubspec.lock";`), and
19not string interpolation.
20
21String interpolation will copy your entire source directory to the Nix store and
22use its store path, meaning that unrelated changes to your source tree will
23cause the generated `pubspec.lock` derivation to rebuild!
24:::
25
26If 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.
27
28The `dart` commands run can be overridden through `pubGetScript` and `dartCompileCommand`, you can also add flags using `dartCompileFlags` or `dartJitFlags`.
29
30Dart supports multiple [outputs types](https://dart.dev/tools/dart-compile#types-of-output), 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`.
31
32```nix
33{ lib, buildDartApplication, fetchFromGitHub }:
34
35buildDartApplication rec {
36 pname = "dart-sass";
37 version = "1.62.1";
38
39 src = fetchFromGitHub {
40 owner = "sass";
41 repo = pname;
42 rev = version;
43 hash = "sha256-U6enz8yJcc4Wf8m54eYIAnVg/jsGi247Wy8lp1r1wg4=";
44 };
45
46 pubspecLock = lib.importJSON ./pubspec.lock.json;
47}
48```
49
50### Patching dependencies {#ssec-dart-applications-patching-dependencies}
51
52Some Dart packages require patches or build environment changes. Package derivations can be customised with the `customSourceBuilders` argument.
53
54A collection of such customisations can be found in Nixpkgs, in the `development/compilers/dart/package-source-builders` directory.
55
56This 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.
57
58### Running executables from dev_dependencies {#ssec-dart-applications-build-tools}
59
60Many Dart applications require executables from the `dev_dependencies` section in `pubspec.yaml` to be run before building them.
61
62This can be done in `preBuild`, in one of two ways:
63
641. Packaging the tool with `buildDartApplication`, adding it to Nixpkgs, and running it like any other application
652. Running the tool from the package cache
66
67Of these methods, the first is recommended when using a tool that does not need
68to be of a specific version.
69
70For the second method, the `packageRun` function from the `dartConfigHook` can be used.
71This is an alternative to `dart run` that does not rely on Pub.
72
73e.g., for `build_runner`:
74
75```bash
76packageRun build_runner build
77```
78
79Do _not_ use `dart run <package_name>`, as this will attempt to download dependencies with Pub.
80
81### Usage with nix-shell {#ssec-dart-applications-nix-shell}
82
83#### Using dependencies from the Nix store {#ssec-dart-applications-nix-shell-deps}
84
85As `buildDartApplication` provides dependencies instead of `pub get`, Dart needs to be explicitly told where to find them.
86
87Run the following commands in the source directory to configure Dart appropriately.
88Do not use `pub` after doing so; it will download the dependencies itself and overwrite these changes.
89
90```bash
91cp --no-preserve=all "$pubspecLockFilePath" pubspec.lock
92mkdir -p .dart_tool && cp --no-preserve=all "$packageConfig" .dart_tool/package_config.json
93```
94
95## Flutter applications {#ssec-dart-flutter}
96
97The function `buildFlutterApplication` builds Flutter applications.
98
99See the [Dart documentation](#ssec-dart-applications) for more details on required files and arguments.
100
101```nix
102{ flutter, fetchFromGitHub }:
103
104flutter.buildFlutterApplication {
105 pname = "firmware-updater";
106 version = "0-unstable-2023-04-30";
107
108 # To build for the Web, use the targetFlutterPlatform argument.
109 # targetFlutterPlatform = "web";
110
111 src = fetchFromGitHub {
112 owner = "canonical";
113 repo = "firmware-updater";
114 rev = "6e7dbdb64e344633ea62874b54ff3990bd3b8440";
115 sha256 = "sha256-s5mwtr5MSPqLMN+k851+pFIFFPa0N1hqz97ys050tFA=";
116 fetchSubmodules = true;
117 };
118
119 pubspecLock = lib.importJSON ./pubspec.lock.json;
120}
121```
122
123### Usage with nix-shell {#ssec-dart-flutter-nix-shell}
124
125Flutter-specific `nix-shell` usage notes are included here. See the [Dart documentation](#ssec-dart-applications-nix-shell) for general `nix-shell` instructions.
126
127#### Entering the shell {#ssec-dart-flutter-nix-shell-enter}
128
129By default, dependencies for only the `targetFlutterPlatform` are available in the
130build environment. This is useful for keeping closures small, but be problematic
131during development. It's common, for example, to build Web apps for Linux during
132development to take advantage of native features such as stateful hot reload.
133
134To enter a shell with all the usual target platforms available, use the `multiShell` attribute.
135
136e.g. `nix-shell '<nixpkgs>' -A fluffychat-web.multiShell`.