Setting Up Flutter Android on NixOS

Recently I, together with friends, set out to make a cross-platform mobile app using Flutter. For that of course I needed to do a couple things first:

Set up Flutter and its dependencies (incl. Android SDK)
Learn Flutter (this we will skip)

Setting up Flutter#

This is actually something I have done this before back in March, 2024. I had the idea to learn Flutter back then, because I wanted a practical reason to learn Dart¹.

That time, it was a really short-lived dream, as I ended up giving up on it not much after just figuring out how to set it up. I recall, all I did was build the example project as a web and Android app, then tweaked some of the text on the main page. But that is useful, as I can reference back to it to figure out what I did.

Installing Flutter itself is very simple. Just add the flutter package to a Nix shell, and you are good to go. Either run nix-shell -p flutter to get a shell temporarily, or create a shell.nix file and then you can run nix-shell by itself:

# shell.nix

with import <nixpkgs> {};

mkShell {
  packages = [
    flutter
  ];
}

Easy as pie.

Creating a Project#

TODO

Getting the Android SDK#

Now we just need to get the Android SDK, and we can build our example project with Flutter.

First Futile Attempt#

Here is where I started to make a big mistake: assume I can just get the Android SDK using Nix. Surely, I can just add it to the packages list, I thought.

After a short bit of searching, I found that there is indeed a package called androidsdk in the nixpkgs repo. Sounds perfect. I edited my shell.nix

# shell.nix

with import <nixpkgs> {};

mkShell {
  packages = [
    flutter
    androidsdk
  ];
}

And then ran nix-shell, clearly oblivious. Immediately got my terminal flooded. It vomited out the entire Android SDK license onto stdout followed by this:

       You must accept the following licenses:
         - android-sdk-license

       a)
         by setting nixpkgs config option 'android_sdk.accept_license = true;'.
       b)
         by an environment variable for a single invocation of the nix tools.
           $ export NIXPKGS_ACCEPT_ANDROID_SDK_LICENSE=1

I do not like the environment variable option, I would rather accept the terms using Nix either way. So I will go with option a). While it does not tell you where to put that snippet of code, having been using Nix for a while I knew what I could do with it.

My immediate thought was that I can just put it in ~/.config/nixpkgs/config.nix, which would work. One could argue that it is the correct solution, since accepting the terms should not be part of the nix shell automatically, but it is something each user should do themselves. But let’s try being naughty and still make it part of the shell so that we never have to deal with it again.

# shell.nix

with import <nixpkgs> {
  config.android_sdk.accept_license = true;
  config.allowUnfree = true;
};

mkShell {
  packages = [
    flutter
    androidsdk
  ];
}

Note that I also set allowUnfree to true, since androidsdk is a non-free package.

After a quick little nix-shell, it seems to work. But it is taking a while…

[...]
copying path '/nix/store/s3yjazzkqjh17f3i4ahcn1963s0s8srd-arm64-v8a-32_r08.zip' from 'https://cache.nixos.org'...
copying path '/nix/store/wpvkqjvrcm7xlsnhv2661qi2zxy0iq9y-arm64-v8a-33_r09.zip' from 'https://cache.nixos.org'...
copying path '/nix/store/kr1rhlrjwgi2376p9icfr551wyxpcx47-arm64-v8a-33_r17.zip' from 'https://cache.nixos.org'...
copying path '/nix/store/7xqwbr2r9bvcy1vl5jyqvi7fqf1cgv8v-arm64-v8a-34_r14.zip' from 'https://cache.nixos.org'...
copying path '/nix/store/fgm7fqhd0q94bzj508kgjqp6xvam85hk-arm64-v8a-34_r14.zip' from 'https://cache.nixos.org'...
copying path '/nix/store/fq8blynrm6xcf71g3x7j1gv7ka80c89f-arm64-v8a-35_r09.zip' from 'https://cache.nixos.org'...
copying path '/nix/store/ys9hc9r69js68gprci2ssq2v4sfykh3k-arm64-v8a-35_r09.zip' from 'https://cache.nixos.org'...
copying path '/nix/store/fa7myxvrvc9hhjbccvd3nx023xqdal1g-arm64-v8a-36_r06.zip' from 'https://cache.nixos.org'...
copying path '/nix/store/yqfppq2cv6wq8mz7afdlbhmzw3kvfb7h-arm64-v8a-36_r06.zip' from 'https://cache.nixos.org'...
[...]

Huh… That is a lot of things getting downloaded. After waiting for a couple minutes, the nix-shell process crashed with “not enough disk space”. Great. That means it was trying to download at least 80GB worth of “android SDK”. For some reason, nixpkgs is on the opinion that the androidsdk package should already contain everything that you may have possibly wanted, even it if takes and outrageous amount of space.

Making Our Own `androidsdk` Package#

Okay, let’s try to work around that. After checking how androidsdk is defined, we find that it is in fact androidenv.androidPkgs.androidsdk. That’s good to know. We can find that androidend.androidPkgs is defined like this in nixpkgs.

Aha! This explains things.

composeAndroidPackages {
  # Support roughly the last 5 years of Android packages and system images by default in nixpkgs.
  numLatestPlatformVersions = 5;
  includeEmulator = "if-supported";
  includeSystemImages = "if-supported";
  includeNDK = "if-supported";
};

It seems the maintainers are very well aware of what they are doing. They are purposely making it contain “roughly the last 5 years of Android packages and system images”.

Well, now that we know how it is defined, we can just use this in our Nix shell instead. Let’s rework it.

# shell.nix

with import <nixpkgs> {
  config.android_sdk.accept_license = true;
  config.allowUnfree = true;
};

let
  androidPkgs = androidenv.composeAndroidPackages {
    numLatestPlatformVersions = 1;
    includeEmulator = true;
    includeSystemImages = true;
    includeNDK = false;
  };
in
mkShell {
  packages = [
    flutter
    # This the 'androidPkgs' defined above
    androidPkgs.androidsdk
  ];
}

After encouraging it with a little nix-shell and less than a minute of waiting, it is done, and put me in a new shell.

Let’s verify that it has worked, just to be sure. We can try invoking an executable from the SDK.

First, let’s find out what binaries it contains… Or rather where the android SDK we just added is. It will be referenced by our shell, so we can just extract it.

$ nix-store -q --references $(nix-build shell.nix) | grep android
/nix/store/6ixvbl3p75xsmxl3h9977xb3c3lmfhba-androidsdk

There it is! Let’s see what executables it has:

$ ls /nix/store/6ixvbl3p75xsmxl3h9977xb3c3lmfhba-androidsdk
bin  libexec
$ ls /nix/store/6ixvbl3p75xsmxl3h9977xb3c3lmfhba-androidsdk/bin
adb          d8        hprof-conv  make_f2fs_casefold  r8                screenshot2
apkanalyzer  etc1tool  lint        mke2fs              resourceshrinker  sdkmanager
avdmanager   fastboot  make_f2fs   profgen             retrace

Alright, so we can try calling adb --version to verify that it got correctly added to our environment. And it did! Awesome.

Try to build with it#

TODO

Alright, so we need to set the ANDROID_HOME variable to point to the SDK. That is actually very simple to do.

# shell.nix

# [...]
mkShell {
  packages = [
    flutter
    androidPkgs.androidsdk
  ];

  ANDROID_HOME = "${androidPkgs.androidsdk}";
}

And voila, after entering the shell with nix-shell, we can see that the environment variable is set.

$ echo "$ANDROID_HOME" 
/nix/store/6ixvbl3p75xsmxl3h9977xb3c3lmfhba-androidsdk

Accepting the License#

Impossible.

Give up#

Instead of trying to do it declaratively, just use Android’s sdkmanager.

# shell.nix

with import <nixpkgs> { };

mkShell {
  buildInputs = [
    flutter
    sdkmanager
  ];

  ANDROID_HOME = "${builtins.getEnv "HOME"}/.androidsdk";
}

And then use sdkmanager to install things to $ANDROID_HOME.

sdkmanager --install 'platform-tools' # or whatever else

And boom, it works.

Flutter uses Dart as the programming language. ↩︎

Setting Up Flutter Android on NixOS