build: make flake usable for host Android builds

.gitignore

@@ -26,7 +26,7 @@ android/local.properties
 tailscale.jks
 
 # android sdk dir
-./android-sdk
+/android-sdk/
 
 # Persistent $HOME/.android for `make docker-*` (keeps debug.keystore so
 # the debug signer is stable across container runs).

README.md

@@ -92,6 +92,37 @@ alias nix='nix --extra-experimental-features "nix-command flakes"'
 nix develop
 ```
 
+The flake provides host tools such as Java, `make`, `curl`, and `git`, and
+points the build at a repo-local Android SDK in `./android-sdk`. The SDK
+directory is ignored by Git and is reused across builds.
+
+On first use, install the Android SDK components:
+
+```sh
+make androidsdk
+```
+
+Then build normally:
+
+```sh
+make tailscale-debug
+```
+
+The debug APK is written to `./tailscale-debug.apk`.
+
+For one-shot commands without entering an interactive shell:
+
+```sh
+nix develop --command make androidsdk
+nix develop --command make tailscale-debug
+```
+
+For faster Kotlin-only iteration while avoiding the `gomobile bind` step:
+
+```sh
+nix develop --command bash -lc 'cd android && ./gradlew ktfmtCheck compileDebugKotlin'
+```
+
 ## Building
 
 ```sh

flake.nix

@@ -1,58 +1,66 @@
 {
-  description = "Tailscale build environment";
+  description = "Tailscale Android build environment";
 
   inputs = {
-    nixpkgs.url = "github:NixOS/nixpkgs";
-    android.url = "github:tadfisher/android-nixpkgs";
-    android.inputs.nixpkgs.follows = "nixpkgs";
+    nixpkgs.url = "github:NixOS/nixpkgs/nixos-unstable";
   };
 
-  outputs = { self, nixpkgs, android }:
+  outputs = { self, nixpkgs }:
     let
       supportedSystems = [ "x86_64-linux" "x86_64-darwin" "aarch64-darwin" ];
       forAllSystems = f: nixpkgs.lib.genAttrs supportedSystems (system: f system);
     in
     {
-      devShells = forAllSystems
-        (system:
-          let
-            pkgs = import nixpkgs {
-              inherit system;
-            };
-            android-sdk = android.sdk.${system} (sdkPkgs: with sdkPkgs;
-              [
-                build-tools-30-0-2
-                cmdline-tools-latest
-                platform-tools
-                platforms-android-31
-                platforms-android-30
-                ndk-23-1-7779620
-                patcher-v4
-              ]);
-          in
-          {
-            default = (with pkgs; buildFHSUserEnv {
-              name = "tailscale";
-              profile = ''
-                export ANDROID_SDK_ROOT="${android-sdk}/share/android-sdk"
-                export JAVA_HOME="${jdk8.home}"
-              '';
-              targetPkgs = pkgs: with pkgs; [
-                android-sdk
-                jdk8
-                clang
-              ] ++ (if stdenv.isLinux then [
-                vulkan-headers
-                libxkbcommon
-                wayland
-                xorg.libX11
-                xorg.libXcursor
-                xorg.libXfixes
-                libGL
-                pkgconfig
-              ] else [ ]);
-            }).env;
-          }
-        );
+      devShells = forAllSystems (system:
+        let
+          pkgs = import nixpkgs { inherit system; };
+
+          commonPackages = with pkgs; [
+            bash
+            cacert
+            curl
+            git
+            gnumake
+            gzip
+            jdk21
+            unzip
+            zip
+          ];
+
+          linuxPackages = with pkgs; [
+            gcc
+            glibc
+            libGL
+            libx11
+            libxcursor
+            libxfixes
+            libxkbcommon
+            pkg-config
+            stdenv.cc.cc.lib
+            wayland
+            zlib
+          ];
+
+          shellProfile = ''
+            export JAVA_HOME="${pkgs.jdk21.home}"
+            export ANDROID_SDK_ROOT="''${ANDROID_SDK_ROOT:-$PWD/android-sdk}"
+            export ANDROID_HOME="''${ANDROID_HOME:-$ANDROID_SDK_ROOT}"
+            export PATH="$PWD/tool:$PWD/android/build/go/bin:$ANDROID_HOME/cmdline-tools/latest/bin:$ANDROID_HOME/platform-tools:$PATH"
+
+            export GOTOOLCHAIN=local
+            export TS_USE_TOOLCHAIN=1
+
+            if [ ! -x "$ANDROID_HOME/cmdline-tools/latest/bin/sdkmanager" ]; then
+              echo "Android SDK not found at $ANDROID_HOME."
+              echo "Run: make androidsdk"
+            fi
+          '';
+        in
+        {
+          default = pkgs.mkShell {
+            packages = commonPackages ++ pkgs.lib.optionals pkgs.stdenv.isLinux linuxPackages;
+            shellHook = shellProfile;
+          };
+        });
     };
 }