Rework androidenv package generation

androidenv did not previously write license files, which caused certain
gradle-based Android tools to fail. Restructure androidenv's list of
Android packages into a single repo.json file to prevent duplication
and enable us to extract the EULA texts, which we then hash with
builtins.hashString to produce the license files that Android gradle
tools look for.

Remove includeDocs and lldbVersions, as these have been removed
from the Android package repositories.

Improve documentation and examples.

1 files changed, 132 insertions, 27 deletions

diff --git a/doc/languages-frameworks/android.section.md b/doc/languages-frameworks/android.section.md
index cfbacf1bccdc..62e544cd48b6 100644
--- a/doc/languages-frameworks/android.section.md
+++ b/doc/languages-frameworks/android.section.md
@@ -13,21 +13,19 @@ with import <nixpkgs> {};
 
 let
   androidComposition = androidenv.composeAndroidPackages {
-    toolsVersion = "25.2.5";
-    platformToolsVersion = "27.0.1";
-    buildToolsVersions = [ "27.0.3" ];
+    toolsVersion = "26.1.1";
+    platformToolsVersion = "30.0.5";
+    buildToolsVersions = [ "30.0.3" ];
     includeEmulator = false;
-    emulatorVersion = "27.2.0";
-    platformVersions = [ "24" ];
+    emulatorVersion = "30.3.4";
+    platformVersions = [ "28" "29" "30" ];
     includeSources = false;
-    includeDocs = false;
     includeSystemImages = false;
-    systemImageTypes = [ "default" ];
-    abiVersions = [ "armeabi-v7a" ];
-    lldbVersions = [ "2.0.2558144" ];
-    cmakeVersions = [ "3.6.4111459" ];
-    includeNDK = false;
-    ndkVersion = "16.1.4479499";
+    systemImageTypes = [ "google_apis_playstore" ];
+    abiVersions = [ "armeabi-v7a" "arm64-v8a" ];
+    cmakeVersions = [ "3.10.2" ];
+    includeNDK = true;
+    ndkVersion = "22.0.7026061";
     useGoogleAPIs = false;
     useGoogleTVAddOns = false;
     includeExtras = [
@@ -46,13 +44,11 @@ The following parameters are supported:
 
 * `toolsVersion`, specifies the version of the tools package to use
 * `platformsToolsVersion` specifies the version of the `platform-tools` plugin
-* `buildToolsVersion` specifies the versions of the `build-tools` plugins to
+* `buildToolsVersions` specifies the versions of the `build-tools` plugins to
   use.
 * `includeEmulator` specifies whether to deploy the emulator package (`false`
   by default). When enabled, the version of the emulator to deploy can be
   specified by setting the `emulatorVersion` parameter.
-* `includeDocs` specifies whether the documentation catalog should be included.
-* `lldbVersions` specifies what LLDB versions should be deployed.
 * `cmakeVersions` specifies which CMake versions should be deployed.
 * `includeNDK` specifies that the Android NDK bundle should be included.
   Defaults to: `false`.
@@ -82,6 +78,38 @@ For each requested system image we can specify the following options:
 
 Most of the function arguments have reasonable default settings.
 
+You can specify license names:
+
+* `extraLicenses` is a list of of license names.
+  You can get these names from repo.json or `querypackages.sh licenses`. The SDK
+  license (`android-sdk-license`) is accepted for you if you set accept_license
+  to true. If you are doing something like working with preview SDKs, you will
+  want to add `android-sdk-preview-license` or whichever license applies here.
+
+Additionally, you can override the repositories that composeAndroidPackages will
+pull from:
+
+* `repoJson` specifies a path to a generated repo.json file. You can generate this
+  by running `generate.sh`, which in turn will call into `mkrepo.rb`.
+* `repoXmls` is an attribute set containing paths to repo XML files. If specified,
+  it takes priority over `repoJson`, and will trigger a local build writing out a
+  repo.json to the Nix store based on the given repository XMLs.
+
+```nix
+repoXmls = {
+  packages = [ ./xml/repository2-1.xml ];
+  images = [
+    ./xml/android-sys-img2-1.xml
+    ./xml/android-tv-sys-img2-1.xml
+    ./xml/android-wear-sys-img2-1.xml
+    ./xml/android-wear-cn-sys-img2-1.xml
+    ./xml/google_apis-sys-img2-1.xml
+    ./xml/google_apis_playstore-sys-img2-1.xml
+  ];
+  addons = [ ./xml/addon2-1.xml ];
+};
+```
+
 When building the above expression with:
 
 ```bash
@@ -104,8 +132,8 @@ in
 androidComposition.platform-tools
 ```
 
-Using predefine Android package compositions
---------------------------------------------
+Using predefined Android package compositions
+---------------------------------------------
 In addition to composing an Android package set manually, it is also possible
 to use a predefined composition that contains all basic packages for a specific
 Android version, such as version 9.0 (API-level 28).
@@ -209,27 +237,104 @@ androidenv.emulateApp {
 In addition to prebuilt APKs, you can also bind the APK parameter to a
 `buildApp {}` function invocation shown in the previous example.
 
+Notes on environment variables in Android projects
+--------------------------------------------------
+* `ANDROID_SDK_ROOT` should point to the Android SDK. In your Nix expressions, this should be
+  `${androidComposition.androidsdk}/libexec/android-sdk`. Note that `ANDROID_HOME` is deprecated,
+  but if you rely on tools that need it, you can export it too.
+* `ANDROID_NDK_ROOT` should point to the Android NDK, if you're doing NDK development.
+  In your Nix expressions, this should be `${ANDROID_SDK_ROOT}/ndk-bundle`.
+
+If you are running the Android Gradle plugin, you need to export GRADLE_OPTS to override aapt2
+to point to the aapt2 binary in the Nix store as well, or use a FHS environment so the packaged
+aapt2 can run. If you don't want to use a FHS environment, something like this should work:
+
+```nix
+let
+  buildToolsVersion = "30.0.3";
+
+  # Use buildToolsVersion when you define androidComposition
+  androidComposition = <...>;
+in
+pkgs.mkShell rec {
+  ANDROID_SDK_ROOT = "${androidComposition.androidsdk}/libexec/android-sdk";
+  ANDROID_NDK_ROOT = "${ANDROID_SDK_ROOT}/ndk-bundle";
+
+  # Use the same buildToolsVersion here
+  GRADLE_OPTS = "-Dorg.gradle.project.android.aapt2FromMavenOverride=${ANDROID_SDK_ROOT}/build-tools/${buildToolsVersion}/aapt2";
+}
+```
+
+If you are using cmake, you need to add it to PATH in a shell hook or FHS env profile.
+The path is suffixed with a build number, but properly prefixed with the version.
+So, something like this should suffice:
+
+```nix
+let
+  cmakeVersion = "3.10.2";
+
+  # Use cmakeVersion when you define androidComposition
+  androidComposition = <...>;
+in
+pkgs.mkShell rec {
+  ANDROID_SDK_ROOT = "${androidComposition.androidsdk}/libexec/android-sdk";
+  ANDROID_NDK_ROOT = "${ANDROID_SDK_ROOT}/ndk-bundle";
+
+  # Use the same cmakeVersion here
+  shellHook = ''
+    export PATH="$(echo "$ANDROID_SDK_ROOT/cmake/${cmakeVersion}".*/bin):$PATH"
+  '';
+}
+```
+
+Note that running Android Studio with ANDROID_SDK_ROOT set will automatically write a
+`local.properties` file with `sdk.dir` set to $ANDROID_SDK_ROOT if one does not already
+exist. If you are using the NDK as well, you may have to add `ndk.dir` to this file.
+
+An example shell.nix that does all this for you is provided in examples/shell.nix.
+This shell.nix includes a shell hook that overwrites local.properties with the correct
+sdk.dir and ndk.dir values. This will ensure that the SDK and NDK directories will
+both be correct when you run Android Studio inside nix-shell.
+
+Notes on improving build.gradle compatibility
+---------------------------------------------
+Ensure that your buildToolsVersion and ndkVersion match what is declared in androidenv.
+If you are using cmake, make sure its declared version is correct too.
+
+Otherwise, you may get cryptic errors from aapt2 and the Android Gradle plugin warning
+that it cannot install the build tools because the SDK directory is not writeable.
+
+```gradle
+android {
+    buildToolsVersion "30.0.3"
+    ndkVersion = "22.0.7026061"
+    externalNativeBuild {
+        cmake {
+            version "3.10.2"
+        }
+    }
+}
+
+```
+
 Querying the available versions of each plugin
 ----------------------------------------------
-When using any of the previously shown functions, it may be a bit inconvenient
-to find out what options are supported, since the Android SDK provides many
-plugins.
+repo.json provides all the options in one file now.
 
-A shell script in the `pkgs/development/mobile/androidenv/` sub directory can be used to retrieve all
+A shell script in the `pkgs/development/mobile/androidenv/` subdirectory can be used to retrieve all
 possible options:
 
 ```bash
-sh ./querypackages.sh packages build-tools
+./querypackages.sh packages
 ```
 
-The above command-line instruction queries all build-tools versions in the
-generated `packages.nix` expression.
+The above command-line instruction queries all package versions in repo.json.
 
 Updating the generated expressions
 ----------------------------------
-Most of the Nix expressions are generated from XML files that the Android
-package manager uses. To update the expressions run the `generate.sh` script
-that is stored in the `pkgs/development/mobile/androidenv/` sub directory:
+repo.json is generated from XML files that the Android Studio package manager uses.
+To update the expressions run the `generate.sh` script that is stored in the
+`pkgs/development/mobile/androidenv/` subdirectory:
 
 ```bash
 ./generate.sh