Add Android precompile workflow (#346)

- add Android `aarch64-linux-android` and `armv7a-linux-androideabi`
  targets to the existing `cc_precompiler` configuration
- map Android precompile targets to the Android NDK clang toolchain
  while keeping the existing Linux/macOS/Windows targets unchanged by
  default
- add an Android precompile workflow that builds one Android target per
  matrix job and publishes matching release artifacts on tags

Note: I validated the normal native build/test path locally on macOS.
The Android cross-compile path depends on the GitHub-hosted Linux
runner's Android NDK installation, so the new workflow is the first full
NDK validation point.

Fixes #165

Author: dl-alexandre

.github/workflows/android-precompile.yml

@@ -0,0 +1,73 @@
+name: android-precompile
+
+on:
+  push:
+    branches:
+      - "main"
+    tags:
+      - 'v*'
+
+permissions:
+  contents: write
+
+jobs:
+  precompile:
+    runs-on: ubuntu-latest
+    env:
+      ImageOS: ubuntu22
+      MIX_ENV: prod
+      ANDROID_API_LEVEL: "24"
+      CC_PRECOMPILER_ONLY_LISTED_TARGETS: "true"
+      CC_PRECOMPILER_PRECOMPILE_ONLY_LOCAL: "true"
+    strategy:
+      matrix:
+        target:
+          - triplet: aarch64-linux-android
+            arch: aarch64
+            os: linux
+            abi: android
+          - triplet: armv7a-linux-androideabi
+            arch: armv7a
+            os: linux
+            abi: androideabi
+        job:
+          - {otp: "27", elixir: "1.17"}
+          - {otp: "25", elixir: "1.16"}
+
+    name: Android ${{ matrix.target.triplet }} - OTP ${{ matrix.job.otp }} - Elixir ${{ matrix.job.elixir }}
+    steps:
+      - name: Checkout
+        uses: actions/checkout@v6
+
+      - uses: erlef/setup-beam@v1
+        with:
+          otp-version: ${{ matrix.job.otp }}
+          elixir-version: ${{ matrix.job.elixir }}
+
+      - name: Add Android NDK toolchain to PATH
+        run: |
+          ANDROID_NDK="${ANDROID_NDK_LATEST_HOME:-${ANDROID_NDK_HOME:-${ANDROID_NDK_ROOT:-}}}"
+
+          if [ -z "${ANDROID_NDK}" ]; then
+            echo "No Android NDK path is set on this runner" >&2
+            exit 1
+          fi
+
+          echo "${ANDROID_NDK}/toolchains/llvm/prebuilt/linux-x86_64/bin" >> "${GITHUB_PATH}"
+
+      - name: Create precompiled ${{ matrix.target.triplet }} library
+        env:
+          TARGET_ARCH: ${{ matrix.target.arch }}
+          TARGET_OS: ${{ matrix.target.os }}
+          TARGET_ABI: ${{ matrix.target.abi }}
+          ELIXIR_MAKE_CACHE_DIR: ${{ github.workspace }}/cache
+        run: |
+          mkdir -p "${ELIXIR_MAKE_CACHE_DIR}"
+          mix deps.get
+          mix elixir_make.precompile
+
+      - uses: softprops/action-gh-release@v1
+        if: startsWith(github.ref, 'refs/tags/')
+        with:
+          files: |
+            cache/*${{ matrix.target.triplet }}*.tar.gz

Makefile

@@ -43,6 +43,10 @@ endif
 
 KERNEL_NAME := $(shell uname -s)
 
+ifneq ($(findstring android,$(CC_PRECOMPILER_CURRENT_TARGET)),)
+	CROSSCOMPILE ?= Android
+endif
+
 PREFIX = $(MIX_APP_PATH)/priv
 BUILD  = $(MIX_APP_PATH)/obj
 LIB_NAME = $(PREFIX)/sqlite3_nif.so

mix.exs

@@ -137,12 +137,16 @@ defmodule Exqlite.MixProject do
   defp cc_precompiler do
     [
       cleanup: "clean",
+      only_listed_targets:
+        System.get_env("CC_PRECOMPILER_ONLY_LISTED_TARGETS") == "true",
       compilers: %{
         {:unix, :linux} => %{
           :include_default_ones => true,
           "x86_64-linux-musl" => "x86_64-linux-musl-",
           "aarch64-linux-musl" => "aarch64-linux-musl-",
-          "riscv64-linux-musl" => "riscv64-linux-musl-"
+          "riscv64-linux-musl" => "riscv64-linux-musl-",
+          "aarch64-linux-android" => android_compilers("aarch64-linux-android"),
+          "armv7a-linux-androideabi" => android_compilers("armv7a-linux-androideabi")
         },
         {:unix, :darwin} => %{
           :include_default_ones => true
@@ -153,4 +157,13 @@ defmodule Exqlite.MixProject do
       }
     ]
   end
+
+  defp android_compilers(target) do
+    api_level = System.get_env("ANDROID_API_LEVEL", "24")
+
+    {
+      "#{target}#{api_level}-clang",
+      "#{target}#{api_level}-clang++"
+    }
+  end
 end