Add Android ICU4C, NuGet packaging, and CI pipeline

.github/workflows/fw_icu4c_ci.yml

@@ -98,7 +98,7 @@ jobs:
     - name: Publish nuget packages
       if: github.event_name == 'push'
       working-directory: icu4c
-      run: nuget push **/*.nupkg -Source 'https://api.nuget.org/v3/index.json' -ApiKey ${{ secrets.ICU_NUGET_API_KEY }}
+      run: nuget push **/*.nupkg -Source 'https://api.nuget.org/v3/index.json' -ApiKey ${{ secrets.SILLSDEV_PUBLISH_NUGET_ORG }}
 
 
   # Run ICU4C tests with SIL mod and stub data
@@ -125,6 +125,79 @@ jobs:
           echo 'Running ICU4C cintltst'
           make -j2 check
 
+  android-build:
+    needs: set-version-number
+    runs-on: ubuntu-latest
+    steps:
+      - name: Checkout
+        uses: actions/checkout@v7
+        with:
+          fetch-depth: 1
+          sparse-checkout-cone-mode: false
+          sparse-checkout: |
+            icu4c/packaging
+            icu4c/source
+            icu4c/nugetpackage/assets/android
+            icu4c/LICENSE
+
+      - name: Set up Android SDK command-line tools
+        uses: android-actions/setup-android@v4
+
+      - name: Setup .NET
+        uses: actions/setup-dotnet@v6
+        with:
+          dotnet-version: 8.0.x
+
+      - name: Install Android NDK
+        run: |
+          sdkmanager --install 'ndk;27.0.12077973'
+          echo "ANDROID_NDK_HOME=$ANDROID_HOME/ndk/27.0.12077973" >> "$GITHUB_ENV"
+
+      - name: Cache Android ICU build output
+        uses: actions/cache@v6
+        with:
+          path: icu4c/out/android-icu
+          key: android-icu-${{ runner.os }}-${{ hashFiles('icu4c/packaging/build-android.sh', 'icu4c/packaging/pack-android-nuget.sh', 'icu4c/source/common/unicode/uvernum.h', 'icu4c/source/configure') }}
+
+      - name: Build Android ICU libraries
+        run: |
+          set -xeo pipefail
+          bash icu4c/packaging/build-android.sh --arch=x86_64,arm64-v8a,armeabi-v7a
+
+      - name: Verify Android ICU output contract
+        run: |
+          set -xeuo pipefail
+          major=$(grep -oP '^#define U_ICU_VERSION_MAJOR_NUM \K[0-9]+' icu4c/source/common/unicode/uvernum.h)
+          test -f "icu4c/out/android-icu/icudt${major}l.dat"
+          for abi in x86_64 arm64-v8a armeabi-v7a; do
+            for library in libc++_shared.so libicuuc.so libicui18n.so libicudata.so; do
+              test -f "icu4c/out/android-icu/$abi/$library"
+            done
+          done
+
+      - name: Pack Android NuGet package
+        run: |
+          set -xeuo pipefail
+          bash icu4c/packaging/pack-android-nuget.sh \
+            --version="${{ needs.set-version-number.outputs.version }}" \
+            --output=icu4c/nugetpackage
+
+      - name: Upload Android NuGet package
+        uses: actions/upload-artifact@v7
+        with:
+          name: android-nuget
+          path: icu4c/nugetpackage/Icu4c.Android.Fw.Lib.*.nupkg
+          if-no-files-found: error
+
+      - name: Publish Android NuGet package
+        if: github.event_name == 'push'
+        run: |
+          set -xeuo pipefail
+          dotnet nuget push icu4c/nugetpackage/Icu4c.Android.Fw.Lib.*.nupkg \
+            --source 'https://api.nuget.org/v3/index.json' \
+            --api-key '${{ secrets.SILLSDEV_PUBLISH_NUGET_ORG }}' \
+            --skip-duplicate
+
   debian-packaging:
     needs: set-version-number
     runs-on: ubuntu-latest

README.md

@@ -14,6 +14,14 @@ Build | Status
 ------|-------
 GitHub Actions | [![FW Branch CI](https://github.com/sillsdev/icu/actions/workflows/fw_icu4c_ci.yml/badge.svg?branch=fw)](https://github.com/sillsdev/icu/actions/workflows/fw_icu4c_ci.yml)
 
+### NuGet packages (`fw` branch)
+
+Package | Version
+--------|--------
+[Icu4c.Win.Fw.Lib](https://www.nuget.org/packages/Icu4c.Win.Fw.Lib/) | [![NuGet version](https://img.shields.io/nuget/v/Icu4c.Win.Fw.Lib.svg?style=flat-square)](https://www.nuget.org/packages/Icu4c.Win.Fw.Lib/)
+[Icu4c.Win.Fw.Bin](https://www.nuget.org/packages/Icu4c.Win.Fw.Bin/) | [![NuGet version](https://img.shields.io/nuget/v/Icu4c.Win.Fw.Bin.svg?style=flat-square)](https://www.nuget.org/packages/Icu4c.Win.Fw.Bin/)
+[Icu4c.Android.Fw.Lib](https://www.nuget.org/packages/Icu4c.Android.Fw.Lib/) | [![NuGet version](https://img.shields.io/nuget/v/Icu4c.Android.Fw.Lib.svg?style=flat-square)](https://www.nuget.org/packages/Icu4c.Android.Fw.Lib/)
+
 # ICU Project info
 
 The ICU project is under the stewardship of [The Unicode Consortium](https://www.unicode.org).
@@ -30,6 +38,7 @@ The ICU project is under the stewardship of [The Unicode Consortium](https://www
 
 #### Subdirectories that we modify and package
 - [`icu4c/`](./icu4c/) [ICU for C/C++](./icu4c/readme.html)
+  - [Android native build guide](./icu4c/packaging/README.android.md)
 #### Subdirectories that we don't care about
 - [`icu4j/`](./icu4j/) [ICU for Java](./icu4j/readme.html)
 - [`tools/`](./tools/) Tools

icu4c/nugetpackage/assets/android/build/Icu4c.Android.Fw.Lib.props

@@ -0,0 +1,10 @@
+<Project xmlns="http://schemas.microsoft.com/developer/msbuild/2003">
+	<PropertyGroup>
+		<!-- Stamped at pack time; consumers (e.g. AndroidIcuBootstrap) may read this. -->
+		<IcuFwAndroidMajorVersion Condition="'$(IcuFwAndroidMajorVersion)' == ''">70</IcuFwAndroidMajorVersion>
+		<IcuFwAndroidPackageDir>$(MSBuildThisFileDirectory)</IcuFwAndroidPackageDir>
+		<!-- Forward slashes: MSBuild normalizes these on Windows and Unix. -->
+		<IcuFwAndroidNativeDir>$(IcuFwAndroidPackageDir)native/</IcuFwAndroidNativeDir>
+		<IcuFwAndroidAssetsDir>$(IcuFwAndroidPackageDir)assets/</IcuFwAndroidAssetsDir>
+	</PropertyGroup>
+</Project>

icu4c/nugetpackage/assets/android/build/Icu4c.Android.Fw.Lib.targets

@@ -0,0 +1,18 @@
+<Project xmlns="http://schemas.microsoft.com/developer/msbuild/2003">
+	<ItemGroup Condition="'$(TargetPlatformIdentifier)' == 'android'">
+		<AndroidNativeLibrary
+			Include="$(IcuFwAndroidNativeDir)x86_64/*.so"
+			Condition="Exists('$(IcuFwAndroidNativeDir)x86_64/libicuuc.so')" />
+		<AndroidNativeLibrary
+			Include="$(IcuFwAndroidNativeDir)arm64-v8a/*.so"
+			Condition="Exists('$(IcuFwAndroidNativeDir)arm64-v8a/libicuuc.so')" />
+		<AndroidNativeLibrary
+			Include="$(IcuFwAndroidNativeDir)armeabi-v7a/*.so"
+			Condition="Exists('$(IcuFwAndroidNativeDir)armeabi-v7a/libicuuc.so')" />
+
+		<AndroidAsset Include="$(IcuFwAndroidAssetsDir)icudt$(IcuFwAndroidMajorVersion)l.dat"
+			Condition="Exists('$(IcuFwAndroidAssetsDir)icudt$(IcuFwAndroidMajorVersion)l.dat')">
+			<LogicalName>%(Filename)%(Extension)</LogicalName>
+		</AndroidAsset>
+	</ItemGroup>
+</Project>

icu4c/nugetpackage/assets/android/icu-android-fw-lib.nuspec

@@ -0,0 +1,31 @@
+<?xml version="1.0" encoding="utf-8"?>
+<package>
+	<metadata>
+		<id>Icu4c.Android.Fw.Lib</id>
+		<version>$version$</version>
+		<authors>SIL International</authors>
+		<copyright>Copyright (c) 2016-2026 SIL International</copyright>
+		<license type="file">LICENSE</license>
+		<projectUrl>https://github.com/sillsdev/icu</projectUrl>
+		<requireLicenseAcceptance>false</requireLicenseAcceptance>
+		<tags>native android maui</tags>
+		<summary>ICU - International Components for Unicode (Android)</summary>
+		<description>ICU - International Components for Unicode
+
+This package contains the FieldWorks version of ICU4C shared libraries for Android
+(x86_64, arm64-v8a, and armeabi-v7a), including libc++_shared.so and the ICU data
+file for MAUI / .NET Android apps.
+
+The major version number of the nuget package corresponds to the ICU release.
+		</description>
+		<language>en-US</language>
+		<releaseNotes>
+$version$ - FieldWorks ICU Android natives (x86_64, arm64-v8a, armeabi-v7a) plus icudt*l.dat
+		</releaseNotes>
+		<references/>
+	</metadata>
+	<files>
+		<file src="LICENSE" target="" />
+		<file src="build/**/*" target="build" />
+	</files>
+</package>

icu4c/packaging/README.android.md

@@ -0,0 +1,137 @@
+# Android ICU4C build
+
+`build-android.sh` cross-compiles the checked-out, SIL-modified ICU4C source in
+`../source` for Android. It does not download, unpack, or substitute an
+upstream ICU release. The current `fw` checkout determines the ICU version and
+therefore the generated data file name.
+
+The build creates host ICU tools first, then uses them with the Android NDK
+toolchain to cross-compile each requested ABI. It validates native-library
+output only; it does not build or run an Android application, emulator, or
+device test.
+
+CI packs the build into the `Icu4c.Android.Fw.Lib` NuGet package for MAUI /
+.NET Android consumers.
+
+## Prerequisites
+
+On Linux or macOS install a POSIX shell environment with `bash`, `make`, `sed`,
+`find`, `sort`, a C/C++ host compiler, and the Android NDK. Android API 21 is
+the default minimum API. The CI configuration uses NDK `27.0.12077973`.
+
+Set `ANDROID_NDK_HOME` to the NDK installation. Alternatively, set
+`ANDROID_HOME` to the Android SDK root and the script selects the latest
+installed `ndk/<version>` directory.
+
+```bash
+export ANDROID_NDK_HOME=/opt/android-ndk-r27
+bash ./icu4c/packaging/build-android.sh --arch=x86_64,arm64-v8a,armeabi-v7a
+```
+
+On Windows, install Git for Windows and an Android NDK installed for Windows,
+then run the script from Git Bash:
+
+```bash
+export ANDROID_NDK_HOME='C:\Android\Sdk\ndk\27.0.12077973'
+bash ./icu4c/packaging/build-android.sh --arch=x86_64,arm64-v8a,armeabi-v7a
+```
+
+Git Bash and WSL need different NDKs: a Windows NDK cannot be reused from WSL,
+and a Linux NDK cannot be used by Git Bash. Under WSL, run the same
+`bash ./icu4c/packaging/build-android.sh` command with an NDK installed for
+Linux inside WSL.
+
+## Controls and cleanup
+
+```bash
+# Default fast validation ABI
+bash ./icu4c/packaging/build-android.sh
+
+# Select an API level and all supported ABIs
+bash ./icu4c/packaging/build-android.sh --api=21 --arch=x86_64,arm64-v8a,armeabi-v7a
+
+# Delete one ABI's build and installed output before rebuilding it
+bash ./icu4c/packaging/build-android.sh --clean-arch=x86_64 --arch=x86_64
+
+# Delete all generated host tools, cross-build trees, data, and libraries
+bash ./icu4c/packaging/build-android.sh --clean
+```
+
+Supported ABI values are `x86_64`, `arm64-v8a`, and `armeabi-v7a`. Use `--help`
+for the full command reference. The generated `icu4c/out/` directory is already
+ignored by this repository.
+
+## Output layout
+
+For the checked-out ICU `70.1`, the output layout is:
+
+```text
+icu4c/out/android-icu/
+  icudt70l.dat
+  x86_64/
+    libc++_shared.so
+    libicuuc.so
+    libicui18n.so
+    libicudata.so
+  arm64-v8a/
+    libc++_shared.so
+    libicuuc.so
+    libicui18n.so
+    libicudata.so
+  armeabi-v7a/
+    libc++_shared.so
+    libicuuc.so
+    libicui18n.so
+    libicudata.so
+```
+
+Cross builds use `--with-data-packaging=archive`, so `libicudata.so` is the
+**stub** data library. Locale data lives in `icudt*l.dat`. Consumers (for
+example `AndroidIcuBootstrap` in icu-dotnet) must load that file via
+`udata_setCommonData` (or equivalent) before using ICU.
+
+Shared libraries are linked with **unversioned** SONAMEs (`libicuuc.so`, and so
+on) so Android APK packaging of those file names alone satisfies `DT_NEEDED`.
+The library major and data-file name are derived from the local ICU source, so
+they change automatically when this branch advances to a different ICU major.
+
+## NuGet package (MAUI / .NET Android)
+
+CI packs unversioned ABI libraries plus `icudt*l.dat` into
+[`Icu4c.Android.Fw.Lib`](https://www.nuget.org/packages/Icu4c.Android.Fw.Lib).
+The major version of the package matches the ICU release (same scheme as
+`Icu4c.Win.Fw.Lib`).
+
+```xml
+<ItemGroup>
+  <PackageReference Include="Icu4c.Android.Fw.Lib" Version="[70.1.0,71.0.0)" />
+</ItemGroup>
+```
+
+The package’s MSBuild targets add `AndroidNativeLibrary` entries for
+`x86_64`, `arm64-v8a`, and `armeabi-v7a` and embed `icudt70l.dat` as an
+`AndroidAsset`.
+Consumers do not need manual `AndroidNativeLibrary` / `AndroidAsset`
+ItemGroups. The props file also stamps `IcuFwAndroidMajorVersion` for
+consumers that need the ICU major (for example aligning
+`AndroidIcuBootstrap`).
+
+Pack a local `.nupkg` after a successful Android build:
+
+```bash
+bash ./icu4c/packaging/pack-android-nuget.sh --version=70.1.0
+```
+
+Keep the consumer’s ICU major (for example `AndroidIcuBootstrap` in
+icu-dotnet) aligned with the referenced package major.
+
+## Troubleshooting
+
+- If the script reports a missing NDK, set `ANDROID_NDK_HOME` explicitly.
+- If it reports a mismatched NDK toolchain, install the NDK for the host that
+  executes the script: Linux for Linux/WSL, Windows for Git Bash, or macOS for
+  macOS.
+- Use `--clean` after changing host compilers, NDK versions, or ICU source
+  configuration to ensure host tools and cross-build output are recreated.
+- ICU operations that need locale data will fail until the app loads
+  `icudt*l.dat` into ICU (stub `libicudata.so` alone is not enough).