swift_android_library
Swift shared library for Android.
Description#
Compiles Swift sources with swiftc into an Android .so and emits an
android_native_library provider. The Swift standard library is linked
statically. Once snapshots the matching C++ shared runtime from the Swift
Software Development Kit and android_binary packages both libraries under
the architecture-specific directory in the Android application package.
Attributes#
| Attribute | Type | Required | Default | Description |
|---|---|---|---|---|
android_abi | string | no | inferred | Android ABI directory such as arm64-v8a, armeabi-v7a, x86, or x86_64. Inferred from common Android target triples when omitted |
android_api | int | no | 28 | Android API level appended to API-less Android target triples |
target | string | no | inferred | Swift target triple. Inferred from android_abi and android_api when omitted, or set directly when the ABI is inferable |
module_name | string | no | target name | Swift module name |
package_name | string | no | empty | Swift package name passed through -package-name when set |
sdk | string | no | Optional sysroot passed to swiftc -sdk | |
resource_dir | string | no | Optional Swift resource directory passed to swiftc -resource-dir | |
cxx_runtime | string | no | Swift Software Development Kit sysroot | Optional absolute path to the C++ shared runtime packaged with the Swift library |
swift_sdk | string | no | first Android SDK | Installed Swift SDK identifier used to discover default Android sysroot and Swift resource paths |
android_ndk | string | no | ANDROID_NDK_HOME | Android NDK root used to find the LLVM tool directory |
tools_directory | string | no | inferred | Directory containing Android clang and linker tools passed as -tools-directory |
swiftc | string | no | PATH | Override Swift compiler path |
swift_flags | list<string> | no | [] | Additional Swift compiler flags |
copts | list<string> | no | [] | Bazel-compatible alias for additional Swift compiler flags |
defines | list<string> | no | [] | Conditional compilation symbols lowered to -D flags and propagated to downstream Swift modules |
linkopts | list<string> | no | [] | Additional linker flags appended after dependency linker flags and propagated downstream |
data | list<string> | no | [] | Runtime data file globs propagated to downstream consumers |
swiftc_inputs | list<string> | no | [] | Bazel-compatible extra Swift compiler input globs |
library_evolution | bool | no | false | Enable Swift library evolution and emit a textual module interface |
Accepted but unsupported attributes:
always_include_developer_search_paths, alwayslink,
generated_header_name, generates_header, linkstatic, plugins, and
private_deps. Non-empty values fail validation.
Dependency Edges#
| Edge | Accepts | Description |
|---|---|---|
deps | swift_module, android_native_library | Swift modules and Android native libraries linked or packaged with this library |
Providers#
The target emits swift_module, android_native_library, and
native_linkable.
Runtime Boundary#
Once follows the official
Swift Software Development Kit for Android packaging model:
the Swift standard library is linked statically, while libc++_shared.so is
snapshotted from the selected toolchain, content-verified, cached, and emitted
as a native dependency. The complete runtime closure therefore reaches the
Android application package without a shell staging command.
Kotlin or Java callers still need a Java Native Interface boundary. The runnable shared-code starter includes direct entry points for its primitive example. Richer application programming interfaces should use the official SwiftJava generator, whose Java Native Interface mode supports Android.
Capabilities#
| Capability | Output groups |
|---|---|
build | default, native_library, swiftmodule |
Source References#
Target kind discovery exposes the official Swift Android Software Development Kit guide for runtime packaging and the SwiftJava project for generated Java Native Interface bindings. A coding harness can fetch either source through Once before adapting a richer interoperation boundary.
Provider Record#
| Field | Type | Meaning |
|---|---|---|
label_id | string | Canonical target id |
module_name | string | Swift module name |
target | string | Swift target triple passed to swiftc |
android_abi | string | APK ABI directory |
swiftmodule_dir | string | Directory holding the generated Swift module |
swiftmodule | string | Generated Swift module artifact |
swiftdoc | string | Generated Swift documentation artifact |
swiftinterface | string | Generated textual module interface when library evolution is enabled |
dylib | string | Android shared library output |
android_native_libraries | list<record> | Direct native libraries with abi and path fields |
transitive_android_native_libraries | list<record> | Direct and dependency native libraries for APK packaging |
transitive_swiftmodule_dirs | list<string> | Swift module search paths for downstream Swift Android libraries |
transitive_swiftmodule_inputs | list<string> | Swift module artifacts declared as downstream compiler inputs |
transitive_swift_defines | list<string> | Conditional compilation symbols propagated downstream |
transitive_linkopts | list<string> | Linker options propagated downstream |
transitive_data | list<string> | Runtime data propagated downstream |
Outputs#
| Output | Location |
|---|---|
| Shared library | .once/out/<target>/lib<module_name>.so |
| C++ shared runtime | .once/out/<target>/libc++_shared.so |
| Swift module | .once/out/<target>/<module_name>.swiftmodule |
| Swift doc | .once/out/<target>/<module_name>.swiftdoc |
| Swift interface | .once/out/<target>/<module_name>.swiftinterface when library evolution is enabled |
Example#
[[target]]
name = "SharedSwift"
kind = "swift_android_library"
srcs = ["Sources/**/*.swift"]
[target.attrs]
android_abi = "arm64-v8a"
module_name = "SharedSwift"
swift_sdk = "swift-6.3.2-RELEASE_android"
android_ndk = "/opt/android-ndk"
swift_flags = ["-O"]