Remove android-activity dependency + add activity features

Instead of depending on android-activity directly, this exposes the
android-native-activity and android-game-activity features from Winit.

This ensures that applications can choose what android-backend they use
while also relying on Winit to decide what version of android-activity to
use - without increasing the risk of a version conflict by having a direct
dependency.

_(NB: Egui doesn't currently use the android-activity API itself)_

Since android-activity provides the `android_main()` entry point for
Android applications it's not possible to link in multiple version of
the android-activity crate and so it's particularly important to
avoid unnecessary direct dependencies that could cause a version
conflict in the future.

To help avoid the need for applications to directly depend on
android-activity the Winit crate re-exports the android-activity API
and exposes features to configure the backend so that application crates
can instead rely on Winit to pull in a compatible version of
android-activity. (This way version bumps for android-activity only
need to be synchronized with the Winit crate).

CI now enables the `android-native-activity` feature for testing.

Fixes: emilk#2829
Fixes: emilk#2720
Closes: emilk#2834

.github/workflows/rust.yml

@@ -185,7 +185,7 @@ jobs:
       - name: Set up cargo cache
         uses: Swatinem/rust-cache@v2
 
-      - run: cargo check --features wgpu --target aarch64-linux-android
+      - run: cargo check --features wgpu,android-native-activity --target aarch64-linux-android
         working-directory: crates/eframe
 
   # ---------------------------------------------------------------------------

crates/eframe/Cargo.toml

@@ -69,6 +69,15 @@ __screenshot = ["dep:image"]
 ## This overrides the `glow` feature.
 wgpu = ["dep:wgpu", "dep:egui-wgpu", "dep:pollster"]
 
+# Allow crates to choose an android-activity backend via Winit
+# - It's important that most applications should not have to depend on android-activity directly, and can
+#   rely on Winit to pull in a suitable version (unlike most Rust crates, any version conflicts won't link)
+# - It's also important that we don't impose an android-activity backend by taking this choice away from applications.
+
+## Enable the `native-activity` backend via `egui-winit` on Android
+android-native-activity = [ "egui-winit/android-native-activity" ]
+## Enable the `game-activity` backend via `egui-winit` on Android
+android-game-activity = [ "egui-winit/android-game-activity" ]
 
 [dependencies]
 egui = { version = "0.21.0", path = "../egui", default-features = false, features = [

crates/egui-winit/Cargo.toml

@@ -42,6 +42,16 @@ serde = ["egui/serde", "dep:serde"]
 ## Enables Wayland support.
 wayland = ["winit/wayland"]
 
+# Allow crates to choose an android-activity backend via Winit
+# - It's important that most applications should not have to depend on android-activity directly, and can
+#   rely on Winit to pull in a suitable version (unlike most Rust crates, any version conflicts won't link)
+# - It's also important that we don't impose an android-activity backend by taking this choice away from applications.
+
+## Enable the `native-activity` backend via Winit on Android
+android-native-activity = [ "winit/android-native-activity" ]
+## Enable the `game-activity` backend via Winit on Android
+android-game-activity = [ "winit/android-game-activity" ]
+
 [dependencies]
 egui = { version = "0.21.0", path = "../egui", default-features = false, features = [
   "tracing",
@@ -76,6 +86,3 @@ smithay-clipboard = { version = "0.6.3", optional = true }
 [target.'cfg(not(target_os = "android"))'.dependencies]
 arboard = { version = "3.2", optional = true, default-features = false }
 
-[target.'cfg(target_os = "android")'.dependencies]
-# TODO(emilk): this is probably not the right place for specifying native-activity, but we need to do it somewhere for the CI
-android-activity = { version = "0.4", features = ["native-activity"] }