release builds shrink with R8: 65 MB down to 30 MB, small enough for IzzyOnDroid. -Pr8 does the same to a debug build for testing

gearslip/build.gradle.kts

@@ -24,6 +24,12 @@ val keystoreProperties = Properties().apply {
     ).firstOrNull { it.exists() }?.inputStream()?.use { load(it) }
 }
 
+// Keeps build output out of the module folder: <root>/build/gearslip/... instead of
+// <root>/gearslip/build/..., so everything this project produces lands under one
+// root-level build/ directory. Set before android {}, which works out the path to R8's default
+// rules from it.
+layout.buildDirectory.set(rootProject.layout.buildDirectory.dir("gearslip"))
+
 android {
     namespace = "app.seb3thehacker.gearslip"
     compileSdk = 37
@@ -57,6 +63,9 @@ android {
     buildTypes {
         release {
             signingConfig = signingConfigs.findByName("release")
+            isMinifyEnabled = true
+            isShrinkResources = true
+            proguardFiles(getDefaultProguardFile("proguard-android-optimize.txt"), "proguard-rules.pro")
         }
         // Its own package, so a debug build installs beside the release one instead of over it.
         // Signed with the release key when it's here: both builds declare the car template
@@ -65,6 +74,12 @@ android {
             applicationIdSuffix = ".dev"
             signingConfigs.findByName("release")?.let { signingConfig = it }
             manifestPlaceholders["appLabel"] = "Gearslip Debug"
+            // -Pr8 shrinks a debug build like a release one, to test R8 in the debug install.
+            if (project.hasProperty("r8")) {
+                isMinifyEnabled = true
+                isShrinkResources = true
+                proguardFiles(getDefaultProguardFile("proguard-android-optimize.txt"), "proguard-rules.pro")
+            }
         }
     }
 
@@ -72,11 +87,6 @@ android {
         buildConfig = true
     }
 
-    // Keeps build output out of the module folder: <root>/build/gearslip/... instead of
-    // <root>/gearslip/build/..., so everything this project produces lands under one
-    // root-level build/ directory.
-    layout.buildDirectory.set(rootProject.layout.buildDirectory.dir("gearslip"))
-
     compileOptions {
         sourceCompatibility = JavaVersion.VERSION_21
         targetCompatibility = JavaVersion.VERSION_21

gearslip/proguard-rules.pro

@@ -0,0 +1,20 @@
+# R8 shrinks the release build; these keep what it can't see being used.
+
+# Names stay readable, so stack traces in shared logs need no mapping file. Shrinking does
+# the real work on size.
+-dontobfuscate
+
+# Gearslip hosts other apps' car screens: their templates arrive as Bundles, and the car
+# library rebuilds them by class name and reflection. Any model class an app might send has to
+# survive, used by Gearslip's code or not.
+-keep class androidx.car.app.** { *; }
+
+# Speech-to-text: the native library calls back into these classes by name.
+-keep class com.k2fsa.sherpa.onnx.** { *; }
+
+# commons-compress refers to optional codecs Gearslip doesn't ship.
+-dontwarn org.tukaani.xz.**
+-dontwarn com.github.luben.zstd.**
+-dontwarn org.brotli.dec.**
+-dontwarn org.objectweb.asm.**
+-dontwarn org.osgi.**