Enable minification for debug builds

README.md

@@ -38,6 +38,10 @@ The above applies only to SMS and MMS messages; the format for call logs and con
 
 SMS Import / Export is available from [Github](https://github.com/tmo1/sms-ie). The repository can be cloned and built locally, from the command line (e.g., by issuing `gradlew assembleDebug` in the root directory of the project) or within Android Studio. Releases, which include pre-built APK packages, can be downloaded from the [Releases page](https://github.com/tmo1/sms-ie/releases), and are also available at [F-Droid](https://f-droid.org/packages/com.github.tmo1.sms_ie/). Automatically built (debug) packages of the latest code pushed to the repository are generally available [here](https://github.com/tmo1/sms-ie/actions/workflows/build.yml) (click on the latest workflow run, then click on `com.github.tmo1.sms_ie` in the `Artifacts` section).
 
+### Building
+
+**Note:** When using Android Studio to build debug builds and deploy them to systems with API level >= 21, it may be desirable to turn off minification; see the comments in `[build.gradle](https://github.com/tmo1/sms-ie/app/build.gradle)` for details.
+
 ## Compatibility
 
 Current versions of SMS Import / Export should run on any Android (phone-like) device running KitKat / 4.4 (API level 19) or later, although message import and scheduled message export are only possible on devices running Marshmallow / 6.0 (API level 23) or later.

app/build.gradle

@@ -46,6 +46,24 @@ android {
             proguardFiles getDefaultProguardFile('proguard-android-optimize.txt'), 'proguard-rules.pro'
             signingConfig signingConfigs.debug
         }
+        /* The following 'debug {}' stanza is necessary to avoid hitting the 64K reference limit:
+         https://developer.android.com/build/multidex
+         Minification can, however, slow down build times, and Android Studio warns about this.
+         This stanza is only necessary for building debug builds from the command line, or when
+         deploying to systems with API level < 21; when deploying from Android Studio to systems
+         with API level >= 21, multidex is enabled by default and the stanza can be deleted for
+         faster build times:
+         https://developer.android.com/build/multidex#mdex-on-l */
+        debug {
+            // https://stackoverflow.com/a/55785351
+            postprocessing {
+                removeUnusedCode true
+                obfuscate false
+                optimizeCode true
+            }
+            proguardFiles getDefaultProguardFile('proguard-android-optimize.txt'), 'proguard-rules.pro'
+        }
+
     }
     compileOptions {
         sourceCompatibility JavaVersion.VERSION_1_8