R8 now have automatic detection of Class.forName and auto generate ke…

…ep rules.

This makes application build with Moshi to keep unwanted Kotlin Metadata that have a huge impact on APK size.

After discussion with R8 team, there's currently no solution to avoid this other than using the trick in this PR.

Fixes square#1115

moshi/pom.xml

@@ -13,6 +13,11 @@
   <name>Moshi</name>
 
   <dependencies>
+    <dependency>
+      <groupId>androidx.annotation</groupId>
+      <artifactId>annotation</artifactId>
+      <version>1.1.0</version>
+    </dependency>
     <dependency>
       <groupId>com.squareup.okio</groupId>
       <artifactId>okio</artifactId>
@@ -34,6 +39,14 @@
     </dependency>
   </dependencies>
 
+  <repositories>
+    <repository>
+      <id>google</id>
+      <name>Google</name>
+      <url>https://maven.google.com/</url>
+    </repository>
+  </repositories>
+
   <build>
     <plugins>
       <plugin>

moshi/src/main/java/com/squareup/moshi/internal/Util.java

@@ -15,6 +15,7 @@
  */
 package com.squareup.moshi.internal;
 
+import androidx.annotation.Keep;
 import com.squareup.moshi.JsonAdapter;
 import com.squareup.moshi.JsonClass;
 import com.squareup.moshi.JsonDataException;
@@ -54,7 +55,7 @@ public final class Util {
     Class<? extends Annotation> metadata = null;
     try {
       //noinspection unchecked
-      metadata = (Class<? extends Annotation>) Class.forName("kotlin.Metadata");
+      metadata = (Class<? extends Annotation>) Class.forName(getKotlinMetadataClassNameForReflection());
     } catch (ClassNotFoundException ignored) {
     }
     METADATA = metadata;
@@ -69,6 +70,11 @@ public final class Util {
     DEFAULT_CONSTRUCTOR_MARKER = defaultConstructorMarker;
   }
 
+  @Keep /* Kept to avoid optimizing out reflection. */
+  private static String getKotlinMetadataClassNameForReflection() {
+    return "kotlin.Metadata";
+  }
+
   private Util() {
   }