From b8fdfa467de2b61b8e6fa0bdc2b4c79e8bb5576e Mon Sep 17 00:00:00 2001
From: Jake Wharton <jw@squareup.com>
Date: Sat, 9 Jan 2016 01:27:58 -0500
Subject: [PATCH] Detect and omit the JVM's lambda factory method.

---
 .../retrolambda/test/LambdaClassesTest.java   | 32 ++++++++++++++++---
 .../lambdas/BackportLambdaClass.java          |  3 ++
 .../retrolambda/lambdas/LambdaNaming.java     |  6 ++++
 3 files changed, 37 insertions(+), 4 deletions(-)

diff --git a/end-to-end-tests/src/test/java/net/orfjackal/retrolambda/test/LambdaClassesTest.java b/end-to-end-tests/src/test/java/net/orfjackal/retrolambda/test/LambdaClassesTest.java
index 173e1671..12856471 100644
--- a/end-to-end-tests/src/test/java/net/orfjackal/retrolambda/test/LambdaClassesTest.java
+++ b/end-to-end-tests/src/test/java/net/orfjackal/retrolambda/test/LambdaClassesTest.java
@@ -6,7 +6,11 @@
 
 import org.junit.Test;
 
+import java.lang.reflect.Method;
+import java.util.*;
+
 import static net.orfjackal.retrolambda.test.TestUtil.assertClassExists;
+import static org.junit.Assert.assertTrue;
 
 public class LambdaClassesTest {
 
@@ -18,10 +22,31 @@ public void the_sequence_number_starts_from_1_for_each_enclosing_class() {
         assertClassExists(Dummy2.class.getName() + "$$Lambda$2");
     }
 
+    @Test
+    public void capturing_lambda_contain_no_unexpected_methods() throws ClassNotFoundException {
+        List<String> expected = new ArrayList<>(Arrays.asList("lambdaFactory$", "run"));
+        Class<?> cls = Class.forName(Dummy1.class.getName() + "$$Lambda$1");
+        for (Method method : cls.getDeclaredMethods()) {
+            assertTrue(method.getName() + " not expected", expected.remove(method.getName()));
+        }
+        assertTrue("Missing methods: " + expected, expected.isEmpty());
+    }
+
+    @Test
+    public void non_capturing_lambda_contain_no_unexpected_methods() throws ClassNotFoundException {
+        List<String> expected = new ArrayList<>(Arrays.asList("lambdaFactory$", "run"));
+        Class<?> cls = Class.forName(Dummy2.class.getName() + "$$Lambda$1");
+        for (Method method : cls.getDeclaredMethods()) {
+            assertTrue(method.getName() + " not expected", expected.remove(method.getName()));
+        }
+        assertTrue("Missing methods: " + expected, expected.isEmpty());
+    }
+
 
     @SuppressWarnings("UnusedDeclaration")
     private class Dummy1 {
         private Dummy1() {
+            // Non-capturing lambdas
             Runnable lambda1 = () -> {
             };
             Runnable lambda2 = () -> {
@@ -32,10 +57,9 @@ private Dummy1() {
     @SuppressWarnings("UnusedDeclaration")
     private class Dummy2 {
         private Dummy2() {
-            Runnable lambda1 = () -> {
-            };
-            Runnable lambda2 = () -> {
-            };
+            // Capturing lambdas
+            Runnable lambda1 = () -> System.out.println(hashCode());
+            Runnable lambda2 = () -> System.out.println(hashCode());
         }
     }
 }
diff --git a/retrolambda/src/main/java/net/orfjackal/retrolambda/lambdas/BackportLambdaClass.java b/retrolambda/src/main/java/net/orfjackal/retrolambda/lambdas/BackportLambdaClass.java
index b58aa0d4..4522c13e 100644
--- a/retrolambda/src/main/java/net/orfjackal/retrolambda/lambdas/BackportLambdaClass.java
+++ b/retrolambda/src/main/java/net/orfjackal/retrolambda/lambdas/BackportLambdaClass.java
@@ -45,6 +45,9 @@ public MethodVisitor visitMethod(int access, String name, String desc, String si
         if (LambdaNaming.isSerializationHook(access, name, desc)) {
             return null; // remove serialization hooks; we serialize lambda instances as-is
         }
+        if (LambdaNaming.isPlatformFactoryMethod(access, name, desc, factoryMethod.getDesc())) {
+            return null; // remove the JVM's factory method which will not be unused
+        }
         MethodVisitor next = super.visitMethod(access, name, desc, signature, exceptions);
         next = new RemoveMagicLambdaConstructorCall(next);
         next = new CallPrivateImplMethodsViaAccessMethods(next);
diff --git a/retrolambda/src/main/java/net/orfjackal/retrolambda/lambdas/LambdaNaming.java b/retrolambda/src/main/java/net/orfjackal/retrolambda/lambdas/LambdaNaming.java
index 9e824045..13d15dc3 100644
--- a/retrolambda/src/main/java/net/orfjackal/retrolambda/lambdas/LambdaNaming.java
+++ b/retrolambda/src/main/java/net/orfjackal/retrolambda/lambdas/LambdaNaming.java
@@ -31,4 +31,10 @@ public static boolean isDeserializationHook(int access, String name, String desc
                 && desc.equals("(Ljava/lang/invoke/SerializedLambda;)Ljava/lang/Object;")
                 && Flags.hasFlag(access, ACC_PRIVATE | ACC_STATIC | ACC_SYNTHETIC);
     }
+
+    public static boolean isPlatformFactoryMethod(int access, String name, String desc, String targetDesc) {
+        return name.equals("get$Lambda")
+                && desc.equals(targetDesc)
+                && Flags.hasFlag(access, ACC_PRIVATE | ACC_STATIC);
+    }
 }