Support for lambda expressions in an interface's constant initializer…

…; the lambda impl method will be moved to a companion class

Fixes #42

README.md

@@ -173,6 +173,8 @@ Version History
   ([Issue #31](https://github.com/orfjackal/retrolambda/issues/31))
   - *Experimental! Can be enabled with the enviroment variable
     DEFAULT_METHODS=2*
+- Backports lambda expressions in an interface's constant initializer
+  ([Issue #42](https://github.com/orfjackal/retrolambda/issues/42))
 
 ### Retrolambda 1.8.0 (2014-11-16)
 

retrolambda/src/main/java/net/orfjackal/retrolambda/Transformers.java

@@ -1,4 +1,4 @@
-// Copyright © 2013-2014 Esko Luontola <www.orfjackal.net>
+// Copyright © 2013-2015 Esko Luontola <www.orfjackal.net>
 // This software is released under the Apache License 2.0.
 // The license text is at http://www.apache.org/licenses/LICENSE-2.0
 
@@ -27,6 +27,9 @@ public byte[] backportLambdaClass(ClassReader reader) {
             } else if (FeatureToggles.DEFAULT_METHODS == 2) {
                 next = new UpdateRelocatedMethodInvocations(next, methodRelocations);
                 next = new AddMethodDefaultImplementations(next, methodRelocations);
+            } else {
+                // needed for lambdas in an interface's constant initializer
+                next = new UpdateRelocatedMethodInvocations(next, methodRelocations);
             }
             next = new BackportLambdaClass(next);
             return next;
@@ -56,24 +59,25 @@ public byte[] backportInterface(ClassReader reader) {
                 next = new RemoveStaticMethods(next);
                 next = new RemoveDefaultMethodBodies(next);
                 next = new UpdateRelocatedMethodInvocations(next, methodRelocations);
+            } else {
+                // needed for lambdas in an interface's constant initializer
+                next = new RemoveStaticMethods(next);
             }
             next = new BackportLambdaInvocations(next);
             return next;
         });
     }
 
     public byte[] extractInterfaceCompanion(ClassReader reader) {
-        String companion;
-        if (FeatureToggles.DEFAULT_METHODS == 2
-                && (companion = methodRelocations.getCompanionClass(reader.getClassName())) != null) {
-            return transform(reader, (next) -> {
-                next = new UpdateRelocatedMethodInvocations(next, methodRelocations);
-                next = new ExtractInterfaceCompanionClass(next, companion);
-                return next;
-            });
-        } else {
+        String companion = methodRelocations.getCompanionClass(reader.getClassName());
+        if (companion == null) {
             return null;
         }
+        return transform(reader, (next) -> {
+            next = new UpdateRelocatedMethodInvocations(next, methodRelocations);
+            next = new ExtractInterfaceCompanionClass(next, companion);
+            return next;
+        });
     }
 
     private byte[] transform(ClassReader reader, ClassVisitorChain chain) {

retrolambda/src/main/java/net/orfjackal/retrolambda/interfaces/ExtractInterfaceCompanionClass.java

@@ -1,4 +1,4 @@
-// Copyright © 2013-2014 Esko Luontola <www.orfjackal.net>
+// Copyright © 2013-2015 Esko Luontola <www.orfjackal.net>
 // This software is released under the Apache License 2.0.
 // The license text is at http://www.apache.org/licenses/LICENSE-2.0
 
@@ -34,6 +34,19 @@ public MethodVisitor visitMethod(int access, String name, String desc, String si
             // do not copy abstract methods to the companion class
             return null;
         }
+        if (Flags.isClassInitializer(name, desc, access)) {
+            // we won't copy constant fields from the interface, so a class initializer won't be needed
+            return null;
+        }
+        if (Flags.hasFlag(access, ACC_STATIC)
+                && Flags.hasFlag(access, ACC_PRIVATE)) {
+            // XXX: Possibly a lambda impl method, which is private. It is the easiest for us to make it visible,
+            // which should be quite safe because static methods are not inherited (and anyways nothing inherits
+            // the companion class). The clean solution would be to generate an access method for it, but due to
+            // the location in code which generates those access methods, it would require complex code changes to
+            // pass around the information from one transformation to another.
+            access &= ~ACC_PRIVATE;
+        }
         if (!Flags.hasFlag(access, ACC_STATIC)) {
             // default method; make static and take 'this' as the first argument
             access |= ACC_STATIC;
@@ -42,4 +55,10 @@ public MethodVisitor visitMethod(int access, String name, String desc, String si
         }
         return super.visitMethod(access, name, desc, signature, exceptions);
     }
+
+    @Override
+    public FieldVisitor visitField(int access, String name, String desc, String signature, Object value) {
+        // an interface can only contain constant fields; they don't need to be copied
+        return null;
+    }
 }

retrolambda/src/main/java/net/orfjackal/retrolambda/interfaces/RemoveStaticMethods.java

@@ -1,4 +1,4 @@
-// Copyright © 2013-2014 Esko Luontola <www.orfjackal.net>
+// Copyright © 2013-2015 Esko Luontola <www.orfjackal.net>
 // This software is released under the Apache License 2.0.
 // The license text is at http://www.apache.org/licenses/LICENSE-2.0
 
@@ -17,7 +17,7 @@ public RemoveStaticMethods(ClassVisitor next) {
 
     @Override
     public MethodVisitor visitMethod(int access, String name, String desc, String signature, String[] exceptions) {
-        if (isStaticMethod(access)) {
+        if (isStaticMethod(access) && !Flags.isClassInitializer(name, desc, access)) {
             return null;
         } else {
             return super.visitMethod(access, name, desc, signature, exceptions);

retrolambda/src/main/java/net/orfjackal/retrolambda/lambdas/BackportLambdaInvocations.java

@@ -1,4 +1,4 @@
-// Copyright © 2013-2014 Esko Luontola <www.orfjackal.net>
+// Copyright © 2013-2015 Esko Luontola <www.orfjackal.net>
 // This software is released under the Apache License 2.0.
 // The license text is at http://www.apache.org/licenses/LICENSE-2.0
 
@@ -57,7 +57,7 @@ public MethodVisitor visitMethod(int access, String name, String desc, String si
         }
         if (FeatureToggles.DEFAULT_METHODS == 0
                 && isNonAbstractMethodOnInterface(access)
-                && !isClassInitializerMethod(name, desc, access)) {
+                && !Flags.isClassInitializer(name, desc, access)) {
             // In case we have missed a case of Java 8 producing non-abstract methods
             // on interfaces, we have this warning here to get a bug report sooner.
             // Not allowed by Java 7:
@@ -85,16 +85,14 @@ private boolean isNonAbstractMethodOnInterface(int methodAccess) {
                 !Flags.hasFlag(methodAccess, ACC_ABSTRACT);
     }
 
-    private static boolean isClassInitializerMethod(String name, String desc, int methodAccess) {
-        return name.equals("<clinit>") &&
-                desc.equals("()V") &&
-                Flags.hasFlag(methodAccess, ACC_STATIC);
-    }
-
     Handle getLambdaAccessMethod(Handle implMethod) {
         if (!implMethod.getOwner().equals(className)) {
             return implMethod;
         }
+        if (Flags.hasFlag(classAccess, ACC_INTERFACE)) {
+            // the method will be relocated to a companion class
+            return implMethod;
+        }
         // TODO: do not generate an access method if the impl method is not private (probably not implementable with a single pass)
         String name = "access$lambda$" + lambdaAccessToImplMethods.size();
         String desc = implMethod.getTag() == H_INVOKESTATIC

retrolambda/src/main/java/net/orfjackal/retrolambda/util/Flags.java

@@ -1,12 +1,20 @@
-// Copyright © 2013-2014 Esko Luontola <www.orfjackal.net>
+// Copyright © 2013-2015 Esko Luontola <www.orfjackal.net>
 // This software is released under the Apache License 2.0.
 // The license text is at http://www.apache.org/licenses/LICENSE-2.0
 
 package net.orfjackal.retrolambda.util;
 
+import static org.objectweb.asm.Opcodes.ACC_STATIC;
+
 public class Flags {
 
     public static boolean hasFlag(int subject, int flag) {
         return (subject & flag) == flag;
     }
+
+    public static boolean isClassInitializer(String name, String desc, int methodAccess) {
+        return name.equals("<clinit>") &&
+                desc.equals("()V") &&
+                hasFlag(methodAccess, ACC_STATIC);
+    }
 }