Merge pull request scala#7843 from smarter/static-mf

Emit mixin forwarders as bridges to avoid needing generic signatures

Author: lrytz

src/compiler/scala/tools/nsc/transform/Mixin.scala

@@ -169,33 +169,7 @@ abstract class Mixin extends Transform with ast.TreeDSL with AccessorSynthesis {
     clazz.info.decls enter member setFlag MIXEDIN resetFlag JAVA_DEFAULTMETHOD
   }
   def cloneAndAddMember(mixinClass: Symbol, mixinMember: Symbol, clazz: Symbol): Symbol =
-    addMember(clazz, cloneBeforeErasure(mixinClass, mixinMember, clazz))
-
-  def cloneBeforeErasure(mixinClass: Symbol, mixinMember: Symbol, clazz: Symbol): Symbol = {
-    val newSym = enteringErasure {
-      // since we used `mixinMember` from the interface that represents the trait that's
-      // being mixed in, have to instantiate the interface type params (that may occur in mixinMember's
-      // info) as they are seen from the class.  We can't use the member that we get from the
-      // implementation class, as it's a clone that was made after erasure, and thus it does not
-      // know its info at the beginning of erasure anymore.
-      val sym = mixinMember cloneSymbol clazz
-
-      val erasureMap = erasure.erasure(mixinMember)
-      val erasedInterfaceInfo: Type = erasureMap(mixinMember.info)
-      val specificForwardInfo       = (clazz.thisType baseType mixinClass) memberInfo mixinMember
-      val forwarderInfo =
-        if (erasureMap(specificForwardInfo) =:= erasedInterfaceInfo)
-          specificForwardInfo
-        else {
-          erasedInterfaceInfo
-        }
-      // Optimize: no need if mixinClass has no typeparams.
-      // !!! JZ Really? What about the effect of abstract types, prefix?
-      if (mixinClass.typeParams.isEmpty) sym
-      else sym modifyInfo (_ => forwarderInfo)
-    }
-    newSym
-  }
+    addMember(clazz, mixinMember.cloneSymbol(clazz).setFlag(BRIDGE))
 
   def publicizeTraitMethods(clazz: Symbol): Unit = {
     if (treatedClassInfos(clazz) != clazz.info) {

test/files/neg/t4749.check

@@ -37,13 +37,13 @@ t4749.scala:28: warning: Fail6 has a valid main method (args: Array[String])Unit
 
   object Fail6 {
          ^
-t4749.scala:44: warning: not a valid main method for bippy.Win3,
-  because main methods must have the exact signature (Array[String])Unit.
+t4749.scala:42: warning: not a valid main method for bippy.Win3,
+  because main methods cannot refer to type parameters or abstract types.
   To define an entry point, please define the main method as:
     def main(args: Array[String]): Unit
 
-  object Win3 extends WinBippy[Unit] { }
-         ^
+    def main(args: Array[String]): T = null.asInstanceOf[T]
+        ^
 error: No warnings can be incurred under -Xfatal-warnings.
 7 warnings found
 one error found

test/files/neg/t5148.check

@@ -1,6 +1,6 @@
-t5148.scala:4: error: Symbol 'term scala.tools.nsc.interpreter.IMain.memberHandlers' is missing from the classpath.
+t5148.scala:4: error: Symbol 'type scala.tools.nsc.interpreter.IMain.Request' is missing from the classpath.
 This symbol is required by 'method scala.tools.nsc.interpreter.Imports.allReqAndHandlers'.
-Make sure that term memberHandlers is in your classpath and check for conflicting dependencies with `-Ylog-classpath`.
+Make sure that type Request is in your classpath and check for conflicting dependencies with `-Ylog-classpath`.
 A full rebuild may help if 'Imports.class' was compiled against an incompatible version of scala.tools.nsc.interpreter.IMain.
 class IMain extends Imports
             ^

test/files/run/mixin-bridge-methods.scala

@@ -0,0 +1 @@
+Foo(0)

test/files/run/mixin-forwarder-overload.check

@@ -0,0 +1,9 @@
+case class Foo(x: Int)
+
+trait A[X]  {
+  def concat[Dummy](suffix: Int): Dummy = ???
+}
+
+class Bar extends A[Foo] {
+  def concat(suffix: Int): Foo = Foo(0)
+}

test/files/run/mixin-forwarder-overload/A.scala

@@ -0,0 +1,7 @@
+public class Test {
+  public static void main(String[] args) {
+    Bar bar = new Bar();
+    Foo x = bar.concat(0);
+    System.out.println(x);
+  }
+}

test/files/run/mixin-forwarder-overload/Test.java

@@ -1,19 +1,19 @@
 class Test$bar1$ {
-  public java.lang.String Test$bar1$.f(java.lang.Object)
   public java.lang.Object Test$bar1$.f(java.lang.Object) <bridge> <synthetic>
+  public java.lang.String Test$bar1$.f(java.lang.Object) <bridge> <synthetic>
   public java.lang.String Test$bar1$.g(java.lang.String)
   public java.lang.Object Test$bar1$.g(java.lang.Object) <bridge> <synthetic>
   public java.lang.String Test$bar1$.g(java.lang.Object) <bridge> <synthetic>
-  public java.lang.Object Test$bar1$.h(java.lang.Object)
+  public java.lang.Object Test$bar1$.h(java.lang.Object) <bridge> <synthetic>
 }
 
 class Test$bar2$ {
-  public java.lang.Object Test$bar2$.f(java.lang.String)
   public java.lang.Object Test$bar2$.f(java.lang.Object) <bridge> <synthetic>
+  public java.lang.Object Test$bar2$.f(java.lang.String) <bridge> <synthetic>
   public java.lang.String Test$bar2$.g(java.lang.String)
   public java.lang.Object Test$bar2$.g(java.lang.Object) <bridge> <synthetic>
   public java.lang.Object Test$bar2$.g(java.lang.String) <bridge> <synthetic>
-  public java.lang.Object Test$bar2$.h(java.lang.Object)
+  public java.lang.Object Test$bar2$.h(java.lang.Object) <bridge> <synthetic>
 }
 
 class Test$bar3$ {
@@ -23,7 +23,7 @@ class Test$bar3$ {
   public java.lang.String Test$bar3$.g(java.lang.String)
   public java.lang.Object Test$bar3$.g(java.lang.Object) <bridge> <synthetic>
   public java.lang.String Test$bar3$.g(java.lang.Object) <bridge> <synthetic>
-  public java.lang.Object Foo3.h(java.lang.Object)
+  public java.lang.Object Foo3.h(java.lang.Object) <bridge> <synthetic>
 }
 
 class Test$bar4$ {
@@ -33,7 +33,7 @@ class Test$bar4$ {
   public java.lang.String Test$bar4$.g(java.lang.String)
   public java.lang.Object Test$bar4$.g(java.lang.Object) <bridge> <synthetic>
   public java.lang.Object Test$bar4$.g(java.lang.String) <bridge> <synthetic>
-  public java.lang.Object Foo4.h(java.lang.Object)
+  public java.lang.Object Foo4.h(java.lang.Object) <bridge> <synthetic>
 }
 
 class Test$bar5$ {
@@ -45,7 +45,7 @@ class Test$bar5$ {
   public java.lang.Object Test$bar5$.g(java.lang.Object) <bridge> <synthetic>
   public java.lang.Object Test$bar5$.g(java.lang.String) <bridge> <synthetic>
   public java.lang.String Test$bar5$.g(java.lang.Object) <bridge> <synthetic>
-  public java.lang.Object Test$bar5$.h(java.lang.Object)
+  public java.lang.Object Test$bar5$.h(java.lang.Object) <bridge> <synthetic>
 }
 
 interface Foo1 {

test/files/run/mixin-signatures.check

@@ -1,11 +1,6 @@
-import scala.collection.immutable.Nil;
-import scala.collection.immutable.List;
-
 public class Test {
 	public static void main(String[] args) {
 		C<String> c = new C<String>();
-		// TODO add a bridge during mixin so we can expose
-		// sharper generic signature for `tail`.
-		/*Traversable<String>*/ Object ls = c.tail();
+		scala.collection.Iterable<String> ls = c.tail();
 	}
 }

test/files/run/t3452d/Test.java

@@ -4,6 +4,8 @@ trait TraversableLike[A, Repr] {
 
 abstract class AbstractTrav[A] extends TraversableLike[A, AbstractTrav[A]]
 
+class C1 extends AbstractTrav[String]
+
 object O extends AbstractTrav[String]
 
-class C[A] extends AbstractTrav[A]
+class C2[A] extends AbstractTrav[A]

test/files/run/t3452g/A.scala

@@ -1,14 +1,10 @@
-
 public class Test {
-	public static void main(String[] args) {
-		// To get better types here, we would need to
-		// add bridge during mixin so we can expose
-		// a generic return type of Traversable<A>, because the erasure
-		// of this (Traversable) differs from the erasure of the mixed
-		// method (erasure(Repr) = Object)
+  public static void main(String[] args) {
+    AbstractTrav<String> lsSharp1 = new C1().tail();
 
-		Object lsSharp = O.tail();
+    // Object is the result type for the static forwarder (might be because of #11305)
+    Object lsSharp2 = O.tail();
 
-		Object lsSharp2 = new C<String>().tail();
-	}
+    AbstractTrav<String> lsSharp3 = new C2<String>().tail();
+  }
 }

test/files/run/t3452g/Test.java

@@ -1,10 +1,10 @@
-public Category<?> C.category()
-public Category<scala.Tuple2> C.category1()
+public Category C.category()
+public Category C.category1()
 public default Category<java.lang.Object> M1.category()
 public default Category<scala.Tuple2> M1.category1()
 public static Category M1.category$(M1)
 public static Category M1.category1$(M1)
 public default Category<java.lang.Object> M2.category()
 public default Category<scala.Tuple2> M2.category1()
 public static Category M2.category$(M2)
-public static Category M2.category1$(M2)
+public static Category M2.category1$(M2)

test/files/run/t7932.check

@@ -0,0 +1,9 @@
+import java.util.Comparator
+
+trait RDDLike[T] {
+  def max(comp: Comparator[T]): T = {
+    (1.0).asInstanceOf[T]
+  }
+}
+
+class DoubleRDD extends RDDLike[java.lang.Double] { }

test/files/run/t8905/DoubleRDD.scala

@@ -0,0 +1,20 @@
+import java.util.Comparator;
+
+public class Test {
+  private static class DoubleComparator implements Comparator<Double> {
+    public int compare(Double o1, Double o2) {
+      return o1.compareTo(o2);
+    }
+  }
+
+  public static void main(String[] args) {
+    DoubleRDD rdd = new DoubleRDD();
+    RDDLike<Double> rddLike = rdd;
+
+    // This call works fine:
+    double rddLikeMax = rddLike.max(new DoubleComparator());
+    // In Scala 2.10.4, this code compiles but this call fails at runtime:
+    // java.lang.NoSuchMethodError: DoubleRDD.max(Ljava/util/Comparator;)Ljava/lang/Double;
+    double rddMax = rdd.max(new DoubleComparator());
+  }
+}