fix: Bad cast in target Java code (#3958)

Fixes #3956

This PR removes a cast that was not accepted by the Java compiler. It
seems the cast is needed at all.

<small>By submitting this pull request, I confirm that my contribution
is made under the terms of the [MIT
license](https://github.com/dafny-lang/dafny/blob/master/LICENSE.txt).</small>

Author: RustanLeino

Source/DafnyCore/Compilers/Java/Compiler-java.cs

@@ -1003,10 +1003,10 @@ private void EmitTypeDescriptorMethod([CanBeNull] TopLevelDecl enclosingTypeDecl
               // we're looking for).
               var tp = targetTypeIgnoringConstraints.AsTypeParameter;
               if (tp == null) {
-                typeDescriptorExpr = $"{DafnyTypeDescriptor}.referenceWithInitializer({StripTypeParameters(targetTypeName)}.class, () -> ({targetTypeName}){d})";
+                typeDescriptorExpr = $"{DafnyTypeDescriptor}.<{targetTypeName}>referenceWithInitializer({StripTypeParameters(targetTypeName)}.class, () -> {d})";
               } else {
                 var td = FormatTypeDescriptorVariable(tp.GetCompileName(Options));
-                typeDescriptorExpr = $"{DafnyTypeDescriptor}.referenceWithInitializerAndTypeDescriptor({td}, () -> {d})";
+                typeDescriptorExpr = $"{DafnyTypeDescriptor}.<{targetTypeName}>referenceWithInitializerAndTypeDescriptor({td}, () -> {d})";
               }
             }
             break;
@@ -1018,7 +1018,7 @@ private void EmitTypeDescriptorMethod([CanBeNull] TopLevelDecl enclosingTypeDecl
 
       if (typeParams.Count == 0) {
         // a static context in Java does not see the enclosing type parameters
-        wr.WriteLine($"private static final {DafnyTypeDescriptor}<{StripTypeParameters(targetTypeName)}> _TYPE = {typeDescriptorExpr};");
+        wr.WriteLine($"private static final {DafnyTypeDescriptor}<{targetTypeName}> _TYPE = {typeDescriptorExpr};");
         typeDescriptorExpr = "_TYPE";
       }
       wr.Write($"public static {TypeParameters(typeParams, " ")}{DafnyTypeDescriptor}<{targetTypeName}> {TypeMethodName}(");

Source/DafnyRuntime/DafnyRuntimeJava/src/main/java/dafny/TypeDescriptor.java

@@ -11,14 +11,14 @@
 import java.util.function.Function;
 
 public abstract class TypeDescriptor<T> {
-    final Class<T> boxedClass;
+    final Class<?> boxedClass;
     final Class<?> unboxedClass;
 
-    TypeDescriptor(Class<T> javaClass) {
+    TypeDescriptor(Class<?> javaClass) {
         this(javaClass, javaClass);
     }
 
-    TypeDescriptor(Class<T> boxedClass, Class<?> unboxedClass) {
+    TypeDescriptor(Class<?> boxedClass, Class<?> unboxedClass) {
         this.boxedClass = boxedClass;
         this.unboxedClass = unboxedClass;
     }
@@ -94,7 +94,7 @@ public static <T> TypeDescriptor<T> referenceWithDefault(
     }
 
     public static <T> TypeDescriptor<T> referenceWithInitializer(
-            Class<T> javaClass, Initializer<T> initializer) {
+            Class<?> javaClass, Initializer<T> initializer) {
         return new ReferenceType<T>(javaClass, initializer);
     }
 
@@ -200,7 +200,7 @@ private static final class ReferenceType<T> extends TypeDescriptor<T> {
         private final Initializer<T> initializer;
         private TypeDescriptor<?> arrayType;
 
-        public ReferenceType(Class<T> javaClass, Initializer<T> initializer) {
+        public ReferenceType(Class<?> javaClass, Initializer<T> initializer) {
             super(javaClass);
 
             assert !javaClass.isPrimitive();

Test/git-issues/git-issue-3956.dfy

@@ -0,0 +1,11 @@
+// RUN: %testDafnyForEachCompiler "%s"
+
+datatype AAA<X> = CtorA
+datatype BBB<Y> = CtorB
+type AaaBbb<R> = AAA<BBB<R>>
+datatype MyType<W> = MyType(n: AaaBbb<W>)
+
+method Main() {
+  var m: MyType<char> := MyType(CtorA);
+  print m, "\n"; // AAA.CtorA
+}

Test/git-issues/git-issue-3956.dfy.expect

@@ -0,0 +1 @@
+AAA.CtorA