[J2KT] Remove redundant casts which were added implicitly by various …

…passes, which are not needed in Kotlin.

PiperOrigin-RevId: 719284651

transpiler/java/com/google/j2cl/transpiler/backend/Backend.java

@@ -174,6 +174,7 @@
 import com.google.j2cl.transpiler.passes.RemoveNoopStatements;
 import com.google.j2cl.transpiler.passes.RemoveUnnecessaryLabels;
 import com.google.j2cl.transpiler.passes.RemoveUnneededCasts;
+import com.google.j2cl.transpiler.passes.RemoveUnneededCastsJ2kt;
 import com.google.j2cl.transpiler.passes.RemoveUnneededJsDocCasts;
 import com.google.j2cl.transpiler.passes.RemoveUnneededNotNullChecks;
 import com.google.j2cl.transpiler.passes.RemoveUnreachableCode;
@@ -775,6 +776,7 @@ public ImmutableList<Supplier<NormalizationPass>> getPassFactories(BackendOption
           () -> new RemoveUnnecessaryLabels(/* onlyLoopsAreBreakable= */ true),
           RemoveNestedBlocks::new,
           RemoveNoopStatements::new,
+          RemoveUnneededCastsJ2kt::new,
 
           // Passes that breaks the invariants for running ConversionContextVisitor related passes.
           NormalizeVarargInvocationsJ2kt::new,

transpiler/java/com/google/j2cl/transpiler/passes/RemoveUnneededCastsJ2kt.java

@@ -0,0 +1,54 @@
+/*
+ * Copyright 2024 Google Inc.
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License"); you may not
+ * use this file except in compliance with the License. You may obtain a copy of
+ * the License at
+ *
+ * http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS, WITHOUT
+ * WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. See the
+ * License for the specific language governing permissions and limitations under
+ * the License.
+ */
+package com.google.j2cl.transpiler.passes;
+
+import com.google.j2cl.transpiler.ast.AbstractRewriter;
+import com.google.j2cl.transpiler.ast.CastExpression;
+import com.google.j2cl.transpiler.ast.CompilationUnit;
+import com.google.j2cl.transpiler.ast.Expression;
+import com.google.j2cl.transpiler.ast.Node;
+
+/** Removes casts which are unneeded in J2KT. */
+public class RemoveUnneededCastsJ2kt extends NormalizationPass {
+
+  @Override
+  public void applyTo(CompilationUnit compilationUnit) {
+    compilationUnit.accept(
+        new AbstractRewriter() {
+          @Override
+          public Node rewriteCastExpression(CastExpression castExpression) {
+            Expression innerExpression = castExpression.getExpression();
+            if (!(innerExpression instanceof CastExpression)) {
+              return castExpression;
+            }
+
+            // Deduplicate casts of the same base type.
+            CastExpression innerCastExpression = (CastExpression) innerExpression;
+            if (!castExpression
+                .getCastTypeDescriptor()
+                .toRawTypeDescriptor()
+                .isSameBaseType(
+                    innerCastExpression.getCastTypeDescriptor().toRawTypeDescriptor())) {
+              return castExpression;
+            }
+
+            return CastExpression.Builder.from(castExpression)
+                .setExpression(innerCastExpression.getExpression())
+                .build();
+          }
+        });
+  }
+}

transpiler/javatests/com/google/j2cl/readable/java/cast/output_kt/CastGenerics.kt.txt

@@ -64,7 +64,7 @@ open class CastGenerics<T, E: Number?> {
  open fun testCastToRawToGeneric(
   @ObjCName("withCastCastGenerics_Foo") foo: CastGenerics.Foo<Any?>?
  ): CastGenerics.Foo<String?>? {
-  return foo as CastGenerics.Foo<Any?>? as CastGenerics.Foo<String?>?
+  return foo as CastGenerics.Foo<String?>?
  }
 
  @ObjCName("outerGenericMethod")
@@ -81,7 +81,7 @@ open class CastGenerics<T, E: Number?> {
   @ObjCName("withId") o: Any?
  ): EE where EE: CastGenerics.Empty1?, EE: CastGenerics.Empty2<EE>? {
   if (o is CastGenerics.Empty1) {
-   return o as EE? as EE
+   return o as EE
   }
   return null as EE
  }

transpiler/javatests/com/google/j2cl/readable/java/intersectiontype/output_kt/IntersectionTypeTest.kt.txt

@@ -175,7 +175,7 @@ open class IntersectionTypeTest<U> {
   private fun <T> m(): T where T: IntersectionTypeTest.A?, T: IntersectionTypeTest.EmptyA? {
    return IntersectionTypeTest.get<Any?>(
     Any(),
-   ) as T? as T
+   ) as T
   }
 
   @JvmStatic

transpiler/javatests/com/google/j2cl/readable/java/j2kt/output_kt/NotNullAssertionProblems.kt.txt

@@ -395,7 +395,7 @@ open class NotNullAssertionProblems {
  @ObjCName("J2ktJ2ktNotNullAssertionProblems_C", exact = true)
  open class C<V> internal constructor() {
   @JvmField
-  internal var defaultValue_pp_j2kt: V = null as V? as V
+  internal var defaultValue_pp_j2kt: V = null as V
 
   internal open fun f_pp_j2kt(): V {
    return (if (true) this.defaultValue_pp_j2kt else this.defaultValue_pp_j2kt) as V