KT-10005 Java to Kotlin: do not convert type cast to cast to nullable if it should not be null

#KT-10005 Fixed

j2k/src/org/jetbrains/kotlin/j2k/ExpressionConverter.kt

@@ -480,12 +480,24 @@ class DefaultExpressionConverter : JavaElementVisitor(), ExpressionConverter {
             result = MethodCallExpression.buildNotNull(operandConverted, typeConversion)
         }
         else {
-            val typeConverted = typeConverter.convertType(castType.getType(),
-                                                          if (operandConverted.isNullable) Nullability.Nullable else Nullability.NotNull)
+            val nullability = if (operandConverted.isNullable && !expression.isQualifier())
+                Nullability.Nullable
+            else
+                Nullability.NotNull
+            val typeConverted = typeConverter.convertType(castType.type, nullability)
             result = TypeCastExpression(typeConverted, operandConverted)
         }
     }
 
+    private fun PsiExpression.isQualifier(): Boolean {
+        val parent = parent
+        when (parent) {
+            is PsiParenthesizedExpression -> return parent.isQualifier()
+            is PsiReferenceExpression -> return this == parent.qualifierExpression
+            else -> return false
+        }
+    }
+
     override fun visitPolyadicExpression(expression: PsiPolyadicExpression) {
         val args = expression.getOperands().map { codeConverter.convertExpression(it, expression.getType()) }
         result = PolyadicExpression(args, getOperatorString(expression.getOperationTokenType()))

j2k/testData/fileOrElement/typeCastExpression/beforeDot.java

@@ -0,0 +1,6 @@
+public class A {
+    void foo(Object o) {
+        if (o == null) return;
+        int length = ((String) o).length();
+    }
+}

j2k/testData/fileOrElement/typeCastExpression/beforeDot.kt

@@ -0,0 +1,6 @@
+class A {
+    internal fun foo(o: Any?) {
+        if (o == null) return
+        val length = (o as String).length
+    }
+}

j2k/tests/org/jetbrains/kotlin/j2k/JavaToKotlinConverterForWebDemoTestGenerated.java

@@ -4318,6 +4318,12 @@ public class JavaToKotlinConverterForWebDemoTestGenerated extends AbstractJavaTo
             KotlinTestUtils.assertAllTestsPresentByMetadata(this.getClass(), new File("j2k/testData/fileOrElement/typeCastExpression"), Pattern.compile("^(.+)\\.java$"), true);
         }
 
+        @TestMetadata("beforeDot.java")
+        public void testBeforeDot() throws Exception {
+            String fileName = KotlinTestUtils.navigationMetadata("j2k/testData/fileOrElement/typeCastExpression/beforeDot.java");
+            doTest(fileName);
+        }
+
         @TestMetadata("castNullable.java")
         public void testCastNullable() throws Exception {
             String fileName = KotlinTestUtils.navigationMetadata("j2k/testData/fileOrElement/typeCastExpression/castNullable.java");

j2k/tests/org/jetbrains/kotlin/j2k/JavaToKotlinConverterSingleFileTestGenerated.java

@@ -4318,6 +4318,12 @@ public class JavaToKotlinConverterSingleFileTestGenerated extends AbstractJavaTo
             KotlinTestUtils.assertAllTestsPresentByMetadata(this.getClass(), new File("j2k/testData/fileOrElement/typeCastExpression"), Pattern.compile("^(.+)\\.java$"), true);
         }
 
+        @TestMetadata("beforeDot.java")
+        public void testBeforeDot() throws Exception {
+            String fileName = KotlinTestUtils.navigationMetadata("j2k/testData/fileOrElement/typeCastExpression/beforeDot.java");
+            doTest(fileName);
+        }
+
         @TestMetadata("castNullable.java")
         public void testCastNullable() throws Exception {
             String fileName = KotlinTestUtils.navigationMetadata("j2k/testData/fileOrElement/typeCastExpression/castNullable.java");