Fix for KT-5410 J2K: someObject + "someString" should be converted to someObject.toString() + "someString"

Otherwise `+` operator will not resolve

idea/src/org/jetbrains/kotlin/idea/j2k/J2kPostProcessings.kt

@@ -18,6 +18,7 @@ package org.jetbrains.kotlin.idea.j2k
 
 import com.intellij.psi.search.LocalSearchScope
 import com.intellij.psi.search.searches.ReferencesSearch
+import org.jetbrains.kotlin.builtins.KotlinBuiltIns
 import org.jetbrains.kotlin.diagnostics.Diagnostic
 import org.jetbrains.kotlin.diagnostics.DiagnosticFactory
 import org.jetbrains.kotlin.diagnostics.Errors
@@ -36,6 +37,7 @@ import org.jetbrains.kotlin.lexer.KtTokens
 import org.jetbrains.kotlin.psi.*
 import org.jetbrains.kotlin.psi.psiUtil.visibilityModifierType
 import org.jetbrains.kotlin.resolve.BindingContext
+import org.jetbrains.kotlin.resolve.calls.callUtil.getType
 import org.jetbrains.kotlin.resolve.diagnostics.Diagnostics
 import org.jetbrains.kotlin.utils.mapToIndex
 import java.util.*
@@ -60,6 +62,7 @@ object J2KPostProcessingRegistrar {
         _processings.add(RemoveExplicitTypeArgumentsProcessing())
         _processings.add(RemoveRedundantOverrideVisibilityProcessing())
         _processings.add(MoveLambdaOutsideParenthesesProcessing())
+        _processings.add(FixObjectStringConcatenationProcessing())
         _processings.add(ConvertToStringTemplateProcessing())
         _processings.add(UsePropertyAccessSyntaxProcessing())
         _processings.add(RemoveRedundantSamAdaptersProcessing())
@@ -243,4 +246,31 @@ object J2KPostProcessingRegistrar {
             return null
         }
     }
+
+    private class FixObjectStringConcatenationProcessing : J2kPostProcessing {
+        override fun createAction(element: KtElement, diagnostics: Diagnostics): (() -> Unit)? {
+            if (element !is KtBinaryExpression ||
+                element.operationToken != KtTokens.PLUS ||
+                diagnostics.forElement(element.operationReference).none {
+                    it.factory == Errors.UNRESOLVED_REFERENCE_WRONG_RECEIVER
+                    || it.factory  == Errors.NONE_APPLICABLE
+                })
+                return null
+
+            val bindingContext = element.analyzeAndGetResult().bindingContext
+            val rightType = element.right?.getType(bindingContext) ?: return null
+
+            if (KotlinBuiltIns.isString(rightType)) {
+                return {
+                    val factory = KtPsiFactory(element)
+                    element.left!!.replace(factory.buildExpression {
+                        appendFixedText("(")
+                        appendExpression(element.left)
+                        appendFixedText(").toString()")
+                    })
+                }
+            }
+            return null
+        }
+    }
 }

j2k/testData/fileOrElement/binaryExpression/lhsObjectPlusString.java

@@ -0,0 +1,22 @@
+public class Test {
+    public static class B {
+        public static class C {
+
+        }
+
+        public C c() {
+            return new C();
+        }
+    }
+
+    public void a() {
+        B b = new B();
+        System.out.println(b + "");
+        String a = 1 + "0";
+        System.out.println(b.c() + "");
+    }
+
+    public static void main(String[] args) {
+        String p = new Test() + "123";
+    }
+}

j2k/testData/fileOrElement/binaryExpression/lhsObjectPlusString.kt

@@ -0,0 +1,23 @@
+class Test {
+    class B {
+        class C
+
+        fun c(): C {
+            return C()
+        }
+    }
+
+    fun a() {
+        val b = B()
+        println(b.toString() + "")
+        val a = 1.toString() + "0"
+        println(b.c().toString() + "")
+    }
+
+    companion object {
+
+        @JvmStatic fun main(args: Array<String>) {
+            val p = Test().toString() + "123"
+        }
+    }
+}

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

@@ -553,6 +553,12 @@ public class JavaToKotlinConverterForWebDemoTestGenerated extends AbstractJavaTo
             doTest(fileName);
         }
 
+        @TestMetadata("lhsObjectPlusString.java")
+        public void testLhsObjectPlusString() throws Exception {
+            String fileName = KotlinTestUtils.navigationMetadata("j2k/testData/fileOrElement/binaryExpression/lhsObjectPlusString.java");
+            doTest(fileName);
+        }
+
         @TestMetadata("minus.java")
         public void testMinus() throws Exception {
             String fileName = KotlinTestUtils.navigationMetadata("j2k/testData/fileOrElement/binaryExpression/minus.java");

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

@@ -553,6 +553,12 @@ public class JavaToKotlinConverterSingleFileTestGenerated extends AbstractJavaTo
             doTest(fileName);
         }
 
+        @TestMetadata("lhsObjectPlusString.java")
+        public void testLhsObjectPlusString() throws Exception {
+            String fileName = KotlinTestUtils.navigationMetadata("j2k/testData/fileOrElement/binaryExpression/lhsObjectPlusString.java");
+            doTest(fileName);
+        }
+
         @TestMetadata("minus.java")
         public void testMinus() throws Exception {
             String fileName = KotlinTestUtils.navigationMetadata("j2k/testData/fileOrElement/binaryExpression/minus.java");