Fix intrinsic for String.plus for explicit calls

#KT-14567 Fixed

compiler/backend/src/org/jetbrains/kotlin/codegen/intrinsics/Concat.kt

@@ -47,12 +47,12 @@ class Concat : IntrinsicMethod() {
             codegen.invokeAppend(element.right)
         }
         else {
-            // LHS?.plus(RHS)
-            receiver.put(AsmTypes.OBJECT_TYPE, v)
+            // Explicit plus call LHS?.plus(RHS) or LHS.plus(RHS)
+            receiver.put(AsmTypes.JAVA_STRING_TYPE, v)
             genStringBuilderConstructor(v)
             v.swap()
             genInvokeAppendMethod(v, returnType)
-            codegen.invokeAppend(arguments.get(0))
+            codegen.invokeAppend(arguments[0])
         }
 
         v.invokevirtual("java/lang/StringBuilder", "toString", "()Ljava/lang/String;", false)

compiler/testData/codegen/box/operatorConventions/plusExplicit.kt

@@ -0,0 +1,29 @@
+// WITH_RUNTIME
+
+fun bar1(): String {
+    val l: List<String> = listOf("O")
+    val s = l[0].plus("K")
+    return s
+}
+
+fun bar2(): String {
+    val l: List<String?> = listOf("O")
+    val s = l[0]?.plus("K")
+    return s!!
+}
+
+fun bar3(): String {
+    val l: List<String> = listOf("O")
+    with(l[0]) {
+        return plus("K")
+    }
+    return "fail"
+}
+
+fun box(): String {
+    if (bar1() != "OK") return "fail 1"
+    if (bar2() != "OK") return "fail 2"
+    if (bar3() != "OK") return "fail 3"
+
+    return "OK"
+}

compiler/testData/codegen/light-analysis/operatorConventions/plusExplicit.txt

@@ -0,0 +1,7 @@
+@kotlin.Metadata
+public final class PlusExplicitKt {
+    public final static @org.jetbrains.annotations.NotNull method bar1(): java.lang.String
+    public final static @org.jetbrains.annotations.NotNull method bar2(): java.lang.String
+    public final static @org.jetbrains.annotations.NotNull method bar3(): java.lang.String
+    public final static @org.jetbrains.annotations.NotNull method box(): java.lang.String
+}

compiler/tests-ir-jvm/tests/org/jetbrains/kotlin/codegen/ir/IrBlackBoxCodegenTestGenerated.java

@@ -11207,6 +11207,12 @@ public class IrBlackBoxCodegenTestGenerated extends AbstractIrBlackBoxCodegenTes
             doTest(fileName);
         }
 
+        @TestMetadata("plusExplicit.kt")
+        public void testPlusExplicit() throws Exception {
+            String fileName = KotlinTestUtils.navigationMetadata("compiler/testData/codegen/box/operatorConventions/plusExplicit.kt");
+            doTest(fileName);
+        }
+
         @TestMetadata("remAssignmentOperation.kt")
         public void testRemAssignmentOperation() throws Exception {
             String fileName = KotlinTestUtils.navigationMetadata("compiler/testData/codegen/box/operatorConventions/remAssignmentOperation.kt");

compiler/tests/org/jetbrains/kotlin/codegen/BlackBoxCodegenTestGenerated.java

@@ -11207,6 +11207,12 @@ public class BlackBoxCodegenTestGenerated extends AbstractBlackBoxCodegenTest {
             doTest(fileName);
         }
 
+        @TestMetadata("plusExplicit.kt")
+        public void testPlusExplicit() throws Exception {
+            String fileName = KotlinTestUtils.navigationMetadata("compiler/testData/codegen/box/operatorConventions/plusExplicit.kt");
+            doTest(fileName);
+        }
+
         @TestMetadata("remAssignmentOperation.kt")
         public void testRemAssignmentOperation() throws Exception {
             String fileName = KotlinTestUtils.navigationMetadata("compiler/testData/codegen/box/operatorConventions/remAssignmentOperation.kt");

js/js.tests/test/org/jetbrains/kotlin/js/test/semantics/JsCodegenBoxTestGenerated.java

@@ -12936,6 +12936,12 @@ public class JsCodegenBoxTestGenerated extends AbstractJsCodegenBoxTest {
             doTest(fileName);
         }
 
+        @TestMetadata("plusExplicit.kt")
+        public void testPlusExplicit() throws Exception {
+            String fileName = KotlinTestUtils.navigationMetadata("compiler/testData/codegen/box/operatorConventions/plusExplicit.kt");
+            doTest(fileName);
+        }
+
         @TestMetadata("remAssignmentOperation.kt")
         public void testRemAssignmentOperation() throws Exception {
             String fileName = KotlinTestUtils.navigationMetadata("compiler/testData/codegen/box/operatorConventions/remAssignmentOperation.kt");