USELESS_ELVIS_RIGHT_IS_NULL is no more reported for flexible left argument #KT-13593 Fixed

compiler/frontend/src/org/jetbrains/kotlin/types/expressions/BasicExpressionTypingVisitor.java

@@ -1284,7 +1284,7 @@ public class BasicExpressionTypingVisitor extends ExpressionTypingVisitor {
         if (leftType != null && isKnownToBeNotNull(left, leftType, context)) {
             context.trace.report(USELESS_ELVIS.on(expression, leftType));
         }
-        else if (KtPsiUtil.isNullConstant(right)) {
+        else if (KtPsiUtil.isNullConstant(right) && leftType != null && !FlexibleTypesKt.isNullabilityFlexible(leftType)) {
             context.trace.report(USELESS_ELVIS_RIGHT_IS_NULL.on(expression));
         }
         KotlinTypeInfo rightTypeInfo = BindingContextUtils.getRecordedTypeInfo(right, context.trace.getBindingContext());

compiler/testData/diagnostics/tests/platformTypes/nullabilityWarnings/uselessElvisRightIsNull.kt

@@ -9,11 +9,30 @@ public class J {
     public static J staticN;
 }
 
+// FILE: JJ.java
+
+public class JJ {
+    public static JJ staticNN;
+}
+
+// FILE: JJJ.java
+
+import org.jetbrains.annotations.*;
+
+public class JJJ {
+    @NotNull
+    public static JJJ staticNNN;
+}
+
 // FILE: k.kt
 
 fun test() {
     val a = J.staticN <!USELESS_ELVIS_RIGHT_IS_NULL!>?: null<!>
     foo(a)
+    val b = JJ.staticNN ?: null
+    foo(b)
+    val c = JJJ.staticNNN <!USELESS_ELVIS!>?: null<!>
+    foo(c)
 }
 
 fun foo(a: Any?) {

compiler/testData/diagnostics/tests/platformTypes/nullabilityWarnings/uselessElvisRightIsNull.txt

@@ -12,3 +12,23 @@ public open class J {
     // Static members
     @org.jetbrains.annotations.Nullable public final var staticN: J?
 }
+
+public open class JJ {
+    public constructor JJ()
+    public open override /*1*/ /*fake_override*/ fun equals(/*0*/ other: kotlin.Any?): kotlin.Boolean
+    public open override /*1*/ /*fake_override*/ fun hashCode(): kotlin.Int
+    public open override /*1*/ /*fake_override*/ fun toString(): kotlin.String
+
+    // Static members
+    public final var staticNN: JJ!
+}
+
+public open class JJJ {
+    public constructor JJJ()
+    public open override /*1*/ /*fake_override*/ fun equals(/*0*/ other: kotlin.Any?): kotlin.Boolean
+    public open override /*1*/ /*fake_override*/ fun hashCode(): kotlin.Int
+    public open override /*1*/ /*fake_override*/ fun toString(): kotlin.String
+
+    // Static members
+    @org.jetbrains.annotations.NotNull public final var staticNNN: JJJ
+}