SONARKT-286 Fix S6619 false positives caused by resolving binary expression operations too far (#393)

Author: johann-beleites-sonarsource

kotlin-checks-test-sources/src/main/kotlin/checks/UselessNullCheckCheckSample.kt

@@ -127,3 +127,10 @@ private fun <E : Throwable> moo(exception: E) =
         cachedCtor(exception) as E?
     }
 
+private class FooBar(
+    something: Any
+) {
+    private val someString: String? = something as? String
+    val isString: Boolean
+        get() = someString != null // Compliant
+}

sonar-kotlin-checks/src/main/java/org/sonarsource/kotlin/checks/UselessNullCheckCheck.kt

@@ -113,12 +113,12 @@ class UselessNullCheckCheck : AbstractCheck() {
     }
 
     private fun KtBinaryExpression.operandComparedToNull(bc: BindingContext): KtExpression? {
-        val left = left?.predictRuntimeValueExpression(bc) ?: return null
-        val right = right?.predictRuntimeValueExpression(bc) ?: return null
+        val leftResolved = left?.predictRuntimeValueExpression(bc) ?: return null
+        val rightResolved = right?.predictRuntimeValueExpression(bc) ?: return null
 
         return when {
-            left.isNull() -> right
-            right.isNull() -> left
+            leftResolved.isNull() -> right
+            rightResolved.isNull() -> left
             else -> null
         }
     }