FIR/UAST: handle nullable receiver parameter of extension function as anchor

^KTIJ-25925 Fixed

GitOrigin-RevId: 46bbe1b0ee60f25039911c16b22b85e88d9abbc3

plugins/kotlin/uast/uast-kotlin-base/src/org/jetbrains/uast/kotlin/declarations/AbstractKotlinUVariable.kt

@@ -79,7 +79,9 @@ abstract class AbstractKotlinUVariable(
                 is KtNamedDeclaration -> sourcePsi.nameIdentifier
                 is KtTypeReference -> sourcePsi.typeElement?.let {
                     // receiver param in extension function
-                    (it as? KtUserType)?.referenceExpression?.getIdentifier() ?: it
+                    // Unwrap the type if the receiver param is nullable
+                    val typeElement = (it as? KtNullableType)?.innerType ?: it
+                    (typeElement as? KtUserType)?.referenceExpression?.getIdentifier() ?: it
                 } ?: sourcePsi
                 is KtNameReferenceExpression -> sourcePsi.getReferencedNameElement()
                 is KtBinaryExpression, is KtCallExpression -> null // e.g. `foo("Lorem ipsum") ?: foo("dolor sit amet")`

plugins/kotlin/uast/uast-kotlin-base/tests/test/org/jetbrains/uast/test/common/kotlin/UastApiFixtureTestBase.kt

@@ -640,4 +640,30 @@ interface UastApiFixtureTestBase : UastPluginSelection {
         })
     }
 
+    fun checkIdentifierOfNullableExtensionReceiver(myFixture: JavaCodeInsightTestFixture) {
+        myFixture.configureByText(
+            "main.kt", """
+                enum class SortOrder {
+                  ASCENDING, DESCENDING, UNSORTED
+                }
+
+                fun <C> Comparator<C>?.withOrder(sortOrder: SortOrder): Comparator<C>? =
+                  this?.let {
+                    when (sortOrder) {
+                      SortOrder.ASCENDING -> it
+                      SortOrder.DESCENDING -> it.reversed()
+                      SortOrder.UNSORTED -> null
+                    }
+                  }
+            """.trimIndent()
+        )
+
+        val uFile = myFixture.file.toUElement()!!
+        val withOrder = uFile.findElementByTextFromPsi<UMethod>("withOrder", strict = false)
+            .orFail("can't convert extension function: withOrder")
+        val extensionReceiver = withOrder.uastParameters.first()
+        val identifier = extensionReceiver.uastAnchor as? UIdentifier
+        TestCase.assertNotNull(identifier)
+    }
+
 }

plugins/kotlin/uast/uast-kotlin-fir/tests/test/org/jetbrains/fir/uast/test/FirUastApiFixtureTest.kt

@@ -82,4 +82,8 @@ class FirUastApiFixtureTest : KotlinLightCodeInsightFixtureTestCase(), UastApiFi
         doCheck("LambdaImplicitParameters", ::checkLambdaImplicitParameters)
     }
 
+    fun testIdentifierOfNullableExtensionReceiver() {
+        checkIdentifierOfNullableExtensionReceiver(myFixture)
+    }
+
 }

plugins/kotlin/uast/uast-kotlin/tests/test/org/jetbrains/uast/test/kotlin/comparison/FE1UastApiFixtureTest.kt

@@ -75,4 +75,8 @@ class FE1UastApiFixtureTest : KotlinLightCodeInsightFixtureTestCase(), UastApiFi
         checkLambdaImplicitParameters(myFixture)
     }
 
+    fun testIdentifierOfNullableExtensionReceiver() {
+        checkIdentifierOfNullableExtensionReceiver(myFixture)
+    }
+
 }