K2 UAST: make nullity computation compatible with K1 UAST

In particular, for flexible type due to platform type, it's unknown.

^KTIJ-30464 fixed

GitOrigin-RevId: cb7327a4f6291b94d627b3929c2b10b348b060c5

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

@@ -616,6 +616,41 @@ interface UastResolveApiFixtureTestBase {
         TestCase.assertEquals("it", resolved.name)
     }
 
+    fun checkNullityOfResolvedLambdaParameter(myFixture: JavaCodeInsightTestFixture) {
+        myFixture.addClass(
+            """
+                class MyLiveData<T> {
+                  public void addSource(MyLiveData<S> source, Observer<? super S> onChanged) {}
+                  public void setValue(T value) {}
+                }
+            """.trimIndent()
+        )
+        myFixture.configureByText(
+            "main.kt", """
+                fun interface Observer<T> {
+                  fun onChanged(value: T)
+                }
+                
+                class Test {
+                  val myData = MyLiveData<List<Boolean>>()
+                  
+                  init {
+                    myData.addSource(getSources()) { data ->
+                      myData.value = da<caret>ta
+                    }
+                  }
+                  
+                  private fun getSources(): MyLiveData<List<Boolean>> = TODO()
+                }
+            """.trimIndent()
+        )
+        val ref = myFixture.file.findElementAt(myFixture.caretOffset).toUElement()?.getParentOfType<UReferenceExpression>()
+            .orFail("cant convert to UReferenceExpression")
+        val resolved = (ref.resolve() as? PsiParameter)
+            .orFail("cant resolve lambda parameter")
+        TestCase.assertFalse(resolved.annotations.any { it.isNullnessAnnotation })
+    }
+
     fun checkResolveSyntheticMethod(myFixture: JavaCodeInsightTestFixture) {
         myFixture.configureByText(
             "MyClass.kt", """

plugins/kotlin/uast/uast-kotlin-fir/src/org/jetbrains/uast/kotlin/internal/firKotlinInternalUastUtils.kt

@@ -367,10 +367,12 @@ context(KaSession)
 internal fun nullability(ktType: KaType?): KaTypeNullability? {
     if (ktType == null) return null
     if (ktType is KaErrorType) return null
-    return if (ktType.fullyExpandedType.canBeNull)
+    val expanded = ktType.fullyExpandedType
-        KaTypeNullability.NULLABLE
+    return when {
-    else
+        expanded.hasFlexibleNullability -> KaTypeNullability.UNKNOWN
-        KaTypeNullability.NON_NULLABLE
+        expanded.canBeNull -> KaTypeNullability.NULLABLE
+        else -> KaTypeNullability.NON_NULLABLE
+    }
 }
 
 context(KaSession)

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

@@ -142,6 +142,10 @@ class FirUastResolveApiFixtureTest : KotlinLightCodeInsightFixtureTestCase(), Ua
         checkResolveImplicitLambdaParameter_binary(myFixture)
     }
 
+    fun testNullityOfResolvedLambdaParameter() {
+        checkNullityOfResolvedLambdaParameter(myFixture)
+    }
+
     fun testResolveSyntheticMethod() {
         checkResolveSyntheticMethod(myFixture)
     }

plugins/kotlin/uast/uast-kotlin/tests/test/org/jetbrains/uast/test/kotlin/comparison/FE1UastResolveApiFixtureTest.kt

@@ -98,6 +98,10 @@ class FE1UastResolveApiFixtureTest : KotlinLightCodeInsightFixtureTestCase(), Ua
         checkResolveImplicitLambdaParameter_binary(myFixture)
     }
 
+    fun testNullityOfResolvedLambdaParameter() {
+        checkNullityOfResolvedLambdaParameter(myFixture)
+    }
+
     fun testResolveSyntheticMethod() {
         checkResolveSyntheticMethod(myFixture)
     }