FIR/UAST: introduce fake nullability annotation for fake method

@Deprecated or synthetic methods won't be generated by LC.
For source analysis purpose, though, UAST adds "fake" light method.
While doing so, it needs to mimic the addition of nullability annotation
by LC. Otherwise, e.g., if one method becomes @Deprecated, its return
type nullability could be stripped too, which can be seen as a breaking
API change (for some tool, such as Metalava).

^KTIJ-23807 Fixed

plugins/kotlin/uast/uast-kotlin-base/src/org/jetbrains/uast/kotlin/psi/UastFakeLightMethod.kt

@@ -9,12 +9,15 @@ import com.intellij.psi.impl.light.LightModifierList
 import com.intellij.psi.impl.light.LightParameterListBuilder
 import com.intellij.psi.impl.light.LightReferenceListBuilder
 import org.jetbrains.annotations.ApiStatus
-import org.jetbrains.kotlin.asJava.elements.KotlinLightTypeParameterBuilder
-import org.jetbrains.kotlin.asJava.elements.KotlinLightTypeParameterListBuilder
-import org.jetbrains.kotlin.asJava.elements.KtLightAnnotationForSourceEntry
+import org.jetbrains.annotations.NotNull
+import org.jetbrains.annotations.Nullable
+import org.jetbrains.kotlin.analysis.api.types.KtTypeNullability
+import org.jetbrains.kotlin.asJava.classes.cannotModify
+import org.jetbrains.kotlin.asJava.elements.*
 import org.jetbrains.kotlin.lexer.KtTokens
 import org.jetbrains.kotlin.name.StandardClassIds
 import org.jetbrains.kotlin.psi.*
+import org.jetbrains.kotlin.utils.SmartList
 import org.jetbrains.kotlin.utils.addToStdlib.safeAs
 import org.jetbrains.uast.UastErrorType
 import org.jetbrains.uast.kotlin.BaseKotlinUastResolveProviderService
@@ -149,14 +152,27 @@ abstract class UastFakeLightMethodBase<T: KtDeclaration>(
     }
 
     private val _annotations: Array<PsiAnnotation> by lz {
-        original.annotationEntries.map { entry ->
+        val annotations = SmartList<PsiAnnotation>()
+
+        val isUnitFunction = original is KtFunction && _returnType == PsiType.VOID
+        // Do not annotate Unit function
+        if (!isUnitFunction) {
+            val nullability = baseResolveProviderService.nullability(original)
+            if (nullability != null && nullability != KtTypeNullability.UNKNOWN) {
+                annotations.add(
+                    UastFakeLightNullabilityAnnotation(nullability, this)
+                )
+            }
+        }
+        original.annotationEntries.mapTo(annotations) { entry ->
             KtLightAnnotationForSourceEntry(
                 name = entry.shortName?.identifier,
                 lazyQualifiedName = { baseResolveProviderService.qualifiedAnnotationName(entry) },
                 kotlinOrigin = entry,
                 parent = original,
             )
-        }.toTypedArray()
+        }
+        annotations.toTypedArray()
     }
 
     override fun getAnnotations(): Array<PsiAnnotation> {
@@ -177,8 +193,12 @@ abstract class UastFakeLightMethodBase<T: KtDeclaration>(
         return original is KtConstructor<*>
     }
 
+    private val _returnType: PsiType? by lz {
+        baseResolveProviderService.getType(original, this)
+    }
+
     override fun getReturnType(): PsiType? {
-        return baseResolveProviderService.getType(original, this)
+        return _returnType
     }
 
     override fun getParent(): PsiElement? = containingClass
@@ -196,3 +216,31 @@ abstract class UastFakeLightMethodBase<T: KtDeclaration>(
 
     override fun hashCode(): Int = original.hashCode()
 }
+
+private class UastFakeLightNullabilityAnnotation(
+    private val nullability: KtTypeNullability,
+    parent: PsiElement
+) : KtLightAbstractAnnotation(parent) {
+
+    override val kotlinOrigin: KtCallElement?
+        get() = null
+
+    override fun findAttributeValue(attributeName: String?): PsiAnnotationMemberValue? = null
+
+    override fun findDeclaredAttributeValue(attributeName: String?): PsiAnnotationMemberValue? = null
+
+    override fun getNameReferenceElement(): PsiJavaCodeReferenceElement? = null
+
+    override fun getParameterList(): PsiAnnotationParameterList = KtLightEmptyAnnotationParameterList(this)
+
+    override fun getQualifiedName(): String? =
+        when (nullability) {
+            KtTypeNullability.NON_NULLABLE -> NotNull::class.qualifiedName
+            KtTypeNullability.NULLABLE -> Nullable::class.qualifiedName
+            KtTypeNullability.UNKNOWN -> null
+        }
+
+    override fun toString() = "@$qualifiedName"
+
+    override fun <T : PsiAnnotationMemberValue?> setDeclaredAttributeValue(attributeName: String?, value: T?): T = cannotModify()
+}
\ No newline at end of file

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

@@ -52,11 +52,12 @@ interface UastApiFixtureTestBase : UastPluginSelection {
 
     fun checkDetailsOfDeprecatedHidden(myFixture: JavaCodeInsightTestFixture) {
         myFixture.configureByText(
+            // Example from KTIJ-18039
             "MyClass.kt", """
             @Deprecated(level = DeprecationLevel.WARNING, message="subject to change")
             fun test1() { }
             @Deprecated(level = DeprecationLevel.HIDDEN, message="no longer supported")
-            fun test2() { }
+            fun test2() = Test(22)
             
             class Test(private val parameter: Int)  {
                 @Deprecated(message = "Binary compatibility", level = DeprecationLevel.HIDDEN)
@@ -69,20 +70,31 @@ interface UastApiFixtureTestBase : UastPluginSelection {
 
         val test1 = uFile.findElementByTextFromPsi<UMethod>("test1", strict = false)
         TestCase.assertNotNull("can't convert function test1", test1)
+        // KTIJ-18716
         TestCase.assertTrue("Warning level, hasAnnotation", test1.javaPsi.hasAnnotation("kotlin.Deprecated"))
+        // KTIJ-18039
         TestCase.assertTrue("Warning level, isDeprecated", test1.javaPsi.isDeprecated)
+        // KTIJ-18720
         TestCase.assertTrue("Warning level, public", test1.javaPsi.hasModifierProperty(PsiModifier.PUBLIC))
+        // KTIJ-23807
+        TestCase.assertTrue("Warning level, nullability", test1.javaPsi.annotations.none { it.isNullnessAnnotation })
 
         val test2 = uFile.findElementByTextFromPsi<UMethod>("test2", strict = false)
         TestCase.assertNotNull("can't convert function test2", test2)
+        // KTIJ-18716
         TestCase.assertTrue("Hidden level, hasAnnotation", test2.javaPsi.hasAnnotation("kotlin.Deprecated"))
+        // KTIJ-18039
         TestCase.assertTrue("Hidden level, isDeprecated", test2.javaPsi.isDeprecated)
+        // KTIJ-18720
         TestCase.assertTrue("Hidden level, public", test2.javaPsi.hasModifierProperty(PsiModifier.PUBLIC))
+        // KTIJ-23807
+        TestCase.assertNotNull("Hidden level, nullability", test2.javaPsi.annotations.singleOrNull { it.isNullnessAnnotation })
 
         val testClass = uFile.findElementByTextFromPsi<UClass>("Test", strict = false)
         TestCase.assertNotNull("can't convert class Test", testClass)
         testClass.methods.forEach { mtd ->
             if (mtd.sourcePsi is KtConstructor<*>) {
+                // KTIJ-20200
                 TestCase.assertTrue("$mtd should be marked as a constructor", mtd.isConstructor)
             }
         }

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

@@ -842,11 +842,6 @@ interface UastResolveApiFixtureTestBase : UastPluginSelection {
         )
     }
 
-    private val PsiAnnotation.isNullnessAnnotation: Boolean
-        get() {
-            return qualifiedName?.endsWith("NotNull") == true || qualifiedName?.endsWith("Nullable") == true
-        }
-
     fun checkArrayAccessOverloads(myFixture: JavaCodeInsightTestFixture) {
         myFixture.addClass(
             """

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

@@ -2,6 +2,7 @@
 
 package org.jetbrains.uast.test.common.kotlin
 
+import com.intellij.psi.PsiAnnotation
 import com.intellij.util.PairProcessor
 import com.intellij.util.ref.DebugReflectionUtil
 import junit.framework.TestCase
@@ -36,4 +37,9 @@ fun checkDescriptorsLeak(node: UElement) {
 fun <T> T?.orFail(msg: String): T {
     return this
         ?: throw AssertionError(msg)
-}
\ No newline at end of file
+}
+
+internal val PsiAnnotation.isNullnessAnnotation: Boolean
+    get() {
+        return qualifiedName?.endsWith("NotNull") == true || qualifiedName?.endsWith("Nullable") == true
+    }
\ No newline at end of file