FIR IDE: introduce KtFirDefinitelyNotNullType

idea/idea-frontend-api/src/org/jetbrains/kotlin/idea/frontend/api/types/KtType.kt

@@ -57,6 +57,12 @@ abstract class KtTypeParameterType : KtTypeWithNullability {
 
 abstract class KtCapturedType : KtType
 
+abstract class KtDefinitelyNotNullType : KtType, KtTypeWithNullability {
+    abstract val original: KtType
+
+    final override val nullability: KtTypeNullability get() = KtTypeNullability.NON_NULLABLE
+}
+
 abstract class KtFlexibleType : KtType {
     abstract val lowerBound: KtType
     abstract val upperBound: KtType

idea/idea-frontend-fir/src/org/jetbrains/kotlin/idea/frontend/api/fir/KtSymbolByFirBuilder.kt

@@ -319,7 +319,7 @@ internal class KtSymbolByFirBuilder private constructor(
                     is ConeClassErrorType -> KtFirClassErrorType(coneType, token)
                     is ConeFlexibleType -> KtFirFlexibleType(coneType, token, this@KtSymbolByFirBuilder)
                     is ConeIntersectionType -> KtFirIntersectionType(coneType, token, this@KtSymbolByFirBuilder)
-                    is ConeDefinitelyNotNullType -> buildKtType(coneType.original)
+                    is ConeDefinitelyNotNullType -> KtFirDefinitelyNotNullType(coneType, token, this@KtSymbolByFirBuilder)
                     is ConeCapturedType -> KtFirCapturedType(coneType, token)
                     else -> throwUnexpectedElementError(coneType)
                 }

idea/idea-frontend-fir/src/org/jetbrains/kotlin/idea/frontend/api/fir/types/FirKtType.kt

@@ -109,6 +109,19 @@ internal class KtFirCapturedType(
     override fun asStringForDebugging(): String = withValidityAssertion { coneType.render() }
 }
 
+internal class KtFirDefinitelyNotNullType(
+    coneType: ConeDefinitelyNotNullType,
+    override val token: ValidityToken,
+    private val firBuilder: KtSymbolByFirBuilder,
+) : KtDefinitelyNotNullType(), KtFirType {
+    override val coneType by weakRef(coneType)
+
+    override val original: KtType by cached { firBuilder.typeBuilder.buildKtType(this.coneType.original) }
+
+    override fun asStringForDebugging(): String = withValidityAssertion { coneType.render() }
+}
+
+
 
 internal class KtFirTypeParameterType(
     coneType: ConeTypeParameterType,