Minor fix of around flexible and not-null FIR types (by semoro)

compiler/fir/cones/src/org/jetbrains/kotlin/fir/types/ConeTypes.kt

@@ -107,7 +107,7 @@ abstract class ConeTypeParameterType : ConeLookupTagBasedType() {
 
 
 
-class ConeFlexibleType(val lowerBound: ConeLookupTagBasedType, val upperBound: ConeLookupTagBasedType) : ConeKotlinType(),
+class ConeFlexibleType(val lowerBound: ConeKotlinType, val upperBound: ConeKotlinType) : ConeKotlinType(),
     FlexibleTypeMarker {
     override val typeArguments: Array<out ConeKotlinTypeProjection>
         get() = emptyArray()
@@ -116,6 +116,9 @@ class ConeFlexibleType(val lowerBound: ConeLookupTagBasedType, val upperBound: C
         get() = lowerBound.nullability.takeIf { it == upperBound.nullability } ?: ConeNullability.UNKNOWN
 }
 
+fun ConeKotlinType.upperBoundIfFlexible() = (this as? ConeFlexibleType)?.upperBound ?: this
+fun ConeKotlinType.lowerBoundIfFlexible() = (this as? ConeFlexibleType)?.lowerBound ?: this
+
 class ConeCapturedTypeConstructor(val projection: ConeKotlinTypeProjection, var supertypes: List<ConeKotlinType>? = null) :
     TypeConstructorMarker {
 

compiler/fir/resolve/src/org/jetbrains/kotlin/fir/resolve/substitution/ConeSubstitutor.kt

@@ -57,7 +57,7 @@ abstract class AbstractConeSubstitutor : ConeSubstitutor {
 
     override fun substituteOrNull(type: ConeKotlinType): ConeKotlinType? {
         val newType = substituteType(type)
-        return (newType ?: type).substituteRecursive() ?: newType
+        return (newType ?: type.substituteRecursive()) ?: newType
     }
 
     private fun ConeKotlinType.substituteRecursive(): ConeKotlinType? {
@@ -78,10 +78,13 @@ abstract class AbstractConeSubstitutor : ConeSubstitutor {
     }
 
     private fun ConeFlexibleType.substituteBounds(): ConeFlexibleType? {
-        val newLowerBound = substituteOrNull(lowerBound) as ConeLookupTagBasedType?
-        val newUpperBound = substituteOrNull(upperBound) as ConeLookupTagBasedType?
+        val newLowerBound = substituteOrNull(lowerBound)
+        val newUpperBound = substituteOrNull(upperBound)
         if (newLowerBound != null || newUpperBound != null) {
-            return ConeFlexibleType(newLowerBound ?: lowerBound, newUpperBound ?: upperBound)
+            return ConeFlexibleType(
+                newLowerBound?.lowerBoundIfFlexible() ?: lowerBound,
+                newUpperBound?.upperBoundIfFlexible() ?: upperBound
+            )
         }
         return null
     }

compiler/fir/resolve/src/org/jetbrains/kotlin/fir/types/ConeTypeContext.kt

@@ -86,12 +86,12 @@ interface ConeTypeContext : TypeSystemContext, TypeSystemOptimizationContext {
 
     override fun FlexibleTypeMarker.upperBound(): SimpleTypeMarker {
         require(this is ConeFlexibleType)
-        return this.upperBound
+        return this.upperBound as SimpleTypeMarker
     }
 
     override fun FlexibleTypeMarker.lowerBound(): SimpleTypeMarker {
         require(this is ConeFlexibleType)
-        return this.lowerBound
+        return this.lowerBound as SimpleTypeMarker
     }
 
     override fun SimpleTypeMarker.asCapturedType(): CapturedTypeMarker? {