NI: Fix some unwanted exclusions constraints with remained corresponding optimization

compiler/resolution/src/org/jetbrains/kotlin/resolve/calls/inference/components/ConstraintIncorporator.kt

@@ -157,6 +157,11 @@ class ConstraintIncorporator(
         isSubtype: Boolean
     ) {
         if (targetVariable in getNestedTypeVariables(newConstraint)) return
+
+        val isUsefulForNullabilityConstraint =
+            isPotentialUsefulNullabilityConstraint(newConstraint, otherConstraint.type, otherConstraint.kind)
+
+        if (!isUsefulForNullabilityConstraint && !containsConstrainingTypeWithoutProjection(newConstraint, otherConstraint)) return
         if (trivialConstraintTypeInferenceOracle.isGeneratedConstraintTrivial(
                 baseConstraint, otherConstraint, newConstraint, isSubtype
             )
@@ -172,6 +177,28 @@ class ConstraintIncorporator(
         addNewIncorporatedConstraint(targetVariable, newConstraint, ConstraintContext(kind, derivedFrom))
     }
 
+    fun Context.containsConstrainingTypeWithoutProjection(
+        newConstraint: KotlinTypeMarker,
+        otherConstraint: Constraint
+    ): Boolean {
+        return getNestedArguments(newConstraint).any {
+            it.getType().typeConstructor() == otherConstraint.type.typeConstructor() && it.getVariance() == TypeVariance.INV
+        }
+    }
+
+    private fun Context.isPotentialUsefulNullabilityConstraint(
+        newConstraint: KotlinTypeMarker,
+        otherConstraint: KotlinTypeMarker,
+        kind: ConstraintKind
+    ): Boolean {
+        val otherConstraintCanAddNullabilityToNewOne =
+            !newConstraint.isNullableType() && otherConstraint.isNullableType() && kind == ConstraintKind.LOWER
+        val newConstraintCanAddNullabilityToOtherOne =
+            newConstraint.isNullableType() && !otherConstraint.isNullableType() && kind == ConstraintKind.UPPER
+
+        return otherConstraintCanAddNullabilityToNewOne || newConstraintCanAddNullabilityToOtherOne
+    }
+
     fun Context.getNestedTypeVariables(type: KotlinTypeMarker): List<TypeVariableMarker> =
         getNestedArguments(type).mapNotNull { getTypeVariable(it.getType().typeConstructor()) }
 
@@ -189,19 +216,36 @@ class ConstraintIncorporator(
 
 private fun TypeSystemInferenceExtensionContext.getNestedArguments(type: KotlinTypeMarker): List<TypeArgumentMarker> {
     val result = ArrayList<TypeArgumentMarker>()
-
     val stack = ArrayDeque<TypeArgumentMarker>()
+
+    when (type) {
+        is FlexibleType -> {
+            stack.push(createTypeArgument(type.lowerBound, TypeVariance.INV))
+            stack.push(createTypeArgument(type.upperBound, TypeVariance.INV))
+        }
+        else -> stack.push(createTypeArgument(type, TypeVariance.INV))
+    }
+
     stack.push(createTypeArgument(type, TypeVariance.INV))
 
+    val addArgumentsToStack = { projectedType: KotlinTypeMarker ->
+        for (argumentIndex in 0 until projectedType.argumentsCount()) {
+            stack.add(projectedType.getArgument(argumentIndex))
+        }
+    }
+
     while (!stack.isEmpty()) {
         val typeProjection = stack.pop()
         if (typeProjection.isStarProjection()) continue
 
         result.add(typeProjection)
 
-        val projectedType = typeProjection.getType()
-        for (argumentIndex in 0 until projectedType.argumentsCount()) {
-            stack.add(projectedType.getArgument(argumentIndex))
+        when (val projectedType = typeProjection.getType()) {
+            is FlexibleType -> {
+                addArgumentsToStack(projectedType.lowerBound)
+                addArgumentsToStack(projectedType.upperBound)
+            }
+            else -> addArgumentsToStack(projectedType)
         }
     }
     return result

compiler/testData/diagnostics/tests/inference/commonSystem/kt32818.kt

@@ -2,4 +2,4 @@
 
 fun <T : Any> nullable(): T? = null
 
-val value = nullable<Int>() <!NI;TYPE_MISMATCH!>?:<!> <!OI;TYPE_INFERENCE_EXPECTED_TYPE_MISMATCH!>nullable()<!>
+val value = nullable<Int>() ?: <!OI;TYPE_INFERENCE_EXPECTED_TYPE_MISMATCH!>nullable()<!>