[NI] Discriminate Nothing? result type from nullability constraints

Nullability constraints should not be chosen when proper
argument constraints for variables in contravariant position present.

^KT-32106 Fixed
^KT-33166 Fixed

compiler/testData/diagnostics/tests/inference/nestedCalls/preferArgumentToNullability.fir.kt

@@ -0,0 +1,15 @@
+// !LANGUAGE: +NewInference
+// !DIAGNOSTICS: -UNUSED_PARAMETER
+
+open class Cls
+
+abstract class In<in I>
+class SubIn : In<Cls?>()
+
+inline fun <reified T : Cls> materialize(): T? = TODO()
+
+fun <D> transform(transformer: In<D>, data: D): Unit = TODO()
+
+fun test(subIn: SubIn) {
+    transform(subIn, materialize()) // D should be inferred to Cls?, not Nothing?
+}

compiler/testData/diagnostics/tests/inference/nestedCalls/preferArgumentToNullability.kt

@@ -0,0 +1,15 @@
+// !LANGUAGE: +NewInference
+// !DIAGNOSTICS: -UNUSED_PARAMETER
+
+open class Cls
+
+abstract class In<in I>
+class SubIn : In<Cls?>()
+
+inline fun <reified T : Cls> materialize(): T? = TODO()
+
+fun <D> transform(transformer: In<D>, data: D): Unit = TODO()
+
+fun test(subIn: SubIn) {
+    transform(subIn, materialize()) // D should be inferred to Cls?, not Nothing?
+}

compiler/testData/diagnostics/tests/inference/nestedCalls/preferArgumentToNullability.txt

@@ -0,0 +1,26 @@
+package
+
+public inline fun </*0*/ reified T : Cls> materialize(): T?
+public fun test(/*0*/ subIn: SubIn): kotlin.Unit
+public fun </*0*/ D> transform(/*0*/ transformer: In<D>, /*1*/ data: D): kotlin.Unit
+
+public open class Cls {
+    public constructor Cls()
+    public open override /*1*/ /*fake_override*/ fun equals(/*0*/ other: kotlin.Any?): kotlin.Boolean
+    public open override /*1*/ /*fake_override*/ fun hashCode(): kotlin.Int
+    public open override /*1*/ /*fake_override*/ fun toString(): kotlin.String
+}
+
+public abstract class In</*0*/ in I> {
+    public constructor In</*0*/ in I>()
+    public open override /*1*/ /*fake_override*/ fun equals(/*0*/ other: kotlin.Any?): kotlin.Boolean
+    public open override /*1*/ /*fake_override*/ fun hashCode(): kotlin.Int
+    public open override /*1*/ /*fake_override*/ fun toString(): kotlin.String
+}
+
+public final class SubIn : In<Cls?> {
+    public constructor SubIn()
+    public open override /*1*/ /*fake_override*/ fun equals(/*0*/ other: kotlin.Any?): kotlin.Boolean
+    public open override /*1*/ /*fake_override*/ fun hashCode(): kotlin.Int
+    public open override /*1*/ /*fake_override*/ fun toString(): kotlin.String
+}

compiler/testData/diagnostics/tests/inference/nestedCalls/preferNothingToBound.fir.kt

@@ -0,0 +1,3 @@
+fun <K> id(arg: K): K = arg
+
+val v = id(null)

compiler/testData/diagnostics/tests/inference/nestedCalls/preferNothingToBound.kt

@@ -0,0 +1,3 @@
+fun <K> id(arg: K): K = arg
+
+val v = <!DEBUG_INFO_EXPRESSION_TYPE("kotlin.Nothing?")!>id(null)<!>

compiler/testData/diagnostics/tests/inference/nestedCalls/preferNothingToBound.txt

@@ -0,0 +1,4 @@
+package
+
+public val v: kotlin.Nothing?
+public fun </*0*/ K> id(/*0*/ arg: K): K

compiler/testData/diagnostics/tests/inference/nothingType/inferArgumentToNothingFromNullConstant.fir.kt

@@ -0,0 +1,12 @@
+// !DIAGNOSTICS: -UNUSED_PARAMETER -UNUSED_EXPRESSION -ASSIGNED_BUT_NEVER_ACCESSED_VARIABLE -UNUSED_VALUE
+
+class Out<out T : Any>(result: T?)
+
+fun main() {
+    val a = Out(null)
+
+    a
+
+    var b: Out<Int>? = null
+    b = a
+}

compiler/testData/diagnostics/tests/inference/regressions/kt32106.fir.kt

@@ -1,5 +1,3 @@
-// !LANGUAGE: +NewInference
-
 class Query<out T : Any> private constructor(
     private val result: T?,
     private val error: Throwable?,

compiler/testData/diagnostics/tests/inference/regressions/kt32106.kt

@@ -1,5 +1,3 @@
-// !LANGUAGE: +NewInference
-
 class Query<out T : Any> private constructor(
     private val result: T?,
     private val error: Throwable?,

compiler/testData/diagnostics/testsWithStdLib/inference/annotationsForResolve/onlyInputTypesCommonConstraintSystem.fir.kt

@@ -36,7 +36,6 @@ fun testOK(first: First, bound: Bound, second: Second) {
     strictSelect(OutB(first), OutB(bound))
     strictSelect(In(first), In(bound))
     strictSelect(InB(first), InB(bound))
-    strictSelect(InB(first), InB(second)) // different behaviour in contravariant position
 
     val out: Out<Bound> = strictSelect(Out(first), Out(second))
     val outb: OutB<Bound> = strictSelect(OutB(first), OutB(second))
@@ -49,6 +48,7 @@ fun testFail(first: First, bound: Bound, second: Second) {
     strictSelect(Inv(first), Inv(bound))
     strictSelect(Out(first), Out(second))
     strictSelect(In(first), In(second))
+    strictSelect(InB(first), InB(second))
     strictSelect(Out(Inv(first)), Out(Inv(second)))
     strictSelect(In(Inv(first)), In(Inv(second)))
 }

compiler/testData/diagnostics/testsWithStdLib/inference/annotationsForResolve/onlyInputTypesCommonConstraintSystem.kt

@@ -36,7 +36,6 @@ fun testOK(first: First, bound: Bound, second: Second) {
     strictSelect(OutB(first), OutB(bound))
     strictSelect(In(first), In(bound))
     strictSelect(InB(first), InB(bound))
-    <!OI;TYPE_INFERENCE_ONLY_INPUT_TYPES!>strictSelect<!>(InB(first), InB(second)) // different behaviour in contravariant position
 
     val out: Out<Bound> = strictSelect(Out(first), Out(second))
     val outb: OutB<Bound> = strictSelect(OutB(first), OutB(second))
@@ -49,6 +48,7 @@ fun testFail(first: First, bound: Bound, second: Second) {
     <!TYPE_INFERENCE_ONLY_INPUT_TYPES!>strictSelect<!>(Inv(first), Inv(bound))
     <!TYPE_INFERENCE_ONLY_INPUT_TYPES!>strictSelect<!>(Out(first), Out(second))
     <!TYPE_INFERENCE_ONLY_INPUT_TYPES!>strictSelect<!>(In(first), In(second))
+    <!TYPE_INFERENCE_ONLY_INPUT_TYPES!>strictSelect<!>(InB(first), InB(second))
     <!TYPE_INFERENCE_ONLY_INPUT_TYPES!>strictSelect<!>(Out(Inv(first)), Out(Inv(second)))
     <!TYPE_INFERENCE_ONLY_INPUT_TYPES!>strictSelect<!>(In(Inv(first)), In(Inv(second)))
 }

compiler/testData/diagnostics/testsWithStdLib/tryCatch/tryExpression.kt

@@ -27,7 +27,7 @@ fun test1(): Map<Int, Int> = run {
 }
 
 fun test2(): Map<Int, Int> = run {
-    <!NI;TYPE_MISMATCH, NI;TYPE_MISMATCH, NI;TYPE_MISMATCH, NI;TYPE_MISMATCH, NI;TYPE_MISMATCH, NI;TYPE_MISMATCH, NI;TYPE_MISMATCH, NI;TYPE_MISMATCH!>try {
+    <!NI;TYPE_MISMATCH, NI;TYPE_MISMATCH, NI;TYPE_MISMATCH, NI;TYPE_MISMATCH, NI;TYPE_MISMATCH, NI;TYPE_MISMATCH!>try {
         emptyMap()
     } catch (e: ExcA) {
         <!NI;TYPE_MISMATCH, NI;TYPE_MISMATCH, OI;TYPE_INFERENCE_EXPECTED_TYPE_MISMATCH!>mapOf(<!NI;TYPE_MISMATCH, NI;TYPE_MISMATCH!>"" to ""<!>)<!>