[NI] Don't discriminate Nothing-type from resulting ones

^KT-32106 Fixed

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

@@ -23,15 +23,6 @@ class TrivialConstraintTypeInferenceOracle private constructor(context: TypeSyst
         return constraint.kind == ConstraintKind.LOWER && constraint.type.typeConstructor().isNothingConstructor()
     }
 
-    // This function controls the choice between sub and super result type
-    // Even that Nothing(?) is the most specific type for subtype, it doesn't bring valuable information to the user,
-    // therefore it is discriminated in favor of supertype
-    fun isSuitableResultedType(
-        resultType: KotlinTypeMarker
-    ): Boolean {
-        return !resultType.typeConstructor().isNothingConstructor()
-    }
-
     // It's possible to generate Nothing-like constraints inside incorporation mechanism:
     // For instance, when two type variables are in subtyping relation `T <: K`, after incorporation
     // there will be constraint `approximation(out K) <: K` => `Nothing <: K`, which is innocent

compiler/testData/diagnostics/tests/callableReference/bound/reservedExpressionSyntax3.kt

@@ -23,7 +23,7 @@ class Test {
     val Int.c: Int get() = 42
 
     val test1: () -> Right = <!RESERVED_SYNTAX_IN_CALLABLE_REFERENCE_LHS!><!DEBUG_INFO_MISSING_UNRESOLVED!>a<!>.<!DEBUG_INFO_MISSING_UNRESOLVED!>b<!><<!DEBUG_INFO_MISSING_UNRESOLVED!>Int<!>>.<!DEBUG_INFO_MISSING_UNRESOLVED!>c<!><!>::<!DEBUG_INFO_MISSING_UNRESOLVED!>foo<!>
-    val test1a: () -> Right = a.<!NI;DEBUG_INFO_LEAKING_THIS!>b<!>.<!NI;DEBUG_INFO_LEAKING_THIS!>c<!>::foo
+    val test1a: () -> Right = a.b.c::foo
 
     val test2: () -> Right = <!RESERVED_SYNTAX_IN_CALLABLE_REFERENCE_LHS!><!DEBUG_INFO_MISSING_UNRESOLVED!>a<!>.<!DEBUG_INFO_MISSING_UNRESOLVED!>b<!><<!DEBUG_INFO_MISSING_UNRESOLVED!>Int<!>>.<!DEBUG_INFO_MISSING_UNRESOLVED!>c<!><!>?::<!DEBUG_INFO_MISSING_UNRESOLVED!>foo<!>
 }

compiler/testData/diagnostics/tests/controlFlowAnalysis/throwInLambda.kt

@@ -8,6 +8,6 @@ fun foo(): String {
 }
 fun bar(): String {
     val x = fn() ?: return ""
-    <!OI;UNREACHABLE_CODE!>val <!OI;UNUSED_VARIABLE!>y<!> =<!> x<!UNNECESSARY_SAFE_CALL!>?.<!>let { throw Exception() } <!OI;UNREACHABLE_CODE, OI;USELESS_ELVIS!>?: "unreachable"<!>
+    <!UNREACHABLE_CODE!>val <!UNUSED_VARIABLE!>y<!> =<!> x<!UNNECESSARY_SAFE_CALL!>?.<!>let { throw Exception() } <!NI;UNREACHABLE_CODE, NI;USELESS_ELVIS, OI;UNREACHABLE_CODE, OI;USELESS_ELVIS!>?: "unreachable"<!>
-    <!OI;UNREACHABLE_CODE!>return y<!>
+    <!UNREACHABLE_CODE!>return y<!>
 }

compiler/testData/diagnostics/tests/inference/implicitInvokeExtensionWithFunctionalArgument.kt

@@ -25,5 +25,5 @@ fun test(s: SelectorFor<State>): Double {
     val e = s { return p1 }
     e checkType { _<AbstractSelector<State, Nothing>>() }
 
-    <!OI;UNREACHABLE_CODE!>return<!> null!!
+    <!UNREACHABLE_CODE!>return<!> null!!
 }

compiler/testData/diagnostics/tests/inference/nothingType/inferArgumentToNothingFromNullConstant.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)
+
+    <!DEBUG_INFO_EXPRESSION_TYPE("Out<kotlin.Nothing>")!>a<!>
+
+    var b: Out<Int>? = null
+    b = a
+}

compiler/testData/diagnostics/tests/inference/nothingType/inferArgumentToNothingFromNullConstant.txt

@@ -0,0 +1,10 @@
+package
+
+public fun main(): kotlin.Unit
+
+public final class Out</*0*/ out T : kotlin.Any> {
+    public constructor Out</*0*/ out T : kotlin.Any>(/*0*/ result: T?)
+    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/nothingType/lambdaNothingAndExpectedType.kt

@@ -1,12 +1,12 @@
-// !LANGUAGE: +NewInference
+// !WITH_NEW_INFERENCE
 // !DIAGNOSTICS: -UNUSED_PARAMETER -UNUSED_VARIABLE
 
 fun <K> select2(x: K, y: K): K = TODO()
 fun <K> select3(x: K, y: K, z: K): K = TODO()
 
 fun test2(f: ((String) -> Int)?) {
-    val a0: ((Int) -> Int)? = select2({ it -> it }, null)
+    val a0: ((Int) -> Int)? = select2(<!TYPE_MISMATCH!>{ <!OI;CANNOT_INFER_PARAMETER_TYPE!>it<!> -> <!OI;DEBUG_INFO_ELEMENT_WITH_ERROR_TYPE!>it<!> }<!>, null)
-    val b0: ((Nothing) -> Unit)? = select2({ it -> <!UNUSED_EXPRESSION!>it<!> }, null)
+    val b0: ((Nothing) -> Unit)? = select2(<!TYPE_MISMATCH!>{ <!OI;CANNOT_INFER_PARAMETER_TYPE!>it<!> -> <!OI;DEBUG_INFO_ELEMENT_WITH_ERROR_TYPE!>it<!> }<!>, null)
 
     select3({ it.length }, f, null)
 }

compiler/testData/diagnostics/tests/regressions/kt13685.kt

@@ -2,6 +2,6 @@
 // !DIAGNOSTICS: -UNREACHABLE_CODE
 
 fun foo() {
-    val <!OI;UNUSED_VARIABLE!>text<!>: List<Any> = null!!
+    val <!UNUSED_VARIABLE!>text<!>: List<Any> = null!!
     text.<!UNRESOLVED_REFERENCE!>map<!> <!DEBUG_INFO_ELEMENT_WITH_ERROR_TYPE!>Any<!><!SYNTAX!>?<!>::<!DEBUG_INFO_MISSING_UNRESOLVED!>toString<!>
 }

compiler/testData/diagnostics/tests/resolve/invoke/extensionValueAsNonExtension.kt

@@ -19,5 +19,5 @@ fun foo(): A.() -> Int {
     val b: Int = foo()(A())
     val c: Int = (foo())(A())
 
-    <!OI;UNREACHABLE_CODE!>return<!> null!!
+    <!UNREACHABLE_CODE!>return<!> null!!
 }

compiler/testData/diagnostics/tests/smartCasts/alwaysNull.kt

@@ -4,7 +4,7 @@ fun foo(): String {
     s = null
     <!DEBUG_INFO_CONSTANT!>s<!>?.length
     <!OI;DEBUG_INFO_CONSTANT!>s<!><!UNSAFE_CALL!>.<!>length
-    if (<!SENSELESS_COMPARISON!><!DEBUG_INFO_CONSTANT!>s<!> == null<!>) return <!ALWAYS_NULL!>s<!>!!
+    if (<!SENSELESS_COMPARISON!><!DEBUG_INFO_CONSTANT!>s<!> == null<!>) <!NI;UNREACHABLE_CODE!>return<!> <!ALWAYS_NULL!>s<!>!!
     var t: String? = "y"
     if (t == null) t = "x"
     var x: Int? = null

compiler/testData/diagnostics/tests/smartCasts/varnotnull/postfixNotnullClassIncrement.kt

@@ -1,7 +1,7 @@
 // !WITH_NEW_INFERENCE
 class MyClass
 
-operator fun MyClass.inc(): MyClass { <!OI;UNREACHABLE_CODE!>return<!> null!! }
+operator fun MyClass.inc(): MyClass { <!UNREACHABLE_CODE!>return<!> null!! }
 
 public fun box() : MyClass? {
     var i : MyClass?

compiler/testData/diagnostics/tests/smartCasts/varnotnull/prefixNotnullClassIncrement.kt

@@ -1,7 +1,7 @@
 // !WITH_NEW_INFERENCE
 class MyClass
 
-operator fun MyClass.inc(): MyClass { <!OI;UNREACHABLE_CODE!>return<!> null!! }
+operator fun MyClass.inc(): MyClass { <!UNREACHABLE_CODE!>return<!> null!! }
 
 public fun box() {
     var i : MyClass?

compiler/testData/diagnostics/tests/when/whenAndLambdaWithExpectedType.kt

@@ -7,19 +7,19 @@ val test1: (String) -> Boolean =
 
 val test2: (String) -> Boolean =
         when {
-            true -> {{ true }}
+            true -> <!NI;TYPE_MISMATCH!>{{ true }}<!>
             else -> null!!
         }
 
 val test3: (String) -> Boolean =
         when {
-            true -> { <!UNUSED_ANONYMOUS_PARAMETER!>s<!> -> true }
+            true -> <!NI;TYPE_MISMATCH!>{ <!UNUSED_ANONYMOUS_PARAMETER!>s<!> -> true }<!>
             else -> null!!
         }
 
 val test4: (String) -> Boolean =
         when {
-            true -> <!NI;TYPE_MISMATCH!>{ <!EXPECTED_PARAMETERS_NUMBER_MISMATCH!><!UNUSED_ANONYMOUS_PARAMETER!>s1<!>, <!CANNOT_INFER_PARAMETER_TYPE, UNUSED_ANONYMOUS_PARAMETER!>s2<!><!> -> true }<!>
+            true -> <!NI;TYPE_MISMATCH!>{ <!OI;EXPECTED_PARAMETERS_NUMBER_MISMATCH!><!UNUSED_ANONYMOUS_PARAMETER!>s1<!>, <!OI;CANNOT_INFER_PARAMETER_TYPE, UNUSED_ANONYMOUS_PARAMETER!>s2<!><!> -> true }<!>
             else -> null!!
         }
 

compiler/testData/diagnostics/tests/when/whenWithNothingAndLambdas.kt

@@ -6,7 +6,7 @@ val <!OI;IMPLICIT_NOTHING_PROPERTY_TYPE!>test1<!> = when {
 }
 
 val test1a: () -> Boolean = when {
-    true -> { { true } }
+    true -> <!NI;TYPE_MISMATCH!>{ { true } }<!>
     else -> TODO()
 }
 
@@ -33,7 +33,7 @@ val <!OI;IMPLICIT_NOTHING_PROPERTY_TYPE!>test3<!> = when {
 }
 
 val test3a: () -> Boolean = when {
-    true -> { { true } }
+    true -> <!NI;TYPE_MISMATCH!>{ { true } }<!>
-    true -> { { true } }
+    true -> <!NI;TYPE_MISMATCH!>{ { true } }<!>
     else -> TODO()
 }

compiler/tests-spec/testData/diagnostics/notLinked/dfa/pos/2.kt

@@ -385,7 +385,7 @@ fun case_13(b: Boolean, c: Boolean, d: Boolean) {
  * ISSUES: KT-28329
  */
 fun case_14(z: Boolean?) {
-    if (true && true && true && true && EnumClassWithNullableProperty.B.prop_1 != null || z != null || <!ALWAYS_NULL!>z<!>!! && true && true) {
+    if (true && true && true && true && EnumClassWithNullableProperty.B.prop_1 != null || z != null || <!ALWAYS_NULL!>z<!>!! <!UNREACHABLE_CODE!>&& true && true<!>) {
 
     } else {
         <!DEBUG_INFO_EXPRESSION_TYPE("kotlin.Int?")!>EnumClassWithNullableProperty.B.prop_1<!>

compiler/tests-spec/testData/diagnostics/notLinked/dfa/pos/36.kt

@@ -123,8 +123,8 @@ fun case_8(x: Any?, z: Any) {
 
 // TESTCASE NUMBER: 9
 fun case_9(x: Any?, z: Any) {
-    var y = select(x) ?: return null!!
+    var y = select(x) ?: <!UNREACHABLE_CODE!>return<!> null!!
-    z == y || throw null!!
+    z == y || <!UNREACHABLE_CODE!>throw<!> null!!
     <!DEBUG_INFO_EXPRESSION_TYPE("kotlin.Any?")!>x<!>
     <!DEBUG_INFO_EXPRESSION_TYPE("kotlin.Any")!>y<!>
     <!DEBUG_INFO_EXPRESSION_TYPE("kotlin.Any")!>y<!>.equals(10)

compiler/tests-spec/testData/diagnostics/notLinked/dfa/pos/4.kt

@@ -285,7 +285,7 @@ fun case_24(a: ((() -> Unit) -> Unit), b: (() -> Unit)) {
 }
 
 // TESTCASE NUMBER: 25
-fun case_25(a: (() -> Unit) -> Unit, b: (() -> Unit) -> Unit = if (<!SENSELESS_COMPARISON!>a == null<!>) <!DEBUG_INFO_EXPRESSION_TYPE("(() -> kotlin.Unit) -> kotlin.Unit & kotlin.Nothing")!>a<!> else {{}}) {
+fun case_25(a: (() -> Unit) -> Unit, b: (() -> Unit) -> Unit = if (<!SENSELESS_COMPARISON!>a == null<!>) <!DEBUG_INFO_EXPRESSION_TYPE("(() -> kotlin.Unit) -> kotlin.Unit & kotlin.Nothing"), DEBUG_INFO_SMARTCAST!>a<!> else <!TYPE_MISMATCH!>{{}}<!>) {
     <!DEBUG_INFO_EXPRESSION_TYPE("(() -> kotlin.Unit) -> kotlin.Unit")!>a<!>
     <!DEBUG_INFO_EXPRESSION_TYPE("(() -> kotlin.Unit) -> kotlin.Unit")!>b<!>
 }

compiler/tests-spec/testData/diagnostics/notLinked/dfa/pos/6.kt

@@ -686,7 +686,7 @@ fun case_33(a: ((Float) -> Int?)?, b: Float?, c: Boolean?) {
 fun case_34(z1: Boolean?) {
     var z = null
 
-    if (true && true && true && true && EnumClassWithNullableProperty.A.prop_1 != <!DEBUG_INFO_CONSTANT!>implicitNullableNothingProperty<!> && <!SENSELESS_COMPARISON!>EnumClassWithNullableProperty.A.prop_1 !== null<!> && EnumClassWithNullableProperty.A.prop_1 !== <!DEBUG_INFO_CONSTANT!>z<!> || z1 != <!DEBUG_INFO_CONSTANT!>implicitNullableNothingProperty<!> || <!ALWAYS_NULL!>z1<!>!! && true && true) {
+    if (true && true && true && true && EnumClassWithNullableProperty.A.prop_1 != <!DEBUG_INFO_CONSTANT!>implicitNullableNothingProperty<!> && <!SENSELESS_COMPARISON!>EnumClassWithNullableProperty.A.prop_1 !== null<!> && EnumClassWithNullableProperty.A.prop_1 !== <!DEBUG_INFO_CONSTANT!>z<!> || z1 != <!DEBUG_INFO_CONSTANT!>implicitNullableNothingProperty<!> || <!ALWAYS_NULL!>z1<!>!! <!UNREACHABLE_CODE!>&& true && true<!>) {
 
     } else {
         <!DEBUG_INFO_EXPRESSION_TYPE("kotlin.Int?")!>EnumClassWithNullableProperty.A.prop_1<!>

compiler/tests/org/jetbrains/kotlin/checkers/DiagnosticsTestGenerated.java

@@ -10602,6 +10602,11 @@ public class DiagnosticsTestGenerated extends AbstractDiagnosticsTest {
                     runTest("compiler/testData/diagnostics/tests/inference/nothingType/implicitNothingConstraintFromReturn.kt");
                 }
 
+                @TestMetadata("inferArgumentToNothingFromNullConstant.kt")
+                public void testInferArgumentToNothingFromNullConstant() throws Exception {
+                    runTest("compiler/testData/diagnostics/tests/inference/nothingType/inferArgumentToNothingFromNullConstant.kt");
+                }
+
                 @TestMetadata("kt24490.kt")
                 public void testKt24490() throws Exception {
                     runTest("compiler/testData/diagnostics/tests/inference/nothingType/kt24490.kt");

compiler/tests/org/jetbrains/kotlin/checkers/javac/DiagnosticsUsingJavacTestGenerated.java

@@ -10597,6 +10597,11 @@ public class DiagnosticsUsingJavacTestGenerated extends AbstractDiagnosticsUsing
                     runTest("compiler/testData/diagnostics/tests/inference/nothingType/implicitNothingConstraintFromReturn.kt");
                 }
 
+                @TestMetadata("inferArgumentToNothingFromNullConstant.kt")
+                public void testInferArgumentToNothingFromNullConstant() throws Exception {
+                    runTest("compiler/testData/diagnostics/tests/inference/nothingType/inferArgumentToNothingFromNullConstant.kt");
+                }
+
                 @TestMetadata("kt24490.kt")
                 public void testKt24490() throws Exception {
                     runTest("compiler/testData/diagnostics/tests/inference/nothingType/kt24490.kt");