Allow type variable fixation into intersection type if it isn't meaningless (i.e. has one or more final classes, or two or more open classes)

^KT-46186 Fixed

compiler/fir/analysis-tests/tests-gen/org/jetbrains/kotlin/test/runners/FirOldFrontendDiagnosticsTestGenerated.java

@@ -29029,6 +29029,12 @@ public class FirOldFrontendDiagnosticsTestGenerated extends AbstractFirDiagnosti
                 runTest("compiler/testData/diagnostics/tests/typeParameters/kt42472.kt");
             }
 
+            @Test
+            @TestMetadata("kt46186.kt")
+            public void testKt46186() throws Exception {
+                runTest("compiler/testData/diagnostics/tests/typeParameters/kt46186.kt");
+            }
+
             @Test
             @TestMetadata("misplacedConstraints.kt")
             public void testMisplacedConstraints() throws Exception {

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

@@ -261,6 +261,10 @@ interface ConeTypeContext : TypeSystemContext, TypeSystemOptimizationContext, Ty
         return this is ConeClassLikeLookupTag
     }
 
+    override fun TypeConstructorMarker.isInterface(): Boolean {
+        return ((this as? ConeClassLikeLookupTag)?.toClassLikeSymbol()?.fir as? FirClass)?.classKind == ClassKind.INTERFACE
+    }
+
     override fun TypeParameterMarker.getVariance(): TypeVariance {
         require(this is ConeTypeParameterLookupTag)
         return this.symbol.fir.variance.convertVariance()

compiler/ir/ir.tree/src/org/jetbrains/kotlin/ir/types/IrTypeSystemContext.kt

@@ -158,6 +158,10 @@ interface IrTypeSystemContext : TypeSystemContext, TypeSystemCommonSuperTypesCon
 
     override fun TypeConstructorMarker.isClassTypeConstructor() = this is IrClassSymbol
 
+    override fun TypeConstructorMarker.isInterface(): Boolean {
+        return (this as? IrClassSymbol)?.owner?.isInterface == true
+    }
+
     override fun TypeParameterMarker.getVariance() = (this as IrTypeParameterSymbol).owner.variance.convertVariance()
 
     private fun getSuperTypes(typeParameterMarker: TypeParameterMarker) = (typeParameterMarker as IrTypeParameterSymbol).owner.superTypes

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

@@ -216,10 +216,18 @@ class ResultTypeResolver(
             variableWithConstraints.constraints.filter { it.kind == ConstraintKind.UPPER && this@findSuperType.isProperTypeForFixation(it.type) }
         if (upperConstraints.isNotEmpty()) {
             val intersectionUpperType = intersectTypes(upperConstraints.map { it.type })
-            val isThereExpectedTypeConstraint = upperConstraints.any { it.isExpectedTypePosition() }
-            val nonExpectedTypeConstraints = upperConstraints.filterNot { it.isExpectedTypePosition() }
             val resultIsActuallyIntersection = intersectionUpperType.typeConstructor().isIntersection()
-            val upperType = if (isThereExpectedTypeConstraint && nonExpectedTypeConstraints.isNotEmpty() && resultIsActuallyIntersection) {
+
+            val isThereUnwantedIntersectedTypes = if (resultIsActuallyIntersection) {
+                val intersectionSupertypes = intersectionUpperType.typeConstructor().supertypes()
+                val intersectionClasses = intersectionSupertypes.count {
+                    it.typeConstructor().isClassTypeConstructor() && !it.typeConstructor().isInterface()
+                }
+                val areThereIntersectionFinalClasses = intersectionSupertypes.any { it.typeConstructor().isCommonFinalClassConstructor() }
+                intersectionClasses > 1 || areThereIntersectionFinalClasses
+            } else false
+
+            val upperType = if (isThereUnwantedIntersectedTypes) {
                 /*
                  * We shouldn't infer a type variable into the intersection type if there is an explicit expected type,
                  * otherwise it can lead to something like this:
@@ -227,7 +235,7 @@ class ResultTypeResolver(
                  * fun <T : String> materialize(): T = null as T
                  * val bar: Int = materialize() // no errors, T is inferred into String & Int
                  */
-                intersectTypes(nonExpectedTypeConstraints.map { it.type })
+                intersectTypes(upperConstraints.filterNot { it.isExpectedTypePosition() }.map { it.type })
             } else intersectionUpperType
 
             return typeApproximator.approximateToSubType(

compiler/testData/diagnostics/tests/typeParameters/kt46186.fir.kt

@@ -0,0 +1,83 @@
+// !DIAGNOSTICS: -FINAL_UPPER_BOUND -CAST_NEVER_SUCCEEDS
+
+interface I
+
+class View1
+open class View2
+interface View3
+abstract class View4
+interface View5
+
+fun <T: View1> findViewById1(): T = null as T
+fun test1(): I = findViewById1()
+
+fun <T: View2> findViewById2(): T = null as T
+fun test2(): I = findViewById2()
+
+inline fun <reified T: View1> findViewById3(): T = null as T
+fun test3(): I = findViewById3()
+
+inline fun <reified T: View2> findViewById4(): T = null as T
+fun test4(): I = findViewById4()
+
+fun <T: View3> findViewById5(): T = null as T
+fun test5(): I = findViewById5()
+
+inline fun <reified T: View3> findViewById6(): T = null as T
+fun test6(): I = findViewById6()
+
+fun <T: View4> findViewById7(): T = null as T
+fun test7(): I = findViewById7()
+
+inline fun <reified T: View4> findViewById8(): T = null as T
+fun test8(): I = findViewById8()
+
+fun <T> findViewById9(): T where T: View3, T: View5 = null as T
+fun test9(): I = findViewById9()
+
+inline fun <reified T> findViewById10(): T where T: View3, T: View5 = null as T
+fun test10(): I = findViewById10()
+
+fun <T: View2> findViewById11(): T = null as T
+fun test11(): View4 = findViewById11()
+
+object Obj {
+    fun <T: I> findViewById1(): T = null as T
+    fun test1(): View1 = findViewById1()
+
+    fun <T: I> findViewById2(): T = null as T
+    fun test2(): View2 = findViewById2()
+
+    inline fun <reified T: I> findViewById3(): T = null as T
+    fun test3(): View1 = findViewById3()
+
+    inline fun <reified T: I> findViewById4(): T = null as T
+    fun test4(): View2 = findViewById4()
+
+    fun <T: I> findViewById5(): T = null as T
+    fun test5(): View3 = findViewById5()
+
+    inline fun <reified T: I> findViewById6(): T = null as T
+    fun test6(): View3 = findViewById6()
+
+    fun <T: I> findViewById7(): T = null as T
+    fun test7(): View4 = findViewById7()
+
+    inline fun <reified T: I> findViewById8(): T = null as T
+    fun test8(): View4 = findViewById8()
+
+    fun <T> findViewById9(): T where T: View3, T: View5 = null as T
+    fun test9(): View1 = findViewById9()
+
+    inline fun <reified T> findViewById10(): T where T: View3, T: View5 = null as T
+    fun test10(): View1 = findViewById10()
+
+    fun <T: View2> findViewById11(): T = null as T
+    fun test11(): View4 = findViewById11()
+}
+
+interface A
+open class B {
+    fun <T> f(): T where T : A, T : B = null as T
+    fun g(): A = f()
+}

compiler/testData/diagnostics/tests/typeParameters/kt46186.kt

@@ -0,0 +1,83 @@
+// !DIAGNOSTICS: -FINAL_UPPER_BOUND -CAST_NEVER_SUCCEEDS
+
+interface I
+
+class View1
+open class View2
+interface View3
+abstract class View4
+interface View5
+
+fun <T: View1> findViewById1(): T = null as T
+fun test1(): I = <!TYPE_MISMATCH!><!TYPE_MISMATCH!>findViewById1<!>()<!>
+
+fun <T: View2> findViewById2(): T = null as T
+fun test2(): I = findViewById2()
+
+inline fun <reified T: View1> findViewById3(): T = null as T
+fun test3(): I = <!TYPE_MISMATCH!><!TYPE_MISMATCH!>findViewById3<!>()<!>
+
+inline fun <reified T: View2> findViewById4(): T = null as T
+fun test4(): I = findViewById4()
+
+fun <T: View3> findViewById5(): T = null as T
+fun test5(): I = findViewById5()
+
+inline fun <reified T: View3> findViewById6(): T = null as T
+fun test6(): I = findViewById6()
+
+fun <T: View4> findViewById7(): T = null as T
+fun test7(): I = findViewById7()
+
+inline fun <reified T: View4> findViewById8(): T = null as T
+fun test8(): I = findViewById8()
+
+fun <T> findViewById9(): T where T: View3, T: View5 = null as T
+fun test9(): I = findViewById9()
+
+inline fun <reified T> findViewById10(): T where T: View3, T: View5 = null as T
+fun test10(): I = findViewById10()
+
+fun <T: View2> findViewById11(): T = null as T
+fun test11(): View4 = <!TYPE_MISMATCH!><!TYPE_MISMATCH!>findViewById11<!>()<!>
+
+object Obj {
+    fun <T: I> findViewById1(): T = null as T
+    fun test1(): View1 = <!TYPE_MISMATCH!><!TYPE_MISMATCH!>findViewById1<!>()<!>
+
+    fun <T: I> findViewById2(): T = null as T
+    fun test2(): View2 = findViewById2()
+
+    inline fun <reified T: I> findViewById3(): T = null as T
+    fun test3(): View1 = <!TYPE_MISMATCH!><!TYPE_MISMATCH!>findViewById3<!>()<!>
+
+    inline fun <reified T: I> findViewById4(): T = null as T
+    fun test4(): View2 = findViewById4()
+
+    fun <T: I> findViewById5(): T = null as T
+    fun test5(): View3 = findViewById5()
+
+    inline fun <reified T: I> findViewById6(): T = null as T
+    fun test6(): View3 = findViewById6()
+
+    fun <T: I> findViewById7(): T = null as T
+    fun test7(): View4 = findViewById7()
+
+    inline fun <reified T: I> findViewById8(): T = null as T
+    fun test8(): View4 = findViewById8()
+
+    fun <T> findViewById9(): T where T: View3, T: View5 = null as T
+    fun test9(): View1 = <!TYPE_MISMATCH!><!TYPE_MISMATCH!>findViewById9<!>()<!>
+
+    inline fun <reified T> findViewById10(): T where T: View3, T: View5 = null as T
+    fun test10(): View1 = <!TYPE_MISMATCH!><!TYPE_MISMATCH!>findViewById10<!>()<!>
+
+    fun <T: View2> findViewById11(): T = null as T
+    fun test11(): View4 = <!TYPE_MISMATCH!><!TYPE_MISMATCH!>findViewById11<!>()<!>
+}
+
+interface A
+open class B {
+    fun <T> f(): T where T : A, T : B = null as T
+    fun g(): A = f()
+}

compiler/testData/diagnostics/tests/typeParameters/kt46186.txt

@@ -0,0 +1,107 @@
+package
+
+public fun </*0*/ T : View1> findViewById1(): T
+public inline fun </*0*/ reified T : View3> findViewById10(): T where T : View5
+public fun </*0*/ T : View2> findViewById11(): T
+public fun </*0*/ T : View2> findViewById2(): T
+public inline fun </*0*/ reified T : View1> findViewById3(): T
+public inline fun </*0*/ reified T : View2> findViewById4(): T
+public fun </*0*/ T : View3> findViewById5(): T
+public inline fun </*0*/ reified T : View3> findViewById6(): T
+public fun </*0*/ T : View4> findViewById7(): T
+public inline fun </*0*/ reified T : View4> findViewById8(): T
+public fun </*0*/ T : View3> findViewById9(): T where T : View5
+public fun test1(): I
+public fun test10(): I
+public fun test11(): View4
+public fun test2(): I
+public fun test3(): I
+public fun test4(): I
+public fun test5(): I
+public fun test6(): I
+public fun test7(): I
+public fun test8(): I
+public fun test9(): I
+
+public interface A {
+    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 open class B {
+    public constructor B()
+    public open override /*1*/ /*fake_override*/ fun equals(/*0*/ other: kotlin.Any?): kotlin.Boolean
+    public final fun </*0*/ T : A> f(): T where T : B
+    public final fun g(): A
+    public open override /*1*/ /*fake_override*/ fun hashCode(): kotlin.Int
+    public open override /*1*/ /*fake_override*/ fun toString(): kotlin.String
+}
+
+public interface 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 object Obj {
+    private constructor Obj()
+    public open override /*1*/ /*fake_override*/ fun equals(/*0*/ other: kotlin.Any?): kotlin.Boolean
+    public final fun </*0*/ T : I> findViewById1(): T
+    public final inline fun </*0*/ reified T : View3> findViewById10(): T where T : View5
+    public final fun </*0*/ T : View2> findViewById11(): T
+    public final fun </*0*/ T : I> findViewById2(): T
+    public final inline fun </*0*/ reified T : I> findViewById3(): T
+    public final inline fun </*0*/ reified T : I> findViewById4(): T
+    public final fun </*0*/ T : I> findViewById5(): T
+    public final inline fun </*0*/ reified T : I> findViewById6(): T
+    public final fun </*0*/ T : I> findViewById7(): T
+    public final inline fun </*0*/ reified T : I> findViewById8(): T
+    public final fun </*0*/ T : View3> findViewById9(): T where T : View5
+    public open override /*1*/ /*fake_override*/ fun hashCode(): kotlin.Int
+    public final fun test1(): View1
+    public final fun test10(): View1
+    public final fun test11(): View4
+    public final fun test2(): View2
+    public final fun test3(): View1
+    public final fun test4(): View2
+    public final fun test5(): View3
+    public final fun test6(): View3
+    public final fun test7(): View4
+    public final fun test8(): View4
+    public final fun test9(): View1
+    public open override /*1*/ /*fake_override*/ fun toString(): kotlin.String
+}
+
+public final class View1 {
+    public constructor View1()
+    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 open class View2 {
+    public constructor View2()
+    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 interface View3 {
+    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 View4 {
+    public constructor View4()
+    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 interface View5 {
+    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/tests-common-new/tests-gen/org/jetbrains/kotlin/test/runners/DiagnosticTestGenerated.java

@@ -29125,6 +29125,12 @@ public class DiagnosticTestGenerated extends AbstractDiagnosticTest {
                 runTest("compiler/testData/diagnostics/tests/typeParameters/kt42472.kt");
             }
 
+            @Test
+            @TestMetadata("kt46186.kt")
+            public void testKt46186() throws Exception {
+                runTest("compiler/testData/diagnostics/tests/typeParameters/kt46186.kt");
+            }
+
             @Test
             @TestMetadata("misplacedConstraints.kt")
             public void testMisplacedConstraints() throws Exception {

core/compiler.common/src/org/jetbrains/kotlin/types/model/TypeSystemContext.kt

@@ -303,6 +303,7 @@ interface TypeSystemContext : TypeSystemOptimizationContext {
     fun TypeConstructorMarker.supertypes(): Collection<KotlinTypeMarker>
     fun TypeConstructorMarker.isIntersection(): Boolean
     fun TypeConstructorMarker.isClassTypeConstructor(): Boolean
+    fun TypeConstructorMarker.isInterface(): Boolean
     fun TypeConstructorMarker.isIntegerLiteralTypeConstructor(): Boolean
     fun TypeConstructorMarker.isLocalType(): Boolean
 

core/descriptors/src/org/jetbrains/kotlin/types/checker/ClassicTypeSystemContext.kt

@@ -15,6 +15,7 @@ import org.jetbrains.kotlin.descriptors.impl.AbstractTypeParameterDescriptor
 import org.jetbrains.kotlin.name.FqName
 import org.jetbrains.kotlin.name.FqNameUnsafe
 import org.jetbrains.kotlin.name.Name
+import org.jetbrains.kotlin.resolve.DescriptorUtils
 import org.jetbrains.kotlin.resolve.calls.inference.CapturedType
 import org.jetbrains.kotlin.resolve.constants.IntegerLiteralTypeConstructor
 import org.jetbrains.kotlin.resolve.descriptorUtil.*
@@ -237,6 +238,11 @@ interface ClassicTypeSystemContext : TypeSystemInferenceExtensionContext, TypeSy
         return declarationDescriptor is ClassDescriptor
     }
 
+    override fun TypeConstructorMarker.isInterface(): Boolean {
+        require(this is TypeConstructor, this::errorMessage)
+        return DescriptorUtils.isInterface(declarationDescriptor)
+    }
+
     override fun TypeConstructorMarker.isCommonFinalClassConstructor(): Boolean {
         require(this is TypeConstructor, this::errorMessage)
         val classDescriptor = declarationDescriptor as? ClassDescriptor ?: return false