Type<*> is inferred now if Type<A> and Type<B> common supertype is Type<X> and X is not within parameter upper bound. #KT-7585 Fixed. #EA-68943 Fixed.

It provides also a fix for KT-7585 (empty type intersection assertion).
A set of relevant tests, one fixed test

compiler/testData/diagnostics/tests/enum/commonSupertype.txt

@@ -1,6 +1,6 @@
 package
 
-internal val x: kotlin.Enum<out kotlin.Enum<out kotlin.Enum<out kotlin.Enum<out kotlin.Enum<out kotlin.Any?>>>>>
+internal val x: kotlin.Enum<*>
 
 internal final enum class A : kotlin.Enum<A> {
     enum entry A

compiler/testData/diagnostics/tests/regressions/kt7585/base.kt

@@ -0,0 +1,20 @@
+open class A
+
+class E
+
+abstract class Wrapper<T: A>(protected val t: T)
+
+class MyWrapper(a: A): Wrapper<A>(a)
+
+// This wrapper is not legal
+class TheirWrapper(e: E): Wrapper<<!UPPER_BOUND_VIOLATED, UPPER_BOUND_VIOLATED!>E<!>>(e)
+
+data class Pair<out T>(val a: T, val b: T)
+
+fun foo(): String {
+    val matrix: Pair<Wrapper<*>>
+    // It's not legal to do such a thing because E is not derived from A
+    // But we should not have assertion errors because of it!
+    matrix = Pair(MyWrapper(A()), TheirWrapper(E()))
+    return matrix.toString()
+}

compiler/testData/diagnostics/tests/regressions/kt7585/base.txt

@@ -0,0 +1,53 @@
+package
+
+internal fun foo(): kotlin.String
+
+internal open class A {
+    public constructor 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
+}
+
+internal final class E {
+    public constructor E()
+    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
+}
+
+internal final class MyWrapper : Wrapper<A> {
+    public constructor MyWrapper(/*0*/ a: A)
+    protected final override /*1*/ /*fake_override*/ val t: 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
+}
+
+kotlin.data() internal final class Pair</*0*/ out T> {
+    public constructor Pair</*0*/ out T>(/*0*/ a: T, /*1*/ b: T)
+    internal final val a: T
+    internal final val b: T
+    internal final /*synthesized*/ fun component1(): T
+    internal final /*synthesized*/ fun component2(): T
+    public final /*synthesized*/ fun copy(/*0*/ a: T = ..., /*1*/ b: T = ...): Pair<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
+}
+
+internal final class TheirWrapper : Wrapper<E> {
+    public constructor TheirWrapper(/*0*/ e: E)
+    protected final override /*1*/ /*fake_override*/ val t: E
+    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
+}
+
+internal abstract class Wrapper</*0*/ T : A> {
+    public constructor Wrapper</*0*/ T : A>(/*0*/ t: T)
+    protected final val t: 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/regressions/kt7585/java.kt

@@ -0,0 +1,30 @@
+// FILE: A.java
+
+class A {}
+
+// FILE: Wrapper.java
+
+abstract class Wrapper<T extends A> {
+    protected T t;
+
+    Wrapper(T t) { this.t = t; }
+}
+
+// FILE: kt7585.kt
+
+class E
+
+class MyWrapper(a: A): Wrapper<A>(a)
+
+// This wrapper is not legal
+class TheirWrapper(e: E): Wrapper<<!UPPER_BOUND_VIOLATED, UPPER_BOUND_VIOLATED!>E<!>>(e)
+
+data class Pair<out T>(val a: T, val b: T)
+
+fun foo(): String {
+    val matrix: Pair<Wrapper<*>>
+    // It's not legal to do such a thing because E is not derived from A
+    // But we should not have assertion errors because of it!
+    matrix = Pair(MyWrapper(A()), TheirWrapper(E()))
+    return matrix.toString()
+}

compiler/testData/diagnostics/tests/regressions/kt7585/java.txt

@@ -0,0 +1,53 @@
+package
+
+internal fun foo(): kotlin.String
+
+public/*package*/ open class A {
+    public/*package*/ constructor 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
+}
+
+internal final class E {
+    public constructor E()
+    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
+}
+
+internal final class MyWrapper : Wrapper<A> {
+    public constructor MyWrapper(/*0*/ a: A)
+    protected/*protected and package*/ final override /*1*/ /*fake_override*/ var t: 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
+}
+
+kotlin.data() internal final class Pair</*0*/ out T> {
+    public constructor Pair</*0*/ out T>(/*0*/ a: T, /*1*/ b: T)
+    internal final val a: T
+    internal final val b: T
+    internal final /*synthesized*/ fun component1(): T
+    internal final /*synthesized*/ fun component2(): T
+    public final /*synthesized*/ fun copy(/*0*/ a: T = ..., /*1*/ b: T = ...): Pair<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
+}
+
+internal final class TheirWrapper : Wrapper<E> {
+    public constructor TheirWrapper(/*0*/ e: E)
+    protected/*protected and package*/ final override /*1*/ /*fake_override*/ var t: E!
+    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/*package*/ abstract class Wrapper</*0*/ T : A!> {
+    public/*package*/ constructor Wrapper</*0*/ T : A!>(/*0*/ t: T!)
+    protected/*protected and package*/ final var t: 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/regressions/kt7585/twoparents.kt

@@ -0,0 +1,16 @@
+interface X {
+    fun foo(): Int = 42
+}
+
+interface Y
+
+class A: X, Y
+
+class B: X, Y
+
+class Out<out T: X>(val x: T)
+
+fun bar(a: Out<A>, b: Out<B>, f: Boolean): Int {
+    val x = if (f) a else b
+    return x.x.foo()    
+}

compiler/testData/diagnostics/tests/regressions/kt7585/twoparents.txt

@@ -0,0 +1,40 @@
+package
+
+internal fun bar(/*0*/ a: Out<A>, /*1*/ b: Out<B>, /*2*/ f: kotlin.Boolean): kotlin.Int
+
+internal final class A : X, Y {
+    public constructor A()
+    public open override /*2*/ /*fake_override*/ fun equals(/*0*/ other: kotlin.Any?): kotlin.Boolean
+    internal open override /*1*/ /*fake_override*/ fun foo(): kotlin.Int
+    public open override /*2*/ /*fake_override*/ fun hashCode(): kotlin.Int
+    public open override /*2*/ /*fake_override*/ fun toString(): kotlin.String
+}
+
+internal final class B : X, Y {
+    public constructor B()
+    public open override /*2*/ /*fake_override*/ fun equals(/*0*/ other: kotlin.Any?): kotlin.Boolean
+    internal open override /*1*/ /*fake_override*/ fun foo(): kotlin.Int
+    public open override /*2*/ /*fake_override*/ fun hashCode(): kotlin.Int
+    public open override /*2*/ /*fake_override*/ fun toString(): kotlin.String
+}
+
+internal final class Out</*0*/ out T : X> {
+    public constructor Out</*0*/ out T : X>(/*0*/ x: T)
+    internal final val x: 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
+}
+
+internal interface X {
+    public open override /*1*/ /*fake_override*/ fun equals(/*0*/ other: kotlin.Any?): kotlin.Boolean
+    internal open fun foo(): kotlin.Int
+    public open override /*1*/ /*fake_override*/ fun hashCode(): kotlin.Int
+    public open override /*1*/ /*fake_override*/ fun toString(): kotlin.String
+}
+
+internal interface Y {
+    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/testsWithStdLib/kt7585/delegate.kt

@@ -0,0 +1,73 @@
+// FILE: Base.java
+
+interface Base {}
+
+// FILE: Other.java
+
+interface Other {}
+
+// FILE: Derived.java
+
+final class Derived<T> implements Base, Other {}
+
+// FILE: Exotic.java
+
+final class Exotic implements Base, Other {
+
+    int x;
+
+    Exotic(int x) {
+        this.x = x;
+    }
+}
+
+// FILE: Properties.java
+
+import kotlin.jvm.functions.Function0;
+
+class Val<T> {
+
+    Function0<T> initializer;
+
+    Val(Function0<T> initializer) {
+        this.initializer = initializer;
+    }
+
+    T get(Object instance, Object metadata) {
+        return initializer.invoke();
+    }
+}
+
+class Properties {
+    static <T> Val<T> calcVal(Function0<T> initializer) {
+        return new Val<T>(initializer);
+    }
+}
+
+// FILE: My.kt
+
+open class Wrapper<out T: Base>(val v: T)
+
+class DerivedWrapper(v: Derived<*>): Wrapper<Derived<*>>(v)
+
+class ExoticWrapper(v: Exotic): Wrapper<Exotic>(v)
+
+object MyBase {
+
+    fun derived() = Derived<String>()
+    fun exotic(x: Int) = Exotic(x)
+
+    fun derivedWrapper() = DerivedWrapper(derived())
+    fun exoticWrapper(x: Int) = ExoticWrapper(exotic(x))
+}
+
+class My(val x: Int) {
+    val wrapper/*: Wrapper<*>*/ by Properties.calcVal {
+        val y = x + 1
+        when {
+            y > 0 -> MyBase.derivedWrapper()
+            x < 0 -> MyBase.exoticWrapper(x)
+            else  -> throw java.lang.NullPointerException("")
+        }
+    }
+}

compiler/testData/diagnostics/testsWithStdLib/kt7585/delegate.txt

@@ -0,0 +1,82 @@
+package
+
+public/*package*/ interface Base {
+    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/*package*/ final class Derived</*0*/ T : kotlin.Any!> : Base, Other {
+    public/*package*/ constructor Derived</*0*/ T : kotlin.Any!>()
+    public open override /*2*/ /*fake_override*/ fun equals(/*0*/ other: kotlin.Any?): kotlin.Boolean
+    public open override /*2*/ /*fake_override*/ fun hashCode(): kotlin.Int
+    public open override /*2*/ /*fake_override*/ fun toString(): kotlin.String
+}
+
+internal final class DerivedWrapper : Wrapper<Derived<*>> {
+    public constructor DerivedWrapper(/*0*/ v: Derived<*>)
+    internal final override /*1*/ /*fake_override*/ val v: Derived<*>
+    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/*package*/ final class Exotic : Base, Other {
+    public/*package*/ constructor Exotic(/*0*/ x: kotlin.Int)
+    public/*package*/ final var x: kotlin.Int
+    public open override /*2*/ /*fake_override*/ fun equals(/*0*/ other: kotlin.Any?): kotlin.Boolean
+    public open override /*2*/ /*fake_override*/ fun hashCode(): kotlin.Int
+    public open override /*2*/ /*fake_override*/ fun toString(): kotlin.String
+}
+
+internal final class ExoticWrapper : Wrapper<Exotic> {
+    public constructor ExoticWrapper(/*0*/ v: Exotic)
+    internal final override /*1*/ /*fake_override*/ val v: Exotic
+    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
+}
+
+internal final class My {
+    public constructor My(/*0*/ x: kotlin.Int)
+    internal final val wrapper: Wrapper<*>!
+    internal final val x: kotlin.Int
+    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
+}
+
+internal object MyBase {
+    private constructor MyBase()
+    internal final fun derived(): Derived<kotlin.String>
+    internal final fun derivedWrapper(): DerivedWrapper
+    public open override /*1*/ /*fake_override*/ fun equals(/*0*/ other: kotlin.Any?): kotlin.Boolean
+    internal final fun exotic(/*0*/ x: kotlin.Int): Exotic
+    internal final fun exoticWrapper(/*0*/ x: kotlin.Int): ExoticWrapper
+    public open override /*1*/ /*fake_override*/ fun hashCode(): kotlin.Int
+    public open override /*1*/ /*fake_override*/ fun toString(): kotlin.String
+}
+
+public/*package*/ interface Other {
+    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/*package*/ open class Properties {
+    public/*package*/ constructor Properties()
+    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
+
+    // Static members
+    public/*package*/ open fun </*0*/ T : kotlin.Any!> calcVal(/*0*/ initializer: (() -> T!)!): Val<T!>!
+}
+
+internal open class Wrapper</*0*/ out T : Base> {
+    public constructor Wrapper</*0*/ out T : Base>(/*0*/ v: T)
+    internal final val v: 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
+}