FIR: Weaken some UPPER_BOUND_VIOLATED restrictions

See test data at starProjectionInsteadOutCaptured.kt

^KT-49412 Fixed
^KT-50230 Relates
^KT-48044 Fixed

compiler/testData/diagnostics/tests/inference/unsoundness1.fir.kt

@@ -0,0 +1,23 @@
+// SKIP_TXT
+// !LANGUAGE: +ProperTypeInferenceConstraintsProcessing
+
+class A<T, F : T>
+fun foo(a: A<*, in CharSequence>) {}
+fun <T, U> coerce(t: T): U {
+    val constrain: Constrain<U, *, in T>? = null
+    val bind = Bind(constrain)
+    return bind.upcast(t)
+}
+
+class Constrain<A, B : A, C : B>
+
+class Bind<A, B : A, C : B>(val constrain: Constrain<A, B, C>?) {
+    fun upcast(c: C): A = c
+}
+
+fun <T, U> coerce2(t: T): U {
+    // We might report an error on unsound type reference Constrain<U, *, T>?, too
+    val constrain: Constrain<U, *, T>? = null
+    val bind = Bind(<!ARGUMENT_TYPE_MISMATCH!>constrain<!>) // WARNING: Type mismatch: inferred type is T but U was expected
+    return bind.upcast(t)
+}

compiler/testData/diagnostics/tests/inference/unsoundness1.kt

@@ -0,0 +1,23 @@
+// SKIP_TXT
+// !LANGUAGE: +ProperTypeInferenceConstraintsProcessing
+
+class A<T, F : T>
+fun foo(a: A<*, in CharSequence>) {}
+fun <T, U> coerce(t: T): U {
+    val constrain: Constrain<U, *, in T>? = null
+    val bind = Bind(constrain)
+    return bind.upcast(t)
+}
+
+class Constrain<A, B : A, C : B>
+
+class Bind<A, B : A, C : B>(val constrain: Constrain<A, B, C>?) {
+    fun upcast(c: C): A = c
+}
+
+fun <T, U> coerce2(t: T): U {
+    // We might report an error on unsound type reference Constrain<U, *, T>?, too
+    val constrain: Constrain<U, *, T>? = null
+    val bind = Bind(<!TYPE_MISMATCH, TYPE_MISMATCH!>constrain<!>) // WARNING: Type mismatch: inferred type is T but U was expected
+    return bind.upcast(t)
+}

compiler/testData/diagnostics/tests/inference/unsoundness2.kt

@@ -0,0 +1,22 @@
+// FIR_IDENTICAL
+// SKIP_TXT
+// !LANGUAGE: +ProperTypeInferenceConstraintsProcessing
+
+fun main(args: Array<String>) {
+    val zero = coerce<Int, String>(0)
+}
+
+fun <T, U> coerce(t: T): U {
+    // Should be an error somewhere because this code leads to unsoundness
+    // We may report that `Constrain<U, *, in T>?` type definition is unsound or the call `Bind(constrain)`
+    // See KT-50230
+    val constrain: Constrain<U, *, in T>? = null
+    val bind = Bind(constrain)
+    return bind.upcast(t)
+}
+
+class Constrain<A, B : A, C : B>
+
+class Bind<A, B : A, C : B>(val constrain: Constrain<A, B, C>?) {
+    fun upcast(c: C): A = c
+}

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

@@ -0,0 +1,11 @@
+// FIR_IDENTICAL
+// SKIP_TXT
+interface A
+interface B<X : A>
+interface C<E : A, F : B<E>>
+
+fun foo1(c: C<out A, out B<*>>) {}
+
+fun foo2(c: C<*, B<*>>) {}
+fun <T : B<*>> foo3(c: C<*, T>) {}
+fun <T : B<*>> foo4(c: C<out A, T>) {}