NI: remove separation of variable fixation order by constraint kind

The commit partially reverts ec4d9d2f1f

^KT-37914 Fixed

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

@@ -10534,6 +10534,11 @@ public class FirOldFrontendDiagnosticsTestGenerated extends AbstractFirOldFronte
                 runTest("compiler/testData/diagnostics/tests/inference/commonSystem/boundOnNullableVariable.kt");
             }
 
+            @TestMetadata("castToSubtype.kt")
+            public void testCastToSubtype() throws Exception {
+                runTest("compiler/testData/diagnostics/tests/inference/commonSystem/castToSubtype.kt");
+            }
+
             @TestMetadata("cstFromNullableChildAndNonParameterizedType.kt")
             public void testCstFromNullableChildAndNonParameterizedType() throws Exception {
                 runTest("compiler/testData/diagnostics/tests/inference/commonSystem/cstFromNullableChildAndNonParameterizedType.kt");

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

@@ -54,8 +54,7 @@ class VariableFixationFinder(
     enum class TypeVariableFixationReadiness {
         FORBIDDEN,
         WITHOUT_PROPER_ARGUMENT_CONSTRAINT, // proper constraint from arguments -- not from upper bound for type parameters
-        WITH_COMPLEX_DEPENDENCY_LOWER, // if type variable T has constraint with non fixed type variable inside (non-top-level): Foo<S> <: T
-        WITH_COMPLEX_DEPENDENCY_UPPER, // T <: Foo<S>
+        WITH_COMPLEX_DEPENDENCY, // if type variable T has constraint with non fixed type variable inside (non-top-level): T <: Foo<S>
         WITH_TRIVIAL_OR_NON_PROPER_CONSTRAINTS, // proper trivial constraint from arguments, Nothing <: T
         RELATED_TO_ANY_OUTPUT_TYPE,
         READY_FOR_FIXATION,
@@ -69,8 +68,7 @@ class VariableFixationFinder(
         !notFixedTypeVariables.contains(variable) ||
                 dependencyProvider.isVariableRelatedToTopLevelType(variable) -> TypeVariableFixationReadiness.FORBIDDEN
         !variableHasProperArgumentConstraints(variable) -> TypeVariableFixationReadiness.WITHOUT_PROPER_ARGUMENT_CONSTRAINT
-        hasDependencyToOtherTypeVariables(variable, ConstraintKind.LOWER) -> TypeVariableFixationReadiness.WITH_COMPLEX_DEPENDENCY_LOWER
-        hasDependencyToOtherTypeVariables(variable, ConstraintKind.UPPER) -> TypeVariableFixationReadiness.WITH_COMPLEX_DEPENDENCY_UPPER
+        hasDependencyToOtherTypeVariables(variable) -> TypeVariableFixationReadiness.WITH_COMPLEX_DEPENDENCY
         variableHasTrivialOrNonProperConstraints(variable) -> TypeVariableFixationReadiness.WITH_TRIVIAL_OR_NON_PROPER_CONSTRAINTS
         dependencyProvider.isVariableRelatedToAnyOutputType(variable) -> TypeVariableFixationReadiness.RELATED_TO_ANY_OUTPUT_TYPE
         isReified(variable) -> TypeVariableFixationReadiness.READY_FOR_FIXATION_REIFIED
@@ -114,12 +112,6 @@ class VariableFixationFinder(
         return when (candidateReadiness) {
             TypeVariableFixationReadiness.FORBIDDEN -> null
             TypeVariableFixationReadiness.WITHOUT_PROPER_ARGUMENT_CONSTRAINT -> VariableForFixation(candidate, false)
-            TypeVariableFixationReadiness.WITH_COMPLEX_DEPENDENCY_UPPER,
-            TypeVariableFixationReadiness.WITH_COMPLEX_DEPENDENCY_LOWER -> VariableForFixation(
-                candidate,
-                hasProperConstraint = variableHasProperArgumentConstraints(candidate),
-                hasOnlyTrivialProperConstraint = variableHasTrivialOrNonProperConstraints(candidate)
-            )
             TypeVariableFixationReadiness.WITH_TRIVIAL_OR_NON_PROPER_CONSTRAINTS ->
                 VariableForFixation(candidate, hasProperConstraint = true, hasOnlyTrivialProperConstraint = true)
 
@@ -127,15 +119,13 @@ class VariableFixationFinder(
         }
     }
 
-    private fun Context.hasDependencyToOtherTypeVariables(typeVariable: TypeConstructorMarker, kind: ConstraintKind): Boolean {
+    private fun Context.hasDependencyToOtherTypeVariables(typeVariable: TypeConstructorMarker): Boolean {
         for (constraint in notFixedTypeVariables[typeVariable]?.constraints ?: return false) {
-            if (constraint.kind != kind || constraint.kind == ConstraintKind.EQUALITY) continue
-            if (constraint.type.lowerBoundIfFlexible().argumentsCount() != 0
-                && constraint.type.contains {
-                    it.typeConstructor() != typeVariable && notFixedTypeVariables.containsKey(it.typeConstructor())
-                }) {
-                return true
+            val dependencyPresenceCondition = { type: KotlinTypeMarker ->
+                type.typeConstructor() != typeVariable && notFixedTypeVariables.containsKey(type.typeConstructor())
             }
+            if (constraint.type.lowerBoundIfFlexible().argumentsCount() != 0 && constraint.type.contains(dependencyPresenceCondition))
+                return true
         }
         return false
     }

compiler/testData/diagnostics/tests/inference/commonSystem/castToSubtype.kt

@@ -0,0 +1,60 @@
+// FIR_IDENTICAL
+// !DIAGNOSTICS: -UNCHECKED_CAST
+// Issue: KT-37914
+
+interface I
+
+fun <R, U : R> castToSubtype(obj: R) = obj as U
+
+fun <T> select(vararg x: T) = x[0]
+
+fun <S> materialize(): S = null as S
+
+// Case 1 (using intermediate supertype)
+
+/*
+ Constraint system:
+     R:
+        TypeVariable(U) <: TypeVariable(R)
+        I <: TypeVariable(R)
+     U:
+        I >: TypeVariable(U)
+        Foo<TypeVariable(P)> >: TypeVariable(U)
+     T:
+        Foo<Any> <: TypeVariable(T)
+        Bar<TypeVariable(P)> <: TypeVariable(T)
+
+ Fixation order before the fix: R, U, T, P
+ Fixation order after the fix: R, T, P, U
+
+ `U` has begun to have lower priority so it can be fixed to more specific type (to `Foo<Any>` instead of `I`).
+ */
+
+interface Foo<T> : I
+
+class Bar<T>(val x: Foo<T>) : Foo<T>
+
+fun main2() {
+    select(
+        materialize<Foo<Any>>(),
+        Bar(
+            castToSubtype(materialize<I>()) // NI: "required – Foo<Any>, found – I" afther the commit, OI – OK
+        )
+    )
+}
+
+// Case 2 (using deep supertype)
+
+interface Foo1<Y> : I
+interface Foo2<Y> : Foo1<Y>
+
+class Bar1<P>(val x: Foo2<P>) : Foo2<P>
+
+fun main1() {
+    select(
+        materialize<Foo2<Any>>(),
+        Bar1(
+            castToSubtype(materialize<I>()) // NI: "required – Foo<Any>, found – I" afther the commit, OI – OK
+        )
+    )
+}

compiler/testData/diagnostics/tests/inference/commonSystem/castToSubtype.txt

@@ -0,0 +1,47 @@
+package
+
+public fun </*0*/ R, /*1*/ U : R> castToSubtype(/*0*/ obj: R): U
+public fun main1(): kotlin.Unit
+public fun main2(): kotlin.Unit
+public fun </*0*/ S> materialize(): S
+public fun </*0*/ T> select(/*0*/ vararg x: T /*kotlin.Array<out T>*/): T
+
+public final class Bar</*0*/ T> : Foo<T> {
+    public constructor Bar</*0*/ T>(/*0*/ x: Foo<T>)
+    public final val x: Foo<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
+}
+
+public final class Bar1</*0*/ P> : Foo2<P> {
+    public constructor Bar1</*0*/ P>(/*0*/ x: Foo2<P>)
+    public final val x: Foo2<P>
+    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 Foo</*0*/ T> : 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 interface Foo1</*0*/ Y> : 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 interface Foo2</*0*/ Y> : Foo1<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
+}
+
+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
+}

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

@@ -10541,6 +10541,11 @@ public class DiagnosticsTestGenerated extends AbstractDiagnosticsTestWithFirVali
                     runTest("compiler/testData/diagnostics/tests/inference/commonSystem/boundOnNullableVariable.kt");
                 }
 
+                @TestMetadata("castToSubtype.kt")
+                public void testCastToSubtype() throws Exception {
+                    runTest("compiler/testData/diagnostics/tests/inference/commonSystem/castToSubtype.kt");
+                }
+
                 @TestMetadata("cstFromNullableChildAndNonParameterizedType.kt")
                 public void testCstFromNullableChildAndNonParameterizedType() throws Exception {
                     runTest("compiler/testData/diagnostics/tests/inference/commonSystem/cstFromNullableChildAndNonParameterizedType.kt");

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

@@ -10536,6 +10536,11 @@ public class DiagnosticsUsingJavacTestGenerated extends AbstractDiagnosticsUsing
                     runTest("compiler/testData/diagnostics/tests/inference/commonSystem/boundOnNullableVariable.kt");
                 }
 
+                @TestMetadata("castToSubtype.kt")
+                public void testCastToSubtype() throws Exception {
+                    runTest("compiler/testData/diagnostics/tests/inference/commonSystem/castToSubtype.kt");
+                }
+
                 @TestMetadata("cstFromNullableChildAndNonParameterizedType.kt")
                 public void testCstFromNullableChildAndNonParameterizedType() throws Exception {
                     runTest("compiler/testData/diagnostics/tests/inference/commonSystem/cstFromNullableChildAndNonParameterizedType.kt");