[NI] Support fixation to subtype in completion mode calculator

Allow full compltion mode for return type depending on type parameters in
contravariant position only if they have proper equality constraint.

compiler/fir/resolve/tests/org/jetbrains/kotlin/fir/FirOldFrontendDiagnosticsTestGenerated.java

@@ -10379,6 +10379,11 @@ public class FirOldFrontendDiagnosticsTestGenerated extends AbstractFirOldFronte
                 runTest("compiler/testData/diagnostics/tests/inference/completion/basic.kt");
             }
 
+            @TestMetadata("equalityConstraintUpstairs.kt")
+            public void testEqualityConstraintUpstairs() throws Exception {
+                runTest("compiler/testData/diagnostics/tests/inference/completion/equalityConstraintUpstairs.kt");
+            }
+
             @TestMetadata("kt33166.kt")
             public void testKt33166() throws Exception {
                 runTest("compiler/testData/diagnostics/tests/inference/completion/kt33166.kt");
@@ -10389,6 +10394,11 @@ public class FirOldFrontendDiagnosticsTestGenerated extends AbstractFirOldFronte
                 runTest("compiler/testData/diagnostics/tests/inference/completion/partialForIlt.kt");
             }
 
+            @TestMetadata("transitiveConstraint.kt")
+            public void testTransitiveConstraint() throws Exception {
+                runTest("compiler/testData/diagnostics/tests/inference/completion/transitiveConstraint.kt");
+            }
+
             @TestMetadata("withExact.kt")
             public void testWithExact() throws Exception {
                 runTest("compiler/testData/diagnostics/tests/inference/completion/withExact.kt");

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

@@ -13,6 +13,7 @@ import org.jetbrains.kotlin.resolve.calls.model.KotlinResolutionCandidate
 import org.jetbrains.kotlin.types.AbstractTypeChecker
 import org.jetbrains.kotlin.types.UnwrappedType
 import org.jetbrains.kotlin.types.model.*
+import org.jetbrains.kotlin.utils.newLinkedHashMapWithExpectedSize
 import java.util.*
 
 typealias CsCompleterContext = KotlinConstraintSystemCompleter.Context
@@ -45,10 +46,11 @@ class CompletionModeCalculator {
         private val csCompleterContext: CsCompleterContext
     ) {
         private enum class FixationDirection {
-            TO_SUBTYPE, TO_SUPERTYPE, EQUALITY
+            TO_SUBTYPE, EQUALITY
         }
 
-        private val fixationDirectionsForVariables = mutableMapOf<VariableWithConstraints, FixationDirection>()
+        private val fixationDirectionsForVariables: MutableMap<VariableWithConstraints, FixationDirection> =
+            newLinkedHashMapWithExpectedSize(csCompleterContext.notFixedTypeVariables.size)
         private val variablesWithQueuedConstraints = mutableSetOf<TypeVariableMarker>()
         private val typesToProcess: Queue<KotlinTypeMarker> = ArrayDeque()
 
@@ -68,14 +70,14 @@ class CompletionModeCalculator {
             while (typesToProcess.isNotEmpty()) {
                 val type = typesToProcess.poll() ?: break
 
-                fixationRequirementForTopLevel(type)?.let { directionForVariable ->
+                fixationDirectionForTopLevel(type)?.let { directionForVariable ->
                     updateDirection(directionForVariable)
                     enqueueTypesFromConstraints(directionForVariable.variable)
                 }
 
                 // find all variables in type and make requirements for them
-                type.contains { fromReturnType ->
+                type.contains { typePart ->
-                    for (directionForVariable in directionsForVariablesInTypeArguments(fromReturnType)) {
+                    for (directionForVariable in directionsForVariablesInTypeArguments(typePart)) {
                         updateDirection(directionForVariable)
                         enqueueTypesFromConstraints(directionForVariable.variable)
                     }
@@ -106,16 +108,16 @@ class CompletionModeCalculator {
         private fun updateDirection(directionForVariable: FixationDirectionForVariable) {
             val (variable, newDirection) = directionForVariable
             fixationDirectionsForVariables[variable]?.let { oldDirection ->
-                // To sub and to super are merged into equality, old equality stays
                 if (oldDirection != FixationDirection.EQUALITY && oldDirection != newDirection)
                     fixationDirectionsForVariables[variable] = FixationDirection.EQUALITY
+            } ?: run {
+                fixationDirectionsForVariables[variable] = newDirection
             }
-            fixationDirectionsForVariables[variable] = newDirection
         }
 
         private data class FixationDirectionForVariable(val variable: VariableWithConstraints, val direction: FixationDirection)
 
-        private fun CsCompleterContext.fixationRequirementForTopLevel(type: KotlinTypeMarker): FixationDirectionForVariable? {
+        private fun CsCompleterContext.fixationDirectionForTopLevel(type: KotlinTypeMarker): FixationDirectionForVariable? {
             return notFixedTypeVariables[type.typeConstructor()]?.let {
                 FixationDirectionForVariable(it, FixationDirection.TO_SUBTYPE)
             }
@@ -138,10 +140,10 @@ class CompletionModeCalculator {
 
                 val parameter = type.typeConstructor().getParameter(position)
                 val effectiveVariance = AbstractTypeChecker.effectiveVariance(parameter.getVariance(), argument.getVariance())
-                    ?: TypeVariance.OUT // Discuss
+                    ?: TypeVariance.INV
 
                 val direction = when (effectiveVariance) {
-                    TypeVariance.IN -> FixationDirection.TO_SUPERTYPE
+                    TypeVariance.IN -> FixationDirection.EQUALITY // Assuming that variables in contravariant positions are fixed to subtype
                     TypeVariance.OUT -> FixationDirection.TO_SUBTYPE
                     TypeVariance.INV -> FixationDirection.EQUALITY
                 }
@@ -169,7 +171,6 @@ class CompletionModeCalculator {
 
         private fun Constraint.hasRequiredKind(direction: FixationDirection) = when (direction) {
             FixationDirection.TO_SUBTYPE -> kind.isLower() || kind.isEqual()
-            FixationDirection.TO_SUPERTYPE -> kind.isUpper() || kind.isEqual()
             FixationDirection.EQUALITY -> kind.isEqual()
         }
     }

compiler/testData/diagnostics/tests/inference/completion/basic.fir.kt

@@ -57,7 +57,6 @@ fun test7(cls: Cls) {
 }
 
 fun test8(cls: Cls) {
-    // TODO
     id(
         wrapIn(cls)
     )

compiler/testData/diagnostics/tests/inference/completion/equalityConstraintUpstairs.fir.kt

@@ -0,0 +1,17 @@
+// !LANGUAGE: +NewInference
+// !DIAGNOSTICS: -UNUSED_PARAMETER
+
+class In<in I>(arg: I)
+class Out<out O>(val prop: O)
+class Inv<T>(val prop: T)
+
+interface Upper
+class Lower : Upper
+
+fun <K> id(arg: K): K = arg
+
+fun test(lower: Lower) {
+    id<Inv<Upper>>(Inv(lower))
+    id<In<Upper>>(In(lower))
+    id<Out<Upper>>(Out(lower))
+}

compiler/testData/diagnostics/tests/inference/completion/equalityConstraintUpstairs.kt

@@ -0,0 +1,17 @@
+// !LANGUAGE: +NewInference
+// !DIAGNOSTICS: -UNUSED_PARAMETER
+
+class In<in I>(arg: I)
+class Out<out O>(val prop: O)
+class Inv<T>(val prop: T)
+
+interface Upper
+class Lower : Upper
+
+fun <K> id(arg: K): K = arg
+
+fun test(lower: Lower) {
+    id<Inv<Upper>>(Inv(lower))
+    id<In<Upper>>(In(lower))
+    id<Out<Upper>>(Out(lower))
+}

compiler/testData/diagnostics/tests/inference/completion/equalityConstraintUpstairs.txt

@@ -0,0 +1,40 @@
+package
+
+public fun </*0*/ K> id(/*0*/ arg: K): K
+public fun test(/*0*/ lower: Lower): kotlin.Unit
+
+public final class In</*0*/ in I> {
+    public constructor In</*0*/ in I>(/*0*/ arg: 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 final class Inv</*0*/ T> {
+    public constructor Inv</*0*/ T>(/*0*/ prop: T)
+    public final val prop: 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 Lower : Upper {
+    public constructor Lower()
+    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 Out</*0*/ out O> {
+    public constructor Out</*0*/ out O>(/*0*/ prop: O)
+    public final val prop: O
+    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 Upper {
+    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/completion/transitiveConstraint.fir.kt

@@ -0,0 +1,15 @@
+// !LANGUAGE: +NewInference
+// !DIAGNOSTICS: -UNUSED_PARAMETER -UNUSED_VARIABLE
+
+interface Bound
+interface Upper : Bound
+class Lower : Upper
+
+class Inv<T>
+
+fun <T : Bound, U : T> makeInv(v: U): Inv<T> = TODO()
+fun <K> id(arg: K): K = arg
+
+fun test(lower: Lower) {
+    id<Inv<Upper>>(makeInv(lower))
+}

compiler/testData/diagnostics/tests/inference/completion/transitiveConstraint.kt

@@ -0,0 +1,15 @@
+// !LANGUAGE: +NewInference
+// !DIAGNOSTICS: -UNUSED_PARAMETER -UNUSED_VARIABLE
+
+interface Bound
+interface Upper : Bound
+class Lower : Upper
+
+class Inv<T>
+
+fun <T : Bound, U : T> makeInv(v: U): Inv<T> = TODO()
+fun <K> id(arg: K): K = arg
+
+fun test(lower: Lower) {
+    id<Inv<Upper>>(makeInv(lower))
+}

compiler/testData/diagnostics/tests/inference/completion/transitiveConstraint.txt

@@ -0,0 +1,31 @@
+package
+
+public fun </*0*/ K> id(/*0*/ arg: K): K
+public fun </*0*/ T : Bound, /*1*/ U : T> makeInv(/*0*/ v: U): Inv<T>
+public fun test(/*0*/ lower: Lower): kotlin.Unit
+
+public interface Bound {
+    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 Inv</*0*/ T> {
+    public constructor Inv</*0*/ 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 Lower : Upper {
+    public constructor Lower()
+    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 Upper : Bound {
+    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/dependantOnVariance.kt

@@ -45,7 +45,7 @@ fun test1(int: Int, any: Any) {
     readFromMyList(getMyList(any), int)
     readFromMyList<Int>(<!NI;TYPE_MISMATCH, NI;TYPE_MISMATCH, OI;TYPE_INFERENCE_EXPECTED_TYPE_MISMATCH!>getMyList(any)<!>, int)
 
-    readFromMyList<Int>(<!NI;TYPE_MISMATCH, NI;TYPE_MISMATCH, OI;TYPE_INFERENCE_EXPECTED_TYPE_MISMATCH!>getMyListToReadFrom(any)<!>, int)
+    readFromMyList<Int>(<!NI;TYPE_MISMATCH, OI;TYPE_INFERENCE_EXPECTED_TYPE_MISMATCH!>getMyListToReadFrom(any)<!>, int)
     readFromMyList(getMyListToReadFrom(any), int)
 
     readFromMyList(getMyListToReadFrom(int), any)

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

@@ -10386,6 +10386,11 @@ public class DiagnosticsTestGenerated extends AbstractDiagnosticsTest {
                     runTest("compiler/testData/diagnostics/tests/inference/completion/basic.kt");
                 }
 
+                @TestMetadata("equalityConstraintUpstairs.kt")
+                public void testEqualityConstraintUpstairs() throws Exception {
+                    runTest("compiler/testData/diagnostics/tests/inference/completion/equalityConstraintUpstairs.kt");
+                }
+
                 @TestMetadata("kt33166.kt")
                 public void testKt33166() throws Exception {
                     runTest("compiler/testData/diagnostics/tests/inference/completion/kt33166.kt");
@@ -10396,6 +10401,11 @@ public class DiagnosticsTestGenerated extends AbstractDiagnosticsTest {
                     runTest("compiler/testData/diagnostics/tests/inference/completion/partialForIlt.kt");
                 }
 
+                @TestMetadata("transitiveConstraint.kt")
+                public void testTransitiveConstraint() throws Exception {
+                    runTest("compiler/testData/diagnostics/tests/inference/completion/transitiveConstraint.kt");
+                }
+
                 @TestMetadata("withExact.kt")
                 public void testWithExact() throws Exception {
                     runTest("compiler/testData/diagnostics/tests/inference/completion/withExact.kt");

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

@@ -10381,6 +10381,11 @@ public class DiagnosticsUsingJavacTestGenerated extends AbstractDiagnosticsUsing
                     runTest("compiler/testData/diagnostics/tests/inference/completion/basic.kt");
                 }
 
+                @TestMetadata("equalityConstraintUpstairs.kt")
+                public void testEqualityConstraintUpstairs() throws Exception {
+                    runTest("compiler/testData/diagnostics/tests/inference/completion/equalityConstraintUpstairs.kt");
+                }
+
                 @TestMetadata("kt33166.kt")
                 public void testKt33166() throws Exception {
                     runTest("compiler/testData/diagnostics/tests/inference/completion/kt33166.kt");
@@ -10391,6 +10396,11 @@ public class DiagnosticsUsingJavacTestGenerated extends AbstractDiagnosticsUsing
                     runTest("compiler/testData/diagnostics/tests/inference/completion/partialForIlt.kt");
                 }
 
+                @TestMetadata("transitiveConstraint.kt")
+                public void testTransitiveConstraint() throws Exception {
+                    runTest("compiler/testData/diagnostics/tests/inference/completion/transitiveConstraint.kt");
+                }
+
                 @TestMetadata("withExact.kt")
                 public void testWithExact() throws Exception {
                     runTest("compiler/testData/diagnostics/tests/inference/completion/withExact.kt");