[Commonizer] Implement CirTypeDistance.penalty

^KT-48288

native/commonizer/src/org/jetbrains/kotlin/commonizer/core/ClassOrTypeAliasTypeCommonizer.kt

@@ -114,7 +114,7 @@ internal class ClassOrTypeAliasTypeCommonizer(
         }
 
         val resolvedClassifierFromDependencies = classifiers.commonDependencies.classifier(destinationClassifierId)
-            ?: classifiers.targetDependencies[targetIndex].classifier(destinationClassifierId)
+            ?: classifiers.targetDependencies[targetIndex].classifier(destinationClassifierId) // necessary?
 
         if (resolvedClassifierFromDependencies != null && resolvedClassifierFromDependencies is CirProvided.TypeAlias) {
             return backwardsSubstitute(targetIndex, sourceType, destinationClassifierId, resolvedClassifierFromDependencies)
@@ -201,20 +201,14 @@ internal class ClassOrTypeAliasTypeCommonizer(
 
         val typeSubstitutionCandidates = resolveTypeSubstitutionCandidates(classifiers, commonId, types)
             .filter { typeSubstitutionCandidate ->
+                assert(typeSubstitutionCandidate.typeDistance.isZero.not()) { "Expected no zero typeDistance" }
                 if (typeSubstitutionCandidate.typeDistance.isNotReachable) return@filter false
                 if (typeSubstitutionCandidate.typeDistance.isNegative && !backwardsSubstitutionAllowed) return@filter false
                 if (typeSubstitutionCandidate.typeDistance.isPositive && !forwardSubstitutionAllowed) return@filter false
                 true
             }
 
-        if (typeSubstitutionCandidates.isEmpty()) return null
-        if (typeSubstitutionCandidates.size == 1) return typeSubstitutionCandidates.first().id
-
-        val forwardSubstitutionCandidates = typeSubstitutionCandidates.filter { it.typeDistance.isPositive }
-        val backwardsSubstitutionCandidates = typeSubstitutionCandidates.filter { it.typeDistance.isNegative }
-
-        return forwardSubstitutionCandidates.minByOrNull { it.typeDistance }?.id
-            ?: backwardsSubstitutionCandidates.maxByOrNull { it.typeDistance }?.id
+        return typeSubstitutionCandidates.minByOrNull { it.typeDistance.penalty }?.id
     }
 }
 
@@ -231,14 +225,7 @@ private fun resolveTypeSubstitutionCandidates(
         if (typeDistances.any { it.isNotReachable }) return@mapCandidateId null
         TypeSubstitutionCandidate(
             id = candidateId,
-            typeDistance = checkNotNull(typeDistances.worstOrNull())
+            typeDistance = checkNotNull(typeDistances.maxByOrNull { it.penalty })
         )
     }
 }
-
-private fun List<CirTypeDistance>.worstOrNull(): CirTypeDistance? {
-    if (this.isEmpty()) return null
-    // Negative Type Distances are considered 'worse'
-    filter { it.isNegative }.minOrNull()?.let { return it }
-    return maxOrNull()
-}

native/commonizer/src/org/jetbrains/kotlin/commonizer/mergedtree/CirTypeDistance.kt

@@ -8,7 +8,6 @@ package org.jetbrains.kotlin.commonizer.mergedtree
 import org.jetbrains.kotlin.commonizer.CommonizerTarget
 import org.jetbrains.kotlin.commonizer.cir.*
 import org.jetbrains.kotlin.commonizer.mergedtree.CirTypeDistance.Companion.unreachable
-import kotlin.math.absoluteValue
 
 @JvmInline
 value class CirTypeDistance(private val value: Int) : Comparable<CirTypeDistance> {
@@ -23,7 +22,25 @@ value class CirTypeDistance(private val value: Int) : Comparable<CirTypeDistance
 
     val isZero: Boolean get() = value == 0
 
-    val absoluteValue get() = CirTypeDistance(value.absoluteValue)
+    /**
+     * Judges the type distance on 'how bad is it'.
+     * This judgement will always prefer positive distances over negative distances.
+     *
+     * The higher this number, the 'worse' the distance.
+     *
+     * Score for unreachable: MAX_VALUE
+     * Score for zero: MIN_VALUE
+     * Range for negative type distances: [1, MAX_VALUE[
+     * Range for positive type distances: ]MIN_VALUE, -1]
+     */
+    val penalty: Int
+        get() = when {
+            isNotReachable -> Int.MAX_VALUE
+            isNegative -> -value
+            isZero -> Int.MIN_VALUE
+            isPositive -> Int.MIN_VALUE + value
+            else -> throw IllegalStateException("Unable to calculate penalty for $this")
+        }
 
     operator fun plus(value: Int) = if (isReachable) CirTypeDistance(this.value + value) else this
 

native/commonizer/tests/org/jetbrains/kotlin/commonizer/CirTypeDistanceTest.kt

@@ -308,9 +308,23 @@ class CirTypeDistanceTest : KtInlineSourceCommonizerTestCase() {
         assertUnreachable(CirTypeDistance.unreachable.dec())
         assertUnreachable(CirTypeDistance.unreachable - CirTypeDistance(1))
         assertUnreachable(CirTypeDistance(1) - CirTypeDistance.unreachable)
-        assertUnreachable(CirTypeDistance.unreachable.absoluteValue)
         assertEquals(CirTypeDistance(Int.MAX_VALUE), CirTypeDistance.unreachable)
     }
+
+    fun `test penalty`() {
+        assertEquals(1, CirTypeDistance(-1).penalty)
+        assertEquals(2, CirTypeDistance(-2).penalty)
+        assertEquals(Int.MIN_VALUE, CirTypeDistance(0).penalty)
+        assertEquals(Int.MAX_VALUE, CirTypeDistance.unreachable.penalty)
+        assertEquals(Int.MIN_VALUE + 1, CirTypeDistance(1).penalty)
+        assertEquals(Int.MIN_VALUE + 2, CirTypeDistance(2).penalty)
+        assertTrue(CirTypeDistance(-1).penalty > CirTypeDistance(1).penalty)
+        assertTrue(CirTypeDistance(-1).penalty > CirTypeDistance(10).penalty)
+        assertTrue(CirTypeDistance(2).penalty > CirTypeDistance(1).penalty)
+        assertTrue(CirTypeDistance(-2).penalty > CirTypeDistance(-1).penalty)
+        assertTrue(CirTypeDistance(1).penalty > CirTypeDistance(0).penalty)
+        assertTrue(CirTypeDistance(-1).penalty > CirTypeDistance(0).penalty)
+    }
 }
 
 private fun assertUnreachable(typeDistance: CirTypeDistance) {