[Gradle] Simplify 'isHostSpecificKonanTargetsSet' implementation

The method is called pretty often during import and can return
faster and create less objects.

libraries/tools/kotlin-gradle-plugin/src/common/kotlin/org/jetbrains/kotlin/gradle/targets/native/KotlinNativeTarget.kt

@@ -144,12 +144,15 @@ open class KotlinNativeTarget @Inject constructor(
 
 private val hostManager by lazy { HostManager() }
 
-internal fun isHostSpecificKonanTargetsSet(konanTargets: Iterable<KonanTarget>): Boolean {
-    val enabledByHost = hostManager.enabledByHost
-    val allHosts = enabledByHost.keys
-    fun canBeBuiltOnHosts(konanTarget: KonanTarget) = enabledByHost.filterValues { konanTarget in it }.keys
-    return konanTargets.flatMapTo(mutableSetOf(), ::canBeBuiltOnHosts) != allHosts
-}
+private val targetsEnabledOnAllHosts by lazy { hostManager.enabledByHost.values.reduce { acc, targets -> acc intersect targets } }
+
+/**
+ * The set of konanTargets is considered 'host specific' if the shared compilation of said set can *not* be built
+ * on *all* potential hosts. e.g. a set like (iosX64, macosX64) can only be built on macos hosts, and is therefore considered
+ * 'host specific'.
+ */
+internal fun isHostSpecificKonanTargetsSet(konanTargets: Iterable<KonanTarget>): Boolean =
+    konanTargets.none { target -> target in targetsEnabledOnAllHosts }
 
 private fun <T> getHostSpecificElements(
     fragments: Iterable<T>,

libraries/tools/kotlin-gradle-plugin/src/test/kotlin/org/jetbrains/kotlin/gradle/plugin/mpp/IsHostSpecificKonanTargetsSetTest.kt

@@ -0,0 +1,49 @@
+/*
+ * Copyright 2010-2022 JetBrains s.r.o. and Kotlin Programming Language contributors.
+ * Use of this source code is governed by the Apache 2.0 license that can be found in the license/LICENSE.txt file.
+ */
+
+package org.jetbrains.kotlin.gradle.plugin.mpp
+
+import org.jetbrains.kotlin.konan.target.HostManager
+import org.jetbrains.kotlin.konan.target.KonanTarget
+import org.junit.Test
+import kotlin.test.assertEquals
+
+class IsHostSpecificKonanTargetsSetTest {
+
+    private val hostManager = HostManager()
+
+    @Test
+    fun `matches previous implementation`() {
+        fun previousImplementation(konanTargets: Iterable<KonanTarget>): Boolean {
+            val enabledByHost = hostManager.enabledByHost
+            val allHosts = enabledByHost.keys
+            fun canBeBuiltOnHosts(konanTarget: KonanTarget) = enabledByHost.filterValues { konanTarget in it }.keys
+            return konanTargets.flatMapTo(mutableSetOf(), ::canBeBuiltOnHosts) != allHosts
+        }
+
+        val testInputs = sequence {
+            yield(emptyList())
+
+            KonanTarget.predefinedTargets.values.forEach { first ->
+                yield(listOf(first))
+
+                KonanTarget.predefinedTargets.values.forEach { second ->
+                    yield(listOf(first, second))
+
+                    KonanTarget.predefinedTargets.values.forEach { third ->
+                        yield(listOf(first, second, third))
+                    }
+                }
+            }
+        }.toList()
+
+        testInputs.forEach { targets ->
+            assertEquals(
+                previousImplementation(targets), isHostSpecificKonanTargetsSet(targets),
+                "Expected 'isHostSpecificKonanTargetsSet' to return same as previous implementation for $targets"
+            )
+        }
+    }
+}