[KGP] Align daemon classpath between BTA and non-BTA compilations

Otherwise, compiling JVM with BTA and JS without BTA will spin up two
daemons, possibly affecting performance.

^KT-81415 Fixed

Author: wojtek-kalicinski

libraries/tools/kotlin-gradle-plugin-integration-tests/src/test/kotlin/org/jetbrains/kotlin/gradle/KotlinDaemonJvmArgsTest.kt

@@ -6,7 +6,10 @@
 package org.jetbrains.kotlin.gradle
 
 import org.gradle.api.logging.LogLevel
+import org.gradle.kotlin.dsl.kotlin
 import org.gradle.util.GradleVersion
+import org.jetbrains.kotlin.gradle.internals.asFinishLogMessage
+import org.jetbrains.kotlin.gradle.tasks.KotlinCompilerExecutionStrategy
 import org.jetbrains.kotlin.gradle.testbase.*
 import org.junit.jupiter.api.DisplayName
 import kotlin.io.path.writeText
@@ -196,4 +199,39 @@ class KotlinDaemonJvmArgsTest : KGPDaemonsBaseTest() {
             }
         }
     }
+
+    @GradleTest
+    @DisplayName("Ensures that only one Kotlin compiler daemon is started for both JVM and JavaScript compilation")
+    fun ensureOnlyOneDaemonStartedForJvmAndJsWithBta(gradleVersion: GradleVersion) {
+        ensureOnlyOneDaemonStartedForJvmAndJs(gradleVersion, withBta = true)
+    }
+
+    @GradleTest
+    @DisplayName("Ensures that only one Kotlin compiler daemon is started for both JVM and JavaScript compilation when BTA disabled")
+    fun ensureOnlyOneDaemonStartedForJvmAndJsWithoutBta(gradleVersion: GradleVersion) {
+        ensureOnlyOneDaemonStartedForJvmAndJs(gradleVersion, withBta = false)
+    }
+
+    fun ensureOnlyOneDaemonStartedForJvmAndJs(gradleVersion: GradleVersion, withBta: Boolean) {
+        project("emptyKts", gradleVersion) {
+            plugins {
+                kotlin("multiplatform")
+            }
+            buildScriptInjection {
+                kotlinMultiplatform.jvm()
+                kotlinMultiplatform.js()
+                kotlinMultiplatform.sourceSets.getByName("commonMain").compileSource("class Common")
+            }
+            build(
+                "assemble",
+                buildOptions = buildOptions.copy(
+                    configurationCache = BuildOptions.ConfigurationCacheValue.DISABLED,
+                    runViaBuildToolsApi = withBta
+                )
+            ) {
+                assertOutputContains(KotlinCompilerExecutionStrategy.DAEMON.asFinishLogMessage)
+                assertOutputContainsExactlyTimes("starting the daemon as", 1)
+            }
+        }
+    }
 }

libraries/tools/kotlin-gradle-plugin/src/common/kotlin/org/jetbrains/kotlin/gradle/plugin/KotlinPluginWrapper.kt

@@ -108,9 +108,18 @@ abstract class DefaultKotlinBasePlugin : KotlinBasePlugin {
             .configurations
             .maybeCreateResolvable(COMPILER_CLASSPATH_CONFIGURATION_NAME)
             .defaultDependencies {
-                it.add(
-                    project.dependencies.create("$KOTLIN_MODULE_GROUP:$KOTLIN_COMPILER_EMBEDDABLE:${project.getKotlinPluginVersion()}")
-                )
+                if (project.kotlinPropertiesProvider.runKotlinCompilerViaBuildToolsApi.get()) {
+                    it.add(
+                        project.dependencies.create("$KOTLIN_MODULE_GROUP:$KOTLIN_BUILD_TOOLS_API_COMPAT:$pluginVersion")
+                    )
+                    it.add(
+                        project.dependencies.create("$KOTLIN_MODULE_GROUP:$KOTLIN_BUILD_TOOLS_API_IMPL:$pluginVersion")
+                    )
+                } else {
+                    it.add(
+                        project.dependencies.create("$KOTLIN_MODULE_GROUP:$KOTLIN_COMPILER_EMBEDDABLE:${project.getKotlinPluginVersion()}")
+                    )
+                }
             }
         project
             .configurations

libraries/tools/kotlin-gradle-plugin/src/functionalTest/kotlin/org/jetbrains/kotlin/gradle/unitTests/KotlinCompileApiTest.kt

@@ -10,7 +10,7 @@ import org.gradle.api.tasks.compile.JavaCompile
 import org.jetbrains.kotlin.gradle.dsl.ExplicitApiMode
 import org.jetbrains.kotlin.gradle.dsl.JvmTarget
 import org.jetbrains.kotlin.gradle.dsl.KotlinJvmCompilerOptions
-import org.jetbrains.kotlin.gradle.internal.KOTLIN_COMPILER_EMBEDDABLE
+import org.jetbrains.kotlin.gradle.internal.KOTLIN_BUILD_TOOLS_API_IMPL
 import org.jetbrains.kotlin.gradle.internal.KOTLIN_MODULE_GROUP
 import org.jetbrains.kotlin.gradle.plugin.COMPILER_CLASSPATH_CONFIGURATION_NAME
 import org.jetbrains.kotlin.gradle.plugin.KotlinApiPlugin
@@ -183,10 +183,10 @@ class KotlinCompileApiTest {
             .getByName(COMPILER_CLASSPATH_CONFIGURATION_NAME)
             .incoming
             .dependencies
-            .single()
+            .single { it.name == KOTLIN_BUILD_TOOLS_API_IMPL }
 
         assertEquals(
-            "$KOTLIN_MODULE_GROUP:$KOTLIN_COMPILER_EMBEDDABLE:${plugin.pluginVersion}",
+            "$KOTLIN_MODULE_GROUP:$KOTLIN_BUILD_TOOLS_API_IMPL:${plugin.pluginVersion}",
             "${compilerDependency.group}:${compilerDependency.name}:${compilerDependency.version}"
         )
     }