Fix ConcurrentModificationException iterating over tasks (KT-29971)

Issue #KT-29971 Fixed

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

@@ -815,4 +815,12 @@ class KotlinGradleIT : BaseGradleIT() {
             assertContains("Kotlin build report is written to")
         }
     }
+
+    @Test
+    fun testKt29971() = with(Project("kt-29971", GradleVersionRequired.AtLeast("5.0"))) {
+        build("jvm-app:build") {
+            assertSuccessful()
+            assertTasksExecuted(":jvm-app:compileKotlin")
+        }
+    }
 }

libraries/tools/kotlin-gradle-plugin-integration-tests/src/test/resources/testProject/kt-29971/build.gradle

@@ -0,0 +1,16 @@
+buildscript {
+	repositories {
+		mavenLocal()
+		jcenter()
+	} 
+	dependencies {
+		classpath "org.jetbrains.kotlin:kotlin-gradle-plugin:$kotlin_version"
+	}
+}
+
+allprojects {
+	repositories {
+		mavenLocal()
+		jcenter()
+	}
+}

libraries/tools/kotlin-gradle-plugin-integration-tests/src/test/resources/testProject/kt-29971/jvm-app/build.gradle

@@ -0,0 +1,6 @@
+plugins {
+    id "org.jetbrains.kotlin.jvm"
+}
+
+group = "com.example.jvm"
+version = "1.0"

libraries/tools/kotlin-gradle-plugin-integration-tests/src/test/resources/testProject/kt-29971/jvm-app/src/main/kotlin/A.kt

@@ -0,0 +1 @@
+fun main() = Unit

libraries/tools/kotlin-gradle-plugin-integration-tests/src/test/resources/testProject/kt-29971/mpp-lib/build.gradle

@@ -0,0 +1,24 @@
+plugins {
+	id "org.jetbrains.kotlin.multiplatform"
+}
+
+kotlin {
+	js()
+
+	sourceSets {
+		commonMain {
+			dependencies {
+				implementation 'org.jetbrains.kotlin:kotlin-stdlib-common'
+			}
+		}
+		jsMain {
+			dependencies {
+				implementation 'org.jetbrains.kotlin:kotlin-stdlib-js'
+			}
+		}
+	}
+}
+
+// While this plugin seems not to do anything in this setup, IT IS needed to reproduce KT-29971
+apply plugin: "application"
+mainClassName = "foo"

libraries/tools/kotlin-gradle-plugin-integration-tests/src/test/resources/testProject/kt-29971/settings.gradle

@@ -0,0 +1,3 @@
+enableFeaturePreview('GRADLE_METADATA')
+
+include(":mpp-lib", ":jvm-app")

libraries/tools/kotlin-gradle-plugin/src/main/kotlin/org/jetbrains/kotlin/compilerRunner/GradleKotlinCompilerRunner.kt

@@ -31,13 +31,15 @@ import org.jetbrains.kotlin.cli.common.messages.MessageCollector
 import org.jetbrains.kotlin.daemon.client.CompileServiceSession
 import org.jetbrains.kotlin.daemon.common.*
 import org.jetbrains.kotlin.gradle.dsl.KotlinMultiplatformExtension
-import org.jetbrains.kotlin.gradle.plugin.internal.state.TaskLoggers
 import org.jetbrains.kotlin.gradle.logging.kotlinDebug
+import org.jetbrains.kotlin.gradle.plugin.internal.state.TaskLoggers
 import org.jetbrains.kotlin.gradle.plugin.KotlinCompilation
 import org.jetbrains.kotlin.gradle.tasks.*
 import org.jetbrains.kotlin.gradle.utils.newTmpFile
 import org.jetbrains.kotlin.gradle.utils.relativeToRoot
-import org.jetbrains.kotlin.incremental.*
+import org.jetbrains.kotlin.incremental.classpathAsList
+import org.jetbrains.kotlin.incremental.destinationAsFile
+import org.jetbrains.kotlin.incremental.makeModuleFile
 import java.io.File
 import java.lang.ref.WeakReference
 
@@ -194,7 +196,7 @@ internal open class GradleCompilerRunner(protected val task: Task) {
             val jarToModule = HashMap<File, IncrementalModuleEntry>()
 
             for (project in gradle.rootProject.allprojects) {
-                project.tasks.withType(AbstractKotlinCompile::class.java).forEach { task ->
+              project.tasks.withType(AbstractKotlinCompile::class.java).toList().forEach { task ->
                     val module = IncrementalModuleEntry(project.path, task.moduleName, project.buildDir, task.buildHistoryFile)
                     dirToModule[task.destinationDir] = module
                     task.javaOutputDir?.let { dirToModule[it] = module }