FIR: Prevent registering compiler plugins twice

compiler/fir/entrypoint/src/org/jetbrains/kotlin/fir/extensions/FirExtensionRegistrar.kt

@@ -9,6 +9,7 @@ import com.intellij.openapi.project.Project
 import org.jetbrains.kotlin.fir.FirSession
 import org.jetbrains.kotlin.fir.SessionConfiguration
 import org.jetbrains.kotlin.fir.analysis.extensions.FirAdditionalCheckersExtension
+import java.util.concurrent.atomic.AtomicBoolean
 import kotlin.reflect.KClass
 
 abstract class FirExtensionRegistrar : FirExtensionRegistrarAdapter() {
@@ -71,7 +72,14 @@ abstract class FirExtensionRegistrar : FirExtensionRegistrarAdapter() {
 
     @OptIn(PluginServicesInitialization::class)
     fun configure(): BunchOfRegisteredExtensions {
-        ExtensionRegistrarContext().configurePlugin()
+        if (isInitialized.compareAndSet(false, true)) {
+            // Extension registrars can survive FirSession recreation in IDE mode, but we don't want to
+            // call `configurePlugin` more than once, because it will lead to registering all plugins twice.
+            // Please see KT-51444 for the details.
+
+            ExtensionRegistrarContext().configurePlugin()
+        }
+
         return BunchOfRegisteredExtensions(map.values)
     }
 
@@ -83,6 +91,8 @@ abstract class FirExtensionRegistrar : FirExtensionRegistrarAdapter() {
         it to RegisteredExtensionsFactories(it)
     }.toMap()
 
+    private var isInitialized: AtomicBoolean = AtomicBoolean(false)
+
     private fun <P : FirExtension> registerExtension(kClass: KClass<out P>, factory: FirExtension.Factory<P>) {
         @Suppress("UNCHECKED_CAST")
         val registeredExtensions = map.getValue(kClass)