[Test] Reset ApplicationManager.application when shared application environments are disposed

- Shared application environments can be disposed in the middle of test
  plan execution when the project count reaches zero. So resetting
  `ApplicationManager` only on "test plan execution finished" is
  incorrect, because it does not account for that scenario. Instead, we
  should reset `ApplicationManager` every time the application
  environment is disposed.
- We should also keep the manual reset in `testPlanExecutionFinished`
  because `disposeApplicationEnvironment` may not need to dispose
  anything if there isn't a shared application environment, but we
  should still reset `ApplicationManager` if an unshared application
  environment was created.
- This fixes "Some test disposed, but forgot to clear MockApplication"
  exceptions which appeared after KT-64099 because it opened up proper
  disposal of the shared application environment (instead of it being in
  a state of leakage because not all project disposables were properly
  disposed).

^KT-63650
^KT-64099

compiler/cli/cli-base/src/org/jetbrains/kotlin/cli/jvm/compiler/KotlinCoreEnvironment.kt

@@ -16,6 +16,7 @@ import com.intellij.ide.highlighter.JavaFileType
 import com.intellij.lang.java.JavaParserDefinition
 import com.intellij.mock.MockProject
 import com.intellij.openapi.Disposable
+import com.intellij.openapi.application.Application
 import com.intellij.openapi.application.ApplicationManager
 import com.intellij.openapi.application.TransactionGuard
 import com.intellij.openapi.application.TransactionGuardImpl
@@ -594,10 +595,37 @@ class KotlinCoreEnvironment private constructor(
                 val environment = ourApplicationEnvironment ?: return
                 ourApplicationEnvironment = null
                 Disposer.dispose(environment.parentDisposable)
+                resetApplicationManager(environment.application)
                 ZipHandler.clearFileAccessorCache()
             }
         }
 
+        /**
+         * Resets the application managed by [ApplicationManager] to `null`. If [applicationToReset] is specified, [resetApplicationManager]
+         * will only reset the application if it's the expected one. Otherwise, the application will already have been changed to another
+         * application. For example, application disposal can trigger one of the disposables registered via
+         * [ApplicationManager.setApplication], which reset the managed application to the previous application.
+         */
+        @JvmStatic
+        fun resetApplicationManager(applicationToReset: Application? = null) {
+            val currentApplication = ApplicationManager.getApplication() ?: return
+            if (applicationToReset != null && applicationToReset != currentApplication) {
+                return
+            }
+
+            try {
+                val ourApplicationField = ApplicationManager::class.java.getDeclaredField("ourApplication")
+                ourApplicationField.isAccessible = true
+                ourApplicationField.set(null, null)
+            } catch (exception: Exception) {
+                // Resetting the application manager is not critical in a production context. If the reflective access fails, we shouldn't
+                // expose the user to the failure.
+                if (currentApplication.isUnitTestMode) {
+                    throw exception
+                }
+            }
+        }
+
         @JvmStatic
         fun ProjectEnvironment.configureProjectEnvironment(
             configuration: CompilerConfiguration,

compiler/tests-common-new/tests/org/jetbrains/kotlin/test/ApplicationEnvironmentDisposer.kt

@@ -6,13 +6,11 @@
 package org.jetbrains.kotlin.test
 
 import com.intellij.openapi.Disposable
-import com.intellij.openapi.application.ApplicationManager
 import com.intellij.openapi.util.Disposer
 import org.jetbrains.kotlin.cli.jvm.compiler.KotlinCoreEnvironment
 import org.jetbrains.kotlin.test.services.ApplicationDisposableProvider
 import org.junit.platform.launcher.TestExecutionListener
 import org.junit.platform.launcher.TestPlan
-import java.lang.reflect.Field
 
 class ApplicationEnvironmentDisposer : TestExecutionListener {
     companion object {
@@ -22,9 +20,7 @@ class ApplicationEnvironmentDisposer : TestExecutionListener {
     override fun testPlanExecutionFinished(testPlan: TestPlan) {
         KotlinCoreEnvironment.disposeApplicationEnvironment()
         Disposer.dispose(ROOT_DISPOSABLE)
-        val ourApplicationField: Field = ApplicationManager::class.java.getDeclaredField("ourApplication")
-        ourApplicationField.isAccessible = true
-        ourApplicationField.set(null, null)
+        KotlinCoreEnvironment.resetApplicationManager()
     }
 }
 

compiler/tests-common/tests/org/jetbrains/kotlin/test/testFramework/TestApplicationUtil.kt

@@ -6,9 +6,8 @@
 package org.jetbrains.kotlin.test.testFramework
 
 import com.intellij.openapi.application.Application
-import com.intellij.openapi.application.ApplicationManager
+import org.jetbrains.kotlin.cli.jvm.compiler.KotlinCoreEnvironment
 import org.jetbrains.kotlin.utils.rethrow
-import java.lang.reflect.Field
 
 fun resetApplicationToNull(old: Application?) {
     if (old != null) return
@@ -17,9 +16,7 @@ fun resetApplicationToNull(old: Application?) {
 
 fun resetApplicationToNull() {
     try {
-        val ourApplicationField: Field = ApplicationManager::class.java.getDeclaredField("ourApplication")
-        ourApplicationField.setAccessible(true)
-        ourApplicationField.set(null, null)
+        KotlinCoreEnvironment.resetApplicationManager()
     } catch (e: Exception) {
         throw rethrow(e)
     }