diff --git a/platform/lang-impl/src/com/intellij/analysis/problemsView/ProblemsCollector.kt b/platform/lang-impl/src/com/intellij/analysis/problemsView/ProblemsCollector.kt
index a6a480199f5e..721cad5b202d 100644
--- a/platform/lang-impl/src/com/intellij/analysis/problemsView/ProblemsCollector.kt
+++ b/platform/lang-impl/src/com/intellij/analysis/problemsView/ProblemsCollector.kt
@@ -1,10 +1,17 @@
 // Copyright 2000-2020 JetBrains s.r.o. Use of this source code is governed by the Apache 2.0 license that can be found in the LICENSE file.
 package com.intellij.analysis.problemsView
 
+import com.intellij.openapi.project.Project
 import com.intellij.openapi.vfs.VirtualFile
 
 interface ProblemsCollector : ProblemsListener {
+  companion object {
+    @JvmStatic
+    fun getInstance(project: Project) = project.getService(ProblemsCollector::class.java)!!
+  }
+
   fun getProblemCount(): Int
+  fun getProblemFiles(): Collection<VirtualFile>
 
   fun getFileProblemCount(file: VirtualFile): Int
   fun getFileProblems(file: VirtualFile): Collection<Problem>
diff --git a/platform/lang-impl/src/com/intellij/analysis/problemsView/ProblemsListener.kt b/platform/lang-impl/src/com/intellij/analysis/problemsView/ProblemsListener.kt
index 83f2f6b34965..92437cce0437 100644
--- a/platform/lang-impl/src/com/intellij/analysis/problemsView/ProblemsListener.kt
+++ b/platform/lang-impl/src/com/intellij/analysis/problemsView/ProblemsListener.kt
@@ -1,14 +1,7 @@
 // Copyright 2000-2020 JetBrains s.r.o. Use of this source code is governed by the Apache 2.0 license that can be found in the LICENSE file.
 package com.intellij.analysis.problemsView
 
-import com.intellij.openapi.project.Project
-
 interface ProblemsListener {
-  companion object {
-    @JvmStatic
-    fun getInstance(project: Project) = project.getService(ProblemsListener::class.java)!!
-  }
-
   fun problemAppeared(problem: Problem)
   fun problemDisappeared(problem: Problem)
   fun problemUpdated(problem: Problem)
diff --git a/platform/lang-impl/src/com/intellij/analysis/problemsView/toolWindow/HighlightingErrorsProvider.kt b/platform/lang-impl/src/com/intellij/analysis/problemsView/toolWindow/HighlightingErrorsProvider.kt
index 998357b2d8f7..2998be8a639d 100644
--- a/platform/lang-impl/src/com/intellij/analysis/problemsView/toolWindow/HighlightingErrorsProvider.kt
+++ b/platform/lang-impl/src/com/intellij/analysis/problemsView/toolWindow/HighlightingErrorsProvider.kt
@@ -1,7 +1,7 @@
 // Copyright 2000-2020 JetBrains s.r.o. Use of this source code is governed by the Apache 2.0 license that can be found in the LICENSE file.
 package com.intellij.analysis.problemsView.toolWindow
 
-import com.intellij.analysis.problemsView.ProblemsListener
+import com.intellij.analysis.problemsView.ProblemsCollector
 import com.intellij.analysis.problemsView.ProblemsProvider
 import com.intellij.codeInsight.problems.WolfTheProblemSolverImpl
 import com.intellij.lang.annotation.HighlightSeverity.ERROR
@@ -30,7 +30,7 @@ internal class HighlightingErrorsProvider(override val project: Project) : Probl
   override fun problemsAppeared(file: VirtualFile) {
     synchronized(watchers) {
       watchers.computeIfAbsent(file) { file ->
-        HighlightingWatcher(this, ProblemsListener.getInstance(project), file, ERROR.myVal).also { watcher ->
+        HighlightingWatcher(this, ProblemsCollector.getInstance(project), file, ERROR.myVal).also { watcher ->
           Disposer.register(this, watcher)
         }
       }
diff --git a/platform/lang-impl/src/com/intellij/analysis/problemsView/toolWindow/ProjectErrorsCollector.kt b/platform/lang-impl/src/com/intellij/analysis/problemsView/toolWindow/ProjectErrorsCollector.kt
index 8759df9be1b2..38a9d47cf2ac 100644
--- a/platform/lang-impl/src/com/intellij/analysis/problemsView/toolWindow/ProjectErrorsCollector.kt
+++ b/platform/lang-impl/src/com/intellij/analysis/problemsView/toolWindow/ProjectErrorsCollector.kt
@@ -10,13 +10,17 @@ import com.intellij.openapi.vfs.VirtualFile
 import com.intellij.ui.AppUIUtil
 import java.util.concurrent.atomic.AtomicInteger
 
-internal class ProjectErrorsCollector(val project: Project) : ProblemsCollector {
+private class ProjectErrorsCollector(val project: Project) : ProblemsCollector {
   private val fileProblems = mutableMapOf<VirtualFile, MutableSet<FileProblem>>()
   private val otherProblems = mutableSetOf<Problem>()
   private val problemCount = AtomicInteger()
 
   override fun getProblemCount() = problemCount.get()
 
+  override fun getProblemFiles() = synchronized(fileProblems) {
+    fileProblems.keys.toSet()
+  }
+
   override fun getFileProblemCount(file: VirtualFile) = synchronized(fileProblems) {
     fileProblems[file]?.size ?: 0
   }
@@ -67,17 +71,17 @@ internal class ProjectErrorsCollector(val project: Project) : ProblemsCollector
   private fun notify(problem: Problem, state: SetUpdateState) {
     when (state) {
       SetUpdateState.ADDED -> {
-        getProjectErrors()?.addProblem(problem)
+        getProblemsListener()?.problemAppeared(problem)
         val emptyBefore = problemCount.getAndIncrement() == 0
         if (emptyBefore) updateToolWindowIcon()
       }
       SetUpdateState.REMOVED -> {
-        getProjectErrors()?.removeProblem(problem)
+        getProblemsListener()?.problemDisappeared(problem)
         val emptyAfter = problemCount.decrementAndGet() == 0
         if (emptyAfter) updateToolWindowIcon()
       }
       SetUpdateState.UPDATED -> {
-        getProjectErrors()?.updateProblem(problem)
+        getProblemsListener()?.problemUpdated(problem)
       }
       SetUpdateState.IGNORED -> {
       }
@@ -94,7 +98,7 @@ internal class ProjectErrorsCollector(val project: Project) : ProblemsCollector
     else -> Toolwindows.ToolWindowProblems
   }
 
-  private fun getProjectErrors() = ProblemsView.getToolWindow(project)
+  private fun getProblemsListener() = ProblemsView.getToolWindow(project)
     ?.contentManagerIfCreated
     ?.contents
     ?.mapNotNull { it.component as? ProjectErrorsPanel }
diff --git a/platform/lang-impl/src/com/intellij/analysis/problemsView/toolWindow/ProjectErrorsPanel.kt b/platform/lang-impl/src/com/intellij/analysis/problemsView/toolWindow/ProjectErrorsPanel.kt
index b9c8e138ef8a..318f77b09d2d 100644
--- a/platform/lang-impl/src/com/intellij/analysis/problemsView/toolWindow/ProjectErrorsPanel.kt
+++ b/platform/lang-impl/src/com/intellij/analysis/problemsView/toolWindow/ProjectErrorsPanel.kt
@@ -3,11 +3,12 @@ package com.intellij.analysis.problemsView.toolWindow
 
 import com.intellij.analysis.problemsView.FileProblem
 import com.intellij.analysis.problemsView.Problem
+import com.intellij.analysis.problemsView.ProblemsListener
 import com.intellij.openapi.actionSystem.ToggleOptionAction.Option
 import com.intellij.openapi.project.Project
 
 internal class ProjectErrorsPanel(project: Project, state: ProblemsViewState)
-  : ProblemsViewPanel(project, state) {
+  : ProblemsViewPanel(project, state), ProblemsListener {
 
   private val root = Root(this)
 
@@ -20,15 +21,15 @@ internal class ProjectErrorsPanel(project: Project, state: ProblemsViewState)
   override fun getSortFoldersFirst(): Option? = null
   override fun getSortBySeverity(): Option? = null
 
-  fun addProblem(problem: Problem) {
+  override fun problemAppeared(problem: Problem) {
     if (problem is FileProblem) root.addProblems(problem.file, problem)
   }
 
-  fun removeProblem(problem: Problem) {
+  override fun problemDisappeared(problem: Problem) {
     if (problem is FileProblem) root.removeProblems(problem.file, problem)
   }
 
-  fun updateProblem(problem: Problem) {
+  override fun problemUpdated(problem: Problem) {
     if (problem is FileProblem) root.updateProblem(problem.file, problem)
   }
 }
diff --git a/platform/platform-resources/src/META-INF/LangExtensions.xml b/platform/platform-resources/src/META-INF/LangExtensions.xml
index 29e51347e0cf..fbdb0fc82be9 100644
--- a/platform/platform-resources/src/META-INF/LangExtensions.xml
+++ b/platform/platform-resources/src/META-INF/LangExtensions.xml
@@ -945,7 +945,7 @@
                         serviceImplementation="com.intellij.codeInsight.template.TemplateBuilderFactoryImpl"/>
 
     <projectService serviceImplementation="com.intellij.analysis.problemsView.toolWindow.HighlightingErrorsProvider"/>
-    <projectService serviceInterface="com.intellij.analysis.problemsView.ProblemsListener"
+    <projectService serviceInterface="com.intellij.analysis.problemsView.ProblemsCollector"
                     serviceImplementation="com.intellij.analysis.problemsView.toolWindow.ProjectErrorsCollector"/>
 
     <projectViewPane implementation="com.intellij.ide.scopeView.ScopeViewPane"/>