diff --git a/java/idea-ui/testSrc/com/intellij/facet/mock/MockFacetDetector.java b/java/idea-ui/testSrc/com/intellij/facet/mock/MockFacetDetector.java
index 9fd63667e067..52a69634c43b 100644
--- a/java/idea-ui/testSrc/com/intellij/facet/mock/MockFacetDetector.java
+++ b/java/idea-ui/testSrc/com/intellij/facet/mock/MockFacetDetector.java
@@ -43,14 +43,14 @@ public final class MockFacetDetector extends FacetBasedFrameworkDetector<MockFac
 
   @NotNull
   @Override
-  public List<Pair<MockFacetConfiguration, Collection<VirtualFile>>> createConfigurations(@NotNull Collection<VirtualFile> files,
-                                                                     @NotNull Collection<MockFacetConfiguration> existentFacetConfigurations) {
+  public List<Pair<MockFacetConfiguration, Collection<VirtualFile>>> createConfigurations(@NotNull Collection<? extends VirtualFile> files,
+                                                                                          @NotNull Collection<? extends MockFacetConfiguration> existentFacetConfigurations) {
 
     return doDetect(files, existentFacetConfigurations);
   }
 
-  public static List<Pair<MockFacetConfiguration, Collection<VirtualFile>>> doDetect(Collection<VirtualFile> files,
-                                                                                     Collection<MockFacetConfiguration> existentFacetConfigurations) {
+  public static List<Pair<MockFacetConfiguration, Collection<VirtualFile>>> doDetect(Collection<? extends VirtualFile> files,
+                                                                                     Collection<? extends MockFacetConfiguration> existentFacetConfigurations) {
     final List<Pair<MockFacetConfiguration, Collection<VirtualFile>>> result = new ArrayList<>();
     MultiMap<String, VirtualFile> filesByName = new MultiMap<>();
     for (VirtualFile file : files) {
@@ -79,7 +79,7 @@ public final class MockFacetDetector extends FacetBasedFrameworkDetector<MockFac
 
   @Nullable
   private static MockFacetConfiguration detectConfiguration(final String fileName,
-                                                           final Collection<MockFacetConfiguration> existentFacetConfigurations) {
+                                                           final Collection<? extends MockFacetConfiguration> existentFacetConfigurations) {
     for (MockFacetConfiguration configuration : existentFacetConfigurations) {
       if (fileName.equals(configuration.getData())) {
         return null;
diff --git a/java/idea-ui/testSrc/com/intellij/facet/mock/MockSubFacetDetector.java b/java/idea-ui/testSrc/com/intellij/facet/mock/MockSubFacetDetector.java
index fbae1793545b..b74a3803ecd9 100644
--- a/java/idea-ui/testSrc/com/intellij/facet/mock/MockSubFacetDetector.java
+++ b/java/idea-ui/testSrc/com/intellij/facet/mock/MockSubFacetDetector.java
@@ -35,8 +35,8 @@ public final class MockSubFacetDetector extends FacetBasedFrameworkDetector<Face
 
   @NotNull
   @Override
-  public List<Pair<MockFacetConfiguration, Collection<VirtualFile>>> createConfigurations(@NotNull Collection<VirtualFile> files,
-                                                                                          @NotNull Collection<MockFacetConfiguration> existentFacetConfigurations) {
+  public List<Pair<MockFacetConfiguration, Collection<VirtualFile>>> createConfigurations(@NotNull Collection<? extends VirtualFile> files,
+                                                                                          @NotNull Collection<? extends MockFacetConfiguration> existentFacetConfigurations) {
     return MockFacetDetector.doDetect(files, existentFacetConfigurations);
   }
 
@@ -49,7 +49,7 @@ public final class MockSubFacetDetector extends FacetBasedFrameworkDetector<Face
   @Override
   public boolean isSuitableUnderlyingFacetConfiguration(FacetConfiguration underlying,
                                                         MockFacetConfiguration configuration,
-                                                        Set<VirtualFile> files) {
+                                                        Set<? extends VirtualFile> files) {
     return underlying instanceof MockFacetConfiguration && ("sub-" + ((MockFacetConfiguration)underlying).getData()).equals(configuration.getData());
   }
 
diff --git a/java/java-impl/src/com/intellij/refactoring/changeSignature/JavaChangeSignatureUsageProcessor.java b/java/java-impl/src/com/intellij/refactoring/changeSignature/JavaChangeSignatureUsageProcessor.java
index c293f9cbb77b..b0f0c250cc65 100644
--- a/java/java-impl/src/com/intellij/refactoring/changeSignature/JavaChangeSignatureUsageProcessor.java
+++ b/java/java-impl/src/com/intellij/refactoring/changeSignature/JavaChangeSignatureUsageProcessor.java
@@ -700,7 +700,7 @@ public class JavaChangeSignatureUsageProcessor implements ChangeSignatureUsagePr
   }
 
   @Override
-  public void registerConflictResolvers(List<ResolveSnapshotProvider.ResolveSnapshot> snapshots,
+  public void registerConflictResolvers(List<? super ResolveSnapshotProvider.ResolveSnapshot> snapshots,
                                         @NotNull ResolveSnapshotProvider resolveSnapshotProvider,
                                         UsageInfo[] usages, ChangeInfo changeInfo) {
     snapshots.add(resolveSnapshotProvider.createSnapshot(changeInfo.getMethod()));
diff --git a/platform/indexing-api/src/com/intellij/util/indexing/FileBasedIndex.java b/platform/indexing-api/src/com/intellij/util/indexing/FileBasedIndex.java
index af67cc7d035e..9a1ef2b9350a 100644
--- a/platform/indexing-api/src/com/intellij/util/indexing/FileBasedIndex.java
+++ b/platform/indexing-api/src/com/intellij/util/indexing/FileBasedIndex.java
@@ -275,7 +275,7 @@ public abstract class FileBasedIndex {
    * which optimized to perform several queries for different indexes.
    */
   @ApiStatus.Experimental
-  public boolean processFilesContainingAllKeys(@NotNull Collection<AllKeysQuery<?, ?>> queries,
+  public boolean processFilesContainingAllKeys(@NotNull Collection<? extends AllKeysQuery<?, ?>> queries,
                                                @NotNull GlobalSearchScope filter,
                                                @NotNull Processor<? super VirtualFile> processor) {
     throw new UnsupportedOperationException();
diff --git a/platform/lang-api/src/com/intellij/facet/ui/FacetBasedFrameworkSupportProvider.java b/platform/lang-api/src/com/intellij/facet/ui/FacetBasedFrameworkSupportProvider.java
index 120a7d23b7c7..bf7363b27bd4 100644
--- a/platform/lang-api/src/com/intellij/facet/ui/FacetBasedFrameworkSupportProvider.java
+++ b/platform/lang-api/src/com/intellij/facet/ui/FacetBasedFrameworkSupportProvider.java
@@ -136,10 +136,9 @@ public abstract class FacetBasedFrameworkSupportProvider<F extends Facet> extend
 
   /**
    * Override to e.g. add libraries to artifacts.
-   *
-   * @param module         Module.
+   *  @param module         Module.
    * @param addedLibraries Framework libraries.
    */
-  public void processAddedLibraries(final Module module, final List<Library> addedLibraries) {
+  public void processAddedLibraries(final Module module, final List<? extends Library> addedLibraries) {
   }
 }
diff --git a/platform/lang-api/src/com/intellij/framework/detection/FacetBasedFrameworkDetector.java b/platform/lang-api/src/com/intellij/framework/detection/FacetBasedFrameworkDetector.java
index 6da8c589523a..82e4eabbc914 100644
--- a/platform/lang-api/src/com/intellij/framework/detection/FacetBasedFrameworkDetector.java
+++ b/platform/lang-api/src/com/intellij/framework/detection/FacetBasedFrameworkDetector.java
@@ -56,11 +56,11 @@ public abstract class FacetBasedFrameworkDetector<F extends Facet, C extends Fac
    * @return configurations with corresponding files
    */
   @NotNull
-  public List<Pair<C,Collection<VirtualFile>>> createConfigurations(@NotNull Collection<VirtualFile> files,
-                                                                    @NotNull Collection<C> existentFacetConfigurations) {
+  public List<Pair<C,Collection<VirtualFile>>> createConfigurations(@NotNull Collection<? extends VirtualFile> files,
+                                                                    @NotNull Collection<? extends C> existentFacetConfigurations) {
     final C configuration = createConfiguration(files);
     if (configuration != null) {
-      return Collections.singletonList(Pair.create(configuration, files));
+      return Collections.singletonList(Pair.create(configuration, (Collection<VirtualFile>)files));
     }
     return Collections.emptyList();
   }
@@ -71,7 +71,7 @@ public abstract class FacetBasedFrameworkDetector<F extends Facet, C extends Fac
    * @return configuration for detected facet
    */
   @Nullable
-  protected C createConfiguration(Collection<VirtualFile> files) {
+  protected C createConfiguration(Collection<? extends VirtualFile> files) {
     return getFacetType().createDefaultConfiguration();
   }
 
@@ -79,7 +79,7 @@ public abstract class FacetBasedFrameworkDetector<F extends Facet, C extends Fac
   }
 
   @Override
-  public List<? extends DetectedFrameworkDescription> detect(@NotNull Collection<VirtualFile> newFiles,
+  public List<? extends DetectedFrameworkDescription> detect(@NotNull Collection<? extends VirtualFile> newFiles,
                                                              @NotNull FrameworkDetectionContext context) {
     return context.createDetectedFacetDescriptions(this, newFiles);
   }
@@ -102,7 +102,7 @@ public abstract class FacetBasedFrameworkDetector<F extends Facet, C extends Fac
     return underlyingTypeId != null ? createFrameworkType(FacetTypeRegistry.getInstance().findFacetType(underlyingTypeId)) : null;
   }
 
-  public boolean isSuitableUnderlyingFacetConfiguration(FacetConfiguration underlying, C configuration, Set<VirtualFile> files) {
+  public boolean isSuitableUnderlyingFacetConfiguration(FacetConfiguration underlying, C configuration, Set<? extends VirtualFile> files) {
     return true;
   }
 
diff --git a/platform/lang-api/src/com/intellij/framework/detection/FrameworkDetector.java b/platform/lang-api/src/com/intellij/framework/detection/FrameworkDetector.java
index 0d80891c640e..78093f6244ec 100644
--- a/platform/lang-api/src/com/intellij/framework/detection/FrameworkDetector.java
+++ b/platform/lang-api/src/com/intellij/framework/detection/FrameworkDetector.java
@@ -67,7 +67,7 @@ public abstract class FrameworkDetector {
    * @param context provides
    * @return list of detected framework descriptions (it may be empty)
    */
-  public abstract List<? extends DetectedFrameworkDescription> detect(@NotNull Collection<VirtualFile> newFiles,
+  public abstract List<? extends DetectedFrameworkDescription> detect(@NotNull Collection<? extends VirtualFile> newFiles,
                                                                       @NotNull FrameworkDetectionContext context);
 
   /**
diff --git a/platform/lang-api/src/com/intellij/refactoring/changeSignature/ChangeSignatureUsageProcessor.java b/platform/lang-api/src/com/intellij/refactoring/changeSignature/ChangeSignatureUsageProcessor.java
index 31f8dc89f721..1c4b6236680f 100644
--- a/platform/lang-api/src/com/intellij/refactoring/changeSignature/ChangeSignatureUsageProcessor.java
+++ b/platform/lang-api/src/com/intellij/refactoring/changeSignature/ChangeSignatureUsageProcessor.java
@@ -45,8 +45,8 @@ public interface ChangeSignatureUsageProcessor {
 
   boolean setupDefaultValues(ChangeInfo changeInfo, Ref<UsageInfo[]> refUsages, Project project);
 
-  void registerConflictResolvers(List<ResolveSnapshotProvider.ResolveSnapshot> snapshots,
+  void registerConflictResolvers(List<? super ResolveSnapshotProvider.ResolveSnapshot> snapshots,
                                  @NotNull ResolveSnapshotProvider resolveSnapshotProvider,
-                                 UsageInfo[] usages, 
+                                 UsageInfo[] usages,
                                  ChangeInfo changeInfo);
 }
diff --git a/platform/lang-api/src/com/intellij/refactoring/listeners/RefactoringEventData.java b/platform/lang-api/src/com/intellij/refactoring/listeners/RefactoringEventData.java
index 33e36d9ea513..352822eeb3f0 100644
--- a/platform/lang-api/src/com/intellij/refactoring/listeners/RefactoringEventData.java
+++ b/platform/lang-api/src/com/intellij/refactoring/listeners/RefactoringEventData.java
@@ -30,7 +30,7 @@ public class RefactoringEventData extends UserDataHolderBase {
   public static final Key<PsiElement> PSI_ELEMENT_KEY = Key.create("element");
   public static final Key<String[]> STRING_PROPERTIES = Key.create("stringProperties");
   public static final Key<PsiElement[]> PSI_ELEMENT_ARRAY_KEY = Key.create("elementArray");
-  public static final Key<Collection<UsageInfo>> USAGE_INFOS_KEY = Key.create("usageInfos");
+  public static final Key<Collection<? extends UsageInfo>> USAGE_INFOS_KEY = Key.create("usageInfos");
 
   public void addElement(PsiElement element) {
     putUserData(PSI_ELEMENT_KEY, element);
@@ -44,7 +44,7 @@ public class RefactoringEventData extends UserDataHolderBase {
     addElements(elements);
   }
   
-  public void addElements(Collection<PsiElement> elements) {
+  public void addElements(Collection<? extends PsiElement> elements) {
     putUserData(PSI_ELEMENT_ARRAY_KEY, elements.toArray(PsiElement.EMPTY_ARRAY));
   }
   
@@ -52,7 +52,7 @@ public class RefactoringEventData extends UserDataHolderBase {
     putUserData(PSI_ELEMENT_ARRAY_KEY, elements);
   }
 
-  public void addUsages(Collection<UsageInfo> usageInfos) {
+  public void addUsages(Collection<? extends UsageInfo> usageInfos) {
     putUserData(USAGE_INFOS_KEY, usageInfos);
   }
 
diff --git a/platform/lang-impl/src/com/intellij/util/indexing/EntityIndexingService.java b/platform/lang-impl/src/com/intellij/util/indexing/EntityIndexingService.java
index 437d5268189b..a8783bcb576f 100644
--- a/platform/lang-impl/src/com/intellij/util/indexing/EntityIndexingService.java
+++ b/platform/lang-impl/src/com/intellij/util/indexing/EntityIndexingService.java
@@ -18,5 +18,5 @@ public interface EntityIndexingService {
     return ApplicationManager.getApplication().getService(EntityIndexingService.class);
   }
 
-  void indexChanges(@NotNull Project project, @NotNull List<RootsChangeIndexingInfo> changes);
+  void indexChanges(@NotNull Project project, @NotNull List<? extends RootsChangeIndexingInfo> changes);
 }
diff --git a/platform/lang-impl/src/com/intellij/util/indexing/EntityIndexingServiceImpl.java b/platform/lang-impl/src/com/intellij/util/indexing/EntityIndexingServiceImpl.java
index 85ad13a373cc..50c7b57109ab 100644
--- a/platform/lang-impl/src/com/intellij/util/indexing/EntityIndexingServiceImpl.java
+++ b/platform/lang-impl/src/com/intellij/util/indexing/EntityIndexingServiceImpl.java
@@ -27,7 +27,7 @@ class EntityIndexingServiceImpl implements EntityIndexingService {
   private static final Logger LOG = Logger.getInstance(EntityIndexingServiceImpl.class);
 
   @Override
-  public void indexChanges(@NotNull Project project, @NotNull List<RootsChangeIndexingInfo> changes) {
+  public void indexChanges(@NotNull Project project, @NotNull List<? extends RootsChangeIndexingInfo> changes) {
     if (!(FileBasedIndex.getInstance() instanceof FileBasedIndexImpl)) return;
     if (Registry.is("indexing.full.rescan.on.workspace.model.changes")) {
       DumbService.getInstance(project).queueTask(new UnindexedFilesUpdater(project, "Reindex due to registry setting"));
@@ -130,7 +130,7 @@ class EntityIndexingServiceImpl implements EntityIndexingService {
     return iterators;
   }
 
-  private static @NotNull List<IndexableFilesIterator> mergeIterators(List<IndexableFilesIterator> iterators) {
+  private static @NotNull List<IndexableFilesIterator> mergeIterators(List<? extends IndexableFilesIterator> iterators) {
     List<IndexableFilesIterator> result = new ArrayList<>(iterators.size());
     Collection<ModuleIndexableFilesIteratorImpl> rootIterators = new ArrayList<>();
     Set<IndexableSetOrigin> origins = new HashSet<>();
diff --git a/platform/lang-impl/src/com/intellij/util/indexing/FileBasedIndexEx.java b/platform/lang-impl/src/com/intellij/util/indexing/FileBasedIndexEx.java
index 9a9875a1c4b6..9449a3482fae 100644
--- a/platform/lang-impl/src/com/intellij/util/indexing/FileBasedIndexEx.java
+++ b/platform/lang-impl/src/com/intellij/util/indexing/FileBasedIndexEx.java
@@ -362,7 +362,7 @@ public abstract class FileBasedIndexEx extends FileBasedIndex {
     return set != null && processVirtualFiles(set, filter, processor);
   }
 
-  private boolean processFilesContainingAllKeysInPhysicalFiles(@NotNull Collection<AllKeysQuery<?, ?>> queries,
+  private boolean processFilesContainingAllKeysInPhysicalFiles(@NotNull Collection<? extends AllKeysQuery<?, ?>> queries,
                                                                @NotNull GlobalSearchScope filter,
                                                                Processor<? super VirtualFile> processor,
                                                                IdFilter filesSet) {
@@ -404,7 +404,7 @@ public abstract class FileBasedIndexEx extends FileBasedIndex {
   }
 
   @Override
-  public boolean processFilesContainingAllKeys(@NotNull Collection<AllKeysQuery<?, ?>> queries,
+  public boolean processFilesContainingAllKeys(@NotNull Collection<? extends AllKeysQuery<?, ?>> queries,
                                                @NotNull GlobalSearchScope filter,
                                                @NotNull Processor<? super VirtualFile> processor) {
     Project project = filter.getProject();
diff --git a/plugins/groovy/src/org/jetbrains/plugins/groovy/refactoring/changeSignature/GrChangeSignatureUsageProcessor.java b/plugins/groovy/src/org/jetbrains/plugins/groovy/refactoring/changeSignature/GrChangeSignatureUsageProcessor.java
index 11b87f5e4126..5932fa9639ff 100644
--- a/plugins/groovy/src/org/jetbrains/plugins/groovy/refactoring/changeSignature/GrChangeSignatureUsageProcessor.java
+++ b/plugins/groovy/src/org/jetbrains/plugins/groovy/refactoring/changeSignature/GrChangeSignatureUsageProcessor.java
@@ -166,7 +166,7 @@ public class GrChangeSignatureUsageProcessor implements ChangeSignatureUsageProc
   }
 
   @Override
-  public void registerConflictResolvers(List<ResolveSnapshotProvider.ResolveSnapshot> snapshots,
+  public void registerConflictResolvers(List<? super ResolveSnapshotProvider.ResolveSnapshot> snapshots,
                                         @NotNull ResolveSnapshotProvider resolveSnapshotProvider,
                                         UsageInfo[] usages, ChangeInfo changeInfo) {
   }
diff --git a/plugins/kotlin/idea/src/org/jetbrains/kotlin/idea/refactoring/changeSignature/KotlinChangeSignatureUsageProcessor.kt b/plugins/kotlin/idea/src/org/jetbrains/kotlin/idea/refactoring/changeSignature/KotlinChangeSignatureUsageProcessor.kt
index 4b2451b3d392..72027bdd2d0f 100644
--- a/plugins/kotlin/idea/src/org/jetbrains/kotlin/idea/refactoring/changeSignature/KotlinChangeSignatureUsageProcessor.kt
+++ b/plugins/kotlin/idea/src/org/jetbrains/kotlin/idea/refactoring/changeSignature/KotlinChangeSignatureUsageProcessor.kt
@@ -1209,7 +1209,7 @@ class KotlinChangeSignatureUsageProcessor : ChangeSignatureUsageProcessor {
     override fun setupDefaultValues(changeInfo: ChangeInfo, refUsages: Ref<Array<UsageInfo>>, project: Project) = true
 
     override fun registerConflictResolvers(
-        snapshots: List<ResolveSnapshotProvider.ResolveSnapshot>,
+        snapshots: MutableList<in ResolveSnapshotProvider.ResolveSnapshot>,
         resolveSnapshotProvider: ResolveSnapshotProvider,
         usages: Array<UsageInfo>, changeInfo: ChangeInfo
     ) {
diff --git a/python/src/com/jetbrains/python/buildout/BuildoutFrameworkDetector.java b/python/src/com/jetbrains/python/buildout/BuildoutFrameworkDetector.java
index fd60ffdcf5b2..f2102708a36e 100644
--- a/python/src/com/jetbrains/python/buildout/BuildoutFrameworkDetector.java
+++ b/python/src/com/jetbrains/python/buildout/BuildoutFrameworkDetector.java
@@ -59,7 +59,7 @@ public class BuildoutFrameworkDetector extends FacetBasedFrameworkDetector<Build
 
   @Nullable
   @Override
-  protected BuildoutFacetConfiguration createConfiguration(Collection<VirtualFile> files) {
+  protected BuildoutFacetConfiguration createConfiguration(Collection<? extends VirtualFile> files) {
     VirtualFile source = ContainerUtil.getFirstItem(files);
     LOG.info("Detecting Buildout facet for " + source.getPath());
     final VirtualFile baseDir = source.getParent();
diff --git a/python/src/com/jetbrains/python/refactoring/changeSignature/PyChangeSignatureUsageProcessor.java b/python/src/com/jetbrains/python/refactoring/changeSignature/PyChangeSignatureUsageProcessor.java
index 7afd4112710b..2e6aaedeb2f9 100644
--- a/python/src/com/jetbrains/python/refactoring/changeSignature/PyChangeSignatureUsageProcessor.java
+++ b/python/src/com/jetbrains/python/refactoring/changeSignature/PyChangeSignatureUsageProcessor.java
@@ -397,7 +397,7 @@ public class PyChangeSignatureUsageProcessor implements ChangeSignatureUsageProc
   }
 
   @Override
-  public void registerConflictResolvers(List<ResolveSnapshotProvider.ResolveSnapshot> snapshots,
+  public void registerConflictResolvers(List<? super ResolveSnapshotProvider.ResolveSnapshot> snapshots,
                                         @NotNull ResolveSnapshotProvider resolveSnapshotProvider,
                                         UsageInfo[] usages, ChangeInfo changeInfo) {
   }