bring back the API to mute highlighters in collapsed fold region

platform/diff-impl/src/com/intellij/diff/tools/util/FoldingModelSupport.java

@@ -17,7 +17,6 @@ import com.intellij.openapi.editor.ex.DocumentEx;
 import com.intellij.openapi.editor.ex.EditorEx;
 import com.intellij.openapi.editor.ex.FoldingListener;
 import com.intellij.openapi.editor.ex.FoldingModelEx;
-import com.intellij.openapi.editor.impl.view.EditorPainter;
 import com.intellij.openapi.editor.markup.RangeHighlighter;
 import com.intellij.openapi.util.BooleanGetter;
 import com.intellij.openapi.util.Key;
@@ -209,7 +208,7 @@ public class FoldingModelSupport {
     FoldRegion value = editor.getFoldingModel().addFoldRegion(startOffset, endOffset, PLACEHOLDER);
     if (value != null) {
       value.setExpanded(expanded);
-      EditorPainter.muteInnerHighlighters(value);
+      value.setInnerHighlightersMuted(true);
     }
     return value;
   }

platform/editor-ui-api/src/com/intellij/openapi/editor/FoldRegion.java

@@ -41,4 +41,17 @@ public interface FoldRegion extends RangeMarker {
   FoldingGroup getGroup();
 
   boolean shouldNeverExpand();
+
+  /**
+   * If inner highlighters are muted for a collapsed fold region, there will not be a visual indication
+   * that region contains certain highlighters inside. By default such indication is added.
+   * <p>
+   * See also {@code isVisibleIfFolded()} method in {@code com.intellij.openapi.editor.ex.RangeHighlighterEx} class.
+   */
+  default void setInnerHighlightersMuted(boolean value) {}
+
+  /**
+   * @see #setInnerHighlightersMuted(boolean)
+   */
+  default boolean areInnerHighlightersMuted() { return false; }
 }

platform/editor-ui-ex/src/com/intellij/openapi/editor/ex/RangeHighlighterEx.java

@@ -2,6 +2,7 @@
 
 package com.intellij.openapi.editor.ex;
 
+import com.intellij.openapi.editor.FoldRegion;
 import com.intellij.openapi.editor.markup.RangeHighlighter;
 import com.intellij.openapi.editor.markup.TextAttributes;
 import org.jetbrains.annotations.NotNull;
@@ -27,6 +28,8 @@ public interface RangeHighlighterEx extends RangeHighlighter, RangeMarkerEx {
   /**
    * If {@code true}, there will be a visual indication that this highlighter is present inside a collapsed fold region.
    * By default it won't happen, use {@link #setVisibleIfFolded(boolean)} to change it.
+   *
+   * @see FoldRegion#setInnerHighlightersMuted(boolean)
    */
   boolean isVisibleIfFolded();
 

platform/platform-impl/src/com/intellij/openapi/editor/impl/FoldRegionImpl.java

@@ -8,11 +8,14 @@ import com.intellij.openapi.editor.FoldRegion;
 import com.intellij.openapi.editor.FoldingGroup;
 import com.intellij.openapi.editor.event.DocumentEvent;
 import com.intellij.openapi.util.Getter;
+import com.intellij.openapi.util.Key;
 import com.intellij.util.DocumentUtil;
 import org.jetbrains.annotations.NotNull;
 import org.jetbrains.annotations.Nullable;
 
 class FoldRegionImpl extends RangeMarkerImpl implements FoldRegion, Getter<FoldRegionImpl> {
+  private static final Key<Boolean> MUTE_INNER_HIGHLIGHTERS = Key.create("mute.inner.highlighters");
+
   private boolean myIsExpanded;
   private final EditorImpl myEditor;
   private final String myPlaceholderText;
@@ -155,6 +158,16 @@ class FoldRegionImpl extends RangeMarkerImpl implements FoldRegion, Getter<FoldR
     }
   }
 
+  @Override
+  public void setInnerHighlightersMuted(boolean value) {
+    putUserData(MUTE_INNER_HIGHLIGHTERS, value ? Boolean.TRUE : null);
+  }
+
+  @Override
+  public boolean areInnerHighlightersMuted() {
+    return Boolean.TRUE.equals(getUserData(MUTE_INNER_HIGHLIGHTERS));
+  }
+
   @Override
   public void dispose() {
     myEditor.getFoldingModel().removeRegionFromTree(this);

platform/platform-impl/src/com/intellij/openapi/editor/impl/view/EditorPainter.java

@@ -510,7 +510,7 @@ public class EditorPainter implements TextDrawingCallback {
 
   @Nullable
   private TextAttributes getInnerHighlighterAttributes(@NotNull FoldRegion region) {
-    if (areInnerHighlightersMuted(region)) return null;
+    if (region.areInnerHighlightersMuted()) return null;
     List<RangeHighlighterEx> innerHighlighters = new ArrayList<>();
     collectVisibleInnerHighlighters(region, myEditor.getMarkupModel(), innerHighlighters);
     collectVisibleInnerHighlighters(region, myEditor.getFilteredDocumentMarkupModel(), innerHighlighters);
@@ -1049,22 +1049,6 @@ public class EditorPainter implements TextDrawingCallback {
     }
   }
 
-
-  /**
-   * If {@code Boolean.TRUE} value is set for this key on a collapsed fold region (see {@link #putUserData(Key, Object)}),
-   * there will not be a visual indication that region contains certain highlighters inside. By default such indication is added.
-   *
-   * @see RangeHighlighterImpl#VISIBLE_IF_FOLDED
-   */
-  private static final Key<Boolean> MUTE_INNER_HIGHLIGHTERS = Key.create("mute.inner.highlighters");
-
-  public static void muteInnerHighlighters(@NotNull FoldRegion value) {
-    value.putUserData(MUTE_INNER_HIGHLIGHTERS, Boolean.TRUE);
-  }
-  private static boolean areInnerHighlightersMuted(@NotNull FoldRegion region) {
-    return Boolean.TRUE.equals(region.getUserData(MUTE_INNER_HIGHLIGHTERS));
-  }
-
   private interface MarginWidthConsumer {
     void process(float width);
   }