preserve folding model consistency on document change - remove fold regions which become equal

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

@@ -19,6 +19,8 @@ import com.intellij.openapi.editor.*;
 import com.intellij.openapi.util.Key;
 import com.intellij.util.ArrayUtil;
 import com.intellij.util.containers.ContainerUtil;
+import gnu.trove.THashSet;
+import gnu.trove.TObjectHashingStrategy;
 import org.jetbrains.annotations.NotNull;
 import org.jetbrains.annotations.Nullable;
 
@@ -47,6 +49,18 @@ abstract class FoldRegionsTree {
   };
   private static final Comparator<? super FoldRegion> BY_END_OFFSET_REVERSE = Collections.reverseOrder(BY_END_OFFSET);
 
+  private static final TObjectHashingStrategy<FoldRegion> OFFSET_BASED_HASHING_STRATEGY = new TObjectHashingStrategy<FoldRegion>() {
+    @Override
+    public int computeHashCode(FoldRegion o) {
+      return o.getStartOffset() * 31 + o.getEndOffset();
+    }
+
+    @Override
+    public boolean equals(FoldRegion o1, FoldRegion o2) {
+      return o1.getStartOffset() == o2.getStartOffset() && o1.getEndOffset() == o2.getEndOffset();
+    }
+  };
+  
   void clear() {
     clearCachedValues();
 
@@ -67,11 +81,16 @@ abstract class FoldRegionsTree {
     List<FoldRegion> topLevels = new ArrayList<FoldRegion>(myRegions.size() / 2);
     List<FoldRegion> visible = new ArrayList<FoldRegion>(myRegions.size());
     List<FoldRegion> allValid = new ArrayList<FoldRegion>(myRegions.size());
+    Set<FoldRegion> distinctRegions = new THashSet<FoldRegion>(myRegions.size(), OFFSET_BASED_HASHING_STRATEGY);
     FoldRegion currentCollapsed = null;
     for (FoldRegion region : myRegions) {
       if (!region.isValid()) {
         continue;
       }
+      if (!distinctRegions.add(region)) {
+        region.dispose();
+        continue;
+      }
 
       allValid.add(region);
     }
@@ -134,9 +153,11 @@ abstract class FoldRegionsTree {
       rebuild();
       return;
     }
+    
+    Set<FoldRegion> distinctRegions = new THashSet<FoldRegion>(visibleRegions.length, OFFSET_BASED_HASHING_STRATEGY);
 
     for (FoldRegion foldRegion : visibleRegions) {
-      if (!foldRegion.isValid()) {
+      if (!foldRegion.isValid() || !distinctRegions.add(foldRegion)) {
         rebuild();
         return;
       }

platform/platform-tests/testSrc/com/intellij/openapi/editor/FoldingTest.java

@@ -22,6 +22,7 @@ import com.intellij.testFramework.PlatformTestCase;
 import com.intellij.testFramework.TestFileType;
 
 import static org.junit.Assert.assertArrayEquals;
+import static org.junit.Assert.assertTrue;
 
 /**
  * @author max
@@ -195,4 +196,24 @@ public class FoldingTest extends AbstractEditorTest {
     
     assertTrue(myModel.isOffsetCollapsed(5));
   }
+  
+  public void testIdenticalRegionsAreRemoved() {
+    addFoldRegion(0, 5, "...");
+    addFoldRegion(0, 4, "...");
+    assertNumberOfValidFoldRegions(2);
+    
+    myEditor.getDocument().deleteString(4, 5);
+
+    assertNumberOfValidFoldRegions(1);
+  }
+
+  private void assertNumberOfValidFoldRegions(int expectedValue) {
+    int actualValue = 0;
+    for (FoldRegion region : myModel.getAllFoldRegions()) {
+      if (region.isValid()) {
+        actualValue++;
+      }
+    }
+    assertEquals(expectedValue, actualValue);
+  }
 }