IDEA-84772 Scrollbars are blinking in commit dialog when message has the same amount of lines visible in message field

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

@@ -2577,6 +2577,11 @@ public final class EditorImpl extends UserDataHolderBase implements EditorEx, Hi
         BorderEffect.paintFoldedEffect(g, foldingXStart, position.y, foldingXEnd, getLineHeight(), effectColor, effectType);
   //      myBorderEffect.collapsedFolderReached(g, this);
       }
+
+      final SoftWrap softWrap = mySoftWrapModel.getSoftWrap(clipEndOffset);
+      if (softWrap != null) {
+        mySoftWrapModel.paint(g, SoftWrapDrawingType.BEFORE_SOFT_WRAP_LINE_FEED, position.x, position.y, getLineHeight());
+      }
     }
     finally {
       iterationState.dispose();
@@ -2592,7 +2597,7 @@ public final class EditorImpl extends UserDataHolderBase implements EditorEx, Hi
     }
 
     if (KeyboardFocusManager.getCurrentKeyboardFocusManager().getFocusOwner() == myEditorComponent) {
-      // There is a possible case that placeholder text was painted and the editor gets focus now. We want to over-paint previuosly
+      // There is a possible case that placeholder text was painted and the editor gets focus now. We want to over-paint previously
       // used placeholder text then.
       myLastBackgroundColor = getBackgroundColor();
       myLastBackgroundPosition = new Point(0, 0);

platform/platform-impl/src/com/intellij/openapi/editor/impl/softwrap/mapping/SoftWrapApplianceManager.java

@@ -92,6 +92,7 @@ public class SoftWrapApplianceManager implements SoftWrapFoldingListener, Docume
    * during viewport's <code>'y'</code> coordinate adjustment on visual area width change.
    */
   private int myLastTopLeftCornerOffset = -1;
+  private int myVerticalScrollBarWidth  = -1;
 
   private VisibleAreaWidthProvider       myWidthProvider;
   private EditorTextRepresentationHelper myRepresentationHelper;
@@ -810,6 +811,31 @@ public class SoftWrapApplianceManager implements SoftWrapFoldingListener, Docume
       return recalculateSoftWraps(); // Recalculate existing dirty regions if any.
     }
 
+    final JScrollBar scrollBar = myEditor.getScrollPane().getVerticalScrollBar();
+    if (myVerticalScrollBarWidth < 0) {
+      myVerticalScrollBarWidth = scrollBar.getWidth();
+      if (myVerticalScrollBarWidth <= 0) {
+        myVerticalScrollBarWidth = scrollBar.getPreferredSize().width;
+      }
+    }
+    
+    // We experienced the following situation:
+    //   1. Editor is configured to show scroll bars only when necessary;
+    //   2. Editor with active soft wraps is changed in order for the vertical scroll bar to appear;
+    //   3. Vertical scrollbar consumes vertical space, hence, soft wraps are recalculated because of the visual area width change;
+    //   4. Newly recalculated soft wraps trigger editor size update;
+    //   5. Editor size update starts scroll pane update which, in turn, disables vertical scroll bar at first (the reason for that
+    //      lays somewhere at the swing depth);
+    //   6. Soft wraps are recalculated because of visible area width change caused by the disabled vertical scroll bar;
+    //   7. Go to the step 4;
+    // I.e. we have an endless EDT activity that stops only when editor is re-sized in a way to avoid vertical scroll bar.
+    // That's why we don't recalculate soft wraps when visual area width is changed to the vertical scroll bar width value assuming
+    // that such a situation is triggered by the scroll bar (dis)appearance.
+    if (Math.abs(currentVisibleAreaWidth - myVisibleAreaWidth) == myVerticalScrollBarWidth) {
+      myVisibleAreaWidth = currentVisibleAreaWidth;
+      return recalculateSoftWraps();
+    }
+    
     // We want to adjust viewport's 'y' coordinate on complete recalculation, so, we remember number of soft-wrapped lines
     // before the target offset on recalculation start and compare it with the number of soft-wrapped lines before the same offset
     // after the recalculation.