make sure cursor stays visible/valid when text is folded

FIXED-IN: 4.11
BUG: 311866
CCBUG: 200858

part/buffer/katetextfolding.cpp

@@ -156,6 +156,15 @@ qint64 TextFolding::newFoldingRange (const KTextEditor::Range &range, FoldingRan
   return newRange->id;
 }
 
+KTextEditor::Range TextFolding::foldingRange(qint64 id) const
+{
+  FoldingRange* range = m_idToFoldingRange.value (id);
+  if (!range)
+    return KTextEditor::Range::invalid();
+
+  return KTextEditor::Range(range->start->toCursor(), range->end->toCursor());
+}
+
 bool TextFolding::foldRange (qint64 id)
 {
   /**

part/buffer/katetextfolding.h

@@ -78,7 +78,17 @@ class KATEPART_TESTS_EXPORT TextFolding : public QObject {
      *         the ids are stable for one Kate::TextFolding, e.g. you can rely in unit tests that you get 0,1,.... for successfully created ranges!
      */
     qint64 newFoldingRange (const KTextEditor::Range &range, FoldingRangeFlags flags = FoldingRangeFlags());
-    
+
+    /**
+     * Returns the folding range associated with @p id.
+     * If @p id is not a valid id, the returned range matches KTextEditor::Range::invalid().
+     * @note This works for either persistend ranges or folded ranges.
+     *       Note, that the highlighting does not add folds unless text is folded.
+     *
+     * @return the folding range for @p id
+     */
+    KTextEditor::Range foldingRange(qint64 id) const;
+
     /**
      * Fold the given range.
      * @param id id of the range to fold

part/view/kateviewinternal.cpp

@@ -668,13 +668,15 @@ void KateViewInternal::slotRegionVisibilityChanged()
   if (startPos() > max)
     scrollPos(max);
 
-#if 0 // DON'T MESS WITH THE CURSORS https://bugs.kde.org/show_bug.cgi?id=295632 and foldedselection_test
-  m_preserveX = true;
-  KTextEditor::Cursor newPos = toRealCursor(toVirtualCursor(m_cursor));
-  KateTextLayout newLine = cache()->textLayout(newPos);
-  newPos = renderer()->xToCursor(newLine, m_preservedX, !m_view->wrapCursor());
-  updateCursor(newPos, true);
-#endif
+  // if text was folded: make sure the cursor is on a visible line
+  qint64 foldedRangeId = -1;
+  if (!m_view->textFolding().isLineVisible (m_cursor.line(), &foldedRangeId)) {
+    KTextEditor::Range foldingRange = m_view->textFolding().foldingRange(foldedRangeId);
+    Q_ASSERT(foldingRange.start().isValid());
+
+    // set cursor to start of folding region
+    updateCursor(foldingRange.start(), true);
+  }
 
   updateView();
   update();