C++ editor: Drop extra selections before large editing operations.

Updating the text cursors that the extra selections are based on can
get quite slow if there are changes in a lot of positions - like when
reindenting a file.

Dropping some text cursors can increase performance significantly in
these cases.

Done-with: mae

src/plugins/texteditor/basetexteditor.cpp

@@ -3654,6 +3654,7 @@ const DisplaySettings &BaseTextEditor::displaySettings() const
 void BaseTextEditor::indentOrUnindent(bool doIndent)
 {
     QTextCursor cursor = textCursor();
+    maybeClearSomeExtraSelections(cursor);
     cursor.beginEditBlock();
 
     int pos = cursor.position();
@@ -4076,6 +4077,7 @@ void BaseTextEditor::indentBlock(QTextDocument *, QTextBlock, QChar)
 
 void BaseTextEditor::indent(QTextDocument *doc, const QTextCursor &cursor, QChar typedChar)
 {
+    maybeClearSomeExtraSelections(cursor);
     if (cursor.hasSelection()) {
         QTextBlock block = doc->findBlock(cursor.selectionStart());
         const QTextBlock end = doc->findBlock(cursor.selectionEnd()).next();
@@ -4090,6 +4092,7 @@ void BaseTextEditor::indent(QTextDocument *doc, const QTextCursor &cursor, QChar
 
 void BaseTextEditor::reindent(QTextDocument *doc, const QTextCursor &cursor)
 {
+    maybeClearSomeExtraSelections(cursor);
     if (cursor.hasSelection()) {
         QTextBlock block = doc->findBlock(cursor.selectionStart());
         const QTextBlock end = doc->findBlock(cursor.selectionEnd()).next();
@@ -4622,6 +4625,26 @@ QList<QTextEdit::ExtraSelection> BaseTextEditor::extraSelections(ExtraSelectionK
     return d->m_extraSelections[kind];
 }
 
+void BaseTextEditor::maybeClearSomeExtraSelections(const QTextCursor &cursor)
+{
+    const int smallSelectionSize = 50 * 50;
+    if (cursor.selectionEnd() - cursor.selectionStart() < smallSelectionSize)
+        return;
+
+    d->m_extraSelections[TypeSelection].clear();
+    d->m_extraSelections[UndefinedSymbolSelection].clear();
+    d->m_extraSelections[ObjCSelection].clear();
+    d->m_extraSelections[CodeWarningsSelection].clear();
+
+    QList<QTextEdit::ExtraSelection> all;
+    for (int i = 0; i < NExtraSelectionKinds; ++i) {
+        if (i == CodeSemanticsSelection || i == SnippetPlaceholderSelection)
+            continue;
+        all += d->m_extraSelections[i];
+    }
+    QPlainTextEdit::setExtraSelections(all);
+}
+
 QString BaseTextEditor::extraSelectionTooltip(int pos) const
 {
     QList<QTextEdit::ExtraSelection> all;

src/plugins/texteditor/basetexteditor.h

@@ -500,6 +500,8 @@ private:
     void updateHighlights();
     void updateCurrentLineHighlight();
 
+    void maybeClearSomeExtraSelections(const QTextCursor &cursor);
+
     void drawFoldingMarker(QPainter *painter, const QPalette &pal,
                            const QRect &rect,
                            bool expanded,