C++: optimize the semantic highlighting in the UI thread.

Done by reserving enough space in for the various QLists when created,
and by preventing unnecessary copying of lists.

Change-Id: I5a9f0f7042bbaa1cf5eb076b956c35f2191468c6
Reviewed-by: Nikolai Kosjar <nikolai.kosjar@digia.com>

src/plugins/cppeditor/cppeditor.cpp

@@ -2008,7 +2008,8 @@ void CPPEditorWidget::setFontSettings(const TextEditor::FontSettings &fs)
     // Clear all additional formats since they may have changed
     QTextBlock b = document()->firstBlock();
     while (b.isValid()) {
-        highlighter->setExtraAdditionalFormats(b, QList<QTextLayout::FormatRange>());
+        QList<QTextLayout::FormatRange> noFormats;
+        highlighter->setExtraAdditionalFormats(b, noFormats);
         b = b.next();
     }
 

src/plugins/texteditor/semantichighlighter.cpp

@@ -76,13 +76,15 @@ void TextEditor::SemanticHighlighter::incrementalApplyExtraAdditionalFormats(
 
         // clear formats of blocks until blockNumber
         while (currentBlockNumber < blockNumber) {
-            highlighter->setExtraAdditionalFormats(b, QList<QTextLayout::FormatRange>());
+            QList<QTextLayout::FormatRange> noFormats;
+            highlighter->setExtraAdditionalFormats(b, noFormats);
             b = b.next();
             ++currentBlockNumber;
         }
 
         // collect all the formats for the current line
         QList<QTextLayout::FormatRange> formats;
+        formats.reserve(to - from);
         forever {
             QTextLayout::FormatRange formatRange;
 
@@ -131,7 +133,8 @@ void TextEditor::SemanticHighlighter::clearExtraAdditionalFormatsUntilEnd(
     QTextBlock b = doc->findBlockByNumber(firstBlockToClear);
 
     while (b.isValid()) {
-        highlighter->setExtraAdditionalFormats(b, QList<QTextLayout::FormatRange>());
+        QList<QTextLayout::FormatRange> noFormats;
+        highlighter->setExtraAdditionalFormats(b, noFormats);
         b = b.next();
     }
 }

src/plugins/texteditor/syntaxhighlighter.cpp

@@ -694,8 +694,10 @@ static bool byStartOfRange(const QTextLayout::FormatRange &range, const QTextLay
     return range.start < other.start;
 }
 
+// The formats is passed in by reference in order to prevent unnecessary copying of its items.
+// After this method returns, the list is modified, and should be considered invalidated!
 void SyntaxHighlighter::setExtraAdditionalFormats(const QTextBlock& block,
-                                                  const QList<QTextLayout::FormatRange> &fmts)
+                                                  QList<QTextLayout::FormatRange> &formats)
 {
 //    qDebug() << "setAdditionalFormats() on block" << block.blockNumber();
 //    qDebug() << "   is valid:" << (block.isValid() ? "Yes" : "No");
@@ -708,21 +710,21 @@ void SyntaxHighlighter::setExtraAdditionalFormats(const QTextBlock& block,
 //                 << "color:" << overrides.at(i).format.foreground().color();
     Q_D(SyntaxHighlighter);
 
-    if (block.layout() == 0 || block.text().isEmpty())
+    const int blockLength = block.length();
+    if (block.layout() == 0 || blockLength == 0)
         return;
 
-    QList<QTextLayout::FormatRange> formats;
-    formats.reserve(fmts.size());
-    foreach (QTextLayout::FormatRange r, fmts) {
-        r.format.setProperty(QTextFormat::UserProperty, true);
-        formats.append(r);
-    }
     qSort(formats.begin(), formats.end(), byStartOfRange);
 
+    const QList<QTextLayout::FormatRange> all = block.layout()->additionalFormats();
     QList<QTextLayout::FormatRange> previousSemanticFormats;
     QList<QTextLayout::FormatRange> formatsToApply;
+    previousSemanticFormats.reserve(all.size());
+    formatsToApply.reserve(all.size() + formats.size());
+
+    for (int i = 0, ei = formats.size(); i < ei; ++i)
+        formats[i].format.setProperty(QTextFormat::UserProperty, true);
 
-    const QList<QTextLayout::FormatRange> all = block.layout()->additionalFormats();
     foreach (const QTextLayout::FormatRange &r, all) {
         if (r.format.hasProperty(QTextFormat::UserProperty))
             previousSemanticFormats.append(r);
@@ -753,7 +755,7 @@ void SyntaxHighlighter::setExtraAdditionalFormats(const QTextBlock& block,
     bool wasInReformatBlocks = d->inReformatBlocks;
     d->inReformatBlocks = true;
     block.layout()->setAdditionalFormats(formatsToApply);
-    document()->markContentsDirty(block.position(), block.length()-1);
+    document()->markContentsDirty(block.position(), blockLength - 1);
     d->inReformatBlocks = wasInReformatBlocks;
 }
 

src/plugins/texteditor/syntaxhighlighter.h

@@ -64,7 +64,7 @@ public:
     void setDocument(QTextDocument *doc);
     QTextDocument *document() const;
 
-    void setExtraAdditionalFormats(const QTextBlock& block, const QList<QTextLayout::FormatRange> &formats);
+    void setExtraAdditionalFormats(const QTextBlock& block, QList<QTextLayout::FormatRange> &formats);
 
     static QList<QColor> generateColors(int n, const QColor &background);