C# syntax highlighting: Don't colorize punctuation.

AvalonEdit: don't create separate TextRuns when syntax highlighting applies a color-less span.

src/Libraries/AvalonEdit/ICSharpCode.AvalonEdit/Highlighting/HighlightedInlineBuilder.cs

@@ -84,6 +84,12 @@ namespace ICSharpCode.AvalonEdit.Highlighting
 		{
 			if (color == null)
 				throw new ArgumentNullException("color");
+			if (color.Foreground == null && color.FontStyle == null && color.FontWeight == null) {
+				// Optimization: don't split the HighlightingState when we're not changing
+				// any property. For example, the "Punctuation" color in C# is
+				// empty by default.
+				return;
+			}
 			int startIndex = GetIndexForOffset(offset);
 			int endIndex = GetIndexForOffset(offset + length);
 			for (int i = startIndex; i < endIndex; i++) {

src/Libraries/AvalonEdit/ICSharpCode.AvalonEdit/Highlighting/HighlightingColorizer.cs

@@ -137,6 +137,8 @@ namespace ICSharpCode.AvalonEdit.Highlighting
 				HighlightedLine hl = highlighter.HighlightLine(lineNumberBeingColorized);
 				lineNumberBeingColorized = 0;
 				foreach (HighlightedSection section in hl.Sections) {
+					if (IsEmptyColor(section.Color))
+						continue;
 					ChangeLinePart(section.Offset, section.Offset + section.Length,
 					               visualLineElement => ApplyColorToElement(visualLineElement, section.Color));
 				}
@@ -144,6 +146,18 @@ namespace ICSharpCode.AvalonEdit.Highlighting
 			this.lastColorizedLine = line;
 		}
 		
+		/// <summary>
+		/// Gets whether the color is empty (has no effect on a VisualLineTextElement).
+		/// For example, the C# "Punctuation" is an empty color.
+		/// </summary>
+		bool IsEmptyColor(HighlightingColor color)
+		{
+			if (color == null)
+				return true;
+			return color.Background == null && color.Foreground == null
+				&& color.FontStyle == null && color.FontWeight == null;
+		}
+		
 		/// <summary>
 		/// Applies a highlighting color to a visual line element.
 		/// </summary>

src/Libraries/AvalonEdit/ICSharpCode.AvalonEdit/Highlighting/Resources/CSharp-Mode.xshd

@@ -5,7 +5,7 @@
 	<Color name="String" foreground="Blue" exampleText="string text = &quot;Hello, World!&quot;"/>
 	<Color name="Char" foreground="Magenta" exampleText="char linefeed = '\n';"/>
 	<Color name="Preprocessor" foreground="Green" exampleText="#region Title" />
-	<Color name="Punctuation" foreground="DarkGreen" exampleText="a(b.c);" />
+	<Color name="Punctuation" exampleText="a(b.c);" />
 	<Color name="ValueTypes" fontWeight="bold" foreground="Red" exampleText="bool b = true;" />
 	<Color name="ReferenceTypes" foreground="Red" exampleText="object o;" />
 	<Color name="MethodCall" foreground="MidnightBlue" fontWeight="bold" exampleText="o.ToString();"/>