Sam's Blog

25 Nov

A general brace matching tagger for Visual Studio 2010

I haven’t perfected it yet, but here is a fairly general brace matching tagger that seems to work very well. It relies on the classifier for the content type properly tagging comments and literals with classification types derived from PredefinedClassificationTypeNames.Comment and PredefinedClassificationTypeNames.Literal, which any decent classifier will do.

This example really shows a big improvement in Visual Studio 2010. None of my Visual Studio 2008 language services have brace matching this effective and they’re getting jealous.

Here is an example of providing a brace matcher for a “java” content type:

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namespace JavaLanguageService
{
    using System.Collections.Generic;
    using System.ComponentModel.Composition;
    using CustomLanguageService.Text;
    using Microsoft.VisualStudio.Text;
    using Microsoft.VisualStudio.Text.Classification;
    using Microsoft.VisualStudio.Text.Editor;
    using Microsoft.VisualStudio.Text.Tagging;
    using Microsoft.VisualStudio.Utilities;
 
    [Export(typeof(IViewTaggerProvider))]
    [ContentType(Constants.JavaContentType)]
    [TagType(typeof(TextMarkerTag))]
    public sealed class JavaBraceMatchingTaggerProvider : IViewTaggerProvider
    {
        [Import]
        public IClassifierAggregatorService AggregatorService;
 
        public ITagger<T> CreateTagger<T>(ITextView textView, ITextBuffer buffer) where T : ITag
        {
            if (textView == null)
                return null;
 
            var aggregator = AggregatorService.GetClassifier(buffer);
            var pairs = new KeyValuePair<char, char>[]
                {
                    new KeyValuePair<char, char>('(', ')'),
                    new KeyValuePair<char, char>('{', '}'),
                    new KeyValuePair<char, char>('[', ']')
                };
            return new BraceMatchingTagger(textView, buffer, aggregator, pairs) as ITagger<T>;
        }
    }
}

And here is the brace matching tagger. Depending on the characteristics of your language, you may be able to use this will little to no modification.

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namespace CustomLanguageService.Text
{
    using System;
    using System.Collections.Generic;
    using System.Collections.ObjectModel;
    using System.Diagnostics.Contracts;
    using System.Linq;
    using Microsoft.VisualStudio.Language.StandardClassification;
    using Microsoft.VisualStudio.Text;
    using Microsoft.VisualStudio.Text.Classification;
    using Microsoft.VisualStudio.Text.Editor;
    using Microsoft.VisualStudio.Text.Tagging;
 
    internal sealed class BraceMatchingTagger : ITagger<TextMarkerTag>
    {
        public event EventHandler<SnapshotSpanEventArgs> TagsChanged;
 
        public BraceMatchingTagger(ITextView textView, ITextBuffer sourceBuffer, IClassifier aggregator, IEnumerable<KeyValuePair<char, char>> matchingCharacters)
        {
            Contract.Requires<ArgumentNullException>(textView != null);
            Contract.Requires<ArgumentNullException>(sourceBuffer != null);
            Contract.Requires<ArgumentNullException>(aggregator != null);
            Contract.Requires<ArgumentNullException>(matchingCharacters != null);
 
            this.TextView = textView;
            this.SourceBuffer = sourceBuffer;
            this.Aggregator = aggregator;
            this.MatchingCharacters = matchingCharacters.ToList().AsReadOnly();
 
            this.TextView.Caret.PositionChanged += Caret_PositionChanged;
            this.TextView.LayoutChanged += TextView_LayoutChanged;
        }
 
        public ITextView TextView
        {
            get;
            private set;
        }
 
        public ITextBuffer SourceBuffer
        {
            get;
            private set;
        }
 
        public IClassifier Aggregator
        {
            get;
            private set;
        }
 
        public ReadOnlyCollection<KeyValuePair<char, char>> MatchingCharacters
        {
            get;
            private set;
        }
 
        private SnapshotPoint? CurrentChar
        {
            get;
            set;
        }
 
        private static bool IsInCommentOrLiteral(IClassifier aggregator, SnapshotPoint point, PositionAffinity affinity)
        {
            Contract.Requires(aggregator != null);
 
            // TODO: handle affinity
            SnapshotSpan span = new SnapshotSpan(point, 1);
 
            var classifications = aggregator.GetClassificationSpans(span);
            var relevant = classifications.FirstOrDefault(classificationSpan => classificationSpan.Span.Contains(point));
            if (relevant == null || relevant.ClassificationType == null)
                return false;
 
            return relevant.ClassificationType.IsOfType(PredefinedClassificationTypeNames.Comment)
                || relevant.ClassificationType.IsOfType(PredefinedClassificationTypeNames.Literal);
        }
 
        private bool IsMatchStartCharacter(char c)
        {
            return MatchingCharacters.Any(pair => pair.Key == c);
        }
 
        private bool IsMatchCloseCharacter(char c)
        {
            return MatchingCharacters.Any(pair => pair.Value == c);
        }
 
        private char GetMatchCloseCharacter(char c)
        {
            return MatchingCharacters.First(pair => pair.Key == c).Value;
        }
 
        private char GetMatchOpenCharacter(char c)
        {
            return MatchingCharacters.First(pair => pair.Value == c).Key;
        }
 
        private static bool FindMatchingCloseChar(SnapshotPoint start, IClassifier aggregator, char open, char close, int maxLines, out SnapshotSpan pairSpan)
        {
            pairSpan = new SnapshotSpan(start.Snapshot, 1, 1);
            ITextSnapshotLine line = start.GetContainingLine();
            string lineText = line.GetText();
            int lineNumber = line.LineNumber;
            int offset = start.Position - line.Start.Position + 1;
 
            int stopLineNumber = start.Snapshot.LineCount - 1;
            if (maxLines > 0)
                stopLineNumber = Math.Min(stopLineNumber, lineNumber + maxLines);
 
            int openCount = 0;
            while (true)
            {
                while (offset < line.Length)
                {
                    char currentChar = lineText[offset];
                    // TODO: is this the correct affinity
                    if (currentChar == close && !IsInCommentOrLiteral(aggregator, new SnapshotPoint(start.Snapshot, offset + line.Start.Position), PositionAffinity.Successor))
                    {
                        if (openCount > 0)
                        {
                            openCount--;
                        }
                        else
                        {
                            pairSpan = new SnapshotSpan(start.Snapshot, line.Start + offset, 1);
                            return true;
                        }
                    }
                    // TODO: is this the correct affinity
                    else if (currentChar == open && !IsInCommentOrLiteral(aggregator, new SnapshotPoint(start.Snapshot, offset + line.Start.Position), PositionAffinity.Successor))
                    {
                        openCount++;
                    }
 
                    offset++;
                }
 
                // move on to the next line
                lineNumber++;
                if (lineNumber > stopLineNumber)
                    break;
 
                line = line.Snapshot.GetLineFromLineNumber(lineNumber);
                lineText = line.GetText();
                offset = 0;
            }
 
            return false;
        }
 
        private static bool FindMatchingOpenChar(SnapshotPoint start, IClassifier aggregator, char open, char close, int maxLines, out SnapshotSpan pairSpan)
        {
            pairSpan = new SnapshotSpan(start, start);
            ITextSnapshotLine line = start.GetContainingLine();
            int lineNumber = line.LineNumber;
            int offset = start - line.Start - 1;
 
            // if the offset is negative, move to the previous line
            if (offset < 0)
            {
                lineNumber--;
                line = line.Snapshot.GetLineFromLineNumber(lineNumber);
                offset = line.Length - 1;
            }
 
            string lineText = line.GetText();
 
            int stopLineNumber = 0;
            if (maxLines > 0)
                stopLineNumber = Math.Max(stopLineNumber, lineNumber - maxLines);
 
            int closeCount = 0;
            while (true)
            {
                while (offset >= 0)
                {
                    char currentChar = lineText[offset];
                    // TODO: is this the correct affinity
                    if (currentChar == open && !IsInCommentOrLiteral(aggregator, new SnapshotPoint(start.Snapshot, offset + line.Start.Position), PositionAffinity.Successor))
                    {
                        if (closeCount > 0)
                        {
                            closeCount--;
                        }
                        else
                        {
                            pairSpan = new SnapshotSpan(line.Start + offset, 1);
                            return true;
                        }
                    }
                    // TODO: is this the correct affinity
                    else if (currentChar == close && !IsInCommentOrLiteral(aggregator, new SnapshotPoint(start.Snapshot, offset + line.Start.Position), PositionAffinity.Successor))
                    {
                        closeCount++;
                    }
 
                    offset--;
                }
 
                // move to the previous line
                lineNumber--;
                if (lineNumber < stopLineNumber)
                    break;
 
                line = line.Snapshot.GetLineFromLineNumber(lineNumber);
                lineText = line.GetText();
                offset = line.Length - 1;
            }
 
            return false;
        }
 
        public IEnumerable<ITagSpan<TextMarkerTag>> GetTags(NormalizedSnapshotSpanCollection spans)
        {
            if (spans.Count == 0)
                yield break;
 
            // don't do anything if the current SnapshotPoint is not initialized or at the end of the buffer
            if (!CurrentChar.HasValue || CurrentChar.Value.Position >= CurrentChar.Value.Snapshot.Length)
                yield break;
 
            // hold on to a snapshot of the current character
            var currentChar = CurrentChar.Value;
 
            if (IsInCommentOrLiteral(Aggregator, currentChar, TextView.Caret.Position.Affinity))
                yield break;
 
            // if the requested snapshot isn't the same as the one the brace is on, translate our spans to the expected snapshot
            currentChar = currentChar.TranslateTo(spans[0].Snapshot, PointTrackingMode.Positive);
 
            // get the current char and the previous char
            char currentText = currentChar.GetChar();
            // if current char is 0 (beginning of buffer), don't move it back
            SnapshotPoint lastChar = currentChar == 0 ? currentChar : currentChar - 1;
            char lastText = lastChar.GetChar();
            SnapshotSpan pairSpan = new SnapshotSpan();
 
            if (IsMatchStartCharacter(currentText))
            {
                char closeChar = GetMatchCloseCharacter(currentText);
                /* TODO: Need to improve handling of larger blocks. this won't highlight if the matching brace is more
                 *       than 1 screen's worth of lines away. Changing this to 10 * TextView.TextViewLines.Count seemed
                 *       to improve the situation.
                 */
                if (BraceMatchingTagger.FindMatchingCloseChar(currentChar, Aggregator, currentText, closeChar, TextView.TextViewLines.Count, out pairSpan))
                {
                    yield return new TagSpan<TextMarkerTag>(new SnapshotSpan(currentChar, 1), PredefinedTextMarkerTags.BraceHighlight);
                    yield return new TagSpan<TextMarkerTag>(pairSpan, PredefinedTextMarkerTags.BraceHighlight);
                }
            }
            else if (IsMatchCloseCharacter(lastText))
            {
                var open = GetMatchOpenCharacter(lastText);
                if (BraceMatchingTagger.FindMatchingOpenChar(lastChar, Aggregator, open, lastText, TextView.TextViewLines.Count, out pairSpan))
                {
                    yield return new TagSpan<TextMarkerTag>(new SnapshotSpan(lastChar, 1), PredefinedTextMarkerTags.BraceHighlight);
                    yield return new TagSpan<TextMarkerTag>(pairSpan, PredefinedTextMarkerTags.BraceHighlight);
                }
            }
        }
 
        private void UpdateAtCaretPosition(CaretPosition caretPosition)
        {
            CurrentChar = caretPosition.Point.GetPoint(SourceBuffer, caretPosition.Affinity);
            if (!CurrentChar.HasValue)
                return;
 
            var t = TagsChanged;
            if (t != null)
                t(this, new SnapshotSpanEventArgs(new SnapshotSpan(SourceBuffer.CurrentSnapshot, 0, SourceBuffer.CurrentSnapshot.Length)));
        }
 
        private void TextView_LayoutChanged(object sender, TextViewLayoutChangedEventArgs e)
        {
            if (e.NewSnapshot != e.OldSnapshot)
                UpdateAtCaretPosition(TextView.Caret.Position);
        }
 
        private void Caret_PositionChanged(object sender, CaretPositionChangedEventArgs e)
        {
            UpdateAtCaretPosition(e.NewPosition);
        }
    }
}

2 Responses to “A general brace matching tagger for Visual Studio 2010”

  1. 1
    David Piepgrass Says:

    Thanks, this is really handy for any syntax/language service. Just one thing though: where is the definition of PredefinedTextMarkerTags.BraceHighlight? And does this code have a license?

  2. 2
    David Piepgrass Says:

    I couldn’t figure out how to get a TextMarkerTag specifically for brace matching, but the following tag does put an outline rectangle around the brace/paren, just using the color of Operators instead of Brace matching.

    public static readonly TextMarkerTag BraceHighlightTag = new TextMarkerTag(PredefinedClassificationTypeNames.Operator);

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