Adding RazorSyntaxFactsService

This is a code dump from tooling -> Razor

This service will exist to answer questions about syntax trees for the
editor. Right now I'm just moving in the code in the simplest way
possible. Tests + cleanup to follow.

src/Microsoft.VisualStudio.LanguageServices.Razor/ClassifiedSpan.cs

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+// Copyright (c) .NET Foundation. All rights reserved.
+// Licensed under the Apache License, Version 2.0. See License.txt in the project root for license information.
+
+using Microsoft.AspNetCore.Razor.Evolution;
+
+namespace Microsoft.VisualStudio.LanguageServices.Razor
+{
+    public struct ClassifiedSpan
+    {
+        public ClassifiedSpan(SourceSpan span, SourceSpan blockSpan, SpanKind spanKind, BlockKind blockKind, AcceptedCharacters acceptedCharacters)
+        {
+            Span = span;
+            BlockSpan = blockSpan;
+            SpanKind = spanKind;
+            BlockKind = blockKind;
+            AcceptedCharacters = acceptedCharacters;
+        }
+
+        public AcceptedCharacters AcceptedCharacters { get; }
+
+        public BlockKind BlockKind { get; }
+
+        public SourceSpan BlockSpan { get; }
+
+        public SourceSpan Span { get; }
+
+        public SpanKind SpanKind { get; }
+    }
+}

src/Microsoft.VisualStudio.LanguageServices.Razor/DefaultRazorSyntaxFactsService.cs

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+// Copyright (c) .NET Foundation. All rights reserved.
+// Licensed under the Apache License, Version 2.0. See License.txt in the project root for license information.
+
+using System.Collections.Generic;
+using System.ComponentModel.Composition;
+using System.Linq;
+using Microsoft.AspNetCore.Razor.Evolution;
+using Microsoft.AspNetCore.Razor.Evolution.Legacy;
+
+namespace Microsoft.VisualStudio.LanguageServices.Razor
+{
+    [Export(typeof(RazorSyntaxFactsService))]
+    internal class DefaultRazorSyntaxFactsService : RazorSyntaxFactsService
+    {
+        public override IReadOnlyList<ClassifiedSpan> GetClassifiedSpans(RazorSyntaxTree syntaxTree)
+        {
+            var spans = Flatten(syntaxTree);
+
+            var result = new ClassifiedSpan[spans.Count];
+            for (var i = 0; i < spans.Count; i++)
+            {
+                var span = spans[i];
+                result[i] = new ClassifiedSpan(
+                    new SourceSpan(
+                        span.Start.FilePath ?? syntaxTree.Source.FileName,
+                        span.Start.AbsoluteIndex,
+                        span.Start.LineIndex,
+                        span.Start.CharacterIndex,
+                        span.Length),
+                    new SourceSpan(
+                        span.Parent.Start.FilePath ?? syntaxTree.Source.FileName,
+                        span.Parent.Start.AbsoluteIndex,
+                        span.Parent.Start.LineIndex,
+                        span.Parent.Start.CharacterIndex,
+                        span.Parent.Length),
+                    span.Kind,
+                    span.Parent.Type,
+                    span.EditHandler.AcceptedCharacters);
+            }
+
+            return result;
+        }
+
+        private List<Span> Flatten(RazorSyntaxTree syntaxTree)
+        {
+            var result = new List<Span>();
+            AppendFlattenedSpans(syntaxTree.Root, result);
+            return result;
+
+            void AppendFlattenedSpans(SyntaxTreeNode node, List<Span> foundSpans)
+            {
+                Span spanNode = node as Span;
+                if (spanNode != null)
+                {
+                    foundSpans.Add(spanNode);
+                }
+                else
+                {
+                    TagHelperBlock tagHelperNode = node as TagHelperBlock;
+                    if (tagHelperNode != null)
+                    {
+                        // These aren't in document order, sort them first and then dig in
+                        List<SyntaxTreeNode> attributeNodes = tagHelperNode.Attributes.Select(kvp => kvp.Value).Where(att => att != null).ToList();
+                        attributeNodes.Sort((x, y) => x.Start.AbsoluteIndex.CompareTo(y.Start));
+
+                        foreach (SyntaxTreeNode curNode in attributeNodes)
+                        {
+                            AppendFlattenedSpans(curNode, foundSpans);
+                        }
+                    }
+
+                    Block blockNode = node as Block;
+                    if (blockNode != null)
+                    {
+                        foreach (SyntaxTreeNode curNode in blockNode.Children)
+                        {
+                            AppendFlattenedSpans(curNode, foundSpans);
+                        }
+                    }
+                }
+            }
+        }
+    }
+}

src/Microsoft.VisualStudio.LanguageServices.Razor/RazorSyntaxFactsService.cs

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+// Copyright (c) .NET Foundation. All rights reserved.
+// Licensed under the Apache License, Version 2.0. See License.txt in the project root for license information.
+
+using System.Collections.Generic;
+using Microsoft.AspNetCore.Razor.Evolution;
+
+namespace Microsoft.VisualStudio.LanguageServices.Razor
+{
+    public abstract class RazorSyntaxFactsService
+    {
+        public abstract IReadOnlyList<ClassifiedSpan> GetClassifiedSpans(RazorSyntaxTree syntaxTree);
+    }
+}