Classify non-C# inside C#

Fixes a bug with preview formatting for FAR.

So when we ask the Roslyn API to classify C# for us, it will only
classify the actual C# tokens. We are responsible for filling in the
gaps and whitespace.

The bug is that the following text would have all of its whitespace
removed in the VS FAR preview window.

```
@{ var foo = "Hello, world!"; }
```

Would look like:
```
@{varfoo="Hello, world!";}
```

This fixes the issue and makes it look like what one would expect.

src/Microsoft.CodeAnalysis.Razor.Workspaces/RazorDocumentExcerptService.cs

@@ -176,6 +176,10 @@ namespace Microsoft.CodeAnalysis.Razor
                     secondaryDocument, 
                     secondarySpan, 
                     cancellationToken);
+
+                // NOTE: The Classifier will only returns spans for things that it understands. That means
+                // that whitespace is not classified. The preview expects us to provide contiguous spans, 
+                // so we are going to have to fill in the gaps.
                 
                 // Now we have to translate back to the primary document's coordinates.
                 var offset = primarySpan.Start - secondarySpan.Start;
@@ -185,11 +189,29 @@ namespace Microsoft.CodeAnalysis.Razor
                     
                     var updated = new TextSpan(classifiedSecondarySpan.TextSpan.Start + offset, classifiedSecondarySpan.TextSpan.Length);
                     Debug.Assert(primarySpan.Contains(updated));
+
+                    // Make sure that we're not introducing a gap. Remember, we need to fill in the whitespace.
+                    if (remainingSpan.Start < updated.Start)
+                    {
+                        builder.Add(new ClassifiedSpan(
+                            ClassificationTypeNames.Text,
+                            new TextSpan(remainingSpan.Start, updated.Start - remainingSpan.Start)));
+                        remainingSpan = new TextSpan(updated.Start, remainingSpan.Length - (updated.Start - remainingSpan.Start));
+                    }
                     
                     builder.Add(new ClassifiedSpan(classifiedSecondarySpan.ClassificationType, updated));
+                    remainingSpan = new TextSpan(updated.End, remainingSpan.Length - (updated.End - remainingSpan.Start));
+                }
+
+                // Make sure that we're not introducing a gap. Remember, we need to fill in the whitespace.
+                if (remainingSpan.Start < primarySpan.End)
+                {
+                    builder.Add(new ClassifiedSpan(
+                        ClassificationTypeNames.Text,
+                        new TextSpan(remainingSpan.Start, primarySpan.End - remainingSpan.Start)));
+                    remainingSpan = new TextSpan(primarySpan.End, remainingSpan.Length - (primarySpan.End - remainingSpan.Start));
                 }
 
-                remainingSpan = new TextSpan(primarySpan.End, remainingSpan.Length - primarySpan.Length);
             }
 
             // Deal with residue

test/Microsoft.CodeAnalysis.Razor.Workspaces.Test/RazorExcerptServiceTest.cs

@@ -70,22 +70,42 @@ namespace Microsoft.CodeAnalysis.Razor
             Assert.Equal(@"    var foo = ""Hello, World!"";", result.Value.Content.ToString(), ignoreLineEndingDifferences: true);
             Assert.Collection(
                 result.Value.ClassifiedSpans,
+                c =>
+                {
+                    Assert.Equal(ClassificationTypeNames.Text, c.ClassificationType);
+                    Assert.Equal("    ", result.Value.Content.GetSubText(c.TextSpan).ToString());
+                },
                 c => 
                 {
                     Assert.Equal(ClassificationTypeNames.Keyword, c.ClassificationType);
                     Assert.Equal("var", result.Value.Content.GetSubText(c.TextSpan).ToString());
                 },
                 c =>
+                {
+                    Assert.Equal(ClassificationTypeNames.Text, c.ClassificationType);
+                    Assert.Equal(" ", result.Value.Content.GetSubText(c.TextSpan).ToString());
+                },
+                c =>
                 {
                     Assert.Equal(ClassificationTypeNames.LocalName, c.ClassificationType);
                     Assert.Equal("foo", result.Value.Content.GetSubText(c.TextSpan).ToString());
                 },
                 c =>
+                {
+                    Assert.Equal(ClassificationTypeNames.Text, c.ClassificationType);
+                    Assert.Equal(" ", result.Value.Content.GetSubText(c.TextSpan).ToString());
+                },
+                c =>
                 {
                     Assert.Equal(ClassificationTypeNames.Operator, c.ClassificationType);
                     Assert.Equal("=", result.Value.Content.GetSubText(c.TextSpan).ToString());
                 },
                 c =>
+                {
+                    Assert.Equal(ClassificationTypeNames.Text, c.ClassificationType);
+                    Assert.Equal(" ", result.Value.Content.GetSubText(c.TextSpan).ToString());
+                },
+                c =>
                 {
                     Assert.Equal(ClassificationTypeNames.StringLiteral, c.ClassificationType);
                     Assert.Equal("\"Hello, World!\"", result.Value.Content.GetSubText(c.TextSpan).ToString());
@@ -199,11 +219,21 @@ namespace Microsoft.CodeAnalysis.Razor
                     Assert.Equal("3", result.Value.Content.GetSubText(c.TextSpan).ToString());
                 },
                 c =>
+                {
+                    Assert.Equal(ClassificationTypeNames.Text, c.ClassificationType);
+                    Assert.Equal(" ", result.Value.Content.GetSubText(c.TextSpan).ToString());
+                },
+                c =>
                 {
                     Assert.Equal(ClassificationTypeNames.Operator, c.ClassificationType);
                     Assert.Equal("+", result.Value.Content.GetSubText(c.TextSpan).ToString());
                 },
                 c =>
+                {
+                    Assert.Equal(ClassificationTypeNames.Text, c.ClassificationType);
+                    Assert.Equal(" ", result.Value.Content.GetSubText(c.TextSpan).ToString());
+                },
+                c =>
                 {
                     Assert.Equal(ClassificationTypeNames.NumericLiteral, c.ClassificationType);
                     Assert.Equal("4", result.Value.Content.GetSubText(c.TextSpan).ToString());
@@ -219,11 +249,21 @@ namespace Microsoft.CodeAnalysis.Razor
                     Assert.Equal("foo", result.Value.Content.GetSubText(c.TextSpan).ToString());
                 },
                 c =>
+                {
+                    Assert.Equal(ClassificationTypeNames.Text, c.ClassificationType);
+                    Assert.Equal(" ", result.Value.Content.GetSubText(c.TextSpan).ToString());
+                },
+                c =>
                 {
                     Assert.Equal(ClassificationTypeNames.Operator, c.ClassificationType);
                     Assert.Equal("+", result.Value.Content.GetSubText(c.TextSpan).ToString());
                 },
                 c =>
+                {
+                    Assert.Equal(ClassificationTypeNames.Text, c.ClassificationType);
+                    Assert.Equal(" ", result.Value.Content.GetSubText(c.TextSpan).ToString());
+                },
+                c =>
                 {
                     Assert.Equal(ClassificationTypeNames.LocalName, c.ClassificationType);
                     Assert.Equal("foo", result.Value.Content.GetSubText(c.TextSpan).ToString());
@@ -292,21 +332,41 @@ namespace Microsoft.CodeAnalysis.Razor
                             ignoreLineEndingDifferences: true);
                 },
                 c =>
+                {
+                    Assert.Equal(ClassificationTypeNames.Text, c.ClassificationType);
+                    Assert.Equal("\r\n    ", result.Value.Content.GetSubText(c.TextSpan).ToString(), ignoreLineEndingDifferences: true);
+                },
+                c =>
                 {
                     Assert.Equal(ClassificationTypeNames.Keyword, c.ClassificationType);
                     Assert.Equal("var", result.Value.Content.GetSubText(c.TextSpan).ToString());
                 },
                 c =>
+                {
+                    Assert.Equal(ClassificationTypeNames.Text, c.ClassificationType);
+                    Assert.Equal(" ", result.Value.Content.GetSubText(c.TextSpan).ToString());
+                },
+                c =>
                 {
                     Assert.Equal(ClassificationTypeNames.LocalName, c.ClassificationType);
                     Assert.Equal("foo", result.Value.Content.GetSubText(c.TextSpan).ToString());
                 },
                 c =>
+                {
+                    Assert.Equal(ClassificationTypeNames.Text, c.ClassificationType);
+                    Assert.Equal(" ", result.Value.Content.GetSubText(c.TextSpan).ToString());
+                },
+                c =>
                 {
                     Assert.Equal(ClassificationTypeNames.Operator, c.ClassificationType);
                     Assert.Equal("=", result.Value.Content.GetSubText(c.TextSpan).ToString());
                 },
                 c =>
+                {
+                    Assert.Equal(ClassificationTypeNames.Text, c.ClassificationType);
+                    Assert.Equal(" ", result.Value.Content.GetSubText(c.TextSpan).ToString());
+                },
+                c =>
                 {
                     Assert.Equal(ClassificationTypeNames.StringLiteral, c.ClassificationType);
                     Assert.Equal("\"Hello, World!\"", result.Value.Content.GetSubText(c.TextSpan).ToString());
@@ -317,6 +377,11 @@ namespace Microsoft.CodeAnalysis.Razor
                     Assert.Equal(";", result.Value.Content.GetSubText(c.TextSpan).ToString());
                 },
                 c =>
+                {
+                    Assert.Equal(ClassificationTypeNames.Text, c.ClassificationType);
+                    Assert.Equal("\r\n", result.Value.Content.GetSubText(c.TextSpan).ToString(), ignoreLineEndingDifferences: true);
+                },
+                c =>
                 {
                     Assert.Equal(ClassificationTypeNames.Text, c.ClassificationType);
                     Assert.Equal(
@@ -365,21 +430,41 @@ namespace Microsoft.CodeAnalysis.Razor
                     Assert.Equal("@{", result.Value.Content.GetSubText(c.TextSpan).ToString());
                 },
                 c =>
+                {
+                    Assert.Equal(ClassificationTypeNames.Text, c.ClassificationType);
+                    Assert.Equal(" ", result.Value.Content.GetSubText(c.TextSpan).ToString());
+                },
+                c =>
                 {
                     Assert.Equal(ClassificationTypeNames.Keyword, c.ClassificationType);
                     Assert.Equal("var", result.Value.Content.GetSubText(c.TextSpan).ToString());
                 },
                 c =>
+                {
+                    Assert.Equal(ClassificationTypeNames.Text, c.ClassificationType);
+                    Assert.Equal(" ", result.Value.Content.GetSubText(c.TextSpan).ToString());
+                },
+                c =>
                 {
                     Assert.Equal(ClassificationTypeNames.LocalName, c.ClassificationType);
                     Assert.Equal("foo", result.Value.Content.GetSubText(c.TextSpan).ToString());
                 },
                 c =>
+                {
+                    Assert.Equal(ClassificationTypeNames.Text, c.ClassificationType);
+                    Assert.Equal(" ", result.Value.Content.GetSubText(c.TextSpan).ToString());
+                },
+                c =>
                 {
                     Assert.Equal(ClassificationTypeNames.Operator, c.ClassificationType);
                     Assert.Equal("=", result.Value.Content.GetSubText(c.TextSpan).ToString());
                 },
                 c =>
+                {
+                    Assert.Equal(ClassificationTypeNames.Text, c.ClassificationType);
+                    Assert.Equal(" ", result.Value.Content.GetSubText(c.TextSpan).ToString());
+                },
+                c =>
                 {
                     Assert.Equal(ClassificationTypeNames.StringLiteral, c.ClassificationType);
                     Assert.Equal("\"Hello, World!\"", result.Value.Content.GetSubText(c.TextSpan).ToString());
@@ -390,6 +475,11 @@ namespace Microsoft.CodeAnalysis.Razor
                     Assert.Equal(";", result.Value.Content.GetSubText(c.TextSpan).ToString());
                 },
                 c =>
+                {
+                    Assert.Equal(ClassificationTypeNames.Text, c.ClassificationType);
+                    Assert.Equal(" ", result.Value.Content.GetSubText(c.TextSpan).ToString());
+                },
+                c =>
                 {
                     Assert.Equal(ClassificationTypeNames.Text, c.ClassificationType);
                     Assert.Equal("}", result.Value.Content.GetSubText(c.TextSpan).ToString());