Change IR implementations to not hold all information in children.

- Added conditional attribute test.
- Reacted to Html optimization pass in tests.
- Removed directive IR bits since they'll be handled by the extensible directive system.

#844

src/Microsoft.AspNetCore.Razor.Evolution/DefaultRazorIRLoweringPhase.cs

@@ -1,6 +1,8 @@
 // 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.Linq;
 using Microsoft.AspNetCore.Razor.Evolution.Intermediate;
 using Microsoft.AspNetCore.Razor.Evolution.Legacy;
 
@@ -11,7 +13,7 @@ namespace Microsoft.AspNetCore.Razor.Evolution
         protected override void ExecuteCore(RazorCodeDocument codeDocument)
         {
             var syntaxTree = codeDocument.GetSyntaxTree();
-            ThrowForMissingDependency<RazorSyntaxTree>(syntaxTree);
+            ThrowForMissingDependency(syntaxTree);
 
             var visitor = new Visitor();
 
@@ -23,80 +25,89 @@ namespace Microsoft.AspNetCore.Razor.Evolution
 
         private class Visitor : ParserVisitor
         {
+            private readonly Stack<RazorIRBuilder> _builders;
+
             public Visitor()
             {
-                Builder = RazorIRBuilder.Document();
+                _builders = new Stack<RazorIRBuilder>();
+                var document = RazorIRBuilder.Document();
+                _builders.Push(document);
 
                 Namespace = new NamespaceDeclarationIRNode();
-                NamespaceBuilder = RazorIRBuilder.Create(Namespace);
                 Builder.Push(Namespace);
 
                 Class = new ClassDeclarationIRNode();
-                ClassBuilder = RazorIRBuilder.Create(Class);
                 Builder.Push(Class);
 
-                Method = new MethodDeclarationIRNode();
+                Method = new RazorMethodDeclarationIRNode();
                 Builder.Push(Method);
             }
 
-            public RazorIRBuilder Builder { get; }
+            public RazorIRBuilder Builder => _builders.Peek();
 
             public NamespaceDeclarationIRNode Namespace { get; }
 
-            public RazorIRBuilder NamespaceBuilder { get; }
-
             public ClassDeclarationIRNode Class { get; }
 
-            public RazorIRBuilder ClassBuilder { get; }
+            public RazorMethodDeclarationIRNode Method { get; }
 
-            public MethodDeclarationIRNode Method { get; }
+            public override void VisitStartAttributeBlock(AttributeBlockChunkGenerator chunkGenerator, Block block)
-
-            public override void VisitStartAttributeBlock(AttributeBlockChunkGenerator chunk, Block block)
             {
-                Builder.Push(new HtmlAttributeIRNode()
+                var value = new ContainerRazorIRNode();
+                Builder.Add(new HtmlAttributeIRNode()
                 {
-                    Name = chunk.Name,
+                    Name = chunkGenerator.Name,
-                    Prefix = chunk.Prefix,
+                    Prefix = chunkGenerator.Prefix,
-                    Suffix = chunk.Prefix,
+                    Value = value,
+                    Suffix = chunkGenerator.Suffix,
 
                     SourceLocation = block.Start,
                 });
+
+                var valueBuilder = RazorIRBuilder.Create(value);
+                _builders.Push(valueBuilder);
             }
 
-            public override void VisitEndAttributeBlock(AttributeBlockChunkGenerator chunk, Block block)
+            public override void VisitEndAttributeBlock(AttributeBlockChunkGenerator chunkGenerator, Block block)
             {
-                Builder.Pop();
+                _builders.Pop();
             }
 
-            public override void VisitStartDynamicAttributeBlock(DynamicAttributeBlockChunkGenerator chunk, Block block)
+            public override void VisitStartDynamicAttributeBlock(DynamicAttributeBlockChunkGenerator chunkGenerator, Block block)
             {
-                Builder.Push(new CSharpAttributeValueIRNode()
+                var content = new ContainerRazorIRNode();
+                Builder.Add(new CSharpAttributeValueIRNode()
                 {
-                    Prefix = chunk.Prefix,
+                    Prefix = chunkGenerator.Prefix,
+                    Content = content,
                     SourceLocation = block.Start,
                 });
+
+                var valueBuilder = RazorIRBuilder.Create(content);
+                _builders.Push(valueBuilder);
             }
 
-            public override void VisitEndDynamicAttributeBlock(DynamicAttributeBlockChunkGenerator chunk, Block block)
+            public override void VisitEndDynamicAttributeBlock(DynamicAttributeBlockChunkGenerator chunkGenerator, Block block)
             {
-                Builder.Pop();
+                _builders.Pop();
             }
 
-            public override void VisitLiteralAttributeSpan(LiteralAttributeChunkGenerator chunk, Span span)
+            public override void VisitLiteralAttributeSpan(LiteralAttributeChunkGenerator chunkGenerator, Span span)
             {
                 Builder.Add(new HtmlAttributeValueIRNode()
                 {
-                    Prefix = chunk.Prefix,
+                    Prefix = chunkGenerator.Prefix,
+                    Content = chunkGenerator.Value,
                     SourceLocation = span.Start,
                 });
             }
 
-            public override void VisitStartTemplateBlock(TemplateBlockChunkGenerator chunk, Block block)
+            public override void VisitStartTemplateBlock(TemplateBlockChunkGenerator chunkGenerator, Block block)
             {
                 Builder.Push(new TemplateIRNode());
             }
 
-            public override void VisitEndTemplateBlock(TemplateBlockChunkGenerator chunk, Block block)
+            public override void VisitEndTemplateBlock(TemplateBlockChunkGenerator chunkGenerator, Block block)
             {
                 Builder.Pop();
             }
@@ -107,20 +118,25 @@ namespace Microsoft.AspNetCore.Razor.Evolution
             //      @DateTime.@*This is a comment*@Now
             //
             // We need to capture this in the IR so that we can give each piece the correct source mappings
-            public override void VisitStartExpressionBlock(ExpressionChunkGenerator chunk, Block block)
+            public override void VisitStartExpressionBlock(ExpressionChunkGenerator chunkGenerator, Block block)
             {
-                Builder.Push(new CSharpExpressionIRNode()
+                var value = new ContainerRazorIRNode();
+                Builder.Add(new CSharpExpressionIRNode()
                 {
+                    Content = value,
                     SourceLocation = block.Start,
                 });
+
+                var valueBuilder = RazorIRBuilder.Create(value);
+                _builders.Push(valueBuilder);
             }
 
-            public override void VisitEndExpressionBlock(ExpressionChunkGenerator chunk, Block block)
+            public override void VisitEndExpressionBlock(ExpressionChunkGenerator chunkGenerator, Block block)
             {
-                Builder.Pop();
+                _builders.Pop();
             }
 
-            public override void VisitExpressionSpan(ExpressionChunkGenerator chunk, Span span)
+            public override void VisitExpressionSpan(ExpressionChunkGenerator chunkGenerator, Span span)
             {
                 Builder.Add(new CSharpTokenIRNode()
                 {
@@ -129,44 +145,19 @@ namespace Microsoft.AspNetCore.Razor.Evolution
                 });
             }
 
-            public override void VisitStartSectionBlock(SectionChunkGenerator chunk, Block block)
+            public override void VisitTypeMemberSpan(TypeMemberChunkGenerator chunkGenerator, Span span)
             {
-                Builder.Push(new SectionIRNode()
+                var functionsNode = new CSharpStatementIRNode()
-                {
-                    Name = chunk.SectionName,
-                });
-            }
-
-            public override void VisitEndSectionBlock(SectionChunkGenerator chunk, Block block)
-            {
-                Builder.Pop();
-            }
-
-            public override void VisitTypeMemberSpan(TypeMemberChunkGenerator chunk, Span span)
-            {
-                ClassBuilder.Add(new CSharpStatementIRNode()
                 {
                     Content = span.Content,
                     SourceLocation = span.Start,
-                });
+                    Parent = Class,
+                };
+
+                Class.Children.Add(functionsNode);
             }
 
-            public override void VisitAddTagHelperSpan(AddTagHelperChunkGenerator chunk, Span span)
+            public override void VisitStatementSpan(StatementChunkGenerator chunkGenerator, Span span)
-            {
-                // Empty for now
-            }
-
-            public override void VisitRemoveTagHelperSpan(RemoveTagHelperChunkGenerator chunk, Span span)
-            {
-                // Empty for now
-            }
-
-            public override void VisitTagHelperPrefixSpan(TagHelperPrefixDirectiveChunkGenerator chunk, Span span)
-            {
-                // Empty for now
-            }
-
-            public override void VisitStatementSpan(StatementChunkGenerator chunk, Span span)
             {
                 Builder.Add(new CSharpStatementIRNode()
                 {
@@ -175,21 +166,25 @@ namespace Microsoft.AspNetCore.Razor.Evolution
                 });
             }
 
-            public override void VisitSetBaseTypeSpan(SetBaseTypeChunkGenerator chunk, Span span)
+            public override void VisitMarkupSpan(MarkupChunkGenerator chunkGenerator, Span span)
             {
-                Class.BaseType = span.Content;
+                var currentChildren = Builder.Current.Children;
-            }
+                if (currentChildren.Count > 0 && currentChildren[currentChildren.Count - 1] is HtmlContentIRNode)
-
-            public override void VisitMarkupSpan(MarkupChunkGenerator chunk, Span span)
-            {
-                Builder.Add(new HtmlContentIRNode()
                 {
-                    Content = span.Content,
+                    var existingHtmlContent = (HtmlContentIRNode)currentChildren[currentChildren.Count - 1];
-                    SourceLocation = span.Start,
+                    existingHtmlContent.Content = string.Concat(existingHtmlContent.Content, span.Content);
-                });
+                }
+                else
+                {
+                    Builder.Add(new HtmlContentIRNode()
+                    {
+                        Content = span.Content,
+                        SourceLocation = span.Start,
+                    });
+                }
             }
 
-            public override void VisitImportSpan(AddImportChunkGenerator chunk, Span span)
+            public override void VisitImportSpan(AddImportChunkGenerator chunkGenerator, Span span)
             {
                 // For prettiness, let's insert the usings before the class declaration.
                 var i = 0;
@@ -210,6 +205,47 @@ namespace Microsoft.AspNetCore.Razor.Evolution
 
                 Namespace.Children.Insert(i, @using);
             }
+
+            private class ContainerRazorIRNode : RazorIRNode
+            {
+                private SourceLocation? _location;
+
+                public override IList<RazorIRNode> Children { get; } = new List<RazorIRNode>();
+
+                public override RazorIRNode Parent { get; set; }
+
+                internal override SourceLocation SourceLocation
+                {
+                    get
+                    {
+                        if (_location == null)
+                        {
+                            if (Children.Count > 0)
+                            {
+                                return Children[0].SourceLocation;
+                            }
+
+                            return SourceLocation.Undefined;
+                        }
+
+                        return _location.Value;
+                    }
+                    set
+                    {
+                        _location = value;
+                    }
+                }
+
+                public override void Accept(RazorIRNodeVisitor visitor)
+                {
+                    visitor.VisitDefault(this);
+                }
+
+                public override TResult Accept<TResult>(RazorIRNodeVisitor<TResult> visitor)
+                {
+                    return visitor.VisitDefault(this);
+                }
+            }
         }
     }
 }

src/Microsoft.AspNetCore.Razor.Evolution/Intermediate/BlockDirectiveIRNode.cs

@@ -1,29 +0,0 @@
-// 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.Legacy;
-
-namespace Microsoft.AspNetCore.Razor.Evolution.Intermediate
-{
-    public class BlockDirectiveIRNode : RazorIRNode
-    {
-        public string Name { get; set; }
-
-        public override IList<RazorIRNode> Children { get; } = new List<RazorIRNode>();
-
-        public override RazorIRNode Parent { get; set; }
-
-        internal override SourceLocation SourceLocation { get; set; }
-
-        public override void Accept(RazorIRNodeVisitor visitor)
-        {
-            visitor.VisitBlockDirective(this);
-        }
-
-        public override TResult Accept<TResult>(RazorIRNodeVisitor<TResult> visitor)
-        {
-            return visitor.VisitBlockDirective(this);
-        }
-    }
-}

src/Microsoft.AspNetCore.Razor.Evolution/Intermediate/CSharpAttributeValueIRNode.cs

@@ -1,6 +1,7 @@
 // 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;
 using System.Collections.Generic;
 using Microsoft.AspNetCore.Razor.Evolution.Legacy;
 
@@ -8,21 +9,33 @@ namespace Microsoft.AspNetCore.Razor.Evolution.Intermediate
 {
     public class CSharpAttributeValueIRNode : RazorIRNode
     {
-        public string Prefix { get; set; }
+        public override IList<RazorIRNode> Children { get; } = EmptyArray;
-
-        public override IList<RazorIRNode> Children { get; } = new List<RazorIRNode>();
 
         public override RazorIRNode Parent { get; set; }
 
         internal override SourceLocation SourceLocation { get; set; }
 
+        public string Prefix { get; set; }
+
+        public RazorIRNode Content { get; set; }
+
         public override void Accept(RazorIRNodeVisitor visitor)
         {
+            if (visitor == null)
+            {
+                throw new ArgumentNullException(nameof(visitor));
+            }
+
             visitor.VisitCSharpAttributeValue(this);
         }
 
         public override TResult Accept<TResult>(RazorIRNodeVisitor<TResult> visitor)
         {
+            if (visitor == null)
+            {
+                throw new ArgumentNullException(nameof(visitor));
+            }
+
             return visitor.VisitCSharpAttributeValue(this);
         }
     }

src/Microsoft.AspNetCore.Razor.Evolution/Intermediate/CSharpExpressionIRNode.cs

@@ -1,6 +1,7 @@
 // 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;
 using System.Collections.Generic;
 using Microsoft.AspNetCore.Razor.Evolution.Legacy;
 
@@ -8,21 +9,31 @@ namespace Microsoft.AspNetCore.Razor.Evolution.Intermediate
 {
     public class CSharpExpressionIRNode : RazorIRNode
     {
-        public override IList<RazorIRNode> Children { get; } = new List<RazorIRNode>();
+        public override IList<RazorIRNode> Children { get; } = EmptyArray;
 
         public override RazorIRNode Parent { get; set; }
 
         internal override SourceLocation SourceLocation { get; set; }
 
-        public string Content { get; set; }
+        public RazorIRNode Content { get; set; }
 
         public override void Accept(RazorIRNodeVisitor visitor)
         {
+            if (visitor == null)
+            {
+                throw new ArgumentNullException(nameof(visitor));
+            }
+
             visitor.VisitCSharpExpression(this);
         }
 
         public override TResult Accept<TResult>(RazorIRNodeVisitor<TResult> visitor)
         {
+            if (visitor == null)
+            {
+                throw new ArgumentNullException(nameof(visitor));
+            }
+
             return visitor.VisitCSharpExpression(this);
         }
     }

src/Microsoft.AspNetCore.Razor.Evolution/Intermediate/CSharpStatementIRNode.cs

@@ -1,6 +1,7 @@
 // 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;
 using System.Collections.Generic;
 using Microsoft.AspNetCore.Razor.Evolution.Legacy;
 
@@ -8,7 +9,7 @@ namespace Microsoft.AspNetCore.Razor.Evolution.Intermediate
 {
     public class CSharpStatementIRNode : RazorIRNode
     {
-        public override IList<RazorIRNode> Children { get; } = new List<RazorIRNode>();
+        public override IList<RazorIRNode> Children { get; } = EmptyArray;
 
         public override RazorIRNode Parent { get; set; }
 
@@ -18,11 +19,21 @@ namespace Microsoft.AspNetCore.Razor.Evolution.Intermediate
 
         public override void Accept(RazorIRNodeVisitor visitor)
         {
+            if (visitor == null)
+            {
+                throw new ArgumentNullException(nameof(visitor));
+            }
+
             visitor.VisitCSharpStatement(this);
         }
 
         public override TResult Accept<TResult>(RazorIRNodeVisitor<TResult> visitor)
         {
+            if (visitor == null)
+            {
+                throw new ArgumentNullException(nameof(visitor));
+            }
+
             return visitor.VisitCSharpStatement(this);
         }
     }

src/Microsoft.AspNetCore.Razor.Evolution/Intermediate/CSharpTokenIRNode.cs

@@ -1,6 +1,7 @@
 // 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;
 using System.Collections.Generic;
 using Microsoft.AspNetCore.Razor.Evolution.Legacy;
 
@@ -18,11 +19,21 @@ namespace Microsoft.AspNetCore.Razor.Evolution.Intermediate
 
         public override void Accept(RazorIRNodeVisitor visitor)
         {
+            if (visitor == null)
+            {
+                throw new ArgumentNullException(nameof(visitor));
+            }
+
             visitor.VisitCSharpToken(this);
         }
 
         public override TResult Accept<TResult>(RazorIRNodeVisitor<TResult> visitor)
         {
+            if (visitor == null)
+            {
+                throw new ArgumentNullException(nameof(visitor));
+            }
+
             return visitor.VisitCSharpToken(this);
         }
     }

src/Microsoft.AspNetCore.Razor.Evolution/Intermediate/ClassDeclarationIRNode.cs

@@ -9,6 +9,12 @@ namespace Microsoft.AspNetCore.Razor.Evolution.Intermediate
 {
     public class ClassDeclarationIRNode : RazorIRNode
     {
+        public override IList<RazorIRNode> Children { get; } = new List<RazorIRNode>();
+
+        public override RazorIRNode Parent { get; set; }
+
+        internal override SourceLocation SourceLocation { get; set; }
+
         public string AccessModifier { get; set; }
 
         public string Name { get; set; }
@@ -17,19 +23,23 @@ namespace Microsoft.AspNetCore.Razor.Evolution.Intermediate
 
         public IList<string> Interfaces { get; set; }
 
-        public override IList<RazorIRNode> Children { get; } = new List<RazorIRNode>();
-
-        public override RazorIRNode Parent { get; set; }
-
-        internal override SourceLocation SourceLocation { get; set; }
-
         public override void Accept(RazorIRNodeVisitor visitor)
         {
+            if (visitor == null)
+            {
+                throw new ArgumentNullException(nameof(visitor));
+            }
+
             visitor.VisitClass(this);
         }
 
         public override TResult Accept<TResult>(RazorIRNodeVisitor<TResult> visitor)
         {
+            if (visitor == null)
+            {
+                throw new ArgumentNullException(nameof(visitor));
+            }
+
             return visitor.VisitClass(this);
         }
     }

src/Microsoft.AspNetCore.Razor.Evolution/Intermediate/DefaultRazorIRBuilder.cs

@@ -42,10 +42,10 @@ namespace Microsoft.AspNetCore.Razor.Evolution.Intermediate
             {
                 node = Pop();
             }
-            
+
             return node;
         }
-        
+
         public override RazorIRNode Pop()
         {
             if (_depth == 0)

src/Microsoft.AspNetCore.Razor.Evolution/Intermediate/DirectiveTokenIRNode.cs

@@ -1,27 +0,0 @@
-// 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.Legacy;
-
-namespace Microsoft.AspNetCore.Razor.Evolution.Intermediate
-{
-    public class DirectiveTokenIRNode : RazorIRNode
-    {
-        public override IList<RazorIRNode> Children { get; } = new List<RazorIRNode>();
-
-        public override RazorIRNode Parent { get; set; }
-
-        internal override SourceLocation SourceLocation { get; set; }
-
-        public override void Accept(RazorIRNodeVisitor visitor)
-        {
-            visitor.VisitDirectiveToken(this);
-        }
-
-        public override TResult Accept<TResult>(RazorIRNodeVisitor<TResult> visitor)
-        {
-            return visitor.VisitDirectiveToken(this);
-        }
-    }
-}

src/Microsoft.AspNetCore.Razor.Evolution/Intermediate/DocumentIRNode.cs

@@ -1,6 +1,7 @@
 // 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;
 using System.Collections.Generic;
 using Microsoft.AspNetCore.Razor.Evolution.Legacy;
 
@@ -16,11 +17,21 @@ namespace Microsoft.AspNetCore.Razor.Evolution.Intermediate
 
         public override void Accept(RazorIRNodeVisitor visitor)
         {
+            if (visitor == null)
+            {
+                throw new ArgumentNullException(nameof(visitor));
+            }
+
             visitor.VisitDocument(this);
         }
 
         public override TResult Accept<TResult>(RazorIRNodeVisitor<TResult> visitor)
         {
+            if (visitor == null)
+            {
+                throw new ArgumentNullException(nameof(visitor));
+            }
+
             return visitor.VisitDocument(this);
         }
     }

src/Microsoft.AspNetCore.Razor.Evolution/Intermediate/HtmlAttributeIRNode.cs

@@ -1,6 +1,7 @@
 // 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;
 using System.Collections.Generic;
 using Microsoft.AspNetCore.Razor.Evolution.Legacy;
 
@@ -8,25 +9,37 @@ namespace Microsoft.AspNetCore.Razor.Evolution.Intermediate
 {
     public class HtmlAttributeIRNode : RazorIRNode
     {
-        public string Name { get; set; }
+        public override IList<RazorIRNode> Children { get; } = EmptyArray;
-
-        public string Prefix { get; set; }
-
-        public string Suffix { get; set; }
-
-        public override IList<RazorIRNode> Children { get; } = new List<RazorIRNode>();
 
         public override RazorIRNode Parent { get; set; }
 
         internal override SourceLocation SourceLocation { get; set; }
 
+        public string Name { get; set; }
+
+        public string Prefix { get; set; }
+
+        public RazorIRNode Value { get; set; }
+
+        public string Suffix { get; set; }
+
         public override void Accept(RazorIRNodeVisitor visitor)
         {
+            if (visitor == null)
+            {
+                throw new ArgumentNullException(nameof(visitor));
+            }
+
             visitor.VisitHtmlAttribute(this);
         }
 
         public override TResult Accept<TResult>(RazorIRNodeVisitor<TResult> visitor)
         {
+            if (visitor == null)
+            {
+                throw new ArgumentNullException(nameof(visitor));
+            }
+
             return visitor.VisitHtmlAttribute(this);
         }
     }

src/Microsoft.AspNetCore.Razor.Evolution/Intermediate/HtmlAttributeValueIRNode.cs

@@ -1,6 +1,7 @@
 // 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;
 using System.Collections.Generic;
 using Microsoft.AspNetCore.Razor.Evolution.Legacy;
 
@@ -8,21 +9,33 @@ namespace Microsoft.AspNetCore.Razor.Evolution.Intermediate
 {
     public class HtmlAttributeValueIRNode : RazorIRNode
     {
-        public string Prefix { get; set; }
+        public override IList<RazorIRNode> Children { get; } = EmptyArray;
-
-        public override IList<RazorIRNode> Children { get; } = new List<RazorIRNode>();
 
         public override RazorIRNode Parent { get; set; }
 
         internal override SourceLocation SourceLocation { get; set; }
 
+        public string Prefix { get; set; }
+
+        public string Content { get; set; }
+
         public override void Accept(RazorIRNodeVisitor visitor)
         {
+            if (visitor == null)
+            {
+                throw new ArgumentNullException(nameof(visitor));
+            }
+
             visitor.VisitHtmlAttributeValue(this);
         }
 
         public override TResult Accept<TResult>(RazorIRNodeVisitor<TResult> visitor)
         {
+            if (visitor == null)
+            {
+                throw new ArgumentNullException(nameof(visitor));
+            }
+
             return visitor.VisitHtmlAttributeValue(this);
         }
     }

src/Microsoft.AspNetCore.Razor.Evolution/Intermediate/HtmlContentIRNode.cs

@@ -11,7 +11,7 @@ namespace Microsoft.AspNetCore.Razor.Evolution.Intermediate
     {
         public string Content { get; set; }
 
-        public override IList<RazorIRNode> Children { get; } = new List<RazorIRNode>();
+        public override IList<RazorIRNode> Children { get; } = EmptyArray;
 
         public override RazorIRNode Parent { get; set; }
 

src/Microsoft.AspNetCore.Razor.Evolution/Intermediate/NamespaceDeclarationIRNode.cs

@@ -1,6 +1,7 @@
 // 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;
 using System.Collections.Generic;
 using Microsoft.AspNetCore.Razor.Evolution.Legacy;
 
@@ -14,13 +15,25 @@ namespace Microsoft.AspNetCore.Razor.Evolution.Intermediate
 
         internal override SourceLocation SourceLocation { get; set; }
 
+        public string Content { get; set; }
+
         public override void Accept(RazorIRNodeVisitor visitor)
         {
+            if (visitor == null)
+            {
+                throw new ArgumentNullException(nameof(visitor));
+            }
+
             visitor.VisitNamespace(this);
         }
 
         public override TResult Accept<TResult>(RazorIRNodeVisitor<TResult> visitor)
         {
+            if (visitor == null)
+            {
+                throw new ArgumentNullException(nameof(visitor));
+            }
+
             return visitor.VisitNamespace(this);
         }
     }

src/Microsoft.AspNetCore.Razor.Evolution/Intermediate/RazorIRNodeVisitor.cs

@@ -3,7 +3,7 @@
 
 namespace Microsoft.AspNetCore.Razor.Evolution.Intermediate
 {
-    public abstract class RazorIRNodeVisitor 
+    public abstract class RazorIRNodeVisitor
     {
         public virtual void Visit(RazorIRNode node)
         {
@@ -14,21 +14,11 @@ namespace Microsoft.AspNetCore.Razor.Evolution.Intermediate
         {
         }
 
-        public virtual void VisitDirectiveToken(DirectiveTokenIRNode node)
-        {
-            VisitDefault(node);
-        }
-
         public virtual void VisitTemplate(TemplateIRNode node)
         {
             VisitDefault(node);
         }
 
-        public virtual void VisitSection(SectionIRNode node)
-        {
-            VisitDefault(node);
-        }
-
         public virtual void VisitCSharpStatement(CSharpStatementIRNode node)
         {
             VisitDefault(node);
@@ -59,22 +49,12 @@ namespace Microsoft.AspNetCore.Razor.Evolution.Intermediate
             VisitDefault(node);
         }
 
-        public virtual void VisitSingleLineDirective(SingleLineDirectiveIRNode node)
-        {
-            VisitDefault(node);
-        }
-
-        public virtual void VisitBlockDirective(BlockDirectiveIRNode node)
-        {
-            VisitDefault(node);
-        }
-
         public virtual void VisitClass(ClassDeclarationIRNode node)
         {
             VisitDefault(node);
         }
 
-        public virtual void VisitMethodDeclaration(MethodDeclarationIRNode node)
+        public virtual void VisitRazorMethodDeclaration(RazorMethodDeclarationIRNode node)
         {
             VisitDefault(node);
         }

src/Microsoft.AspNetCore.Razor.Evolution/Intermediate/RazorIRNodeVisitorOfT.cs

@@ -15,21 +15,11 @@ namespace Microsoft.AspNetCore.Razor.Evolution.Intermediate
             return default(TResult);
         }
 
-        public virtual TResult VisitDirectiveToken(DirectiveTokenIRNode node)
-        {
-            return VisitDefault(node);
-        }
-
         public virtual TResult VisitTemplate(TemplateIRNode node)
         {
             return VisitDefault(node);
         }
 
-        public virtual TResult VisitSection(SectionIRNode node)
-        {
-            return VisitDefault(node);
-        }
-
         public virtual TResult VisitCSharpStatement(CSharpStatementIRNode node)
         {
             return VisitDefault(node);
@@ -65,16 +55,7 @@ namespace Microsoft.AspNetCore.Razor.Evolution.Intermediate
             return VisitDefault(node);
         }
 
-        public virtual TResult VisitSingleLineDirective(SingleLineDirectiveIRNode node)
+        public virtual TResult VisitRazorMethodDeclaration(RazorMethodDeclarationIRNode node)
-        {
-            return VisitDefault(node);
-        }
-
-        public virtual TResult VisitBlockDirective(BlockDirectiveIRNode node)
-        {
-            return VisitDefault(node);
-        }
-        public virtual TResult VisitMethodDeclaration(MethodDeclarationIRNode node)
         {
             return VisitDefault(node);
         }

src/Microsoft.AspNetCore.Razor.Evolution/Intermediate/RazorMethodDeclarationIRNode.cs

@@ -1,13 +1,20 @@
 // 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;
 using System.Collections.Generic;
 using Microsoft.AspNetCore.Razor.Evolution.Legacy;
 
 namespace Microsoft.AspNetCore.Razor.Evolution.Intermediate
 {
-    public class MethodDeclarationIRNode : RazorIRNode
+    public class RazorMethodDeclarationIRNode : RazorIRNode
     {
+        public override IList<RazorIRNode> Children { get; } = new List<RazorIRNode>();
+
+        public override RazorIRNode Parent { get; set; }
+
+        internal override SourceLocation SourceLocation { get; set; }
+
         public string AccessModifier { get; set; }
 
         public IList<string> Modifiers { get; set; }
@@ -16,20 +23,24 @@ namespace Microsoft.AspNetCore.Razor.Evolution.Intermediate
 
         public string ReturnType { get; set; }
 
-        public override IList<RazorIRNode> Children { get; } = new List<RazorIRNode>();
-
-        public override RazorIRNode Parent { get; set; }
-
-        internal override SourceLocation SourceLocation { get; set; }
-
         public override void Accept(RazorIRNodeVisitor visitor)
         {
-            visitor.VisitMethodDeclaration(this);
+            if (visitor == null)
+            {
+                throw new ArgumentNullException(nameof(visitor));
+            }
+
+            visitor.VisitRazorMethodDeclaration(this);
         }
 
         public override TResult Accept<TResult>(RazorIRNodeVisitor<TResult> visitor)
         {
-            return visitor.VisitMethodDeclaration(this);
+            if (visitor == null)
+            {
+                throw new ArgumentNullException(nameof(visitor));
+            }
+
+            return visitor.VisitRazorMethodDeclaration(this);
         }
     }
 }

src/Microsoft.AspNetCore.Razor.Evolution/Intermediate/SectionIRNode.cs

@@ -1,29 +0,0 @@
-// 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.Legacy;
-
-namespace Microsoft.AspNetCore.Razor.Evolution.Intermediate
-{
-    public class SectionIRNode : RazorIRNode
-    {
-        public string Name { get; set; }
-
-        public override IList<RazorIRNode> Children { get; } = new List<RazorIRNode>();
-
-        public override RazorIRNode Parent { get; set; }
-
-        internal override SourceLocation SourceLocation { get; set; }
-
-        public override void Accept(RazorIRNodeVisitor visitor)
-        {
-            visitor.VisitSection(this);
-        }
-
-        public override TResult Accept<TResult>(RazorIRNodeVisitor<TResult> visitor)
-        {
-            return visitor.VisitSection(this);
-        }
-    }
-}

src/Microsoft.AspNetCore.Razor.Evolution/Intermediate/SingleLineDirectiveIRNode.cs

@@ -1,29 +0,0 @@
-// 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.Legacy;
-
-namespace Microsoft.AspNetCore.Razor.Evolution.Intermediate
-{
-    public class SingleLineDirectiveIRNode : RazorIRNode
-    {
-        public string Name { get; set; }
-
-        public override IList<RazorIRNode> Children { get; } = new List<RazorIRNode>();
-
-        public override RazorIRNode Parent { get; set; }
-
-        internal override SourceLocation SourceLocation { get; set; }
-
-        public override void Accept(RazorIRNodeVisitor visitor)
-        {
-            visitor.VisitSingleLineDirective(this);
-        }
-
-        public override TResult Accept<TResult>(RazorIRNodeVisitor<TResult> visitor)
-        {
-            return visitor.VisitSingleLineDirective(this);
-        }
-    }
-}

src/Microsoft.AspNetCore.Razor.Evolution/Intermediate/TemplateIRNode.cs

@@ -1,6 +1,7 @@
 // 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;
 using System.Collections.Generic;
 using Microsoft.AspNetCore.Razor.Evolution.Legacy;
 
@@ -16,11 +17,21 @@ namespace Microsoft.AspNetCore.Razor.Evolution.Intermediate
 
         public override void Accept(RazorIRNodeVisitor visitor)
         {
+            if (visitor == null)
+            {
+                throw new ArgumentNullException(nameof(visitor));
+            }
+
             visitor.VisitTemplate(this);
         }
 
         public override TResult Accept<TResult>(RazorIRNodeVisitor<TResult> visitor)
         {
+            if (visitor == null)
+            {
+                throw new ArgumentNullException(nameof(visitor));
+            }
+
             return visitor.VisitTemplate(this);
         }
     }

src/Microsoft.AspNetCore.Razor.Evolution/Intermediate/UsingStatementIRNode.cs

@@ -9,7 +9,7 @@ namespace Microsoft.AspNetCore.Razor.Evolution.Intermediate
 {
     public class UsingStatementIRNode : RazorIRNode
     {
-        public override IList<RazorIRNode> Children { get; } = new List<RazorIRNode>();
+        public override IList<RazorIRNode> Children { get; } = EmptyArray;
 
         public override RazorIRNode Parent { get; set; }
 

src/Microsoft.AspNetCore.Razor.Evolution/Legacy/AddTagHelperChunkGenerator.cs

@@ -17,7 +17,6 @@ namespace Microsoft.AspNetCore.Razor.Evolution.Legacy
 
         public override void Accept(ParserVisitor visitor, Span span)
         {
-            visitor.VisitAddTagHelperSpan(this, span);
         }
 
         public override void GenerateChunk(Span target, ChunkGeneratorContext context)

src/Microsoft.AspNetCore.Razor.Evolution/Legacy/ParserVisitor.cs

@@ -8,7 +8,7 @@ namespace Microsoft.AspNetCore.Razor.Evolution.Legacy
         public virtual void VisitBlock(Block block)
         {
             VisitStartBlock(block);
-            
+
             for (var i = 0; i < block.Children.Count; i++)
             {
                 block.Children[i].Accept(this);
@@ -69,14 +69,6 @@ namespace Microsoft.AspNetCore.Razor.Evolution.Legacy
         {
         }
 
-        public virtual void VisitSetBaseTypeSpan(SetBaseTypeChunkGenerator chunk, Span span)
-        {
-        }
-
-        public virtual void VisitTagHelperPrefixSpan(TagHelperPrefixDirectiveChunkGenerator chunk, Span span)
-        {
-        }
-
         public virtual void VisitTypeMemberSpan(TypeMemberChunkGenerator chunk, Span span)
         {
         }
@@ -85,18 +77,10 @@ namespace Microsoft.AspNetCore.Razor.Evolution.Legacy
         {
         }
 
-        public virtual void VisitRemoveTagHelperSpan(RemoveTagHelperChunkGenerator chunk, Span span)
-        {
-        }
-
         public virtual void VisitImportSpan(AddImportChunkGenerator chunk, Span span)
         {
         }
 
-        public virtual void VisitAddTagHelperSpan(AddTagHelperChunkGenerator chunk, Span span)
-        {
-        }
-
         public virtual void VisitStatementSpan(StatementChunkGenerator chunk, Span span)
         {
         }
@@ -113,14 +97,6 @@ namespace Microsoft.AspNetCore.Razor.Evolution.Legacy
         {
         }
 
-        public virtual void VisitStartSectionBlock(SectionChunkGenerator chunk, Block block)
-        {
-        }
-
-        public virtual void VisitEndSectionBlock(SectionChunkGenerator chunk, Block block)
-        {
-        }
-
         public virtual void VisitEndCommentBlock(RazorCommentChunkGenerator chunk, Block block)
         {
         }

src/Microsoft.AspNetCore.Razor.Evolution/Legacy/RemoveTagHelperChunkGenerator.cs

@@ -17,7 +17,6 @@ namespace Microsoft.AspNetCore.Razor.Evolution.Legacy
 
         public override void Accept(ParserVisitor visitor, Span span)
         {
-            visitor.VisitRemoveTagHelperSpan(this, span);
         }
 
         public override void GenerateChunk(Span target, ChunkGeneratorContext context)

src/Microsoft.AspNetCore.Razor.Evolution/Legacy/SectionChunkGenerator.cs

@@ -16,12 +16,10 @@ namespace Microsoft.AspNetCore.Razor.Evolution.Legacy
 
         public override void AcceptStart(ParserVisitor visitor, Block block)
         {
-            visitor.VisitStartSectionBlock(this, block);
         }
 
         public override void AcceptEnd(ParserVisitor visitor, Block block)
         {
-            visitor.VisitEndSectionBlock(this, block);
         }
 
         public override void GenerateStartParentChunk(Block target, ChunkGeneratorContext context)

src/Microsoft.AspNetCore.Razor.Evolution/Legacy/SetBaseTypeChunkGenerator.cs

@@ -16,7 +16,6 @@ namespace Microsoft.AspNetCore.Razor.Evolution.Legacy
 
         public override void Accept(ParserVisitor visitor, Span span)
         {
-            visitor.VisitSetBaseTypeSpan(this, span);
         }
 
         public override void GenerateChunk(Span target, ChunkGeneratorContext context)

src/Microsoft.AspNetCore.Razor.Evolution/Legacy/TagHelperChunkGenerator.cs

@@ -2,8 +2,6 @@
 // Licensed under the Apache License, Version 2.0. See License.txt in the project root for license information.
 
 using System.Collections.Generic;
-using System.Diagnostics;
-using System.Linq;
 
 namespace Microsoft.AspNetCore.Razor.Evolution.Legacy
 {
@@ -85,5 +83,13 @@ namespace Microsoft.AspNetCore.Razor.Evolution.Legacy
         {
             //context.ChunkTreeBuilder.EndParentChunk();
         }
+
+        public override void AcceptStart(ParserVisitor visitor, Block block)
+        {
+        }
+
+        public override void AcceptEnd(ParserVisitor visitor, Block block)
+        {
+        }
     }
 }

src/Microsoft.AspNetCore.Razor.Evolution/Legacy/TagHelperPrefixDirectiveChunkGenerator.cs

@@ -17,7 +17,6 @@ namespace Microsoft.AspNetCore.Razor.Evolution.Legacy
 
         public override void Accept(ParserVisitor visitor, Span span)
         {
-            visitor.VisitTagHelperPrefixSpan(this, span);
         }
 
         public override void GenerateChunk(Span target, ChunkGeneratorContext context)

test/Microsoft.AspNetCore.Razor.Evolution.Test/Intermediate/DefaultRazorIRLoweringPhaseIntegrationTest.cs

@@ -7,18 +7,21 @@ using System;
 
 namespace Microsoft.AspNetCore.Razor.Evolution.Intermediate
 {
-    public class LoweringIntegrationTest
+    public class DefaultRazorIRLoweringPhaseIntegrationTest
     {
         [Fact]
         public void Lower_EmptyDocument()
         {
+            // Arrange
             var codeDocument = TestRazorCodeDocument.CreateEmpty();
 
+            // Act
             var irDocument = Lower(codeDocument);
 
+            // Assert
             var @namespace = SingleChild<NamespaceDeclarationIRNode>(irDocument);
             var @class = SingleChild<ClassDeclarationIRNode>(@namespace);
-            var method = SingleChild<MethodDeclarationIRNode>(@class);
+            var method = SingleChild<RazorMethodDeclarationIRNode>(@class);
             var html = SingleChild<HtmlContentIRNode>(method);
 
             Assert.Equal(string.Empty, html.Content);
@@ -27,68 +30,118 @@ namespace Microsoft.AspNetCore.Razor.Evolution.Intermediate
         [Fact]
         public void Lower_HelloWorld()
         {
+            // Arrange
             var codeDocument = TestRazorCodeDocument.Create("Hello, World!");
 
+            // Act
             var irDocument = Lower(codeDocument);
 
+            // Assert
             var @namespace = SingleChild<NamespaceDeclarationIRNode>(irDocument);
             var @class = SingleChild<ClassDeclarationIRNode>(@namespace);
-            var method = SingleChild<MethodDeclarationIRNode>(@class);
+            var method = SingleChild<RazorMethodDeclarationIRNode>(@class);
             var html = SingleChild<HtmlContentIRNode>(method);
 
             Assert.Equal("Hello, World!", html.Content);
         }
 
         [Fact]
-        public void Lower_HtmlWithAttributes()
+        public void Lower_HtmlWithDataDashAttributes()
         {
+            // Arrange
             var codeDocument = TestRazorCodeDocument.Create(@"
 <html>
     <body>
         <span data-val=""@Hello"" />
     </body>
 </html>");
+
+            // Act
             var irDocument = Lower(codeDocument);
-            
+
+            // Assert
             var @namespace = SingleChild<NamespaceDeclarationIRNode>(irDocument);
             var @class = SingleChild<ClassDeclarationIRNode>(@namespace);
-            var method = SingleChild<MethodDeclarationIRNode>(@class);
+            var method = SingleChild<RazorMethodDeclarationIRNode>(@class);
             Children(method,
-                n => Html(Environment.NewLine, n),
+                n => Html(
-                n => Html("<html>", n),
+@"
-                n => Html(Environment.NewLine + "    ", n),
+<html>
-                n => Html("<body>", n),
+    <body>
-                n => Html(Environment.NewLine + "        ", n),
+        <span data-val=""", n),
-                n => Html("<span", n),
-                n => Html(" data-val=\"", n),
                 n => CSharpExpression("Hello", n),
-                n => Html("\"", n),
+                n => Html(@""" />
-                n => Html(" />", n),
+    </body>
-                n => Html(Environment.NewLine + "    ", n),
+</html>", n));
-                n => Html("</body>", n),
+        }
-                n => Html(Environment.NewLine, n),
+
-                n => Html("</html>", n));
+        [Fact]
+        public void Lower_HtmlWithConditionalAttributes()
+        {
+            // Arrange
+            var codeDocument = TestRazorCodeDocument.Create(@"
+<html>
+    <body>
+        <span val=""@Hello World"" />
+    </body>
+</html>");
+
+            // Act
+            var irDocument = Lower(codeDocument);
+
+            // Assert
+            var @namespace = SingleChild<NamespaceDeclarationIRNode>(irDocument);
+            var @class = SingleChild<ClassDeclarationIRNode>(@namespace);
+            var method = SingleChild<RazorMethodDeclarationIRNode>(@class);
+            Children(method,
+                n => Html(
+@"
+<html>
+    <body>
+        <span", n),
+
+                n => ConditionalAttribute(
+                    prefix: " val=\"",
+                    name: "val",
+                    suffix: "\"",
+                    node: n,
+                    valueValidators: new Action<RazorIRNode>[]
+                    {
+                        value => CSharpAttributeValue(string.Empty, "Hello", value),
+                        value => LiteralAttributeValue(" ",  "World", value)
+                    }),
+                n => Html(@" />
+    </body>
+</html>", n));
         }
 
         [Fact]
         public void Lower_WithUsing()
         {
+            // Arrange
             var codeDocument = TestRazorCodeDocument.Create(@"@functions { public int Foo { get; set; }}");
+
+            // Act
             var irDocument = Lower(codeDocument);
 
+            // Assert
             var @namespace = SingleChild<NamespaceDeclarationIRNode>(irDocument);
             var @class = SingleChild<ClassDeclarationIRNode>(@namespace);
             Children(@class,
-                n => Assert.IsType<MethodDeclarationIRNode>(n),
+                n => Assert.IsType<RazorMethodDeclarationIRNode>(n),
                 n => Assert.IsType<CSharpStatementIRNode>(n));
         }
 
         [Fact]
         public void Lower_WithFunctions()
         {
+            // Arrange
             var codeDocument = TestRazorCodeDocument.Create(@"@using System");
+
+            // Act
             var irDocument = Lower(codeDocument);
 
+            // Assert
             var @namespace = SingleChild<NamespaceDeclarationIRNode>(irDocument);
             Children(@namespace,
                 n => Using("using System", n),

test/Microsoft.AspNetCore.Razor.Evolution.Test/Intermediate/RazorIRAssert.cs

@@ -86,6 +86,60 @@ namespace Microsoft.AspNetCore.Razor.Evolution.Intermediate
             }
         }
 
+        public static void ConditionalAttribute(
+            string prefix,
+            string name,
+            string suffix,
+            RazorIRNode node,
+            params Action<RazorIRNode>[] valueValidators)
+        {
+            var attribute = Assert.IsType<HtmlAttributeIRNode>(node);
+
+            try
+            {
+                Assert.Equal(prefix, attribute.Prefix);
+                Assert.Equal(name, attribute.Name);
+                Assert.Equal(suffix, attribute.Suffix);
+
+                Children(attribute.Value, valueValidators);
+            }
+            catch (XunitException e)
+            {
+                throw new IRAssertException(attribute, attribute.Value.Children, e.Message, e);
+            }
+        }
+
+        public static void CSharpAttributeValue(string prefix, string expected, RazorIRNode node)
+        {
+            var attributeValue = Assert.IsType<CSharpAttributeValueIRNode>(node);
+
+            try
+            {
+                Assert.Equal(prefix, attributeValue.Prefix);
+
+                Children(attributeValue.Content, n => CSharpExpression(expected, n));
+            }
+            catch (XunitException e)
+            {
+                throw new IRAssertException(attributeValue, attributeValue.Content.Children, e.Message, e);
+            }
+        }
+
+        public static void LiteralAttributeValue(string prefix, string expected, RazorIRNode node)
+        {
+            var attributeValue = Assert.IsType<HtmlAttributeValueIRNode>(node);
+
+            try
+            {
+                Assert.Equal(prefix, attributeValue.Prefix);
+                Assert.Equal(expected, attributeValue.Content);
+            }
+            catch (XunitException e)
+            {
+                throw new IRAssertException(attributeValue, e.Message);
+            }
+        }
+
         public static void CSharpExpression(string expected, RazorIRNode node)
         {
             try
@@ -93,9 +147,9 @@ namespace Microsoft.AspNetCore.Razor.Evolution.Intermediate
                 var cSharp = Assert.IsType<CSharpExpressionIRNode>(node);
 
                 var content = new StringBuilder();
-                for (var i = 0; i < cSharp.Children.Count; i++)
+                for (var i = 0; i < cSharp.Content.Children.Count; i++)
                 {
-                    content.Append(((CSharpTokenIRNode)cSharp.Children[i]).Content);
+                    content.Append(((CSharpTokenIRNode)cSharp.Content.Children[i]).Content);
                 }
 
                 Assert.Equal(expected, content.ToString());
@@ -108,7 +162,7 @@ namespace Microsoft.AspNetCore.Razor.Evolution.Intermediate
 
         private class IRAssertException : XunitException
         {
-            public IRAssertException(RazorIRNode node, string userMessage) 
+            public IRAssertException(RazorIRNode node, string userMessage)
                 : base(Format(node, null, userMessage))
             {
                 Node = node;
@@ -119,7 +173,7 @@ namespace Microsoft.AspNetCore.Razor.Evolution.Intermediate
             {
                 Node = node;
                 Nodes = nodes;
-            } 
+            }
 
             public IRAssertException(
                 RazorIRNode node,