Add diagnostics to the IR.

- Added a `Diagnostics` and `HasDiagnostics` properties to `RazorIRNode`. The `HasDiagnostics` property was necessary in order to traverse nodes without forcibly instantiating their diagnostic lists.
- Added `GetAllDiagnostics` extension method for `RazorIRNode` to provide a way to retrieve all diagnostics that exist on and under a `RazorIRNode`.
- Updated `RazorIRNodeWriter` to display any diagnostics that exist on IR nodes.
- Internal `RazorIRNode`s do not have mutable `Diagnostics` because we don't currently add diagnostics to these elements.
- Added `DefaultIRLoweringPhaseTest` to validate that errors flow from syntax tree to IR document. Also added a missing test.
- Updated the `CSharpLoweringPhaseTest`s to properly validate that errors flow from IR document => csharp document. This resulted in movement of code to the ir lowering phase tests.

#1412

src/Microsoft.AspNetCore.Razor.Language/DefaultRazorCSharpLoweringPhase.cs

@@ -20,9 +20,6 @@ namespace Microsoft.AspNetCore.Razor.Language
             var irDocument = codeDocument.GetIRDocument();
             ThrowForMissingDocumentDependency(irDocument);
 
-            var syntaxTree = codeDocument.GetSyntaxTree();
-            ThrowForMissingDocumentDependency(syntaxTree);
-
             var target = irDocument.Target;
             if (target == null)
             {
@@ -59,13 +56,7 @@ namespace Microsoft.AspNetCore.Razor.Language
             documentWriter.WriteDocument(irDocument);
 
             var diagnostics = new List<RazorDiagnostic>();
-            diagnostics.AddRange(syntaxTree.Diagnostics);
-
-            var importSyntaxTrees = codeDocument.GetImportSyntaxTrees();
-            for (var i = 0; i < importSyntaxTrees?.Count; i++)
-            {
-                diagnostics.AddRange(importSyntaxTrees[i].Diagnostics);
-            }
+            diagnostics.AddRange(irDocument.GetAllDiagnostics());
             diagnostics.AddRange(renderingContext.Diagnostics);
 
             var csharpDocument = RazorCSharpDocument.Create(

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

@@ -27,7 +27,7 @@ namespace Microsoft.AspNetCore.Razor.Language
 
             // This might not have been set if there are no tag helpers.
             var tagHelperContext = codeDocument.GetTagHelperContext();
-            
+
             var document = new DocumentIRNode();
             var builder = RazorIRBuilder.Create(document);
 
@@ -76,6 +76,26 @@ namespace Microsoft.AspNetCore.Razor.Language
                 builder.Insert(i++, @using);
             }
 
+            // The document should contain all errors that currently exist in the system. This involves
+            // adding the errors from the primary and imported syntax trees.
+
+            for (i = 0; i < syntaxTree.Diagnostics.Count; i++)
+            {
+                document.Diagnostics.Add(syntaxTree.Diagnostics[i]);
+            }
+
+            if (imports != null)
+            {
+                for (i = 0; i < imports.Count; i++)
+                {
+                    var import = imports[i];
+                    for (var j = 0; j < import.Diagnostics.Count; j++)
+                    {
+                        document.Diagnostics.Add(import.Diagnostics[j]);
+                    }
+                }
+            }
+
             codeDocument.SetIRDocument(document);
         }
 

src/Microsoft.AspNetCore.Razor.Language/Intermediate/AddPreallocatedTagHelperHtmlAttributeIRNode.cs

@@ -8,10 +8,14 @@ namespace Microsoft.AspNetCore.Razor.Language.Intermediate
 {
     internal sealed class AddPreallocatedTagHelperHtmlAttributeIRNode : ExtensionIRNode
     {
+        public override RazorDiagnosticCollection Diagnostics { get; } = ReadOnlyDiagnosticCollection.Instance;
+        
         public override RazorIRNodeCollection Children => ReadOnlyIRNodeCollection.Instance;
 
         public override SourceSpan? Source { get; set; }
 
+        public override bool HasDiagnostics => false;
+
         public string VariableName { get; set; }
 
         public override void Accept(RazorIRNodeVisitor visitor)

src/Microsoft.AspNetCore.Razor.Language/Intermediate/AddTagHelperHtmlAttributeIRNode.cs

@@ -8,12 +8,29 @@ namespace Microsoft.AspNetCore.Razor.Language.Intermediate
 {
     public sealed class AddTagHelperHtmlAttributeIRNode : RazorIRNode
     {
+        private RazorDiagnosticCollection _diagnostics;
+
         public override ItemCollection Annotations => ReadOnlyItemCollection.Empty;
 
+        public override RazorDiagnosticCollection Diagnostics
+        {
+            get
+            {
+                if (_diagnostics == null)
+                {
+                    _diagnostics = new DefaultDiagnosticCollection();
+                }
+
+                return _diagnostics;
+            }
+        }
+
         public override RazorIRNodeCollection Children { get; } = new DefaultIRNodeCollection();
 
         public override SourceSpan? Source { get; set; }
 
+        public override bool HasDiagnostics => _diagnostics != null && _diagnostics.Count > 0;
+
         public string Name { get; set; }
 
         internal HtmlAttributeValueStyle ValueStyle { get; set; }

src/Microsoft.AspNetCore.Razor.Language/Intermediate/CSharpCodeAttributeValueIRNode.cs

@@ -7,12 +7,29 @@ namespace Microsoft.AspNetCore.Razor.Language.Intermediate
 {
     public sealed class CSharpCodeAttributeValueIRNode : RazorIRNode
     {
+        private RazorDiagnosticCollection _diagnostics;
+
         public override ItemCollection Annotations => ReadOnlyItemCollection.Empty;
 
+        public override RazorDiagnosticCollection Diagnostics
+        {
+            get
+            {
+                if (_diagnostics == null)
+                {
+                    _diagnostics = new DefaultDiagnosticCollection();
+                }
+
+                return _diagnostics;
+            }
+        }
+        
         public override RazorIRNodeCollection Children { get; } = new DefaultIRNodeCollection();
 
         public override SourceSpan? Source { get; set; }
 
+        public override bool HasDiagnostics => _diagnostics != null && _diagnostics.Count > 0;
+
         public string Prefix { get; set; }
 
         public override void Accept(RazorIRNodeVisitor visitor)

src/Microsoft.AspNetCore.Razor.Language/Intermediate/CSharpCodeIRNode.cs

@@ -8,6 +8,7 @@ namespace Microsoft.AspNetCore.Razor.Language.Intermediate
     public sealed class CSharpCodeIRNode : RazorIRNode
     {
         private ItemCollection _annotations;
+        private RazorDiagnosticCollection _diagnostics;
 
         public override ItemCollection Annotations
         {
@@ -22,10 +23,25 @@ namespace Microsoft.AspNetCore.Razor.Language.Intermediate
             }
         }
 
+        public override RazorDiagnosticCollection Diagnostics
+        {
+            get
+            {
+                if (_diagnostics == null)
+                {
+                    _diagnostics = new DefaultDiagnosticCollection();
+                }
+
+                return _diagnostics;
+            }
+        }
+
         public override RazorIRNodeCollection Children { get; } = new DefaultIRNodeCollection();
 
         public override SourceSpan? Source { get; set; }
 
+        public override bool HasDiagnostics => _diagnostics != null && _diagnostics.Count > 0;
+
         public override void Accept(RazorIRNodeVisitor visitor)
         {
             if (visitor == null)

src/Microsoft.AspNetCore.Razor.Language/Intermediate/CSharpExpressionAttributeValueIRNode.cs

@@ -7,12 +7,29 @@ namespace Microsoft.AspNetCore.Razor.Language.Intermediate
 {
     public sealed class CSharpExpressionAttributeValueIRNode : RazorIRNode
     {
+        private RazorDiagnosticCollection _diagnostics;
+
         public override ItemCollection Annotations => ReadOnlyItemCollection.Empty;
 
+        public override RazorDiagnosticCollection Diagnostics
+        {
+            get
+            {
+                if (_diagnostics == null)
+                {
+                    _diagnostics = new DefaultDiagnosticCollection();
+                }
+
+                return _diagnostics;
+            }
+        }
+
         public override RazorIRNodeCollection Children { get; } = new DefaultIRNodeCollection();
 
         public override SourceSpan? Source { get; set; }
 
+        public override bool HasDiagnostics => _diagnostics != null && _diagnostics.Count > 0;
+
         public string Prefix { get; set; }
 
         public override void Accept(RazorIRNodeVisitor visitor)

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

@@ -8,6 +8,7 @@ namespace Microsoft.AspNetCore.Razor.Language.Intermediate
     public sealed class CSharpExpressionIRNode : RazorIRNode
     {
         private ItemCollection _annotations;
+        private RazorDiagnosticCollection _diagnostics;
 
         public override ItemCollection Annotations
         {
@@ -22,10 +23,25 @@ namespace Microsoft.AspNetCore.Razor.Language.Intermediate
             }
         }
 
+        public override RazorDiagnosticCollection Diagnostics
+        {
+            get
+            {
+                if (_diagnostics == null)
+                {
+                    _diagnostics = new DefaultDiagnosticCollection();
+                }
+
+                return _diagnostics;
+            }
+        }
+
         public override RazorIRNodeCollection Children { get; } = new DefaultIRNodeCollection();
 
         public override SourceSpan? Source { get; set; }
 
+        public override bool HasDiagnostics => _diagnostics != null && _diagnostics.Count > 0;
+
         public override void Accept(RazorIRNodeVisitor visitor)
         {
             if (visitor == null)

src/Microsoft.AspNetCore.Razor.Language/Intermediate/ChecksumIRNode.cs

@@ -7,12 +7,29 @@ namespace Microsoft.AspNetCore.Razor.Language.Intermediate
 {
     public sealed class ChecksumIRNode : RazorIRNode
     {
+        private RazorDiagnosticCollection _diagnostics;
+
         public override ItemCollection Annotations => ReadOnlyItemCollection.Empty;
 
+        public override RazorDiagnosticCollection Diagnostics
+        {
+            get
+            {
+                if (_diagnostics == null)
+                {
+                    _diagnostics = new DefaultDiagnosticCollection();
+                }
+
+                return _diagnostics;
+            }
+        }
+
         public override RazorIRNodeCollection Children => ReadOnlyIRNodeCollection.Instance;
 
         public override SourceSpan? Source { get; set; }
 
+        public override bool HasDiagnostics => _diagnostics != null && _diagnostics.Count > 0;
+
         public string Bytes { get; set; }
 
         public string FilePath { get; set; }

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

@@ -9,6 +9,7 @@ namespace Microsoft.AspNetCore.Razor.Language.Intermediate
     public sealed class ClassDeclarationIRNode : MemberDeclarationIRNode
     {
         private ItemCollection _annotations;
+        private RazorDiagnosticCollection _diagnostics;
 
         public override ItemCollection Annotations
         {
@@ -23,10 +24,25 @@ namespace Microsoft.AspNetCore.Razor.Language.Intermediate
             }
         }
 
+        public override RazorDiagnosticCollection Diagnostics
+        {
+            get
+            {
+                if (_diagnostics == null)
+                {
+                    _diagnostics = new DefaultDiagnosticCollection();
+                }
+
+                return _diagnostics;
+            }
+        }
+
         public override RazorIRNodeCollection Children { get; } = new DefaultIRNodeCollection();
 
         public override SourceSpan? Source { get; set; }
 
+        public override bool HasDiagnostics => _diagnostics != null && _diagnostics.Count > 0;
+
         public string AccessModifier { get; set; }
 
         public string Name { get; set; }

src/Microsoft.AspNetCore.Razor.Language/Intermediate/CreateTagHelperIRNode.cs

@@ -7,12 +7,29 @@ namespace Microsoft.AspNetCore.Razor.Language.Intermediate
 {
     public sealed class CreateTagHelperIRNode : RazorIRNode
     {
+        private RazorDiagnosticCollection _diagnostics;
+
         public override ItemCollection Annotations => ReadOnlyItemCollection.Empty;
 
+        public override RazorDiagnosticCollection Diagnostics
+        {
+            get
+            {
+                if (_diagnostics == null)
+                {
+                    _diagnostics = new DefaultDiagnosticCollection();
+                }
+
+                return _diagnostics;
+            }
+        }
+
         public override RazorIRNodeCollection Children => ReadOnlyIRNodeCollection.Instance;
 
         public override SourceSpan? Source { get; set; }
 
+        public override bool HasDiagnostics => _diagnostics != null && _diagnostics.Count > 0;
+
         public string TagHelperTypeName { get; set; }
 
         public TagHelperDescriptor Descriptor { get; set; }

src/Microsoft.AspNetCore.Razor.Language/Intermediate/DeclarePreallocatedTagHelperAttributeIRNode.cs

@@ -9,10 +9,14 @@ namespace Microsoft.AspNetCore.Razor.Language.Intermediate
 {
     internal sealed class DeclarePreallocatedTagHelperAttributeIRNode : ExtensionIRNode
     {
+        public override RazorDiagnosticCollection Diagnostics { get; } = ReadOnlyDiagnosticCollection.Instance;
+        
         public override RazorIRNodeCollection Children => ReadOnlyIRNodeCollection.Instance;
 
         public override SourceSpan? Source { get; set; }
 
+        public override bool HasDiagnostics => false;
+
         public string VariableName { get; set; }
 
         public string Name { get; set; }

src/Microsoft.AspNetCore.Razor.Language/Intermediate/DeclarePreallocatedTagHelperHtmlAttributeIRNode.cs

@@ -9,10 +9,14 @@ namespace Microsoft.AspNetCore.Razor.Language.Intermediate
 {
     internal sealed class DeclarePreallocatedTagHelperHtmlAttributeIRNode : ExtensionIRNode
     {
+        public override RazorDiagnosticCollection Diagnostics { get; } = ReadOnlyDiagnosticCollection.Instance;
+        
         public override RazorIRNodeCollection Children => ReadOnlyIRNodeCollection.Instance;
 
         public override SourceSpan? Source { get; set; }
 
+        public override bool HasDiagnostics => false;
+
         public string VariableName { get; set; }
 
         public string Name { get; set; }

src/Microsoft.AspNetCore.Razor.Language/Intermediate/DeclareTagHelperFieldsIRNode.cs

@@ -8,12 +8,29 @@ namespace Microsoft.AspNetCore.Razor.Language.Intermediate
 {
     public sealed class DeclareTagHelperFieldsIRNode : RazorIRNode
     {
+        private RazorDiagnosticCollection _diagnostics;
+
         public override ItemCollection Annotations => ReadOnlyItemCollection.Empty;
 
+        public override RazorDiagnosticCollection Diagnostics
+        {
+            get
+            {
+                if (_diagnostics == null)
+                {
+                    _diagnostics = new DefaultDiagnosticCollection();
+                }
+
+                return _diagnostics;
+            }
+        }
+
         public override RazorIRNodeCollection Children => ReadOnlyIRNodeCollection.Instance;
 
         public override SourceSpan? Source { get; set; }
 
+        public override bool HasDiagnostics => _diagnostics != null && _diagnostics.Count > 0;
+
         public ISet<string> UsedTagHelperTypeNames { get; set; } = new HashSet<string>(StringComparer.Ordinal);
 
         public override void Accept(RazorIRNodeVisitor visitor)

src/Microsoft.AspNetCore.Razor.Language/Intermediate/DefaultDiagnosticCollection.cs

@@ -0,0 +1,128 @@
+// 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;
+
+namespace Microsoft.AspNetCore.Razor.Language.Intermediate
+{
+    public sealed class DefaultDiagnosticCollection : RazorDiagnosticCollection
+    {
+        private readonly List<RazorDiagnostic> _inner = new List<RazorDiagnostic>();
+
+        public override RazorDiagnostic this[int index]
+        {
+            get
+            {
+                if (index < 0 || index >= Count)
+                {
+                    throw new ArgumentOutOfRangeException(nameof(index));
+                }
+
+                return _inner[index];
+            }
+            set
+            {
+                if (index < 0 || index >= Count)
+                {
+                    throw new ArgumentOutOfRangeException(nameof(index));
+                }
+
+                _inner[index] = value;
+            }
+        }
+
+        public override int Count => _inner.Count;
+
+        public override bool IsReadOnly => false;
+
+        public override void Add(RazorDiagnostic item)
+        {
+            if (item == null)
+            {
+                throw new ArgumentNullException(nameof(item));
+            }
+
+            _inner.Add(item);
+        }
+
+        public override void Clear()
+        {
+            _inner.Clear();
+        }
+
+        public override bool Contains(RazorDiagnostic item)
+        {
+            return _inner.Contains(item);
+        }
+
+        public override void CopyTo(RazorDiagnostic[] array, int arrayIndex)
+        {
+            if (array == null)
+            {
+                throw new ArgumentNullException(nameof(array));
+            }
+
+            if (arrayIndex < 0 || arrayIndex > array.Length)
+            {
+                throw new ArgumentOutOfRangeException(nameof(arrayIndex));
+            }
+            else if (array.Length - arrayIndex < Count)
+            {
+                throw new ArgumentOutOfRangeException(nameof(arrayIndex));
+            }
+
+            _inner.CopyTo(array, arrayIndex);
+        }
+
+        public override IEnumerator<RazorDiagnostic> GetEnumerator()
+        {
+            return _inner.GetEnumerator();
+        }
+
+        public override int IndexOf(RazorDiagnostic item)
+        {
+            if (item == null)
+            {
+                throw new ArgumentNullException(nameof(item));
+            }
+
+            return _inner.IndexOf(item);
+        }
+
+        public override void Insert(int index, RazorDiagnostic item)
+        {
+            if (index < 0 || index > Count)
+            {
+                throw new ArgumentOutOfRangeException(nameof(index));
+            }
+
+            if (item == null)
+            {
+                throw new ArgumentNullException(nameof(item));
+            }
+
+            _inner.Insert(index, item);
+        }
+
+        public override bool Remove(RazorDiagnostic item)
+        {
+            if (item == null)
+            {
+                throw new ArgumentNullException(nameof(item));
+            }
+
+            return _inner.Remove(item);
+        }
+
+        public override void RemoveAt(int index)
+        {
+            if (index < 0 || index >= Count)
+            {
+                throw new ArgumentOutOfRangeException(nameof(index));
+            }
+
+            _inner.RemoveAt(index);
+        }
+    }
+}

src/Microsoft.AspNetCore.Razor.Language/Intermediate/DirectiveIRNode.cs

@@ -9,6 +9,7 @@ namespace Microsoft.AspNetCore.Razor.Language.Intermediate
     public sealed class DirectiveIRNode : RazorIRNode
     {
         private ItemCollection _annotations;
+        private RazorDiagnosticCollection _diagnostics;
 
         public override ItemCollection Annotations
         {
@@ -23,10 +24,25 @@ namespace Microsoft.AspNetCore.Razor.Language.Intermediate
             }
         }
 
+        public override RazorDiagnosticCollection Diagnostics
+        {
+            get
+            {
+                if (_diagnostics == null)
+                {
+                    _diagnostics = new DefaultDiagnosticCollection();
+                }
+
+                return _diagnostics;
+            }
+        }
+
         public override RazorIRNodeCollection Children { get; } = new DefaultIRNodeCollection();
 
         public override SourceSpan? Source { get; set; }
 
+        public override bool HasDiagnostics => _diagnostics != null && _diagnostics.Count > 0;
+
         public string Name { get; set; }
 
         public IEnumerable<DirectiveTokenIRNode> Tokens => Children.OfType<DirectiveTokenIRNode>();

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

@@ -5,12 +5,29 @@ namespace Microsoft.AspNetCore.Razor.Language.Intermediate
 {
     public sealed class DirectiveTokenIRNode : RazorIRNode
     {
+        private RazorDiagnosticCollection _diagnostics;
+
         public override ItemCollection Annotations => ReadOnlyItemCollection.Empty;
 
+        public override RazorDiagnosticCollection Diagnostics
+        {
+            get
+            {
+                if (_diagnostics == null)
+                {
+                    _diagnostics = new DefaultDiagnosticCollection();
+                }
+
+                return _diagnostics;
+            }
+        }
+
         public override RazorIRNodeCollection Children => ReadOnlyIRNodeCollection.Instance;
 
         public override SourceSpan? Source { get; set; }
 
+        public override bool HasDiagnostics => _diagnostics != null && _diagnostics.Count > 0;
+
         public string Content { get; set; }
 
         public DirectiveTokenDescriptor Descriptor { get; set; }

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

@@ -9,6 +9,7 @@ namespace Microsoft.AspNetCore.Razor.Language.Intermediate
     public sealed class DocumentIRNode : RazorIRNode
     {
         private ItemCollection _annotations;
+        private RazorDiagnosticCollection _diagnostics;
 
         public override ItemCollection Annotations
         {
@@ -23,6 +24,19 @@ namespace Microsoft.AspNetCore.Razor.Language.Intermediate
             }
         }
 
+        public override RazorDiagnosticCollection Diagnostics
+        {
+            get
+            {
+                if (_diagnostics == null)
+                {
+                    _diagnostics = new DefaultDiagnosticCollection();
+                }
+
+                return _diagnostics;
+            }
+        }
+        
         public override RazorIRNodeCollection Children { get; } = new DefaultIRNodeCollection();
 
         public string DocumentKind { get; set; }
@@ -31,6 +45,8 @@ namespace Microsoft.AspNetCore.Razor.Language.Intermediate
 
         public override SourceSpan? Source { get; set; }
 
+        public override bool HasDiagnostics => _diagnostics != null && _diagnostics.Count > 0;
+
         public CodeTarget Target { get; set; }
 
         public override void Accept(RazorIRNodeVisitor visitor)

src/Microsoft.AspNetCore.Razor.Language/Intermediate/ExtensionIRNode.cs

@@ -8,6 +8,7 @@ namespace Microsoft.AspNetCore.Razor.Language.Intermediate
     public abstract class ExtensionIRNode : RazorIRNode
     {
         private ItemCollection _annotations;
+        private RazorDiagnosticCollection _diagnostics;
 
         public override ItemCollection Annotations
         {
@@ -22,9 +23,24 @@ namespace Microsoft.AspNetCore.Razor.Language.Intermediate
             }
         }
 
+        public override RazorDiagnosticCollection Diagnostics
+        {
+            get
+            {
+                if (_diagnostics == null)
+                {
+                    _diagnostics = new DefaultDiagnosticCollection();
+                }
+
+                return _diagnostics;
+            }
+        }
+
+        public override bool HasDiagnostics => _diagnostics != null && _diagnostics.Count > 0;
+
         public abstract void WriteNode(CodeTarget target, CSharpRenderingContext context);
 
-        protected static void AcceptExtensionNode<TNode>(TNode node, RazorIRNodeVisitor visitor) 
+        protected static void AcceptExtensionNode<TNode>(TNode node, RazorIRNodeVisitor visitor)
             where TNode : ExtensionIRNode
         {
             var typedVisitor = visitor as IExtensionIRNodeVisitor<TNode>;

src/Microsoft.AspNetCore.Razor.Language/Intermediate/FieldDeclarationIRNode.cs

@@ -9,6 +9,7 @@ namespace Microsoft.AspNetCore.Razor.Language.Intermediate
     public sealed class FieldDeclarationIRNode : MemberDeclarationIRNode
     {
         private ItemCollection _annotations;
+        private RazorDiagnosticCollection _diagnostics;
 
         public override ItemCollection Annotations
         {
@@ -23,12 +24,27 @@ namespace Microsoft.AspNetCore.Razor.Language.Intermediate
             }
         }
 
+        public override RazorDiagnosticCollection Diagnostics
+        {
+            get
+            {
+                if (_diagnostics == null)
+                {
+                    _diagnostics = new DefaultDiagnosticCollection();
+                }
+
+                return _diagnostics;
+            }
+        }
+
         public override RazorIRNodeCollection Children => ReadOnlyIRNodeCollection.Instance;
 
         public IList<string> Modifiers { get; set; } = new List<string>();
 
         public override SourceSpan? Source { get; set; }
 
+        public override bool HasDiagnostics => _diagnostics != null && _diagnostics.Count > 0;
+
         public string AccessModifier { get; set; }
 
         public string Name { get; set; }

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

@@ -7,12 +7,29 @@ namespace Microsoft.AspNetCore.Razor.Language.Intermediate
 {
     public sealed class HtmlAttributeIRNode : RazorIRNode
     {
+        private RazorDiagnosticCollection _diagnostics;
+
         public override ItemCollection Annotations => ReadOnlyItemCollection.Empty;
 
+        public override RazorDiagnosticCollection Diagnostics
+        {
+            get
+            {
+                if (_diagnostics == null)
+                {
+                    _diagnostics = new DefaultDiagnosticCollection();
+                }
+
+                return _diagnostics;
+            }
+        }
+
         public override RazorIRNodeCollection Children { get; } = new DefaultIRNodeCollection();
 
         public override SourceSpan? Source { get; set; }
 
+        public override bool HasDiagnostics => _diagnostics != null && _diagnostics.Count > 0;
+
         public string Name { get; set; }
 
         public string Prefix { get; set; }

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

@@ -8,12 +8,29 @@ namespace Microsoft.AspNetCore.Razor.Language.Intermediate
 {
     public sealed class HtmlAttributeValueIRNode : RazorIRNode
     {
+        private RazorDiagnosticCollection _diagnostics;
+
         public override ItemCollection Annotations => ReadOnlyItemCollection.Empty;
 
+        public override RazorDiagnosticCollection Diagnostics
+        {
+            get
+            {
+                if (_diagnostics == null)
+                {
+                    _diagnostics = new DefaultDiagnosticCollection();
+                }
+
+                return _diagnostics;
+            }
+        }
+
         public override RazorIRNodeCollection Children { get; } = new DefaultIRNodeCollection();
 
         public override SourceSpan? Source { get; set; }
 
+        public override bool HasDiagnostics => _diagnostics != null && _diagnostics.Count > 0;
+
         public string Prefix { get; set; }
 
         public override void Accept(RazorIRNodeVisitor visitor)

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

@@ -8,12 +8,29 @@ namespace Microsoft.AspNetCore.Razor.Language.Intermediate
 {
     public sealed class HtmlContentIRNode : RazorIRNode
     {
+        private RazorDiagnosticCollection _diagnostics;
+
         public override ItemCollection Annotations => ReadOnlyItemCollection.Empty;
 
+        public override RazorDiagnosticCollection Diagnostics
+        {
+            get
+            {
+                if (_diagnostics == null)
+                {
+                    _diagnostics = new DefaultDiagnosticCollection();
+                }
+
+                return _diagnostics;
+            }
+        }
+
         public override RazorIRNodeCollection Children { get; } = new DefaultIRNodeCollection();
 
         public override SourceSpan? Source { get; set; }
 
+        public override bool HasDiagnostics => _diagnostics != null && _diagnostics.Count > 0;
+
         public override void Accept(RazorIRNodeVisitor visitor)
         {
             if (visitor == null)

src/Microsoft.AspNetCore.Razor.Language/Intermediate/MethodDeclarationIRNode.cs

@@ -9,6 +9,7 @@ namespace Microsoft.AspNetCore.Razor.Language.Intermediate
     public sealed class MethodDeclarationIRNode : MemberDeclarationIRNode
     {
         private ItemCollection _annotations;
+        private RazorDiagnosticCollection _diagnostics;
 
         public override ItemCollection Annotations
         {
@@ -23,10 +24,25 @@ namespace Microsoft.AspNetCore.Razor.Language.Intermediate
             }
         }
 
+        public override RazorDiagnosticCollection Diagnostics
+        {
+            get
+            {
+                if (_diagnostics == null)
+                {
+                    _diagnostics = new DefaultDiagnosticCollection();
+                }
+
+                return _diagnostics;
+            }
+        }
+
         public override RazorIRNodeCollection Children { get; } = new DefaultIRNodeCollection();
 
         public override SourceSpan? Source { get; set; }
 
+        public override bool HasDiagnostics => _diagnostics != null && _diagnostics.Count > 0;
+
         public string AccessModifier { get; set; }
 
         public IList<string> Modifiers { get; set; } = new List<string>();
@@ -44,5 +60,6 @@ namespace Microsoft.AspNetCore.Razor.Language.Intermediate
 
             visitor.VisitMethodDeclaration(this);
         }
+
     }
 }

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

@@ -8,6 +8,7 @@ namespace Microsoft.AspNetCore.Razor.Language.Intermediate
     public sealed class NamespaceDeclarationIRNode : RazorIRNode
     {
         private ItemCollection _annotations;
+        private RazorDiagnosticCollection _diagnostics;
 
         public override ItemCollection Annotations
         {
@@ -22,10 +23,25 @@ namespace Microsoft.AspNetCore.Razor.Language.Intermediate
             }
         }
 
+        public override RazorDiagnosticCollection Diagnostics
+        {
+            get
+            {
+                if (_diagnostics == null)
+                {
+                    _diagnostics = new DefaultDiagnosticCollection();
+                }
+
+                return _diagnostics;
+            }
+        }
+
         public override RazorIRNodeCollection Children { get; } = new DefaultIRNodeCollection();
 
         public override SourceSpan? Source { get; set; }
 
+        public override bool HasDiagnostics => _diagnostics != null && _diagnostics.Count > 0;
+
         public string Content { get; set; }
 
         public override void Accept(RazorIRNodeVisitor visitor)

src/Microsoft.AspNetCore.Razor.Language/Intermediate/PropertyDeclarationIRNode.cs

@@ -9,6 +9,7 @@ namespace Microsoft.AspNetCore.Razor.Language.Intermediate
     public sealed class PropertyDeclarationIRNode : MemberDeclarationIRNode
     {
         private ItemCollection _annotations;
+        private RazorDiagnosticCollection _diagnostics;
 
         public override ItemCollection Annotations
         {
@@ -23,12 +24,27 @@ namespace Microsoft.AspNetCore.Razor.Language.Intermediate
             }
         }
 
+        public override RazorDiagnosticCollection Diagnostics
+        {
+            get
+            {
+                if (_diagnostics == null)
+                {
+                    _diagnostics = new DefaultDiagnosticCollection();
+                }
+
+                return _diagnostics;
+            }
+        }
+
         public override RazorIRNodeCollection Children => ReadOnlyIRNodeCollection.Instance;
 
         public IList<string> Modifiers { get; set; } = new List<string>();
 
         public override SourceSpan? Source { get; set; }
 
+        public override bool HasDiagnostics => _diagnostics != null && _diagnostics.Count > 0;
+
         public string AccessModifier { get; set; }
 
         public string Name { get; set; }

src/Microsoft.AspNetCore.Razor.Language/Intermediate/RazorDiagnosticCollection.cs

@@ -0,0 +1,40 @@
+// 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;
+using System.Collections.Generic;
+
+namespace Microsoft.AspNetCore.Razor.Language.Intermediate
+{
+    public abstract class RazorDiagnosticCollection : IList<RazorDiagnostic>
+    {
+        public abstract RazorDiagnostic this[int index] { get; set; }
+
+        public abstract int Count { get; }
+
+        public abstract bool IsReadOnly { get; }
+
+        public abstract void Add(RazorDiagnostic item);
+
+        public abstract void Clear();
+
+        public abstract bool Contains(RazorDiagnostic item);
+
+        public abstract void CopyTo(RazorDiagnostic[] array, int arrayIndex);
+
+        public abstract IEnumerator<RazorDiagnostic> GetEnumerator();
+
+        public abstract int IndexOf(RazorDiagnostic item);
+
+        public abstract void Insert(int index, RazorDiagnostic item);
+
+        public abstract bool Remove(RazorDiagnostic item);
+
+        public abstract void RemoveAt(int index);
+
+        IEnumerator IEnumerable.GetEnumerator()
+        {
+            return GetEnumerator();
+        }
+    }
+}

src/Microsoft.AspNetCore.Razor.Language/Intermediate/RazorIRNode.cs

@@ -7,10 +7,14 @@ namespace Microsoft.AspNetCore.Razor.Language.Intermediate
     {
         public abstract ItemCollection Annotations { get; }
 
+        public abstract RazorDiagnosticCollection Diagnostics { get; }
+        
         public abstract RazorIRNodeCollection Children { get; }
 
         public abstract SourceSpan? Source { get; set; }
 
+        public abstract bool HasDiagnostics { get; }
+
         public abstract void Accept(RazorIRNodeVisitor visitor);
     }
 }

src/Microsoft.AspNetCore.Razor.Language/Intermediate/RazorIRNodeExtensions.cs

@@ -0,0 +1,46 @@
+// 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 System.Linq;
+
+namespace Microsoft.AspNetCore.Razor.Language.Intermediate
+{
+    public static class RazorIRNodeExtensions
+    {
+        private static readonly IReadOnlyList<RazorDiagnostic> EmptyDiagnostics = Array.Empty<RazorDiagnostic>();
+
+        public static IReadOnlyList<RazorDiagnostic> GetAllDiagnostics(this RazorIRNode node)
+        {
+            if (node == null)
+            {
+                throw new ArgumentNullException(nameof(node));
+            }
+
+            HashSet<RazorDiagnostic> diagnostics = null;
+
+            AddAllDiagnostics(node);
+
+            return diagnostics?.ToList() ?? EmptyDiagnostics;
+
+            void AddAllDiagnostics(RazorIRNode n)
+            {
+                if (n.HasDiagnostics)
+                {
+                    if (diagnostics == null)
+                    {
+                        diagnostics = new HashSet<RazorDiagnostic>();
+                    }
+
+                    diagnostics.UnionWith(n.Diagnostics);
+                }
+
+                for (var i = 0; i < n.Children.Count; i++)
+                {
+                    AddAllDiagnostics(n.Children[i]);
+                }
+            }
+        }
+    }
+}

src/Microsoft.AspNetCore.Razor.Language/Intermediate/RazorIRToken.cs

@@ -7,8 +7,23 @@ namespace Microsoft.AspNetCore.Razor.Language.Intermediate
 {
     public sealed class RazorIRToken : RazorIRNode
     {
+        private RazorDiagnosticCollection _diagnostics;
+
         public override ItemCollection Annotations => ReadOnlyItemCollection.Empty;
 
+        public override RazorDiagnosticCollection Diagnostics
+        {
+            get
+            {
+                if (_diagnostics == null)
+                {
+                    _diagnostics = new DefaultDiagnosticCollection();
+                }
+
+                return _diagnostics;
+            }
+        }
+
         public override RazorIRNodeCollection Children => ReadOnlyIRNodeCollection.Instance;
 
         public string Content { get; set; }
@@ -21,6 +36,8 @@ namespace Microsoft.AspNetCore.Razor.Language.Intermediate
 
         public override SourceSpan? Source { get; set; }
 
+        public override bool HasDiagnostics => _diagnostics != null && _diagnostics.Count > 0;
+
         public override void Accept(RazorIRNodeVisitor visitor)
         {
             if (visitor == null)

src/Microsoft.AspNetCore.Razor.Language/Intermediate/ReadOnlyDiagnosticCollection.cs

@@ -0,0 +1,133 @@
+// 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 System.Linq;
+
+namespace Microsoft.AspNetCore.Razor.Language.Intermediate
+{
+    public sealed class ReadOnlyDiagnosticCollection : RazorDiagnosticCollection
+    {
+        public static readonly ReadOnlyDiagnosticCollection Instance = new ReadOnlyDiagnosticCollection();
+
+        private ReadOnlyDiagnosticCollection()
+        {
+        }
+
+        public override RazorDiagnostic this[int index]
+        {
+            get
+            {
+                if (index < 0 || index >= Count)
+                {
+                    throw new ArgumentOutOfRangeException(nameof(index));
+                }
+
+                throw null; // Unreachable
+            }
+            set
+            {
+                if (index < 0 || index >= Count)
+                {
+                    throw new ArgumentOutOfRangeException(nameof(index));
+                }
+
+                throw null; // Unreachable
+            }
+        }
+
+        public override int Count => 0;
+
+        public override bool IsReadOnly => true;
+
+        public override void Add(RazorDiagnostic item)
+        {
+            if (item == null)
+            {
+                throw new ArgumentNullException(nameof(item));
+            }
+
+            throw new NotSupportedException();
+        }
+
+        public override void Clear()
+        {
+            throw new NotSupportedException();
+        }
+
+        public override bool Contains(RazorDiagnostic item)
+        {
+            return false;
+        }
+
+        public override void CopyTo(RazorDiagnostic[] array, int arrayIndex)
+        {
+            if (array == null)
+            {
+                throw new ArgumentNullException(nameof(array));
+            }
+
+            if (arrayIndex < 0 || arrayIndex > array.Length)
+            {
+                throw new ArgumentOutOfRangeException(nameof(arrayIndex));
+            }
+            else if (array.Length - arrayIndex < Count)
+            {
+                throw new ArgumentOutOfRangeException(nameof(arrayIndex));
+            }
+
+            throw new NotSupportedException();
+        }
+
+        public override IEnumerator<RazorDiagnostic> GetEnumerator()
+        {
+            return Enumerable.Empty<RazorDiagnostic>().GetEnumerator();
+        }
+
+        public override int IndexOf(RazorDiagnostic item)
+        {
+            if (item == null)
+            {
+                throw new ArgumentNullException(nameof(item));
+            }
+
+            return -1;
+        }
+
+        public override void Insert(int index, RazorDiagnostic item)
+        {
+            if (index < 0 || index > Count)
+            {
+                throw new ArgumentOutOfRangeException(nameof(index));
+            }
+
+            if (item == null)
+            {
+                throw new ArgumentNullException(nameof(item));
+            }
+
+            throw new NotSupportedException();
+        }
+
+        public override bool Remove(RazorDiagnostic item)
+        {
+            if (item == null)
+            {
+                throw new ArgumentNullException(nameof(item));
+            }
+
+            return false;
+        }
+
+        public override void RemoveAt(int index)
+        {
+            if (index < 0 || index >= Count)
+            {
+                throw new ArgumentOutOfRangeException(nameof(index));
+            }
+
+            throw new NotSupportedException();
+        }
+    }
+}

src/Microsoft.AspNetCore.Razor.Language/Intermediate/SetPreallocatedTagHelperPropertyIRNode.cs

@@ -8,10 +8,14 @@ namespace Microsoft.AspNetCore.Razor.Language.Intermediate
 {
     internal sealed class SetPreallocatedTagHelperPropertyIRNode : ExtensionIRNode
     {
+        public override RazorDiagnosticCollection Diagnostics => ReadOnlyDiagnosticCollection.Instance;
+        
         public override RazorIRNodeCollection Children => ReadOnlyIRNodeCollection.Instance;
 
         public override SourceSpan? Source { get; set; }
 
+        public override bool HasDiagnostics => false;
+
         public string VariableName { get; set; }
 
         public string AttributeName { get; set; }

src/Microsoft.AspNetCore.Razor.Language/Intermediate/SetTagHelperPropertyIRNode.cs

@@ -8,12 +8,29 @@ namespace Microsoft.AspNetCore.Razor.Language.Intermediate
 {
     public sealed class SetTagHelperPropertyIRNode : RazorIRNode
     {
+        private RazorDiagnosticCollection _diagnostics;
+
         public override ItemCollection Annotations => ReadOnlyItemCollection.Empty;
 
+        public override RazorDiagnosticCollection Diagnostics
+        {
+            get
+            {
+                if (_diagnostics == null)
+                {
+                    _diagnostics = new DefaultDiagnosticCollection();
+                }
+
+                return _diagnostics;
+            }
+        }
+
         public override RazorIRNodeCollection Children { get; } = new DefaultIRNodeCollection();
 
         public override SourceSpan? Source { get; set; }
 
+        public override bool HasDiagnostics => _diagnostics != null && _diagnostics.Count > 0;
+
         public string TagHelperTypeName { get; set; }
 
         public string PropertyName { get; set; }

src/Microsoft.AspNetCore.Razor.Language/Intermediate/TagHelperBodyIRNode.cs

@@ -7,12 +7,29 @@ namespace Microsoft.AspNetCore.Razor.Language.Intermediate
 {
     public sealed class TagHelperBodyIRNode : RazorIRNode
     {
+        private RazorDiagnosticCollection _diagnostics;
+
         public override ItemCollection Annotations => ReadOnlyItemCollection.Empty;
 
+        public override RazorDiagnosticCollection Diagnostics
+        {
+            get
+            {
+                if (_diagnostics == null)
+                {
+                    _diagnostics = new DefaultDiagnosticCollection();
+                }
+
+                return _diagnostics;
+            }
+        }
+
         public override RazorIRNodeCollection Children { get; } = new DefaultIRNodeCollection();
 
         public override SourceSpan? Source { get; set; }
 
+        public override bool HasDiagnostics => _diagnostics != null && _diagnostics.Count > 0;
+
         public override void Accept(RazorIRNodeVisitor visitor)
         {
             if (visitor == null)

src/Microsoft.AspNetCore.Razor.Language/Intermediate/TagHelperIRNode.cs

@@ -8,6 +8,7 @@ namespace Microsoft.AspNetCore.Razor.Language.Intermediate
     public sealed class TagHelperIRNode : RazorIRNode
     {
         private ItemCollection _annotations;
+        private RazorDiagnosticCollection _diagnostics;
 
         public override ItemCollection Annotations
         {
@@ -22,10 +23,25 @@ namespace Microsoft.AspNetCore.Razor.Language.Intermediate
             }
         }
 
+        public override RazorDiagnosticCollection Diagnostics
+        {
+            get
+            {
+                if (_diagnostics == null)
+                {
+                    _diagnostics = new DefaultDiagnosticCollection();
+                }
+
+                return _diagnostics;
+            }
+        }
+
         public override RazorIRNodeCollection Children { get; } = new DefaultIRNodeCollection();
 
         public override SourceSpan? Source { get; set; }
 
+        public override bool HasDiagnostics => _diagnostics != null && _diagnostics.Count > 0;
+
         public string TagName { get; set; }
 
         public TagMode TagMode { get; set; }

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

@@ -7,12 +7,29 @@ namespace Microsoft.AspNetCore.Razor.Language.Intermediate
 {
     public sealed class UsingStatementIRNode : RazorIRNode
     {
+        private RazorDiagnosticCollection _diagnostics;
+
         public override ItemCollection Annotations => ReadOnlyItemCollection.Empty;
 
+        public override RazorDiagnosticCollection Diagnostics
+        {
+            get
+            {
+                if (_diagnostics == null)
+                {
+                    _diagnostics = new DefaultDiagnosticCollection();
+                }
+
+                return _diagnostics;
+            }
+        }
+
         public override RazorIRNodeCollection Children => ReadOnlyIRNodeCollection.Instance;
 
         public override SourceSpan? Source { get; set; }
 
+        public override bool HasDiagnostics => _diagnostics != null && _diagnostics.Count > 0;
+
         public string Content { get; set; }
 
         public override void Accept(RazorIRNodeVisitor visitor)

test/Microsoft.AspNetCore.Razor.Language.Test/DefaultRazorCSharpLoweringPhaseTest.cs

@@ -30,26 +30,6 @@ namespace Microsoft.AspNetCore.Razor.Language
                 $"provided by the '{nameof(RazorCodeDocument)}'.");
         }
 
-        [Fact]
-        public void Execute_ThrowsForMissingDependency_SyntaxTree()
-        {
-            // Arrange
-            var phase = new DefaultRazorCSharpLoweringPhase();
-
-            var engine = RazorEngine.CreateEmpty(b => b.Phases.Add(phase));
-
-            var codeDocument = TestRazorCodeDocument.CreateEmpty();
-
-            var irDocument = new DocumentIRNode();
-            codeDocument.SetIRDocument(irDocument);
-
-            // Act & Assert
-            ExceptionAssert.Throws<InvalidOperationException>(
-                () => phase.Execute(codeDocument),
-                $"The '{nameof(DefaultRazorCSharpLoweringPhase)}' phase requires a '{nameof(RazorSyntaxTree)}' " +
-                $"provided by the '{nameof(RazorCodeDocument)}'.");
-        }
-
         [Fact]
         public void Execute_ThrowsForMissingDependency_CodeTarget()
         {
@@ -76,13 +56,12 @@ namespace Microsoft.AspNetCore.Razor.Language
         }
 
         [Fact]
-        public void Execute_CollatesSyntaxDiagnosticsFromSourceDocument()
+        public void Execute_CollatesIRDocumentDiagnosticsFromSourceDocument()
         {
             // Arrange
             var phase = new DefaultRazorCSharpLoweringPhase();
             var engine = RazorEngine.CreateEmpty(b => b.Phases.Add(phase));
             var codeDocument = TestRazorCodeDocument.Create("<p class=@(");
-            codeDocument.SetSyntaxTree(RazorSyntaxTree.Parse(codeDocument.Source));
             var options = RazorCodeGenerationOptions.CreateDefault();
             var irDocument = new DocumentIRNode()
             {
@@ -90,6 +69,10 @@ namespace Microsoft.AspNetCore.Razor.Language
                 Target = CodeTarget.CreateDefault(codeDocument, options),
                 Options = options,
             };
+            var expectedDiagnostic = RazorDiagnostic.Create(
+                    new RazorDiagnosticDescriptor("1234", () => "I am an error.", RazorDiagnosticSeverity.Error),
+                    new SourceSpan("SomeFile.cshtml", 11, 0, 11, 1));
+            irDocument.Diagnostics.Add(expectedDiagnostic);
             codeDocument.SetIRDocument(irDocument);
 
             // Act
@@ -98,49 +81,7 @@ namespace Microsoft.AspNetCore.Razor.Language
             // Assert
             var csharpDocument = codeDocument.GetCSharpDocument();
             var diagnostic = Assert.Single(csharpDocument.Diagnostics);
-            Assert.Equal(@"The explicit expression block is missing a closing "")"" character.  Make sure you have a matching "")"" character for all the ""("" characters within this block, and that none of the "")"" characters are being interpreted as markup.",
-                diagnostic.GetMessage());
-        }
-
-        [Fact]
-        public void Execute_CollatesSyntaxDiagnosticsFromImportDocuments()
-        {
-            // Arrange
-            var phase = new DefaultRazorCSharpLoweringPhase();
-            var engine = RazorEngine.CreateEmpty(b => b.Phases.Add(phase));
-
-            var codeDocument = TestRazorCodeDocument.CreateEmpty();
-            codeDocument.SetSyntaxTree(RazorSyntaxTree.Parse(codeDocument.Source));
-            codeDocument.SetImportSyntaxTrees(new[]
-            {
-                RazorSyntaxTree.Parse(TestRazorSourceDocument.Create("@ ")),
-                RazorSyntaxTree.Parse(TestRazorSourceDocument.Create("<p @(")),
-            });
-            var options = RazorCodeGenerationOptions.CreateDefault();
-            var irDocument = new DocumentIRNode()
-            {
-                DocumentKind = "test",
-                Target = CodeTarget.CreateDefault(codeDocument, options),
-                Options = options,
-            };
-            codeDocument.SetIRDocument(irDocument);
-
-            // Act
-            phase.Execute(codeDocument);
-
-            // Assert
-            var csharpDocument = codeDocument.GetCSharpDocument();
-            Assert.Collection(csharpDocument.Diagnostics,
-                diagnostic =>
-                {
-                    Assert.Equal(@"A space or line break was encountered after the ""@"" character.  Only valid identifiers, keywords, comments, ""("" and ""{"" are valid at the start of a code block and they must occur immediately following ""@"" with no space in between.",
-                        diagnostic.GetMessage());
-                },
-                diagnostic =>
-                {
-                    Assert.Equal(@"The explicit expression block is missing a closing "")"" character.  Make sure you have a matching "")"" character for all the ""("" characters within this block, and that none of the "")"" characters are being interpreted as markup.",
-                        diagnostic.GetMessage());
-                });
+            Assert.Same(expectedDiagnostic, diagnostic);
         }
     }
 }

test/Microsoft.AspNetCore.Razor.Language.Test/DefaultRazorIRLoweringPhaseTest.cs

@@ -0,0 +1,85 @@
+// 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 Microsoft.AspNetCore.Razor.Language.CodeGeneration;
+using Microsoft.AspNetCore.Razor.Language.Intermediate;
+using Microsoft.AspNetCore.Testing;
+using Xunit;
+
+namespace Microsoft.AspNetCore.Razor.Language
+{
+    public class DefaultRazorIRLoweringPhaseTest
+    {
+        [Fact]
+        public void Execute_ThrowsForMissingDependency_SyntaxTree()
+        {
+            // Arrange
+            var phase = new DefaultRazorIRLoweringPhase();
+
+            var engine = RazorEngine.CreateEmpty(b => b.Phases.Add(phase));
+
+            var codeDocument = TestRazorCodeDocument.CreateEmpty();
+
+            // Act & Assert
+            ExceptionAssert.Throws<InvalidOperationException>(
+                () => phase.Execute(codeDocument),
+                $"The '{nameof(DefaultRazorIRLoweringPhase)}' phase requires a '{nameof(RazorSyntaxTree)}' " +
+                $"provided by the '{nameof(RazorCodeDocument)}'.");
+        }
+
+        [Fact]
+        public void Execute_CollatesSyntaxDiagnosticsFromSourceDocument()
+        {
+            // Arrange
+            var phase = new DefaultRazorIRLoweringPhase();
+            var engine = RazorEngine.CreateEmpty(b => b.Phases.Add(phase));
+            var codeDocument = TestRazorCodeDocument.Create("<p class=@(");
+            codeDocument.SetSyntaxTree(RazorSyntaxTree.Parse(codeDocument.Source));
+            var options = RazorCodeGenerationOptions.CreateDefault();
+
+            // Act
+            phase.Execute(codeDocument);
+
+            // Assert
+            var irDocument = codeDocument.GetIRDocument();
+            var diagnostic = Assert.Single(irDocument.Diagnostics);
+            Assert.Equal(@"The explicit expression block is missing a closing "")"" character.  Make sure you have a matching "")"" character for all the ""("" characters within this block, and that none of the "")"" characters are being interpreted as markup.",
+                diagnostic.GetMessage());
+        }
+
+        [Fact]
+        public void Execute_CollatesSyntaxDiagnosticsFromImportDocuments()
+        {
+            // Arrange
+            var phase = new DefaultRazorIRLoweringPhase();
+            var engine = RazorEngine.CreateEmpty(b => b.Phases.Add(phase));
+
+            var codeDocument = TestRazorCodeDocument.CreateEmpty();
+            codeDocument.SetSyntaxTree(RazorSyntaxTree.Parse(codeDocument.Source));
+            codeDocument.SetImportSyntaxTrees(new[]
+            {
+                RazorSyntaxTree.Parse(TestRazorSourceDocument.Create("@ ")),
+                RazorSyntaxTree.Parse(TestRazorSourceDocument.Create("<p @(")),
+            });
+            var options = RazorCodeGenerationOptions.CreateDefault();
+
+            // Act
+            phase.Execute(codeDocument);
+
+            // Assert
+            var irDocument = codeDocument.GetIRDocument();
+            Assert.Collection(irDocument.Diagnostics,
+                diagnostic =>
+                {
+                    Assert.Equal(@"A space or line break was encountered after the ""@"" character.  Only valid identifiers, keywords, comments, ""("" and ""{"" are valid at the start of a code block and they must occur immediately following ""@"" with no space in between.",
+                        diagnostic.GetMessage());
+                },
+                diagnostic =>
+                {
+                    Assert.Equal(@"The explicit expression block is missing a closing "")"" character.  Make sure you have a matching "")"" character for all the ""("" characters within this block, and that none of the "")"" characters are being interpreted as markup.",
+                        diagnostic.GetMessage());
+                });
+        }
+    }
+}

test/Microsoft.AspNetCore.Razor.Language.Test/Intermediate/DefaultRazorIRBuilderTest.cs

@@ -210,10 +210,14 @@ namespace Microsoft.AspNetCore.Razor.Language.Intermediate
         {
             public override ItemCollection Annotations { get; } = new DefaultItemCollection();
 
+            public override RazorDiagnosticCollection Diagnostics { get; } = new DefaultDiagnosticCollection();
+            
             public override RazorIRNodeCollection Children { get; } = new DefaultIRNodeCollection();
 
             public override SourceSpan? Source { get; set; }
 
+            public override bool HasDiagnostics => Diagnostics.Count > 0;
+
             public override void Accept(RazorIRNodeVisitor visitor)
             {
                 throw new NotImplementedException();

test/Microsoft.AspNetCore.Razor.Language.Test/Intermediate/RazorIRNodeReferenceTest.cs

@@ -499,10 +499,14 @@ namespace Microsoft.AspNetCore.Razor.Language.Intermediate
 
             public override ItemCollection Annotations { get; } = new DefaultItemCollection();
 
+            public override RazorDiagnosticCollection Diagnostics => new DefaultDiagnosticCollection();
+
             public override RazorIRNodeCollection Children { get; }
 
             public override SourceSpan? Source { get; set; }
 
+            public override bool HasDiagnostics => Diagnostics.Count > 0;
+
             public override void Accept(RazorIRNodeVisitor visitor)
             {
                 throw new System.NotImplementedException();

test/Microsoft.AspNetCore.Razor.Language.Test/Intermediate/RazorIRNodeWalkerTest.cs

@@ -126,10 +126,14 @@ namespace Microsoft.AspNetCore.Razor.Language.Intermediate
 
             public override ItemCollection Annotations { get; } = new DefaultItemCollection();
 
+            public override RazorDiagnosticCollection Diagnostics { get; } = new DefaultDiagnosticCollection();
+            
             public override RazorIRNodeCollection Children { get; } = new DefaultIRNodeCollection();
 
             public override SourceSpan? Source { get; set; }
 
+            public override bool HasDiagnostics => Diagnostics.Count > 0;
+
             public override void Accept(RazorIRNodeVisitor visitor)
             {
                 ((DerivedIRNodeWalker)visitor).VisitBasic(this);

test/Microsoft.AspNetCore.Razor.Test.Common/Langauge/IntegrationTests/RazorIRNodeWriter.cs

@@ -4,6 +4,8 @@
 using System.Collections.Generic;
 using System.IO;
 using System.Linq;
+using System.Security.Cryptography;
+using System.Text;
 using Microsoft.AspNetCore.Razor.Language.Intermediate;
 using Microsoft.AspNetCore.Razor.Language.Legacy;
 
@@ -188,24 +190,66 @@ namespace Microsoft.AspNetCore.Razor.Language.IntegrationTests
         {
             if (node.Source != null)
             {
-                var sourceRange = node.Source.Value;
-                _writer.Write("(");
-                _writer.Write(sourceRange.AbsoluteIndex);
-                _writer.Write(":");
-                _writer.Write(sourceRange.LineIndex);
-                _writer.Write(",");
-                _writer.Write(sourceRange.CharacterIndex);
-                _writer.Write(" [");
-                _writer.Write(sourceRange.Length);
-                _writer.Write("] ");
+                WriteSourceRange(node.Source.Value);
+            }
+        }
 
-                if (sourceRange.FilePath != null)
+        protected void WriteSourceRange(SourceSpan sourceRange)
+        {
+            _writer.Write("(");
+            _writer.Write(sourceRange.AbsoluteIndex);
+            _writer.Write(":");
+            _writer.Write(sourceRange.LineIndex);
+            _writer.Write(",");
+            _writer.Write(sourceRange.CharacterIndex);
+            _writer.Write(" [");
+            _writer.Write(sourceRange.Length);
+            _writer.Write("] ");
+
+            if (sourceRange.FilePath != null)
+            {
+                var fileName = sourceRange.FilePath.Substring(sourceRange.FilePath.LastIndexOf('/') + 1);
+                _writer.Write(fileName);
+            }
+
+            _writer.Write(")");
+        }
+
+        protected void WriteDiagnostics(RazorIRNode node)
+        {
+            if (node.HasDiagnostics)
+            {
+                _writer.Write("| ");
+                for (var i = 0; i < node.Diagnostics.Count; i++)
                 {
-                    var fileName = sourceRange.FilePath.Substring(sourceRange.FilePath.LastIndexOf('/') + 1);
-                    _writer.Write(fileName);
-                }
+                    var diagnostic = node.Diagnostics[i];
+                    _writer.Write("{");
+                    WriteSourceRange(diagnostic.Span);
+                    _writer.Write(": ");
+                    _writer.Write(diagnostic.Severity);
+                    _writer.Write(" ");
+                    _writer.Write(diagnostic.Id);
+                    _writer.Write(": ");
 
-                _writer.Write(")");
+                    // Purposefully not writing out the entire message to ensure readable IR and because messages 
+                    // can span multiple lines. Not using string.GetHashCode because we can't have any collisions.
+                    using (var md5 = MD5.Create())
+                    {
+                        var diagnosticMessage = diagnostic.GetMessage();
+                        var messageBytes = Encoding.UTF8.GetBytes(diagnosticMessage);
+                        var messageHash = md5.ComputeHash(messageBytes);
+                        var stringHashBuilder = new StringBuilder();
+
+                        for (var j = 0; j < messageHash.Length; j++)
+                        {
+                            stringHashBuilder.Append(messageHash[j].ToString("x2"));
+                        }
+
+                        var stringHash = stringHashBuilder.ToString();
+                        _writer.Write(stringHash);
+                    }
+                    _writer.Write("} ");
+                }
             }
         }