In RazorCompiler, reject malformed documents with mismatching tags

src/Microsoft.AspNetCore.Blazor.Build/Cli/Commands/BuildRazorCommand.cs

@@ -2,6 +2,7 @@
 // Licensed under the Apache License, Version 2.0. See License.txt in the project root for license information.
 
 using Microsoft.AspNetCore.Blazor.Build.Core.RazorCompilation;
+using Microsoft.AspNetCore.Blazor.Razor;
 using Microsoft.Extensions.CommandLineUtils;
 using System;
 using System.Collections.Generic;

src/Microsoft.AspNetCore.Blazor.Razor.Extensions/BlazorIntermediateNodeWriter.cs

@@ -27,6 +27,7 @@ namespace Microsoft.AspNetCore.Blazor.Razor
                 new[] { "area", "base", "br", "col", "embed", "hr", "img", "input", "link", "meta", "param", "source", "track", "wbr" },
                 StringComparer.OrdinalIgnoreCase);
 
+        private readonly ScopeStack _scopeStack = new ScopeStack();
         private string _unconsumedHtml;
         private IList<object> _currentAttributeValues;
         private IDictionary<string, PendingAttribute> _currentElementAttributes = new Dictionary<string, PendingAttribute>();
@@ -75,6 +76,7 @@ namespace Microsoft.AspNetCore.Blazor.Razor
             {
                 if (node.Children[i] is IntermediateToken token && token.IsCSharp)
                 {
+                    _scopeStack.IncrementCurrentScopeChildCount();
                     context.CodeWriter.Write(token.Content);
                 }
                 else
@@ -118,6 +120,7 @@ namespace Microsoft.AspNetCore.Blazor.Razor
 
             // Since we're not in the middle of writing an element, this must evaluate as some
             // text to display
+            _scopeStack.IncrementCurrentScopeChildCount();
             context.CodeWriter
                 .WriteStartMethodInvocation($"{builderVarName}.{nameof(RenderTreeBuilder.AddContent)}")
                 .Write((_sourceSequence++).ToString())
@@ -207,6 +210,7 @@ namespace Microsoft.AspNetCore.Blazor.Razor
                     case HtmlTokenType.Character:
                         {
                             // Text node
+                            _scopeStack.IncrementCurrentScopeChildCount();
                             codeWriter
                                 .WriteStartMethodInvocation($"{builderVarName}.{nameof(RenderTreeBuilder.AddContent)}")
                                 .Write((_sourceSequence++).ToString())
@@ -225,6 +229,7 @@ namespace Microsoft.AspNetCore.Blazor.Razor
 
                             if (nextToken.Type == HtmlTokenType.StartTag)
                             {
+                                _scopeStack.IncrementCurrentScopeChildCount();
                                 if (isComponent)
                                 {
                                     codeWriter
@@ -241,40 +246,47 @@ namespace Microsoft.AspNetCore.Blazor.Razor
                                         .WriteStringLiteral(nextTag.Data)
                                         .WriteEndMethodInvocation();
                                 }
-                            }
 
-                            foreach (var attribute in nextTag.Attributes)
+                                foreach (var attribute in nextTag.Attributes)
-                            {
-                                WriteAttribute(codeWriter, attribute.Key, attribute.Value);
-                            }
-
-                            if (_currentElementAttributes.Count > 0)
-                            {
-                                foreach (var pair in _currentElementAttributes)
                                 {
-                                    WriteAttribute(codeWriter, pair.Key, pair.Value.AttributeValue);
+                                    WriteAttribute(codeWriter, attribute.Key, attribute.Value);
                                 }
-                                _currentElementAttributes.Clear();
-                            }
 
-                            if (_currentElementAttributeTokens.Count > 0)
+                                if (_currentElementAttributes.Count > 0)
-                            {
-                                foreach (var token in _currentElementAttributeTokens)
                                 {
-                                    codeWriter
+                                    foreach (var pair in _currentElementAttributes)
-                                        .WriteStartMethodInvocation($"{builderVarName}.{nameof(RenderTreeBuilder.AddAttribute)}")
+                                    {
-                                        .Write((_sourceSequence++).ToString())
+                                        WriteAttribute(codeWriter, pair.Key, pair.Value.AttributeValue);
-                                        .WriteParameterSeparator()
+                                    }
-                                        .Write(token.AttributeValue.Content)
+                                    _currentElementAttributes.Clear();
-                                        .WriteEndMethodInvocation();
                                 }
-                                _currentElementAttributeTokens.Clear();
+
+                                if (_currentElementAttributeTokens.Count > 0)
+                                {
+                                    foreach (var token in _currentElementAttributeTokens)
+                                    {
+                                        codeWriter
+                                            .WriteStartMethodInvocation($"{builderVarName}.{nameof(RenderTreeBuilder.AddAttribute)}")
+                                            .Write((_sourceSequence++).ToString())
+                                            .WriteParameterSeparator()
+                                            .Write(token.AttributeValue.Content)
+                                            .WriteEndMethodInvocation();
+                                    }
+                                    _currentElementAttributeTokens.Clear();
+                                }
+
+                                _scopeStack.OpenScope(
+                                    tagName: isComponent ? tagNameOriginalCase : nextTag.Data,
+                                    isComponent: isComponent);
                             }
 
                             if (nextToken.Type == HtmlTokenType.EndTag
                                 || nextTag.IsSelfClosing
-                                || htmlVoidElementsLookup.Contains(nextTag.Data))
+                                || (!isComponent && htmlVoidElementsLookup.Contains(nextTag.Data)))
                             {
+                                _scopeStack.CloseScope(
+                                    tagName: isComponent ? tagNameOriginalCase : nextTag.Data,
+                                    isComponent: isComponent);
                                 var closeMethodName = isComponent
                                     ? nameof(RenderTreeBuilder.CloseComponent)
                                     : nameof(RenderTreeBuilder.CloseElement);

src/Microsoft.AspNetCore.Blazor.Razor.Extensions/RazorCompilerDiagnostic.cs

@@ -1,7 +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.
 
-namespace Microsoft.AspNetCore.Blazor.Build.Core.RazorCompilation
+namespace Microsoft.AspNetCore.Blazor.Razor
 {
     public class RazorCompilerDiagnostic
     {
@@ -11,7 +11,7 @@ namespace Microsoft.AspNetCore.Blazor.Build.Core.RazorCompilation
         public int Column { get; }
         public string Message { get; }
 
-        internal RazorCompilerDiagnostic(
+        public RazorCompilerDiagnostic(
             DiagnosticType type,
             string sourceFilePath,
             int line,

src/Microsoft.AspNetCore.Blazor.Razor.Extensions/RazorCompilerException.cs

@@ -3,15 +3,15 @@
 
 using System;
 
-namespace Microsoft.AspNetCore.Blazor.Build.Core.RazorCompilation
+namespace Microsoft.AspNetCore.Blazor.Razor
 {
     /// <summary>
     /// Represents a fatal error during the transformation of a Blazor component from
     /// Razor source code to C# source code.
     /// </summary>
-    internal class RazorCompilerException : Exception
+    public class RazorCompilerException : Exception
     {
-        public RazorCompilerException(string message): base(message)
+        public RazorCompilerException(string message) : base(message)
         {
         }
 

src/Microsoft.AspNetCore.Blazor.Razor.Extensions/ScopeStack.cs

@@ -0,0 +1,68 @@
+// Copyright (c) .NET Foundation. All rights reserved.
+// Licensed under the Apache License, Version 2.0. See License.txt in the project root for license information.
+
+using Microsoft.AspNetCore.Razor.Language;
+using System;
+using System.Collections.Generic;
+
+namespace Microsoft.AspNetCore.Blazor.Razor
+{
+    /// <summary>
+    /// Keeps track of the nesting of elements/containers while writing out the C# source code
+    /// for a component. This allows us to detect mismatched start/end tags, as well as inject
+    /// additional C# source to capture component descendants in a lambda.
+    /// </summary>
+    internal class ScopeStack
+    {
+        private readonly Stack<ScopeEntry> _stack = new Stack<ScopeEntry>();
+
+        public void OpenScope(string tagName, bool isComponent)
+        {
+            _stack.Push(new ScopeEntry(tagName, isComponent));
+        }
+
+        public void CloseScope(string tagName, bool isComponent)
+        {
+            if (_stack.Count == 0)
+            {
+                throw new RazorCompilerException(
+                    $"Unexpected closing tag '{tagName}' with no matching start tag.");
+            }
+
+            var expected = _stack.Pop();
+            if (!tagName.Equals(expected.TagName, StringComparison.Ordinal))
+            {
+                throw new RazorCompilerException(
+                    $"Mismatching closing tag. Found '{tagName}' but expected '{expected.TagName}'.");
+            }
+
+            // Note: there's no unit test to cover the following, because there's no known way of
+            // triggering it from user code (i.e., Razor source code). But the test is here anyway
+            // just in case one day it turns out there is some way of causing this error.
+            if (isComponent != expected.IsComponent)
+            {
+                throw new RazorCompilerException(
+                    $"Mismatching closing tag. Found '{tagName}' of type '{(isComponent ? "component" : "element")}' but expected type '{(expected.IsComponent ? "component" : "element")}'.");
+            }
+        }
+
+        public void IncrementCurrentScopeChildCount()
+        {
+
+        }
+
+        private class ScopeEntry
+        {
+            public readonly string TagName;
+            public readonly bool IsComponent;
+            public int ChildCount;
+
+            public ScopeEntry(string tagName, bool isComponent)
+            {
+                TagName = tagName;
+                IsComponent = isComponent;
+                ChildCount = 0;
+            }
+        }
+    }
+}

test/Microsoft.AspNetCore.Blazor.Build.Test/RazorCompilerTest.cs

@@ -4,6 +4,7 @@
 using Microsoft.AspNetCore.Blazor.Build.Core.RazorCompilation;
 using Microsoft.AspNetCore.Blazor.Components;
 using Microsoft.AspNetCore.Blazor.Layouts;
+using Microsoft.AspNetCore.Blazor.Razor;
 using Microsoft.AspNetCore.Blazor.Rendering;
 using Microsoft.AspNetCore.Blazor.RenderTree;
 using Microsoft.AspNetCore.Blazor.Test.Helpers;
@@ -503,6 +504,38 @@ namespace Microsoft.AspNetCore.Blazor.Build.Test
                 diagnostic => Assert.Contains("'invalidVar'", diagnostic.GetMessage()));
         }
 
+        [Fact]
+        public void RejectsEndTagWithNoStartTag()
+        {
+            // Arrange/Act
+            var result = CompileToCSharp(
+                "Line1\nLine2\nLine3</mytag>");
+
+            // Assert
+            Assert.Collection(result.Diagnostics,
+                item =>
+                {
+                    Assert.Equal(RazorCompilerDiagnostic.DiagnosticType.Error, item.Type);
+                    Assert.StartsWith("Unexpected closing tag 'mytag' with no matching start tag.", item.Message);
+                });
+        }
+
+        [Fact]
+        public void RejectsEndTagWithDifferentNameToStartTag()
+        {
+            // Arrange/Act
+            var result = CompileToCSharp(
+                "<root><other />text<child>more text</root></child>");
+
+            // Assert
+            Assert.Collection(result.Diagnostics,
+                item =>
+                {
+                    Assert.Equal(RazorCompilerDiagnostic.DiagnosticType.Error, item.Type);
+                    Assert.StartsWith("Mismatching closing tag. Found 'root' but expected 'child'.", item.Message);
+                });
+        }
+
         private static RenderTreeFrame[] GetRenderTree(IComponent component)
         {
             var renderer = new TestRenderer();
@@ -575,6 +608,13 @@ namespace Microsoft.AspNetCore.Blazor.Build.Test
             }
         }
 
+        private static CompileToCSharpResult CompileToCSharp(string cshtmlContent)
+            => CompileToCSharp(
+                GetArbitraryPlatformValidDirectoryPath(),
+                "test.cshtml",
+                cshtmlContent,
+                "TestNamespace");
+
         private static CompileToCSharpResult CompileToCSharp(string cshtmlRootPath, string cshtmlRelativePath, string cshtmlContent, string outputNamespace)
         {
             using (var resultStream = new MemoryStream())