Fix #1068

This changes the bind lowering pass to be more tolerant of unexpected
and invalid content.

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

@@ -1,4 +1,4 @@
-// Copyright (c) .NET Foundation. All rights reserved.
+// 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;
@@ -478,19 +478,30 @@ namespace Microsoft.AspNetCore.Blazor.Razor
             {
                 // This case can be hit for a 'string' attribute. We want to turn it into
                 // an expression.
-                var content = "\"" + ((IntermediateToken)htmlContentNode.Children.Single()).Content + "\"";
+                var content = "\"" + string.Join(string.Empty, htmlContentNode.Children.OfType<IntermediateToken>().Select(t => t.Content)) + "\"";
                 return new IntermediateToken() { Kind = TokenKind.CSharp, Content = content };
             }
             else if (node.Children[0] is CSharpExpressionIntermediateNode cSharpNode)
             {
                 // This case can be hit when the attribute has an explicit @ inside, which
                 // 'escapes' any special sugar we provide for codegen.
-                return ((IntermediateToken)cSharpNode.Children.Single());
+                return GetToken(cSharpNode);
             }
             else
             {
                 // This is the common case for 'mixed' content
-                return ((IntermediateToken)node.Children.Single());
+                return GetToken(node);
+            }
+
+            // In error cases we won't have a single token, but we still want to generate the code.
+            IntermediateToken GetToken(IntermediateNode parent)
+            {
+                return
+                    parent.Children.Count == 1 ? (IntermediateToken)parent.Children[0] : new IntermediateToken()
+                    {
+                        Kind = TokenKind.CSharp,
+                        Content = string.Join(string.Empty, parent.Children.OfType<IntermediateToken>().Select(t => t.Content)),
+                    };
             }
         }
     }

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

@@ -1,4 +1,4 @@
-// Copyright (c) .NET Foundation. All rights reserved.
+// 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;
@@ -33,20 +33,28 @@ namespace Test
         [Parameter] Action<int> ValueChanged { get; set; }
         [Parameter] string AnotherValue { get; set; }
     }
+
+    public class ModelState
+    {
+        public Action<string> Bind(Func<string, string> func) => throw null;
+    }
 }
 "));
             var text = @"
 @addTagHelper *, TestAssembly
 <div>
   <MyComponent bind-Value=""myValue"" AnotherValue=""hi""/>
-  <input type=""text"" bind=""@value"" />
+  <input type=""text"" bind=""@this.ModelState.Bind(x => x)"" />
   <button ref=""_button"" onsubmit=""@FormSubmitted"">Click me</button>
 </div>
 <MyComponent 
     IntProperty=""123""
     BoolProperty=""true""
     StringProperty=""My string""
-    ObjectProperty=""new SomeType()""/>";
+    ObjectProperty=""new SomeType()""/>
+@functions {
+    Test.ModelState ModelState { get; set; }
+}";
 
             for (var i = 0; i <= text.Length; i++)
             {
@@ -66,5 +74,21 @@ Exception:
                 }
             }
         }
+
+        [Fact] // Regression test for #1068 
+        public void Regression_1068()
+        {
+            // Arrange
+
+            // Act
+            var generated = CompileToCSharp(@"
+<input type=""text"" bind="" />
+@functions {
+    Test.ModelState ModelState { get; set; }
+}
+");
+
+            // Assert
+        }
     }
 }