Emit and map empty csharp tokens (#10969)

* Emit and map empty csharp tokens
- Add test and update baselines
* Unskip test

src/Compiler/Microsoft.AspNetCore.Razor.Language/test/IntegrationTests/ComponentCodeGenerationTestBase.cs

@@ -2103,6 +2103,34 @@ namespace Test
         CompileToAssembly(generated);
     }
 
+    [IntegrationTestFact, WorkItem("https://github.com/dotnet/razor/issues/10965")]
+    public void InvalidCode_EmptyTransition()
+    {
+        // Act
+        var generated = CompileToCSharp("""
+        <TestComponent Value="Hello" />
+
+        @
+
+        @code {
+            [Parameter] public int Param { get; set; }
+        }
+        """);
+
+        // Assert
+        AssertDocumentNodeMatchesBaseline(generated.CodeDocument);
+        AssertCSharpDocumentMatchesBaseline(generated.CodeDocument);
+        CompileToAssembly(generated, DesignTime?[
+            // x:\dir\subdir\Test\TestComponent.cshtml(3,7): error CS1525: Invalid expression term ';'
+            // __o = ;
+            Diagnostic(ErrorCode.ERR_InvalidExprTerm, ";").WithArguments(";").WithLocation(3, 7)
+            ] : [
+            // (24,36): error CS1525: Invalid expression term ')'
+            //             __builder.AddContent(3, 
+            Diagnostic(ErrorCode.ERR_InvalidExprTerm, "").WithArguments(")").WithLocation(24, 36)
+            ]);
+    }
+
     #endregion
 
     #region Bind

src/Compiler/Microsoft.AspNetCore.Razor.Language/test/TestFiles/IntegrationTests/ComponentDesignTimeCodeGenerationTest/InvalidCode_EmptyTransition/TestComponent.codegen.cs

@@ -0,0 +1,57 @@
+// <auto-generated/>
+#pragma warning disable 1591
+namespace Test
+{
+    #line default
+    using global::System;
+    using global::System.Collections.Generic;
+    using global::System.Linq;
+    using global::System.Threading.Tasks;
+    using global::Microsoft.AspNetCore.Components;
+    #line default
+    #line hidden
+    #nullable restore
+    public partial class TestComponent : global::Microsoft.AspNetCore.Components.ComponentBase
+    #nullable disable
+    {
+        #pragma warning disable 219
+        private void __RazorDirectiveTokenHelpers__() {
+        }
+        #pragma warning restore 219
+        #pragma warning disable 0414
+        private static object __o = null;
+        #pragma warning restore 0414
+        #pragma warning disable 1998
+        protected override void BuildRenderTree(global::Microsoft.AspNetCore.Components.Rendering.RenderTreeBuilder __builder)
+        {
+            __o = "";
+            __builder.AddAttribute(-1, "ChildContent", (global::Microsoft.AspNetCore.Components.RenderFragment)((__builder2) => {
+            }
+            ));
+#nullable restore
+#line 1 "x:\dir\subdir\Test\TestComponent.cshtml"
+__o = typeof(global::Test.TestComponent);
+
+#line default
+#line hidden
+#nullable disable
+#nullable restore
+#line 3 "x:\dir\subdir\Test\TestComponent.cshtml"
+__o = ;
+
+#line default
+#line hidden
+#nullable disable
+        }
+        #pragma warning restore 1998
+#nullable restore
+#line 5 "x:\dir\subdir\Test\TestComponent.cshtml"
+       
+    [Parameter] public int Param { get; set; }
+
+#line default
+#line hidden
+#nullable disable
+    }
+}
+#pragma warning restore 1591

src/Compiler/Microsoft.AspNetCore.Razor.Language/test/TestFiles/IntegrationTests/ComponentDesignTimeCodeGenerationTest/InvalidCode_EmptyTransition/TestComponent.diagnostics.txt

@@ -0,0 +1 @@
+x:\dir\subdir\Test\TestComponent.cshtml(3,2): Error RZ1003: 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.

src/Compiler/Microsoft.AspNetCore.Razor.Language/test/TestFiles/IntegrationTests/ComponentDesignTimeCodeGenerationTest/InvalidCode_EmptyTransition/TestComponent.ir.txt

@@ -0,0 +1,28 @@
+Document - 
+    NamespaceDeclaration -  - Test
+        UsingDirective - (3:1,1 [20] ) - global::System
+        UsingDirective - (26:2,1 [40] ) - global::System.Collections.Generic
+        UsingDirective - (69:3,1 [25] ) - global::System.Linq
+        UsingDirective - (97:4,1 [36] ) - global::System.Threading.Tasks
+        UsingDirective - (136:5,1 [45] ) - global::Microsoft.AspNetCore.Components
+        ClassDeclaration -  - public partial - TestComponent - global::Microsoft.AspNetCore.Components.ComponentBase - 
+            DesignTimeDirective - 
+            CSharpCode - 
+                IntermediateToken -  - CSharp - #pragma warning disable 0414
+            CSharpCode - 
+                IntermediateToken -  - CSharp - private static object __o = null;
+            CSharpCode - 
+                IntermediateToken -  - CSharp - #pragma warning restore 0414
+            MethodDeclaration -  - protected override - void - BuildRenderTree
+                Component - (0:0,0 [31] x:\dir\subdir\Test\TestComponent.cshtml) - TestComponent
+                    ComponentAttribute -  - Value -  - AttributeStructure.DoubleQuotes
+                        HtmlContent - (22:0,22 [5] x:\dir\subdir\Test\TestComponent.cshtml)
+                            LazyIntermediateToken - (22:0,22 [5] x:\dir\subdir\Test\TestComponent.cshtml) - Html - Hello
+                HtmlContent - (31:0,31 [4] x:\dir\subdir\Test\TestComponent.cshtml)
+                    LazyIntermediateToken - (31:0,31 [4] x:\dir\subdir\Test\TestComponent.cshtml) - Html - \n\n
+                CSharpExpression - (36:2,1 [0] x:\dir\subdir\Test\TestComponent.cshtml)
+                    LazyIntermediateToken - (36:2,1 [0] x:\dir\subdir\Test\TestComponent.cshtml) - CSharp - 
+                HtmlContent - (36:2,1 [4] x:\dir\subdir\Test\TestComponent.cshtml)
+                    LazyIntermediateToken - (36:2,1 [4] x:\dir\subdir\Test\TestComponent.cshtml) - Html - \n\n
+            CSharpCode - (47:4,7 [50] x:\dir\subdir\Test\TestComponent.cshtml)
+                LazyIntermediateToken - (47:4,7 [50] x:\dir\subdir\Test\TestComponent.cshtml) - CSharp - \n    [Parameter] public int Param { get; set; }\n

src/Compiler/Microsoft.AspNetCore.Razor.Language/test/TestFiles/IntegrationTests/ComponentDesignTimeCodeGenerationTest/InvalidCode_EmptyTransition/TestComponent.mappings.txt

@@ -0,0 +1,14 @@
+Source Location: (36:2,1 [0] x:\dir\subdir\Test\TestComponent.cshtml)
+||
+Generated Location: (1340:39,6 [0] )
+||
+
+Source Location: (47:4,7 [50] x:\dir\subdir\Test\TestComponent.cshtml)
+|
+    [Parameter] public int Param { get; set; }
+|
+Generated Location: (1519:48,7 [50] )
+|
+    [Parameter] public int Param { get; set; }
+|
+

src/Compiler/Microsoft.AspNetCore.Razor.Language/test/TestFiles/IntegrationTests/ComponentRuntimeCodeGenerationTest/FormName_RazorError/TestComponent.codegen.cs

@@ -34,7 +34,15 @@ using Microsoft.AspNetCore.Components.Web
 #line hidden
 #nullable disable
             ));
-            string __formName = global::Microsoft.AspNetCore.Components.CompilerServices.RuntimeHelpers.TypeCheck<string>();
+            string __formName = global::Microsoft.AspNetCore.Components.CompilerServices.RuntimeHelpers.TypeCheck<string>(
+#nullable restore
+#line (2,56)-(2,57) "x:\dir\subdir\Test\TestComponent.cshtml"
+ 
+
+#line default
+#line hidden
+#nullable disable
+            );
             __builder.AddNamedEvent("onsubmit", __formName);
             __builder.CloseElement();
         }

src/Compiler/Microsoft.AspNetCore.Razor.Language/test/TestFiles/IntegrationTests/ComponentRuntimeCodeGenerationTest/FormName_RazorError/TestComponent.mappings.txt

@@ -8,3 +8,8 @@ Source Location: (75:1,31 [9] x:\dir\subdir\Test\TestComponent.cshtml)
 Generated Location: (1138:30,0 [9] )
 |() => { }|
 
+Source Location: (99:1,55 [1] x:\dir\subdir\Test\TestComponent.cshtml)
+| |
+Generated Location: (1422:39,0 [1] )
+| |
+

src/Compiler/Microsoft.AspNetCore.Razor.Language/test/TestFiles/IntegrationTests/ComponentRuntimeCodeGenerationTest/InvalidCode_EmptyTransition/TestComponent.codegen.cs

@@ -0,0 +1,45 @@
+// <auto-generated/>
+#pragma warning disable 1591
+namespace Test
+{
+    #line default
+    using global::System;
+    using global::System.Collections.Generic;
+    using global::System.Linq;
+    using global::System.Threading.Tasks;
+    using global::Microsoft.AspNetCore.Components;
+    #line default
+    #line hidden
+    #nullable restore
+    public partial class TestComponent : global::Microsoft.AspNetCore.Components.ComponentBase
+    #nullable disable
+    {
+        #pragma warning disable 1998
+        protected override void BuildRenderTree(global::Microsoft.AspNetCore.Components.Rendering.RenderTreeBuilder __builder)
+        {
+            __builder.OpenComponent<global::Test.TestComponent>(0);
+            __builder.AddComponentParameter(1, "Value", "Hello");
+            __builder.CloseComponent();
+            __builder.AddMarkupContent(2, "\r\n\r\n");
+            __builder.AddContent(3, 
+#nullable restore
+#line (3,2)-(3,2) "x:\dir\subdir\Test\TestComponent.cshtml"
+
+#line default
+#line hidden
+#nullable disable
+            );
+        }
+        #pragma warning restore 1998
+#nullable restore
+#line (5,8)-(7,1) "x:\dir\subdir\Test\TestComponent.cshtml"
+
+    [Parameter] public int Param { get; set; }
+
+#line default
+#line hidden
+#nullable disable
+
+    }
+}
+#pragma warning restore 1591

src/Compiler/Microsoft.AspNetCore.Razor.Language/test/TestFiles/IntegrationTests/ComponentRuntimeCodeGenerationTest/InvalidCode_EmptyTransition/TestComponent.diagnostics.txt

@@ -0,0 +1 @@
+x:\dir\subdir\Test\TestComponent.cshtml(3,2): Error RZ1003: 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.

src/Compiler/Microsoft.AspNetCore.Razor.Language/test/TestFiles/IntegrationTests/ComponentRuntimeCodeGenerationTest/InvalidCode_EmptyTransition/TestComponent.ir.txt

@@ -0,0 +1,19 @@
+Document - 
+    NamespaceDeclaration -  - Test
+        UsingDirective - (3:1,1 [20] ) - global::System
+        UsingDirective - (26:2,1 [40] ) - global::System.Collections.Generic
+        UsingDirective - (69:3,1 [25] ) - global::System.Linq
+        UsingDirective - (97:4,1 [36] ) - global::System.Threading.Tasks
+        UsingDirective - (136:5,1 [45] ) - global::Microsoft.AspNetCore.Components
+        ClassDeclaration -  - public partial - TestComponent - global::Microsoft.AspNetCore.Components.ComponentBase - 
+            MethodDeclaration -  - protected override - void - BuildRenderTree
+                Component - (0:0,0 [31] x:\dir\subdir\Test\TestComponent.cshtml) - TestComponent
+                    ComponentAttribute -  - Value -  - AttributeStructure.DoubleQuotes
+                        HtmlContent - (22:0,22 [5] x:\dir\subdir\Test\TestComponent.cshtml)
+                            LazyIntermediateToken - (22:0,22 [5] x:\dir\subdir\Test\TestComponent.cshtml) - Html - Hello
+                HtmlContent - (31:0,31 [4] x:\dir\subdir\Test\TestComponent.cshtml)
+                    LazyIntermediateToken - (31:0,31 [4] x:\dir\subdir\Test\TestComponent.cshtml) - Html - \n\n
+                CSharpExpression - (36:2,1 [0] x:\dir\subdir\Test\TestComponent.cshtml)
+                    LazyIntermediateToken - (36:2,1 [0] x:\dir\subdir\Test\TestComponent.cshtml) - CSharp - 
+            CSharpCode - (47:4,7 [50] x:\dir\subdir\Test\TestComponent.cshtml)
+                LazyIntermediateToken - (47:4,7 [50] x:\dir\subdir\Test\TestComponent.cshtml) - CSharp - \n    [Parameter] public int Param { get; set; }\n

src/Compiler/Microsoft.AspNetCore.Razor.Language/test/TestFiles/IntegrationTests/ComponentRuntimeCodeGenerationTest/InvalidCode_EmptyTransition/TestComponent.mappings.txt

@@ -0,0 +1,14 @@
+Source Location: (36:2,1 [0] x:\dir\subdir\Test\TestComponent.cshtml)
+||
+Generated Location: (1005:26,0 [0] )
+||
+
+Source Location: (47:4,7 [50] x:\dir\subdir\Test\TestComponent.cshtml)
+|
+    [Parameter] public int Param { get; set; }
+|
+Generated Location: (1200:35,0 [50] )
+|
+    [Parameter] public int Param { get; set; }
+|
+

src/Compiler/Microsoft.CodeAnalysis.Razor.Compiler/src/Language/Components/ComponentRuntimeNodeWriter.cs

@@ -1188,11 +1188,6 @@ internal class ComponentRuntimeNodeWriter : ComponentNodeWriter
 
     private static void WriteCSharpToken(CodeRenderingContext context, IntermediateToken token)
     {
-        if (string.IsNullOrWhiteSpace(token.Content))
-        {
-            return;
-        }
-
         if (token.Source?.FilePath == null)
         {
             context.CodeWriter.Write(token.Content);

src/Razor/test/Microsoft.VisualStudio.Razor.IntegrationTests/NonRazorSdkTests.cs

@@ -35,7 +35,7 @@ public class NonRazorSdkTests(ITestOutputHelper testOutputHelper) : AbstractRazo
         base.PrepareProjectForFirstOpen(projectFileName);
     }
 
-    [IdeFact(Skip = "https://github.com/dotnet/razor/issues/10965")] // Completion is broken in FUSE for sole `@` characters
+    [IdeFact]
     public async Task Completion_DateTime()
     {
         // We open the Index.razor file, and wait for 3 RazorComponentElement's to be classified, as that