Re-add marker IR tokens to represent CSharp in an expression.

- At design time we weren't generating line mappings when a user would type `@` or `@(`. This results in no C# IntelliSense being provided to the user because the editor hasn't mapped any of Razor to the C# buffer.
- Modified the `DefaultIRLoweringPhase` to allow for marker symbols, these symbols .
- Re-generated test files to account for 0 length line mappings on empty expression nodes.

#1155

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

@@ -367,17 +367,6 @@ namespace Microsoft.AspNetCore.Razor.Evolution
 
             public override void VisitExpressionSpan(ExpressionChunkGenerator chunkGenerator, Span span)
             {
-                if (span.Symbols.Count == 1)
-                {
-                    if (span.Symbols[0] is CSharpSymbol symbol &&
-                        symbol.Type == CSharpSymbolType.Unknown &&
-                        symbol.Content.Length == 0)
-                    {
-                        // We don't want to create IR nodes for marker symbols.
-                        return;
-                    }
-                }
-
                 _builder.Add(new RazorIRToken()
                 {
                     Content = span.Content,

test/Microsoft.AspNetCore.Razor.Evolution.Test/TestFiles/IntegrationTests/CodeGenerationIntegrationTest/EmptyExplicitExpression_DesignTime.codegen.cs

@@ -13,6 +13,11 @@ namespace Microsoft.AspNetCore.Razor.Evolution.IntegrationTests.TestFiles
         #pragma warning disable 1998
         public async System.Threading.Tasks.Task ExecuteAsync()
         {
+#line 3 "TestFiles/IntegrationTests/CodeGenerationIntegrationTest/EmptyExplicitExpression.cshtml"
+__o = ;
+
+#line default
+#line hidden
         }
         #pragma warning restore 1998
     }

test/Microsoft.AspNetCore.Razor.Evolution.Test/TestFiles/IntegrationTests/CodeGenerationIntegrationTest/EmptyExplicitExpression_DesignTime.ir.txt

@@ -17,4 +17,5 @@ Document -
                 RazorIRToken -  - CSharp - private static System.Object __o = null;
             RazorMethodDeclaration -  - public - async - System.Threading.Tasks.Task - ExecuteAsync
                 HtmlContent - (0:0,0 [18] EmptyExplicitExpression.cshtml) - This is markup\n\n
-                CSharpExpression - 
+                CSharpExpression - (20:2,2 [0] EmptyExplicitExpression.cshtml)
+                    RazorIRToken - (20:2,2 [0] EmptyExplicitExpression.cshtml) - CSharp - 

test/Microsoft.AspNetCore.Razor.Evolution.Test/TestFiles/IntegrationTests/CodeGenerationIntegrationTest/EmptyExplicitExpression_DesignTime.mappings.txt

@@ -0,0 +1,5 @@
+Source Location: (20:2,2 [0] TestFiles/IntegrationTests/CodeGenerationIntegrationTest/EmptyExplicitExpression.cshtml)
+||
+Generated Location: (678:16,6 [0] )
+||
+

test/Microsoft.AspNetCore.Razor.Evolution.Test/TestFiles/IntegrationTests/CodeGenerationIntegrationTest/EmptyExplicitExpression_Runtime.codegen.cs

@@ -10,7 +10,11 @@ namespace Microsoft.AspNetCore.Razor.Evolution.IntegrationTests.TestFiles
         public async System.Threading.Tasks.Task ExecuteAsync()
         {
             WriteLiteral("This is markup\r\n\r\n");
-            Write();
+#line 3 "TestFiles/IntegrationTests/CodeGenerationIntegrationTest/EmptyExplicitExpression.cshtml"
+Write();
+
+#line default
+#line hidden
         }
         #pragma warning restore 1998
     }

test/Microsoft.AspNetCore.Razor.Evolution.Test/TestFiles/IntegrationTests/CodeGenerationIntegrationTest/EmptyExplicitExpression_Runtime.ir.txt

@@ -6,4 +6,5 @@ Document -
         ClassDeclaration -  - public - TestFiles_IntegrationTests_CodeGenerationIntegrationTest_EmptyExplicitExpression_Runtime -  - 
             RazorMethodDeclaration -  - public - async - System.Threading.Tasks.Task - ExecuteAsync
                 HtmlContent - (0:0,0 [18] EmptyExplicitExpression.cshtml) - This is markup\n\n
-                CSharpExpression - 
+                CSharpExpression - (20:2,2 [0] EmptyExplicitExpression.cshtml)
+                    RazorIRToken - (20:2,2 [0] EmptyExplicitExpression.cshtml) - CSharp - 

test/Microsoft.AspNetCore.Razor.Evolution.Test/TestFiles/IntegrationTests/CodeGenerationIntegrationTest/EmptyImplicitExpressionInCode_DesignTime.codegen.cs

@@ -15,6 +15,11 @@ namespace Microsoft.AspNetCore.Razor.Evolution.IntegrationTests.TestFiles
         {
               
     
+#line 2 "TestFiles/IntegrationTests/CodeGenerationIntegrationTest/EmptyImplicitExpressionInCode.cshtml"
+__o = ;
+
+#line default
+#line hidden
                  
 
         }

test/Microsoft.AspNetCore.Razor.Evolution.Test/TestFiles/IntegrationTests/CodeGenerationIntegrationTest/EmptyImplicitExpressionInCode_DesignTime.ir.txt

@@ -18,6 +18,7 @@ Document -
             RazorMethodDeclaration -  - public - async - System.Threading.Tasks.Task - ExecuteAsync
                 CSharpStatement - (2:0,2 [6] EmptyImplicitExpressionInCode.cshtml)
                     RazorIRToken - (2:0,2 [6] EmptyImplicitExpressionInCode.cshtml) - CSharp - \n    
-                CSharpExpression - 
+                CSharpExpression - (9:1,5 [0] EmptyImplicitExpressionInCode.cshtml)
+                    RazorIRToken - (9:1,5 [0] EmptyImplicitExpressionInCode.cshtml) - CSharp - 
                 CSharpStatement - (9:1,5 [2] EmptyImplicitExpressionInCode.cshtml)
                     RazorIRToken - (9:1,5 [2] EmptyImplicitExpressionInCode.cshtml) - CSharp - \n

test/Microsoft.AspNetCore.Razor.Evolution.Test/TestFiles/IntegrationTests/CodeGenerationIntegrationTest/EmptyImplicitExpressionInCode_DesignTime.mappings.txt

@@ -5,10 +5,15 @@ Generated Location: (593:15,14 [6] )
 |
     |
 
+Source Location: (9:1,5 [0] TestFiles/IntegrationTests/CodeGenerationIntegrationTest/EmptyImplicitExpressionInCode.cshtml)
+||
+Generated Location: (712:18,6 [0] )
+||
+
 Source Location: (9:1,5 [2] TestFiles/IntegrationTests/CodeGenerationIntegrationTest/EmptyImplicitExpressionInCode.cshtml)
 |
 |
-Generated Location: (618:17,17 [2] )
+Generated Location: (763:22,17 [2] )
 |
 |
 

test/Microsoft.AspNetCore.Razor.Evolution.Test/TestFiles/IntegrationTests/CodeGenerationIntegrationTest/EmptyImplicitExpressionInCode_Runtime.codegen.cs

@@ -9,7 +9,11 @@ namespace Microsoft.AspNetCore.Razor.Evolution.IntegrationTests.TestFiles
         #pragma warning disable 1998
         public async System.Threading.Tasks.Task ExecuteAsync()
         {
-            Write();
+#line 2 "TestFiles/IntegrationTests/CodeGenerationIntegrationTest/EmptyImplicitExpressionInCode.cshtml"
+Write();
+
+#line default
+#line hidden
         }
         #pragma warning restore 1998
     }

test/Microsoft.AspNetCore.Razor.Evolution.Test/TestFiles/IntegrationTests/CodeGenerationIntegrationTest/EmptyImplicitExpressionInCode_Runtime.ir.txt

@@ -7,6 +7,7 @@ Document -
             RazorMethodDeclaration -  - public - async - System.Threading.Tasks.Task - ExecuteAsync
                 CSharpStatement - (2:0,2 [6] EmptyImplicitExpressionInCode.cshtml)
                     RazorIRToken - (2:0,2 [6] EmptyImplicitExpressionInCode.cshtml) - CSharp - \n    
-                CSharpExpression - 
+                CSharpExpression - (9:1,5 [0] EmptyImplicitExpressionInCode.cshtml)
+                    RazorIRToken - (9:1,5 [0] EmptyImplicitExpressionInCode.cshtml) - CSharp - 
                 CSharpStatement - (9:1,5 [2] EmptyImplicitExpressionInCode.cshtml)
                     RazorIRToken - (9:1,5 [2] EmptyImplicitExpressionInCode.cshtml) - CSharp - \n

test/Microsoft.AspNetCore.Razor.Evolution.Test/TestFiles/IntegrationTests/CodeGenerationIntegrationTest/EmptyImplicitExpression_DesignTime.codegen.cs

@@ -13,6 +13,11 @@ namespace Microsoft.AspNetCore.Razor.Evolution.IntegrationTests.TestFiles
         #pragma warning disable 1998
         public async System.Threading.Tasks.Task ExecuteAsync()
         {
+#line 3 "TestFiles/IntegrationTests/CodeGenerationIntegrationTest/EmptyImplicitExpression.cshtml"
+__o = ;
+
+#line default
+#line hidden
         }
         #pragma warning restore 1998
     }

test/Microsoft.AspNetCore.Razor.Evolution.Test/TestFiles/IntegrationTests/CodeGenerationIntegrationTest/EmptyImplicitExpression_DesignTime.ir.txt

@@ -17,5 +17,6 @@ Document -
                 RazorIRToken -  - CSharp - private static System.Object __o = null;
             RazorMethodDeclaration -  - public - async - System.Threading.Tasks.Task - ExecuteAsync
                 HtmlContent - (0:0,0 [18] EmptyImplicitExpression.cshtml) - This is markup\n\n
-                CSharpExpression - 
+                CSharpExpression - (19:2,1 [0] EmptyImplicitExpression.cshtml)
+                    RazorIRToken - (19:2,1 [0] EmptyImplicitExpression.cshtml) - CSharp - 
                 HtmlContent - (19:2,1 [1] EmptyImplicitExpression.cshtml) - !

test/Microsoft.AspNetCore.Razor.Evolution.Test/TestFiles/IntegrationTests/CodeGenerationIntegrationTest/EmptyImplicitExpression_DesignTime.mappings.txt

@@ -0,0 +1,5 @@
+Source Location: (19:2,1 [0] TestFiles/IntegrationTests/CodeGenerationIntegrationTest/EmptyImplicitExpression.cshtml)
+||
+Generated Location: (678:16,6 [0] )
+||
+

test/Microsoft.AspNetCore.Razor.Evolution.Test/TestFiles/IntegrationTests/CodeGenerationIntegrationTest/EmptyImplicitExpression_Runtime.codegen.cs

@@ -10,7 +10,11 @@ namespace Microsoft.AspNetCore.Razor.Evolution.IntegrationTests.TestFiles
         public async System.Threading.Tasks.Task ExecuteAsync()
         {
             WriteLiteral("This is markup\r\n\r\n");
-            Write();
+#line 3 "TestFiles/IntegrationTests/CodeGenerationIntegrationTest/EmptyImplicitExpression.cshtml"
+Write();
+
+#line default
+#line hidden
             WriteLiteral("!");
         }
         #pragma warning restore 1998

test/Microsoft.AspNetCore.Razor.Evolution.Test/TestFiles/IntegrationTests/CodeGenerationIntegrationTest/EmptyImplicitExpression_Runtime.ir.txt

@@ -6,5 +6,6 @@ Document -
         ClassDeclaration -  - public - TestFiles_IntegrationTests_CodeGenerationIntegrationTest_EmptyImplicitExpression_Runtime -  - 
             RazorMethodDeclaration -  - public - async - System.Threading.Tasks.Task - ExecuteAsync
                 HtmlContent - (0:0,0 [18] EmptyImplicitExpression.cshtml) - This is markup\n\n
-                CSharpExpression - 
+                CSharpExpression - (19:2,1 [0] EmptyImplicitExpression.cshtml)
+                    RazorIRToken - (19:2,1 [0] EmptyImplicitExpression.cshtml) - CSharp - 
                 HtmlContent - (19:2,1 [1] EmptyImplicitExpression.cshtml) - !

test/Microsoft.AspNetCore.Razor.Evolution.Test/TestFiles/IntegrationTests/CodeGenerationIntegrationTest/ExplicitExpressionAtEOF_DesignTime.codegen.cs

@@ -13,6 +13,11 @@ namespace Microsoft.AspNetCore.Razor.Evolution.IntegrationTests.TestFiles
         #pragma warning disable 1998
         public async System.Threading.Tasks.Task ExecuteAsync()
         {
+#line 3 "TestFiles/IntegrationTests/CodeGenerationIntegrationTest/ExplicitExpressionAtEOF.cshtml"
+__o = ;
+
+#line default
+#line hidden
         }
         #pragma warning restore 1998
     }

test/Microsoft.AspNetCore.Razor.Evolution.Test/TestFiles/IntegrationTests/CodeGenerationIntegrationTest/ExplicitExpressionAtEOF_DesignTime.ir.txt

@@ -17,4 +17,5 @@ Document -
                 RazorIRToken -  - CSharp - private static System.Object __o = null;
             RazorMethodDeclaration -  - public - async - System.Threading.Tasks.Task - ExecuteAsync
                 HtmlContent - (0:0,0 [18] ExplicitExpressionAtEOF.cshtml) - This is markup\n\n
-                CSharpExpression - 
+                CSharpExpression - (20:2,2 [0] ExplicitExpressionAtEOF.cshtml)
+                    RazorIRToken - (20:2,2 [0] ExplicitExpressionAtEOF.cshtml) - CSharp - 

test/Microsoft.AspNetCore.Razor.Evolution.Test/TestFiles/IntegrationTests/CodeGenerationIntegrationTest/ExplicitExpressionAtEOF_DesignTime.mappings.txt

@@ -0,0 +1,5 @@
+Source Location: (20:2,2 [0] TestFiles/IntegrationTests/CodeGenerationIntegrationTest/ExplicitExpressionAtEOF.cshtml)
+||
+Generated Location: (678:16,6 [0] )
+||
+

test/Microsoft.AspNetCore.Razor.Evolution.Test/TestFiles/IntegrationTests/CodeGenerationIntegrationTest/ExplicitExpressionAtEOF_Runtime.codegen.cs

@@ -10,7 +10,11 @@ namespace Microsoft.AspNetCore.Razor.Evolution.IntegrationTests.TestFiles
         public async System.Threading.Tasks.Task ExecuteAsync()
         {
             WriteLiteral("This is markup\r\n\r\n");
-            Write();
+#line 3 "TestFiles/IntegrationTests/CodeGenerationIntegrationTest/ExplicitExpressionAtEOF.cshtml"
+Write();
+
+#line default
+#line hidden
         }
         #pragma warning restore 1998
     }

test/Microsoft.AspNetCore.Razor.Evolution.Test/TestFiles/IntegrationTests/CodeGenerationIntegrationTest/ExplicitExpressionAtEOF_Runtime.ir.txt

@@ -6,4 +6,5 @@ Document -
         ClassDeclaration -  - public - TestFiles_IntegrationTests_CodeGenerationIntegrationTest_ExplicitExpressionAtEOF_Runtime -  - 
             RazorMethodDeclaration -  - public - async - System.Threading.Tasks.Task - ExecuteAsync
                 HtmlContent - (0:0,0 [18] ExplicitExpressionAtEOF.cshtml) - This is markup\n\n
-                CSharpExpression - 
+                CSharpExpression - (20:2,2 [0] ExplicitExpressionAtEOF.cshtml)
+                    RazorIRToken - (20:2,2 [0] ExplicitExpressionAtEOF.cshtml) - CSharp - 

test/Microsoft.AspNetCore.Razor.Evolution.Test/TestFiles/IntegrationTests/CodeGenerationIntegrationTest/ExplicitExpressionWithMarkup_DesignTime.ir.txt

@@ -20,3 +20,4 @@ Document -
                 CSharpExpression - (8:0,8 [6] ExplicitExpressionWithMarkup.cshtml)
                     Template - (8:0,8 [6] ExplicitExpressionWithMarkup.cshtml)
                         HtmlContent - (8:0,8 [6] ExplicitExpressionWithMarkup.cshtml) - </div>
+                    RazorIRToken - (14:0,14 [0] ExplicitExpressionWithMarkup.cshtml) - CSharp - 

test/Microsoft.AspNetCore.Razor.Evolution.Test/TestFiles/IntegrationTests/CodeGenerationIntegrationTest/ExplicitExpressionWithMarkup_DesignTime.mappings.txt

@@ -0,0 +1,5 @@
+Source Location: (14:0,14 [0] TestFiles/IntegrationTests/CodeGenerationIntegrationTest/ExplicitExpressionWithMarkup.cshtml)
+||
+Generated Location: (787:18,1 [0] )
+||
+

test/Microsoft.AspNetCore.Razor.Evolution.Test/TestFiles/IntegrationTests/CodeGenerationIntegrationTest/ExplicitExpressionWithMarkup_Runtime.ir.txt

@@ -9,3 +9,4 @@ Document -
                 CSharpExpression - (8:0,8 [6] ExplicitExpressionWithMarkup.cshtml)
                     Template - (8:0,8 [6] ExplicitExpressionWithMarkup.cshtml)
                         HtmlContent - (8:0,8 [6] ExplicitExpressionWithMarkup.cshtml) - </div>
+                    RazorIRToken - (14:0,14 [0] ExplicitExpressionWithMarkup.cshtml) - CSharp - 

test/Microsoft.AspNetCore.Razor.Evolution.Test/TestFiles/IntegrationTests/CodeGenerationIntegrationTest/ImplicitExpressionAtEOF_DesignTime.codegen.cs

@@ -13,6 +13,11 @@ namespace Microsoft.AspNetCore.Razor.Evolution.IntegrationTests.TestFiles
         #pragma warning disable 1998
         public async System.Threading.Tasks.Task ExecuteAsync()
         {
+#line 3 "TestFiles/IntegrationTests/CodeGenerationIntegrationTest/ImplicitExpressionAtEOF.cshtml"
+__o = ;
+
+#line default
+#line hidden
         }
         #pragma warning restore 1998
     }

test/Microsoft.AspNetCore.Razor.Evolution.Test/TestFiles/IntegrationTests/CodeGenerationIntegrationTest/ImplicitExpressionAtEOF_DesignTime.ir.txt

@@ -17,4 +17,5 @@ Document -
                 RazorIRToken -  - CSharp - private static System.Object __o = null;
             RazorMethodDeclaration -  - public - async - System.Threading.Tasks.Task - ExecuteAsync
                 HtmlContent - (0:0,0 [18] ImplicitExpressionAtEOF.cshtml) - This is markup\n\n
-                CSharpExpression - 
+                CSharpExpression - (19:2,1 [0] ImplicitExpressionAtEOF.cshtml)
+                    RazorIRToken - (19:2,1 [0] ImplicitExpressionAtEOF.cshtml) - CSharp - 

test/Microsoft.AspNetCore.Razor.Evolution.Test/TestFiles/IntegrationTests/CodeGenerationIntegrationTest/ImplicitExpressionAtEOF_DesignTime.mappings.txt

@@ -0,0 +1,5 @@
+Source Location: (19:2,1 [0] TestFiles/IntegrationTests/CodeGenerationIntegrationTest/ImplicitExpressionAtEOF.cshtml)
+||
+Generated Location: (678:16,6 [0] )
+||
+

test/Microsoft.AspNetCore.Razor.Evolution.Test/TestFiles/IntegrationTests/CodeGenerationIntegrationTest/ImplicitExpressionAtEOF_Runtime.codegen.cs

@@ -10,7 +10,11 @@ namespace Microsoft.AspNetCore.Razor.Evolution.IntegrationTests.TestFiles
         public async System.Threading.Tasks.Task ExecuteAsync()
         {
             WriteLiteral("This is markup\r\n\r\n");
-            Write();
+#line 3 "TestFiles/IntegrationTests/CodeGenerationIntegrationTest/ImplicitExpressionAtEOF.cshtml"
+Write();
+
+#line default
+#line hidden
         }
         #pragma warning restore 1998
     }

test/Microsoft.AspNetCore.Razor.Evolution.Test/TestFiles/IntegrationTests/CodeGenerationIntegrationTest/ImplicitExpressionAtEOF_Runtime.ir.txt

@@ -6,4 +6,5 @@ Document -
         ClassDeclaration -  - public - TestFiles_IntegrationTests_CodeGenerationIntegrationTest_ImplicitExpressionAtEOF_Runtime -  - 
             RazorMethodDeclaration -  - public - async - System.Threading.Tasks.Task - ExecuteAsync
                 HtmlContent - (0:0,0 [18] ImplicitExpressionAtEOF.cshtml) - This is markup\n\n
-                CSharpExpression - 
+                CSharpExpression - (19:2,1 [0] ImplicitExpressionAtEOF.cshtml)
+                    RazorIRToken - (19:2,1 [0] ImplicitExpressionAtEOF.cshtml) - CSharp -