Correctly stitch @ characters to following identifiers when rewriting tag helpers

Because of how we were rewriting tag helper attribute values, we didn't output a single, unified token when moving an implicit C# transition back to standard C#. This meant that, when we emit `#line` directives, we considered the `@` and the identifier that followed it to be separate tokens; when we added more precise info for FUSE, this then meant that they were emitted on separate lines during runtime codegen and everything fell apart. To fix this, we now unify those implicit transition tokens, rather than trying to keep them as separate tokens. Fixes #10186, for real this time.

Author: 333fred

src/Compiler/Microsoft.AspNetCore.Razor.Language/legacyTest/TestFiles/ParserTests/TagHelperBlockRewriterTest/CreatesMarkupCodeSpansForNonStringTagHelperAttributes7.cspans.txt

@@ -1,18 +1,15 @@
 Code span at (13:0,13 [1] ) (Accepts:AnyExceptNewline) - Parent: Markup block at (13:0,13 [14] )
 Code span at (14:0,14 [2] ) (Accepts:AnyExceptNewline) - Parent: Markup block at (13:0,13 [14] )
 Code span at (16:0,16 [1] ) (Accepts:AnyExceptNewline) - Parent: Markup block at (16:0,16 [7] )
-Code span at (17:0,17 [1] ) (Accepts:AnyExceptNewline) - Parent: Expression block at (17:0,17 [6] )
-Code span at (18:0,18 [5] ) (Accepts:AnyExceptNewline) - Parent: Expression block at (17:0,17 [6] )
+Code span at (17:0,17 [6] ) (Accepts:AnyExceptNewline) - Parent: Expression block at (17:0,17 [6] )
 Code span at (23:0,23 [2] ) (Accepts:AnyExceptNewline) - Parent: Markup block at (13:0,13 [14] )
 Code span at (25:0,25 [2] ) (Accepts:AnyExceptNewline) - Parent: Markup block at (13:0,13 [14] )
 Code span at (39:0,39 [6] ) (Accepts:AnyExceptNewline) - Parent: Markup block at (39:0,39 [46] )
-Code span at (45:0,45 [1] ) (Accepts:AnyExceptNewline) - Parent: Expression block at (45:0,45 [11] )
-Code span at (46:0,46 [10] ) (Accepts:AnyExceptNewline) - Parent: Expression block at (45:0,45 [11] )
+Code span at (45:0,45 [11] ) (Accepts:AnyExceptNewline) - Parent: Expression block at (45:0,45 [11] )
 Code span at (56:0,56 [2] ) (Accepts:AnyExceptNewline) - Parent: Markup block at (39:0,39 [46] )
 Code span at (58:0,58 [2] ) (Accepts:AnyExceptNewline) - Parent: Markup block at (58:0,58 [3] )
 Code span at (60:0,60 [1] ) (Accepts:AnyExceptNewline) - Parent: Markup block at (58:0,58 [3] )
 Code span at (61:0,61 [8] ) (Accepts:AnyExceptNewline) - Parent: Markup block at (39:0,39 [46] )
 Code span at (69:0,69 [2] ) (Accepts:AnyExceptNewline) - Parent: Markup block at (39:0,39 [46] )
 Code span at (71:0,71 [1] ) (Accepts:AnyExceptNewline) - Parent: Markup block at (71:0,71 [14] )
-Code span at (72:0,72 [1] ) (Accepts:AnyExceptNewline) - Parent: Expression block at (72:0,72 [13] )
-Code span at (73:0,73 [12] ) (Accepts:AnyExceptNewline) - Parent: Expression block at (72:0,72 [13] )
+Code span at (72:0,72 [13] ) (Accepts:AnyExceptNewline) - Parent: Expression block at (72:0,72 [13] )

src/Compiler/Microsoft.AspNetCore.Razor.Language/legacyTest/TestFiles/ParserTests/TagHelperBlockRewriterTest/CreatesMarkupCodeSpansForNonStringTagHelperAttributes7.stree.txt

@@ -27,10 +27,8 @@
                                         Transition;[<Missing>];
                                     CSharpImplicitExpressionBody - [17..23)::6
                                         CSharpCodeBlock - [17..23)::6
-                                            CSharpExpressionLiteral - [17..18)::1 - [@] - Gen<Expr> - ImplicitExpressionEditHandler;Accepts:AnyExceptNewline;ImplicitExpression[ATD];K15
-                                                Transition;[@];
-                                            CSharpExpressionLiteral - [18..23)::5 - [value] - Gen<Expr> - ImplicitExpressionEditHandler;Accepts:AnyExceptNewline;ImplicitExpression[ATD];K15
-                                                Identifier;[value];
+                                            CSharpExpressionLiteral - [17..23)::6 - [@value] - Gen<Expr> - ImplicitExpressionEditHandler;Accepts:AnyExceptNewline;ImplicitExpression[ATD];K15
+                                                Identifier;[@value];
                         CSharpExpressionLiteral - [23..25)::2 - [ +] - Gen<None> - ImplicitExpressionEditHandler;Accepts:AnyExceptNewline;ImplicitExpression[ATD];K15
                             Whitespace;[ ];
                             Text;[+];
@@ -57,10 +55,8 @@
                                         Transition;[<Missing>];
                                     CSharpImplicitExpressionBody - [45..56)::11
                                         CSharpCodeBlock - [45..56)::11
-                                            CSharpExpressionLiteral - [45..46)::1 - [@] - Gen<Expr> - ImplicitExpressionEditHandler;Accepts:AnyExceptNewline;ImplicitExpression[ATD];K15
-                                                Transition;[@];
-                                            CSharpExpressionLiteral - [46..56)::10 - [Bag["val"]] - Gen<Expr> - ImplicitExpressionEditHandler;Accepts:AnyExceptNewline;ImplicitExpression[ATD];K15
-                                                Identifier;[Bag];
+                                            CSharpExpressionLiteral - [45..56)::11 - [@Bag["val"]] - Gen<Expr> - ImplicitExpressionEditHandler;Accepts:AnyExceptNewline;ImplicitExpression[ATD];K15
+                                                Identifier;[@Bag];
                                                 LeftBracket;[[];
                                                 StringLiteral;["val"];
                                                 RightBracket;[]];
@@ -87,10 +83,8 @@
                                         Transition;[<Missing>];
                                     CSharpImplicitExpressionBody - [72..85)::13
                                         CSharpCodeBlock - [72..85)::13
-                                            CSharpExpressionLiteral - [72..73)::1 - [@] - Gen<Expr> - ImplicitExpressionEditHandler;Accepts:AnyExceptNewline;ImplicitExpression[ATD];K15
-                                                Transition;[@];
-                                            CSharpExpressionLiteral - [73..85)::12 - [DateTime.Now] - Gen<Expr> - ImplicitExpressionEditHandler;Accepts:AnyExceptNewline;ImplicitExpression[ATD];K15
-                                                Identifier;[DateTime];
+                                            CSharpExpressionLiteral - [72..85)::13 - [@DateTime.Now] - Gen<Expr> - ImplicitExpressionEditHandler;Accepts:AnyExceptNewline;ImplicitExpression[ATD];K15
+                                                Identifier;[@DateTime];
                                                 Dot;[.];
                                                 Identifier;[Now];
                     MarkupTextLiteral - [85..86)::1 - ['] - Gen<Markup> - SpanEditHandler;Accepts:Any

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

@@ -9,6 +9,7 @@
 using System.Runtime.CompilerServices;
 using Microsoft.AspNetCore.Razor.Language.Extensions;
 using Microsoft.AspNetCore.Razor.Test.Common;
+using Roslyn.Test.Utilities;
 
 namespace Microsoft.AspNetCore.Razor.Language.IntegrationTests;
 
@@ -255,6 +256,9 @@ public class CodeGenerationIntegrationTest(bool designTime = false)
     [IntegrationTestFact]
     public void AddTagHelperDirective() => RunTest();
 
+    [IntegrationTestFact, WorkItem("https://github.com/dotnet/razor/issues/10186")]
+    public void EscapedIdentifier() => RunTagHelpersTest(TestTagHelperDescriptors.SimpleTagHelperDescriptors);
+
     public override string GetTestFileName(string testName)
     {
         return base.GetTestFileName(testName) + (designTime ? "_DesignTime" : "_Runtime");

src/Compiler/Microsoft.AspNetCore.Razor.Language/test/Legacy/TagHelperBlockRewriterTest.cs

@@ -8,6 +8,7 @@
 using System.Collections.Immutable;
 using System.Globalization;
 using Microsoft.AspNetCore.Razor.Language.Components;
+using Roslyn.Test.Utilities;
 using Xunit;
 using static Microsoft.AspNetCore.Razor.Language.CommonMetadata;
 
@@ -555,6 +556,83 @@ public void CreatesMarkupCodeSpansForNonStringTagHelperAttributes12()
         EvaluateData(CodeTagHelperAttributes_Descriptors, "<person age=\"@{flag == 0 ? 11 : 12}\" />");
     }
 
+    [Fact, WorkItem("https://github.com/dotnet/razor/issues/10186")]
+    public void CreatesMarkupCodeSpansForNonStringTagHelperAttributes13()
+    {
+        EvaluateData(CodeTagHelperAttributes_Descriptors, """
+            @{ 
+                var count = "1";
+            }
+            <person age="Convert.ToInt32(@count)" />
+            """);
+    }
+
+    [Fact, WorkItem("https://github.com/dotnet/razor/issues/10186")]
+    public void CreatesMarkupCodeSpansForNonStringTagHelperAttributes14()
+    {
+        EvaluateData(CodeTagHelperAttributes_Descriptors, """
+            @{ 
+                var @string = "1";
+            }
+            <person age="Convert.ToInt32(@string)" />
+            """);
+    }
+
+    [Fact, WorkItem("https://github.com/dotnet/razor/issues/10186")]
+    public void CreatesMarkupCodeSpansForNonStringTagHelperAttributes15()
+    {
+        EvaluateData(CodeTagHelperAttributes_Descriptors, """
+            @{ 
+                var count = "1";
+            }
+            <person age=Convert.ToInt32(@count) />
+            """);
+    }
+
+    [Fact, WorkItem("https://github.com/dotnet/razor/issues/10186")]
+    public void CreatesMarkupCodeSpansForNonStringTagHelperAttributes16()
+    {
+        EvaluateData(CodeTagHelperAttributes_Descriptors, """
+            @{ 
+                var count = "1";
+            }
+            <person age='Convert.ToInt32(@count + "2")' />
+            """);
+    }
+
+    [Fact, WorkItem("https://github.com/dotnet/razor/issues/10186")]
+    public void CreatesMarkupCodeSpansForNonStringTagHelperAttributes17()
+    {
+        EvaluateData(CodeTagHelperAttributes_Descriptors, """
+            @{ 
+                var count = 1;
+            }
+            <person age='@@count' />
+            """);
+    }
+
+    [Fact, WorkItem("https://github.com/dotnet/razor/issues/10186")]
+    public void CreatesMarkupCodeSpansForNonStringTagHelperAttributes18()
+    {
+        EvaluateData(CodeTagHelperAttributes_Descriptors, """
+            @{ 
+                var count = 1;
+            }
+            <person age="@@count" />
+            """);
+    }
+
+    [Fact, WorkItem("https://github.com/dotnet/razor/issues/10186")]
+    public void CreatesMarkupCodeSpansForNonStringTagHelperAttributes19()
+    {
+        EvaluateData(CodeTagHelperAttributes_Descriptors, """
+            @{ 
+                var count = 1;
+            }
+            <person age=@@count />
+            """);
+    }
+
     [Fact]
     public void TagHelperParseTreeRewriter_CreatesErrorForIncompleteTagHelper1()
     {

src/Compiler/Microsoft.AspNetCore.Razor.Language/test/TestFiles/IntegrationTests/CodeGenerationIntegrationTest/ComplexTagHelpers_DesignTime.ir.txt

@@ -217,8 +217,7 @@
                         LazyIntermediateToken - (933:25,21 [2] ComplexTagHelpers.cshtml) - CSharp -  +
                         LazyIntermediateToken - (935:25,23 [1] ComplexTagHelpers.cshtml) - CSharp -  
                         CSharpExpression - (936:25,24 [24] ComplexTagHelpers.cshtml)
-                            LazyIntermediateToken - (936:25,24 [1] ComplexTagHelpers.cshtml) - CSharp - @
-                            LazyIntermediateToken - (937:25,25 [23] ComplexTagHelpers.cshtml) - CSharp - DateTimeOffset.Now.Year
+                            LazyIntermediateToken - (936:25,24 [24] ComplexTagHelpers.cshtml) - CSharp - @DateTimeOffset.Now.Year
                     DefaultTagHelperExecute - 
                 HtmlContent - (1075:27,12 [10] ComplexTagHelpers.cshtml)
                     LazyIntermediateToken - (1075:27,12 [10] ComplexTagHelpers.cshtml) - Html - \n        

src/Compiler/Microsoft.AspNetCore.Razor.Language/test/TestFiles/IntegrationTests/CodeGenerationIntegrationTest/ComplexTagHelpers_DesignTime.mappings.txt

@@ -189,15 +189,10 @@ Source Location: (935:25,23 [1] TestFiles/IntegrationTests/CodeGenerationIntegra
 Generated Location: (9254:213,40 [1] )
 | |
 
-Source Location: (936:25,24 [1] TestFiles/IntegrationTests/CodeGenerationIntegrationTest/ComplexTagHelpers.cshtml)
-|@|
-Generated Location: (9255:213,41 [1] )
-|@|
-
-Source Location: (937:25,25 [23] TestFiles/IntegrationTests/CodeGenerationIntegrationTest/ComplexTagHelpers.cshtml)
-|DateTimeOffset.Now.Year|
-Generated Location: (9256:213,42 [23] )
-|DateTimeOffset.Now.Year|
+Source Location: (936:25,24 [24] TestFiles/IntegrationTests/CodeGenerationIntegrationTest/ComplexTagHelpers.cshtml)
+|@DateTimeOffset.Now.Year|
+Generated Location: (9255:213,41 [24] )
+|@DateTimeOffset.Now.Year|
 
 Source Location: (1155:29,28 [30] TestFiles/IntegrationTests/CodeGenerationIntegrationTest/ComplexTagHelpers.cshtml)
 |DateTimeOffset.Now.Year > 2014|

src/Compiler/Microsoft.AspNetCore.Razor.Language/test/TestFiles/IntegrationTests/CodeGenerationIntegrationTest/ComplexTagHelpers_Runtime.codegen.cs

@@ -493,15 +493,8 @@ public async System.Threading.Tasks.Task ExecuteAsync()
 #line hidden
 #nullable disable
 #nullable restore
-#line (26,25)-(26,26) "TestFiles/IntegrationTests/CodeGenerationIntegrationTest/ComplexTagHelpers.cshtml"
-@
-
-#line default
-#line hidden
-#nullable disable
-#nullable restore
-#line (26,26)-(26,49) "TestFiles/IntegrationTests/CodeGenerationIntegrationTest/ComplexTagHelpers.cshtml"
-DateTimeOffset.Now.Year
+#line (26,25)-(26,49) "TestFiles/IntegrationTests/CodeGenerationIntegrationTest/ComplexTagHelpers.cshtml"
+@DateTimeOffset.Now.Year
 
 #line default
 #line hidden

src/Compiler/Microsoft.AspNetCore.Razor.Language/test/TestFiles/IntegrationTests/CodeGenerationIntegrationTest/ComplexTagHelpers_Runtime.ir.txt

@@ -218,8 +218,7 @@
                         LazyIntermediateToken - (933:25,21 [2] ComplexTagHelpers.cshtml) - CSharp -  +
                         LazyIntermediateToken - (935:25,23 [1] ComplexTagHelpers.cshtml) - CSharp -  
                         CSharpExpression - (936:25,24 [24] ComplexTagHelpers.cshtml)
-                            LazyIntermediateToken - (936:25,24 [1] ComplexTagHelpers.cshtml) - CSharp - @
-                            LazyIntermediateToken - (937:25,25 [23] ComplexTagHelpers.cshtml) - CSharp - DateTimeOffset.Now.Year
+                            LazyIntermediateToken - (936:25,24 [24] ComplexTagHelpers.cshtml) - CSharp - @DateTimeOffset.Now.Year
                     DefaultTagHelperExecute - 
                 HtmlContent - (1075:27,12 [10] ComplexTagHelpers.cshtml)
                     LazyIntermediateToken - (1075:27,12 [10] ComplexTagHelpers.cshtml) - Html - \n        

src/Compiler/Microsoft.AspNetCore.Razor.Language/test/TestFiles/IntegrationTests/CodeGenerationIntegrationTest/EscapedIdentifier.cshtml

@@ -0,0 +1,6 @@
+@addTagHelper "*, TestAssembly"
+
+@{
+    var count = "1";
+}
+<input age="Convert.ToInt32(@count)" />

src/Compiler/Microsoft.AspNetCore.Razor.Language/test/TestFiles/IntegrationTests/CodeGenerationIntegrationTest/EscapedIdentifier_DesignTime.codegen.cs

@@ -0,0 +1,55 @@
+// <auto-generated/>
+#pragma warning disable 1591
+namespace Microsoft.AspNetCore.Razor.Language.IntegrationTests.TestFiles
+{
+    #line hidden
+    public class TestFiles_IntegrationTests_CodeGenerationIntegrationTest_EscapedIdentifier_DesignTime
+    {
+        #line hidden
+        #pragma warning disable 0649
+        private global::Microsoft.AspNetCore.Razor.Runtime.TagHelpers.TagHelperExecutionContext __tagHelperExecutionContext;
+        #pragma warning restore 0649
+        private global::Microsoft.AspNetCore.Razor.Runtime.TagHelpers.TagHelperRunner __tagHelperRunner = new global::Microsoft.AspNetCore.Razor.Runtime.TagHelpers.TagHelperRunner();
+        private global::InputTagHelper __InputTagHelper;
+        #pragma warning disable 219
+        private void __RazorDirectiveTokenHelpers__() {
+        ((global::System.Action)(() => {
+#nullable restore
+#line 1 "TestFiles/IntegrationTests/CodeGenerationIntegrationTest/EscapedIdentifier.cshtml"
+global::System.Object __typeHelper = "*, TestAssembly";
+
+#line default
+#line hidden
+#nullable disable
+        }
+        ))();
+        }
+        #pragma warning restore 219
+        #pragma warning disable 0414
+        private static object __o = null;
+        #pragma warning restore 0414
+        #pragma warning disable 1998
+        public async System.Threading.Tasks.Task ExecuteAsync()
+        {
+#nullable restore
+#line 3 "TestFiles/IntegrationTests/CodeGenerationIntegrationTest/EscapedIdentifier.cshtml"
+  
+    var count = "1";
+
+#line default
+#line hidden
+#nullable disable
+            __InputTagHelper = CreateTagHelper<global::InputTagHelper>();
+#nullable restore
+#line 6 "TestFiles/IntegrationTests/CodeGenerationIntegrationTest/EscapedIdentifier.cshtml"
+__InputTagHelper.AgeProp = Convert.ToInt32(@count);
+
+#line default
+#line hidden
+#nullable disable
+            await __tagHelperRunner.RunAsync(__tagHelperExecutionContext);
+        }
+        #pragma warning restore 1998
+    }
+}
+#pragma warning restore 1591