Allow @@ as a fallback (#10752)

* Added new tests for the specific regressed scenario.

* Allow `@@` sequences. Fixes dotnet/sdk#42730 for now. When we move to the new lexer, these will once again be disallowed; attempting to use runtime compilation will necessitate using the native lexer.

* Fixup legacy test baselines

src/Compiler/Microsoft.AspNetCore.Razor.Language/legacyTest/TestFiles/ParserTests/CSharpBlockTest/TreatsAtSignsAfterFirstPairAsPartOfCSharpStatement.stree.txt

@@ -17,7 +17,7 @@
                 Transition;[@];
             CSharpStatementLiteral - [12..28)::16 - [@@@class.Foo() }] - Gen<Stmt> - SpanEditHandler;Accepts:Any
                 Transition;[@];
-                Identifier;[@];
+                Transition;[@];
                 Identifier;[@class];
                 Dot;[.];
                 Identifier;[Foo];

src/Compiler/Microsoft.AspNetCore.Razor.Language/legacyTest/TestFiles/ParserTests/CSharpErrorTest/CorrectlyParsesAtSignInDelimitedBlock.stree.txt

@@ -18,8 +18,7 @@
                             Whitespace;[ ];
                             NullCoalesce;[??];
                             Whitespace;[ ];
-                            Transition;[@];
-                            Identifier;[photo];
+                            Identifier;[@photo];
                             Dot;[.];
                             Identifier;[Description];
                     RazorMetaCode - [46..47)::1 - Gen<None> - SpanEditHandler;Accepts:None

src/Compiler/Microsoft.AspNetCore.Razor.Language/legacyTest/TestFiles/ParserTests/CSharpFunctionsTest/MarkupInFunctionsBlock_DoesNotParseWhenNotSupported.stree.txt

@@ -34,8 +34,7 @@
                                 LessThan;[<];
                                 Identifier;[h3];
                                 GreaterThan;[>];
-                                Transition;[@];
-                                Identifier;[message];
+                                Identifier;[@message];
                                 LessThan;[<];
                                 Slash;[/];
                                 Identifier;[h3];

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

@@ -10516,6 +10516,21 @@ public void AtTransitions()
         CompileToAssembly(generated);
     }
 
+    [IntegrationTestFact, WorkItem("https://github.com/dotnet/sdk/issues/42730")]
+    public void AtAtHandled()
+    {
+        var generated = CompileToCSharp("""
+            @{ var validationMessage = @Html.ValidationMessage("test", "", new { @@class = "invalid-feedback" }, "div"); }
+            """);
+
+        AssertDocumentNodeMatchesBaseline(generated.CodeDocument);
+        AssertCSharpDocumentMatchesBaseline(generated.CodeDocument);
+        CompileToAssembly(generated,
+                // x:\dir\subdir\Test\TestComponent.cshtml(1,28): error CS0103: The name 'Html' does not exist in the current context
+                //    var validationMessage = @Html.ValidationMessage("test", "", new { @@class = "invalid-feedback" }, "div");
+                Diagnostic(ErrorCode.ERR_NameNotInContext, "@Html").WithArguments("Html").WithLocation(1, 28));
+    }
+
     #endregion
 
     #region LinePragmas

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

@@ -3,6 +3,7 @@
 
 #nullable disable
 
+using Roslyn.Test.Utilities;
 using Xunit;
 
 namespace Microsoft.AspNetCore.Razor.Language.Legacy;
@@ -880,6 +881,31 @@ public void EscapedIdentifiers_10()
             """);
     }
 
+    [Fact, WorkItem("https://github.com/dotnet/sdk/issues/42730")]
+    public void EscapedIdentifiers_11()
+    {
+        ParseDocumentTest("""
+             @{ var validationMessage = @Html.ValidationMessage(Model.Binding, "", new { @@class = "invalid-feedback" }, "div"); }
+            """);
+    }
+
+    [Fact, WorkItem("https://github.com/dotnet/sdk/issues/42730")]
+    public void EscapedIdentifiers_12()
+    {
+        ParseDocumentTest("""
+            @{
+                @@
+            """);
+    }
+
+    [Fact, WorkItem("https://github.com/dotnet/sdk/issues/42730")]
+    public void EscapedIdentifiers_13()
+    {
+        ParseDocumentTest("""
+             @{ var validationMessage = new { @@
+            """);
+    }
+
     private void RunRazorCommentBetweenClausesTest(string preComment, string postComment, AcceptedCharactersInternal acceptedCharacters = AcceptedCharactersInternal.Any)
     {
         ParseDocumentTest(preComment + "@* Foo *@ @* Bar *@" + postComment);

src/Compiler/Microsoft.AspNetCore.Razor.Language/test/TestFiles/IntegrationTests/ComponentDesignTimeCodeGenerationTest/AtAtHandled/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 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)
+        {
+#nullable restore
+#line 1 "x:\dir\subdir\Test\TestComponent.cshtml"
+   var validationMessage = @Html.ValidationMessage("test", "", new { 
+
+#line default
+#line hidden
+#nullable disable
+#nullable restore
+#line 1 "x:\dir\subdir\Test\TestComponent.cshtml"
+                                                                      @class = "invalid-feedback" }, "div"); 
+
+#line default
+#line hidden
+#nullable disable
+        }
+        #pragma warning restore 1998
+    }
+}
+#pragma warning restore 1591

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

@@ -0,0 +1,20 @@
+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
+                CSharpCode - (2:0,2 [67] x:\dir\subdir\Test\TestComponent.cshtml)
+                    LazyIntermediateToken - (2:0,2 [67] x:\dir\subdir\Test\TestComponent.cshtml) - CSharp -  var validationMessage = @Html.ValidationMessage("test", "", new { 
+                CSharpCode - (70:0,70 [39] x:\dir\subdir\Test\TestComponent.cshtml)
+                    LazyIntermediateToken - (70:0,70 [39] x:\dir\subdir\Test\TestComponent.cshtml) - CSharp - @class = "invalid-feedback" }, "div"); 

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

@@ -0,0 +1,10 @@
+Source Location: (2:0,2 [67] x:\dir\subdir\Test\TestComponent.cshtml)
+| var validationMessage = @Html.ValidationMessage("test", "", new { |
+Generated Location: (987:28,2 [67] )
+| var validationMessage = @Html.ValidationMessage("test", "", new { |
+
+Source Location: (70:0,70 [39] x:\dir\subdir\Test\TestComponent.cshtml)
+|@class = "invalid-feedback" }, "div"); |
+Generated Location: (1246:35,70 [39] )
+|@class = "invalid-feedback" }, "div"); |
+

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

@@ -0,0 +1,40 @@
+// <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)
+        {
+#nullable restore
+#line (1,3)-(1,70) "x:\dir\subdir\Test\TestComponent.cshtml"
+ var validationMessage = @Html.ValidationMessage("test", "", new { 
+
+#line default
+#line hidden
+#nullable disable
+
+#nullable restore
+#line (1,71)-(1,110) "x:\dir\subdir\Test\TestComponent.cshtml"
+@class = "invalid-feedback" }, "div"); 
+
+#line default
+#line hidden
+#nullable disable
+
+        }
+        #pragma warning restore 1998
+    }
+}
+#pragma warning restore 1591

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

@@ -0,0 +1,13 @@
+Document - 
+    NamespaceDeclaration -  - Test
+        UsingDirective - (3:1,1 [22] ) - global::System
+        UsingDirective - (26:2,1 [42] ) - global::System.Collections.Generic
+        UsingDirective - (69:3,1 [27] ) - global::System.Linq
+        UsingDirective - (97:4,1 [38] ) - global::System.Threading.Tasks
+        UsingDirective - (136:5,1 [47] ) - global::Microsoft.AspNetCore.Components
+        ClassDeclaration -  - public partial - TestComponent - global::Microsoft.AspNetCore.Components.ComponentBase - 
+            MethodDeclaration -  - protected override - void - BuildRenderTree
+                CSharpCode - (2:0,2 [67] x:\dir\subdir\Test\TestComponent.cshtml)
+                    LazyIntermediateToken - (2:0,2 [67] x:\dir\subdir\Test\TestComponent.cshtml) - CSharp -  var validationMessage = @Html.ValidationMessage("test", "", new { 
+                CSharpCode - (70:0,70 [39] x:\dir\subdir\Test\TestComponent.cshtml)
+                    LazyIntermediateToken - (70:0,70 [39] x:\dir\subdir\Test\TestComponent.cshtml) - CSharp - @class = "invalid-feedback" }, "div"); 

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

@@ -0,0 +1,10 @@
+Source Location: (2:0,2 [67] x:\dir\subdir\Test\TestComponent.cshtml)
+| var validationMessage = @Html.ValidationMessage("test", "", new { |
+Generated Location: (735:21,0 [67] )
+| var validationMessage = @Html.ValidationMessage("test", "", new { |
+
+Source Location: (70:0,70 [39] x:\dir\subdir\Test\TestComponent.cshtml)
+|@class = "invalid-feedback" }, "div"); |
+Generated Location: (939:29,0 [39] )
+|@class = "invalid-feedback" }, "div"); |
+

src/Compiler/Microsoft.AspNetCore.Razor.Language/test/TestFiles/ParserTests/CSharpBlockTest/EscapedIdentifiers_01.stree.txt

@@ -37,8 +37,7 @@
                         LeftParenthesis;[(];
                     CSharpCodeBlock - [38..45)::7
                         CSharpExpressionLiteral - [38..45)::7 - [@string] - Gen<Expr>
-                            Transition;[@];
-                            Keyword;[string];
+                            Identifier;[@string];
                     RazorMetaCode - [45..46)::1 - Gen<None>
                         RightParenthesis;[)];
         MarkupTextLiteral - [46..46)::0 - [] - Gen<Markup>

src/Compiler/Microsoft.AspNetCore.Razor.Language/test/TestFiles/ParserTests/CSharpBlockTest/EscapedIdentifiers_03.stree.txt

@@ -15,7 +15,7 @@
                             Whitespace;[    ];
                             Identifier;[var];
                             Whitespace;[ ];
-                            Identifier;[@];
+                            Transition;[@];
                             Identifier;[@class];
                             Whitespace;[ ];
                             Assign;[=];
@@ -30,7 +30,7 @@
                             Whitespace;[ ];
                             Assign;[=];
                             Whitespace;[ ];
-                            Identifier;[@];
+                            Transition;[@];
                             Identifier;[@class];
                             Semicolon;[;];
                             NewLine;[LF];

src/Compiler/Microsoft.AspNetCore.Razor.Language/test/TestFiles/ParserTests/CSharpBlockTest/EscapedIdentifiers_04.stree.txt

@@ -53,8 +53,7 @@
                         LeftParenthesis;[(];
                     CSharpCodeBlock - [74..81)::7
                         CSharpExpressionLiteral - [74..81)::7 - [@string] - Gen<Expr>
-                            Transition;[@];
-                            Keyword;[string];
+                            Identifier;[@string];
                     RazorMetaCode - [81..82)::1 - Gen<None>
                         RightParenthesis;[)];
         MarkupTextLiteral - [82..82)::0 - [] - Gen<Markup>

src/Compiler/Microsoft.AspNetCore.Razor.Language/test/TestFiles/ParserTests/CSharpBlockTest/EscapedIdentifiers_05.stree.txt

@@ -49,8 +49,7 @@
                         LeftParenthesis;[(];
                     CSharpCodeBlock - [75..82)::7
                         CSharpExpressionLiteral - [75..82)::7 - [@string] - Gen<Expr>
-                            Transition;[@];
-                            Keyword;[string];
+                            Identifier;[@string];
                     RazorMetaCode - [82..83)::1 - Gen<None>
                         RightParenthesis;[)];
         MarkupTextLiteral - [83..83)::0 - [] - Gen<Markup>

src/Compiler/Microsoft.AspNetCore.Razor.Language/test/TestFiles/ParserTests/CSharpBlockTest/EscapedIdentifiers_06.stree.txt

@@ -75,8 +75,7 @@
                         LeftParenthesis;[(];
                     CSharpCodeBlock - [115..122)::7
                         CSharpExpressionLiteral - [115..122)::7 - [@string] - Gen<Expr>
-                            Transition;[@];
-                            Keyword;[string];
+                            Identifier;[@string];
                     RazorMetaCode - [122..123)::1 - Gen<None>
                         RightParenthesis;[)];
         MarkupTextLiteral - [123..123)::0 - [] - Gen<Markup>

src/Compiler/Microsoft.AspNetCore.Razor.Language/test/TestFiles/ParserTests/CSharpBlockTest/EscapedIdentifiers_07.stree.txt

@@ -67,8 +67,7 @@
                         LeftParenthesis;[(];
                     CSharpCodeBlock - [117..124)::7
                         CSharpExpressionLiteral - [117..124)::7 - [@string] - Gen<Expr>
-                            Transition;[@];
-                            Keyword;[string];
+                            Identifier;[@string];
                     RazorMetaCode - [124..125)::1 - Gen<None>
                         RightParenthesis;[)];
         MarkupTextLiteral - [125..125)::0 - [] - Gen<Markup>

src/Compiler/Microsoft.AspNetCore.Razor.Language/test/TestFiles/ParserTests/CSharpBlockTest/EscapedIdentifiers_11.cspans.txt

@@ -0,0 +1,9 @@
+Markup span at (0:0,0 [0] ) - Parent: Markup block at (0:0,0 [118] )
+Code span at (0:0,0 [1] ) - Parent: Statement block at (0:0,0 [118] )
+Transition span at (1:0,1 [1] ) - Parent: Statement block at (1:0,1 [117] )
+MetaCode span at (2:0,2 [1] ) - Parent: Statement block at (1:0,1 [117] )
+Code span at (3:0,3 [74] ) - Parent: Statement block at (1:0,1 [117] )
+Code span at (77:0,77 [1] ) - Parent: Statement block at (1:0,1 [117] )
+Code span at (78:0,78 [39] ) - Parent: Statement block at (1:0,1 [117] )
+MetaCode span at (117:0,117 [1] ) - Parent: Statement block at (1:0,1 [117] )
+Markup span at (118:0,118 [0] ) - Parent: Markup block at (0:0,0 [118] )

src/Compiler/Microsoft.AspNetCore.Razor.Language/test/TestFiles/ParserTests/CSharpBlockTest/EscapedIdentifiers_11.stree.txt

@@ -0,0 +1,59 @@
+RazorDocument - [0..118)::118 - [ @{ var validationMessage = @Html.ValidationMessage(Model.Binding, "", new { @@class = "invalid-feedback" }, "div"); }]
+    MarkupBlock - [0..118)::118
+        MarkupTextLiteral - [0..0)::0 - [] - Gen<Markup>
+            Marker;[];
+        CSharpCodeBlock - [0..118)::118
+            CSharpStatementLiteral - [0..1)::1 - [ ] - Gen<Stmt>
+                Whitespace;[ ];
+            CSharpStatement - [1..118)::117
+                CSharpTransition - [1..2)::1 - Gen<None>
+                    Transition;[@];
+                CSharpStatementBody - [2..118)::116
+                    RazorMetaCode - [2..3)::1 - Gen<None>
+                        LeftBrace;[{];
+                    CSharpCodeBlock - [3..117)::114
+                        CSharpStatementLiteral - [3..77)::74 - [ var validationMessage = @Html.ValidationMessage(Model.Binding, "", new { ] - Gen<Stmt>
+                            Whitespace;[ ];
+                            Identifier;[var];
+                            Whitespace;[ ];
+                            Identifier;[validationMessage];
+                            Whitespace;[ ];
+                            Assign;[=];
+                            Whitespace;[ ];
+                            Identifier;[@Html];
+                            Dot;[.];
+                            Identifier;[ValidationMessage];
+                            LeftParenthesis;[(];
+                            Identifier;[Model];
+                            Dot;[.];
+                            Identifier;[Binding];
+                            Comma;[,];
+                            Whitespace;[ ];
+                            StringLiteral;[""];
+                            Comma;[,];
+                            Whitespace;[ ];
+                            Keyword;[new];
+                            Whitespace;[ ];
+                            LeftBrace;[{];
+                            Whitespace;[ ];
+                        CSharpEphemeralTextLiteral - [77..78)::1 - [@] - Gen<Stmt>
+                            Transition;[@];
+                        CSharpStatementLiteral - [78..117)::39 - [@class = "invalid-feedback" }, "div"); ] - Gen<Stmt>
+                            Identifier;[@class];
+                            Whitespace;[ ];
+                            Assign;[=];
+                            Whitespace;[ ];
+                            StringLiteral;["invalid-feedback"];
+                            Whitespace;[ ];
+                            RightBrace;[}];
+                            Comma;[,];
+                            Whitespace;[ ];
+                            StringLiteral;["div"];
+                            RightParenthesis;[)];
+                            Semicolon;[;];
+                            Whitespace;[ ];
+                    RazorMetaCode - [117..118)::1 - Gen<None>
+                        RightBrace;[}];
+        MarkupTextLiteral - [118..118)::0 - [] - Gen<Markup>
+            Marker;[];
+    EndOfFile;[];

src/Compiler/Microsoft.AspNetCore.Razor.Language/test/TestFiles/ParserTests/CSharpBlockTest/EscapedIdentifiers_12.cspans.txt

@@ -0,0 +1,6 @@
+Markup span at (0:0,0 [0] ) - Parent: Markup block at (0:0,0 [10] )
+Transition span at (0:0,0 [1] ) - Parent: Statement block at (0:0,0 [10] )
+MetaCode span at (1:0,1 [1] ) - Parent: Statement block at (0:0,0 [10] )
+Code span at (2:0,2 [6] ) - Parent: Statement block at (0:0,0 [10] )
+Code span at (8:1,4 [1] ) - Parent: Statement block at (0:0,0 [10] )
+Code span at (9:1,5 [1] ) - Parent: Statement block at (0:0,0 [10] )

src/Compiler/Microsoft.AspNetCore.Razor.Language/test/TestFiles/ParserTests/CSharpBlockTest/EscapedIdentifiers_12.diag.txt

@@ -0,0 +1 @@
+(1,2): Error RZ1006: The code block is missing a closing "}" character.  Make sure you have a matching "}" character for all the "{" characters within this block, and that none of the "}" characters are being interpreted as markup.