Add global:: to default usings

src/Compiler/Microsoft.AspNetCore.Razor.Language/src/Components/ComponentImportProjectFeature.cs

@@ -16,11 +16,11 @@ internal class ComponentImportProjectFeature : IImportProjectFeature
     // Using explicit newlines here to avoid fooling our baseline tests
     private const string DefaultUsingImportContent =
         "\r\n" +
-        "@using System\r\n" +
-        "@using System.Collections.Generic\r\n" +
-        "@using System.Linq\r\n" +
-        "@using System.Threading.Tasks\r\n" +
-        "@using " + ComponentsApi.RenderFragment.Namespace + "\r\n"; // Microsoft.AspNetCore.Components
+        "@using global::System\r\n" +
+        "@using global::System.Collections.Generic\r\n" +
+        "@using global::System.Linq\r\n" +
+        "@using global::System.Threading.Tasks\r\n" +
+        "@using global::" + ComponentsApi.RenderFragment.Namespace + "\r\n"; // Microsoft.AspNetCore.Components
 
     public RazorProjectEngine ProjectEngine { get; set; }
 

src/Compiler/Microsoft.AspNetCore.Razor.Language/src/DefaultRazorIntermediateNodeLoweringPhase.cs

@@ -83,9 +83,14 @@ protected override void ExecuteCore(RazorCodeDocument codeDocument)
         var usingReferences = new List<UsingReference>(visitor.Usings);
         for (var j = importedUsings.Count - 1; j >= 0; j--)
         {
-            if (!usingReferences.Contains(importedUsings[j]))
+            var importedUsing = importedUsings[j];
+            if (!usingReferences.Contains(importedUsing) &&
+                // If the using is from the default import, avoid adding it
+                // if a user using exists which is the same except for the `global::` prefix.
+                (!TryRemoveGlobalPrefixFromDefaultUsing(in importedUsing, out var trimmedUsing) ||
+                !usingReferences.Contains(trimmedUsing)))
             {
-                usingReferences.Insert(0, importedUsings[j]);
+                usingReferences.Insert(0, importedUsing);
             }
         }
 
@@ -125,6 +130,21 @@ protected override void ExecuteCore(RazorCodeDocument codeDocument)
         }
 
         codeDocument.SetDocumentIntermediateNode(document);
+
+        static bool TryRemoveGlobalPrefixFromDefaultUsing(in UsingReference usingReference, out UsingReference trimmed)
+        {
+            const string globalPrefix = "global::";
+            if (usingReference.Source is { FilePath: null } && // the default import has null file path
+                usingReference.Namespace.StartsWith(globalPrefix, StringComparison.Ordinal))
+            {
+                trimmed = new UsingReference(
+                    usingReference.Namespace.Substring(globalPrefix.Length),
+                    usingReference.Source);
+                return true;
+            }
+            trimmed = usingReference;
+            return false;
+        }
     }
 
     private IReadOnlyList<UsingReference> ImportDirectives(

src/Compiler/Microsoft.AspNetCore.Razor.Language/src/Extensions/DesignTimeDirectivePass.cs

@@ -52,7 +52,7 @@ public override void VisitClassDeclaration(ClassDeclarationIntermediateNode node
                         new IntermediateToken()
                         {
                             Kind = TokenKind.CSharp,
-                            Content = $"private static {typeof(object).FullName} {DesignTimeVariable} = null;",
+                            Content = $"private static object {DesignTimeVariable} = null;",
                         }
                     }
             });

src/Compiler/Microsoft.AspNetCore.Razor.Language/src/Extensions/DesignTimeDirectiveTargetExtension.cs

@@ -54,10 +54,7 @@ private void WriteDesignTimeDirectiveToken(CodeRenderingContext context, DesignT
         }
 
         // Wrap the directive token in a lambda to isolate variable names.
-        context.CodeWriter
-            .Write("((")
-            .Write(typeof(Action).FullName)
-            .Write(")(");
+        context.CodeWriter.Write("((global::System.Action)(");
         using (context.CodeWriter.BuildLambda())
         {
             var originalIndent = context.CodeWriter.CurrentIndent;

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

@@ -8215,6 +8215,20 @@ @namespace New.Test
         CompileToAssembly(generated);
     }
 
+    [Fact] // https://github.com/dotnet/razor/issues/7091
+    public void Component_NamespaceDirective_ContainsSystem()
+    {
+        // Act
+        var generated = CompileToCSharp("""
+            @namespace X.System.Y
+            """);
+
+        // Assert
+        AssertDocumentNodeMatchesBaseline(generated.CodeDocument);
+        AssertCSharpDocumentMatchesBaseline(generated.CodeDocument);
+        CompileToAssembly(generated);
+    }
+
     [Fact]
     public void Component_PreserveWhitespaceDirective_InImports()
     {

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

@@ -0,0 +1,37 @@
+// <auto-generated/>
+#pragma warning disable 1591
+namespace X.System.Y
+{
+    #line hidden
+    using global::System;
+    using global::System.Collections.Generic;
+    using global::System.Linq;
+    using global::System.Threading.Tasks;
+    using global::Microsoft.AspNetCore.Components;
+    public partial class TestComponent : global::Microsoft.AspNetCore.Components.ComponentBase
+    {
+        #pragma warning disable 219
+        private void __RazorDirectiveTokenHelpers__() {
+        ((global::System.Action)(() => {
+#nullable restore
+#line 1 "x:\dir\subdir\Test\TestComponent.cshtml"
+global::System.Object __typeHelper = nameof(X.System.Y);
+
+#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
+        protected override void BuildRenderTree(global::Microsoft.AspNetCore.Components.Rendering.RenderTreeBuilder __builder)
+        {
+        }
+        #pragma warning restore 1998
+    }
+}
+#pragma warning restore 1591

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

@@ -0,0 +1,17 @@
+Document - 
+    NamespaceDeclaration -  - X.System.Y
+        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 - 
+                DirectiveToken - (11:0,11 [10] x:\dir\subdir\Test\TestComponent.cshtml) - X.System.Y
+            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

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

@@ -0,0 +1,5 @@
+Source Location: (11:0,11 [10] x:\dir\subdir\Test\TestComponent.cshtml)
+|X.System.Y|
+Generated Location: (649:17,44 [10] )
+|X.System.Y|
+

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

@@ -0,0 +1,20 @@
+// <auto-generated/>
+#pragma warning disable 1591
+namespace X.System.Y
+{
+    #line hidden
+    using global::System;
+    using global::System.Collections.Generic;
+    using global::System.Linq;
+    using global::System.Threading.Tasks;
+    using global::Microsoft.AspNetCore.Components;
+    public partial class TestComponent : global::Microsoft.AspNetCore.Components.ComponentBase
+    {
+        #pragma warning disable 1998
+        protected override void BuildRenderTree(global::Microsoft.AspNetCore.Components.Rendering.RenderTreeBuilder __builder)
+        {
+        }
+        #pragma warning restore 1998
+    }
+}
+#pragma warning restore 1591

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

@@ -0,0 +1,9 @@
+Document - 
+    NamespaceDeclaration -  - X.System.Y
+        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