Give an error when a file type is used in a global using static

src/Compilers/CSharp/Portable/CSharpResources.resx

@@ -7115,6 +7115,9 @@ To remove the warning, you can use /reference instead (set the Embed Interop Typ
   <data name="ERR_FileTypeNested" xml:space="preserve">
     <value>File type '{0}' must be defined in a top level type; '{0}' is a nested type.</value>
   </data>
+  <data name="ERR_GlobalUsingStaticFileType" xml:space="preserve">
+    <value>File type '{0}' cannot be used in a 'global using static' directive.</value>
+  </data>
   <data name="IDS_FeatureUnsignedRightShift" xml:space="preserve">
     <value>unsigned right shift</value>
   </data>

src/Compilers/CSharp/Portable/Errors/ErrorCode.cs

@@ -2096,6 +2096,7 @@ internal enum ErrorCode
         ERR_FileTypeNoExplicitAccessibility = 9301,
         ERR_FileTypeBase = 9302,
         ERR_FileTypeNested = 9303,
+        ERR_GlobalUsingStaticFileType = 9304
 
         #endregion
 

src/Compilers/CSharp/Portable/Symbols/Source/SourceNamespaceSymbol.AliasesAndUsings.cs

@@ -757,6 +757,11 @@ UsingsAndDiagnostics buildUsings(
                                 else
                                 {
                                     var importedType = (NamedTypeSymbol)imported;
+                                    if (usingDirective.GlobalKeyword != default(SyntaxToken) && importedType.IsFileTypeOrUsesFileTypes())
+                                    {
+                                        diagnostics.Add(ErrorCode.ERR_GlobalUsingStaticFileType, usingDirective.Name.Location, imported);
+                                    }
+
                                     if (!getOrCreateUniqueUsings(ref uniqueUsings, globalUsingNamespacesOrTypes).Add(importedType))
                                     {
                                         diagnostics.Add(!globalUsingNamespacesOrTypes.IsEmpty && getOrCreateUniqueGlobalUsingsNotInTree(ref uniqueGlobalUsings, globalUsingNamespacesOrTypes, declarationSyntax.SyntaxTree).Contains(imported) ?

src/Compilers/CSharp/Test/Symbol/Symbols/Source/FileModifierTests.cs

@@ -2364,15 +2364,56 @@ public static void Main()
             }
             """;
 
-        // PROTOTYPE(ft): it should probably be an error to reference a file type in a global using static
         var compilation = CreateCompilation(new[] { source, main });
         compilation.VerifyDiagnostics(
-            // (1,1): hidden CS8019: Unnecessary using directive.
-            // global using static C;
-            Diagnostic(ErrorCode.HDN_UnusedUsingDirective, "global using static C;").WithLocation(1, 1),
-            // (5,9): error CS0103: The name 'M' does not exist in the current context
-            //         M();
-            Diagnostic(ErrorCode.ERR_NameNotInContext, "M").WithArguments("M").WithLocation(5, 9));
+                // (1,1): hidden CS8019: Unnecessary using directive.
+                // global using static C;
+                Diagnostic(ErrorCode.HDN_UnusedUsingDirective, "global using static C;").WithLocation(1, 1),
+                // (1,21): error CS9304: File type 'C' cannot be used in a 'global using static' directive.
+                // global using static C;
+                Diagnostic(ErrorCode.ERR_GlobalUsingStaticFileType, "C").WithArguments("C").WithLocation(1, 21),
+                // (5,9): error CS0103: The name 'M' does not exist in the current context
+                //         M();
+                Diagnostic(ErrorCode.ERR_NameNotInContext, "M").WithArguments("M").WithLocation(5, 9));
+    }
+
+    [Fact]
+    public void GlobalUsingStatic_02()
+    {
+        var source = """
+            global using static Container<C>;
+
+            public class Container<T>
+            {
+            }
+
+            file class C
+            {
+                public static void M() { }
+            }
+            """;
+
+        var main = """
+            class Program
+            {
+                public static void Main()
+                {
+                    M();
+                }
+            }
+            """;
+
+        var compilation = CreateCompilation(new[] { source, main });
+        compilation.VerifyDiagnostics(
+                // (1,1): hidden CS8019: Unnecessary using directive.
+                // global using static Container<C>;
+                Diagnostic(ErrorCode.HDN_UnusedUsingDirective, "global using static Container<C>;").WithLocation(1, 1),
+                // (1,21): error CS9304: File type 'Container<C>' cannot be used in a 'global using static' directive.
+                // global using static Container<C>;
+                Diagnostic(ErrorCode.ERR_GlobalUsingStaticFileType, "Container<C>").WithArguments("Container<C>").WithLocation(1, 21),
+                // (5,9): error CS0103: The name 'M' does not exist in the current context
+                //         M();
+                Diagnostic(ErrorCode.ERR_NameNotInContext, "M").WithArguments("M").WithLocation(5, 9));
     }
 
     [Fact]