Add separate error for disallowed members in global namespace

src/Compilers/CSharp/Portable/CSharpResources.resx

@@ -699,6 +699,9 @@
   <data name="ERR_NamespaceUnexpected" xml:space="preserve">
     <value>A namespace cannot directly contain members such as fields, methods or statements</value>
   </data>
+  <data name="ERR_CompilationUnitUnexpected" xml:space="preserve">
+    <value>A compilation unit cannot directly contain members such as fields, methods or properties</value>
+  </data>
   <data name="ERR_NoSuchMember" xml:space="preserve">
     <value>'{0}' does not contain a definition for '{1}'</value>
   </data>

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

@@ -2445,6 +2445,7 @@ internal enum ErrorCode
         ERR_EqualityOperatorInPatternNotSupported = 9344,
         ERR_InequalityOperatorInPatternNotSupported = 9345,
         ERR_EncUpdateRequiresEmittingExplicitInterfaceImplementationNotSupportedByTheRuntime = 9346,
+        ERR_CompilationUnitUnexpected = 9347,
 
         // Note: you will need to do the following after adding errors:
         //  1) Update ErrorFacts.IsBuildOnlyDiagnostic (src/Compilers/CSharp/Portable/Errors/ErrorFacts.cs)

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

@@ -2553,6 +2553,7 @@ or ErrorCode.ERR_UnexpectedArgumentListInBaseTypeWithoutParameterList
                 or ErrorCode.ERR_EqualityOperatorInPatternNotSupported
                 or ErrorCode.ERR_InequalityOperatorInPatternNotSupported
                 or ErrorCode.ERR_DesignatorBeforePropertyPattern
+                or ErrorCode.ERR_CompilationUnitUnexpected
                     => false,
             };
 #pragma warning restore CS8524 // The switch expression does not handle some values of its input type (it is not exhaustive) involving an unnamed enum value.

src/Compilers/CSharp/Portable/Symbols/Source/SourceMemberContainerSymbol.cs

@@ -5516,12 +5516,10 @@ private void AddNonTypeMembers(
 
                             // Lang version check for ref-fields is done inside SourceMemberFieldSymbol;
                             _ = fieldSyntax.Declaration.Type.SkipScoped(out _).SkipRefInField(out var refKind);
-
-                            if (IsImplicitClass && reportMisplacedGlobalCode)
-                            {
-                                diagnostics.Add(ErrorCode.ERR_NamespaceUnexpected,
-                                    new SourceLocation(fieldSyntax.Declaration.Variables.First().Identifier));
-                            }
+                            reportMisplacedMemberInNamespace(
+                                 fieldSyntax,
+                                 fieldSyntax.Declaration.Variables.First().Identifier,
+                                 reportMisplacedGlobalCode);
 
                             bool modifierErrors;
                             var modifiers = SourceMemberFieldSymbol.MakeModifiers(this, fieldSyntax.Declaration.Variables[0].Identifier, fieldSyntax.Modifiers, isRefField: refKind != RefKind.None, diagnostics, out modifierErrors);
@@ -5561,11 +5559,10 @@ private void AddNonTypeMembers(
                     case SyntaxKind.MethodDeclaration:
                         {
                             var methodSyntax = (MethodDeclarationSyntax)m;
-                            if (IsImplicitClass && reportMisplacedGlobalCode)
-                            {
-                                diagnostics.Add(ErrorCode.ERR_NamespaceUnexpected,
-                                    new SourceLocation(methodSyntax.Identifier));
-                            }
+                            reportMisplacedMemberInNamespace(
+                                 methodSyntax,
+                                 methodSyntax.Identifier,
+                                 reportMisplacedGlobalCode);
 
                             var method = SourceOrdinaryMethodSymbol.CreateMethodSymbol(this, bodyBinder, methodSyntax, compilation.IsNullableAnalysisEnabledIn(methodSyntax), diagnostics);
                             builder.NonTypeMembersWithPartialImplementations.Add(method);
@@ -5575,11 +5572,10 @@ private void AddNonTypeMembers(
                     case SyntaxKind.ConstructorDeclaration:
                         {
                             var constructorSyntax = (ConstructorDeclarationSyntax)m;
-                            if (IsImplicitClass && reportMisplacedGlobalCode)
-                            {
-                                diagnostics.Add(ErrorCode.ERR_NamespaceUnexpected,
-                                    new SourceLocation(constructorSyntax.Identifier));
-                            }
+                            reportMisplacedMemberInNamespace(
+                                 constructorSyntax,
+                                 constructorSyntax.Identifier,
+                                 reportMisplacedGlobalCode);
 
                             bool isNullableEnabled = compilation.IsNullableAnalysisEnabledIn(constructorSyntax);
                             var constructor = SourceConstructorSymbol.CreateConstructorSymbol(this, constructorSyntax, isNullableEnabled, diagnostics);
@@ -5594,11 +5590,10 @@ private void AddNonTypeMembers(
                     case SyntaxKind.DestructorDeclaration:
                         {
                             var destructorSyntax = (DestructorDeclarationSyntax)m;
-                            if (IsImplicitClass && reportMisplacedGlobalCode)
-                            {
-                                diagnostics.Add(ErrorCode.ERR_NamespaceUnexpected,
-                                    new SourceLocation(destructorSyntax.Identifier));
-                            }
+                            reportMisplacedMemberInNamespace(
+                                 destructorSyntax,
+                                 destructorSyntax.Identifier,
+                                 reportMisplacedGlobalCode);
 
                             // CONSIDER: if this doesn't (directly or indirectly) override object.Finalize, the
                             // runtime won't consider it a finalizer and it will not be marked as a destructor
@@ -5612,11 +5607,10 @@ private void AddNonTypeMembers(
                     case SyntaxKind.PropertyDeclaration:
                         {
                             var propertySyntax = (PropertyDeclarationSyntax)m;
-                            if (IsImplicitClass && reportMisplacedGlobalCode)
-                            {
-                                diagnostics.Add(ErrorCode.ERR_NamespaceUnexpected,
-                                    new SourceLocation(propertySyntax.Identifier));
-                            }
+                            reportMisplacedMemberInNamespace(
+                                 propertySyntax,
+                                 propertySyntax.Identifier,
+                                 reportMisplacedGlobalCode);
 
                             var property = SourcePropertySymbol.Create(this, bodyBinder, propertySyntax, diagnostics);
                             builder.NonTypeMembersWithPartialImplementations.Add(property);
@@ -5663,12 +5657,10 @@ private void AddNonTypeMembers(
                     case SyntaxKind.EventFieldDeclaration:
                         {
                             var eventFieldSyntax = (EventFieldDeclarationSyntax)m;
-                            if (IsImplicitClass && reportMisplacedGlobalCode)
-                            {
-                                diagnostics.Add(
-                                    ErrorCode.ERR_NamespaceUnexpected,
-                                    new SourceLocation(eventFieldSyntax.Declaration.Variables.First().Identifier));
-                            }
+                            reportMisplacedMemberInNamespace(
+                                 eventFieldSyntax,
+                                 eventFieldSyntax.Declaration.Variables.First().Identifier,
+                                 reportMisplacedGlobalCode);
 
                             foreach (VariableDeclaratorSyntax declarator in eventFieldSyntax.Declaration.Variables)
                             {
@@ -5717,11 +5709,10 @@ private void AddNonTypeMembers(
                     case SyntaxKind.EventDeclaration:
                         {
                             var eventSyntax = (EventDeclarationSyntax)m;
-                            if (IsImplicitClass && reportMisplacedGlobalCode)
-                            {
-                                diagnostics.Add(ErrorCode.ERR_NamespaceUnexpected,
-                                    new SourceLocation(eventSyntax.Identifier));
-                            }
+                            reportMisplacedMemberInNamespace(
+                                eventSyntax,
+                                eventSyntax.Identifier,
+                                reportMisplacedGlobalCode);
 
                             var @event = new SourceCustomEventSymbol(this, bodyBinder, eventSyntax, diagnostics);
 
@@ -5737,11 +5728,10 @@ private void AddNonTypeMembers(
                     case SyntaxKind.IndexerDeclaration:
                         {
                             var indexerSyntax = (IndexerDeclarationSyntax)m;
-                            if (IsImplicitClass && reportMisplacedGlobalCode)
-                            {
-                                diagnostics.Add(ErrorCode.ERR_NamespaceUnexpected,
-                                    new SourceLocation(indexerSyntax.ThisKeyword));
-                            }
+                            reportMisplacedMemberInNamespace(
+                                indexerSyntax,
+                                indexerSyntax.ThisKeyword,
+                                reportMisplacedGlobalCode);
 
                             var indexer = SourcePropertySymbol.Create(this, bodyBinder, indexerSyntax, diagnostics);
                             builder.HaveIndexers = true;
@@ -5754,11 +5744,10 @@ private void AddNonTypeMembers(
                     case SyntaxKind.ConversionOperatorDeclaration:
                         {
                             var conversionOperatorSyntax = (ConversionOperatorDeclarationSyntax)m;
-                            if (IsImplicitClass && reportMisplacedGlobalCode)
-                            {
-                                diagnostics.Add(ErrorCode.ERR_NamespaceUnexpected,
-                                    new SourceLocation(conversionOperatorSyntax.OperatorKeyword));
-                            }
+                            reportMisplacedMemberInNamespace(
+                                conversionOperatorSyntax,
+                                conversionOperatorSyntax.OperatorKeyword,
+                                reportMisplacedGlobalCode);
 
                             var method = SourceUserDefinedConversionSymbol.CreateUserDefinedConversionSymbol(
                                 this, bodyBinder, conversionOperatorSyntax, compilation.IsNullableAnalysisEnabledIn(conversionOperatorSyntax), diagnostics);
@@ -5769,11 +5758,10 @@ private void AddNonTypeMembers(
                     case SyntaxKind.OperatorDeclaration:
                         {
                             var operatorSyntax = (OperatorDeclarationSyntax)m;
-                            if (IsImplicitClass && reportMisplacedGlobalCode)
-                            {
-                                diagnostics.Add(ErrorCode.ERR_NamespaceUnexpected,
-                                    new SourceLocation(operatorSyntax.OperatorKeyword));
-                            }
+                            reportMisplacedMemberInNamespace(
+                                operatorSyntax,
+                                operatorSyntax.OperatorKeyword,
+                                reportMisplacedGlobalCode);
 
                             var method = SourceUserDefinedOperatorSymbol.CreateUserDefinedOperatorSymbol(
                                 this, bodyBinder, operatorSyntax, compilation.IsNullableAnalysisEnabledIn(operatorSyntax), diagnostics);
@@ -5849,6 +5837,18 @@ SyntaxKind.FileScopedNamespaceDeclaration or
 
             AddInitializers(builder.InstanceInitializers, instanceInitializers);
             AddInitializers(builder.StaticInitializers, staticInitializers);
+
+            void reportMisplacedMemberInNamespace(SyntaxNode member, SyntaxToken locationSyntax, bool reportMisplacedGlobalCode)
+            {
+                if (IsImplicitClass && reportMisplacedGlobalCode)
+                {
+                    var parentSyntax = member.Parent;
+                    var errorCode = parentSyntax.IsKind(SyntaxKind.CompilationUnit)
+                        ? ErrorCode.ERR_CompilationUnitUnexpected
+                        : ErrorCode.ERR_NamespaceUnexpected;
+                    diagnostics.Add(errorCode, new SourceLocation(locationSyntax));
+                }
+            }
         }
 
         private void AddAccessorIfAvailable(ArrayBuilder<Symbol> symbols, MethodSymbol? accessorOpt)