Allow top-level extension methods in VB script code

src/Compilers/VisualBasic/Portable/Symbols/NamedTypeSymbolExtensions.vb

@@ -113,5 +113,10 @@ Namespace Microsoft.CodeAnalysis.VisualBasic.Symbols
             Return False
         End Function
 
+        <Extension()>
+        Friend Function AllowsExtensionMethods(container As NamedTypeSymbol) As Boolean
+            Return container.TypeKind = TypeKind.Module OrElse container.IsScriptClass
+        End Function
+
     End Module
 End Namespace

src/Compilers/VisualBasic/Portable/Symbols/Source/SourceMemberContainerTypeSymbol.vb

@@ -3333,7 +3333,7 @@ Namespace Microsoft.CodeAnalysis.VisualBasic.Symbols
                 ' Only Modules can declare extension methods.
 
                 If _lazyContainsExtensionMethods = ThreeState.Unknown Then
-                    If Not (_containingSymbol.Kind = SymbolKind.Namespace AndAlso Me.TypeKind = TypeKind.Module AndAlso Me.AnyMemberHasAttributes) Then
+                    If Not (_containingSymbol.Kind = SymbolKind.Namespace AndAlso Me.AllowsExtensionMethods() AndAlso Me.AnyMemberHasAttributes) Then
                         _lazyContainsExtensionMethods = ThreeState.False
                     End If
                 End If

src/Compilers/VisualBasic/Portable/Symbols/Source/SourceMemberMethodSymbol.vb

@@ -85,7 +85,7 @@ Namespace Microsoft.CodeAnalysis.VisualBasic.Symbols
 
             ' Check attributes quickly.
             _quickAttributes = binder.QuickAttributeChecker.CheckAttributes(syntax.AttributeLists)
-            If containingType.TypeKind <> TypeKind.Module Then
+            If Not containingType.AllowsExtensionMethods() Then
                 ' Extension methods in source can only be inside modules.
                 _quickAttributes = _quickAttributes And Not QuickAttributes.Extension
             End If

src/Compilers/VisualBasic/Portable/Symbols/Source/SourceMethodSymbol.vb

@@ -1471,7 +1471,7 @@ lReportErrorOnTwoTokens:
                     Dim isExtensionMethod As Boolean = False
 
                     If Not (Me.MethodKind <> MethodKind.Ordinary AndAlso Me.MethodKind <> MethodKind.DeclareMethod) AndAlso
-                        m_containingType.TypeKind = TYPEKIND.Module AndAlso
+                        m_containingType.AllowsExtensionMethods() AndAlso
                         Me.ParameterCount <> 0 Then
 
                         Debug.Assert(Me.IsShared)
@@ -1569,7 +1569,7 @@ lReportErrorOnTwoTokens:
                 If Me.MethodKind <> MethodKind.Ordinary AndAlso Me.MethodKind <> MethodKind.DeclareMethod Then
                     arguments.Diagnostics.Add(ERRID.ERR_ExtensionOnlyAllowedOnModuleSubOrFunction, arguments.AttributeSyntaxOpt.GetLocation())
 
-                ElseIf m_containingType.TypeKind <> TYPEKIND.Module Then
+                ElseIf Not m_containingType.AllowsExtensionMethods() Then
                     arguments.Diagnostics.Add(ERRID.ERR_ExtensionMethodNotInModule, arguments.AttributeSyntaxOpt.GetLocation())
 
                 ElseIf Me.ParameterCount = 0 Then

src/Compilers/VisualBasic/Test/Symbol/SymbolsTests/ExtensionMethods/ExtensionMethodTests.vb

@@ -2431,6 +2431,59 @@ End Module
 
         End Sub
 
+        <Fact>
+        Public Sub ScriptExtensionMethods()
+            Dim comp = CreateCompilationWithMscorlib(
+                <compilation>
+                    <file name="a.vbx"><![CDATA[
+Imports System.Runtime.CompilerServices
+<Extension>
+Shared Function F(o As Object) As Object
+    Return Nothing
+End Function
+Dim o As New Object()
+o.F()]]></file>
+                </compilation>,
+                parseOptions:=TestOptions.Script,
+                references:={MscorlibRef, SystemCoreRef})
+            comp.VerifyDiagnostics()
+            Assert.True(comp.SourceAssembly.MightContainExtensionMethods)
+        End Sub
+
+        <Fact>
+        Public Sub InteractiveExtensionMethods()
+            Dim parseOptions = TestOptions.Interactive
+            Dim references = {MscorlibRef, SystemCoreRef}
+            Dim source0 = <![CDATA[
+Imports System.Runtime.CompilerServices
+<Extension>
+Shared Function F(o As Object) As Object
+    Return 0
+End Function
+Dim o As New Object()
+? o.F()]]>
+            Dim source1 = <![CDATA[
+<Extension>
+Shared Function G(o As Object) As Object
+    Return 1
+End Function
+Dim o As New Object()
+? o.G().F()]]>
+            Dim s0 = VisualBasicCompilation.CreateSubmission(
+                "s0.dll",
+                syntaxTree:=Parse(source0.Value, parseOptions),
+                references:=references)
+            s0.VerifyDiagnostics()
+            Assert.True(s0.SourceAssembly.MightContainExtensionMethods)
+            Dim s1 = VisualBasicCompilation.CreateSubmission(
+                "s1.dll",
+                syntaxTree:=Parse(source0.Value, parseOptions),
+                previousSubmission:=s0,
+                references:=references)
+            s1.VerifyDiagnostics()
+            Assert.True(s1.SourceAssembly.MightContainExtensionMethods)
+        End Sub
+
     End Class
 
 End Namespace