Allow extension methods in script code

src/Compilers/CSharp/Portable/Binder/InContainerBinder.cs

@@ -146,6 +146,17 @@ internal override bool SupportsExtensionMethods
                 {
                     ((NamespaceSymbol)_container).GetExtensionMethods(methods, name, arity, options);
                 }
+                else if (((NamedTypeSymbol)_container).IsScriptClass)
+                {
+                    for (var submission = this.Compilation; submission != null; submission = submission.PreviousSubmission)
+                    {
+                        var scriptClass = submission.ScriptClass;
+                        if ((object)scriptClass != null)
+                        {
+                            scriptClass.GetExtensionMethods(methods, name, arity, options);
+                        }
+                    }
+                }
             }
         }
 

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

@@ -3151,7 +3151,7 @@ internal bool ContainsExtensionMethods
             {
                 if (!_lazyContainsExtensionMethods.HasValue())
                 {
-                    bool containsExtensionMethods = (this.IsStatic && !this.IsGenericType && this.declaration.ContainsExtensionMethods);
+                    bool containsExtensionMethods = ((this.IsStatic && !this.IsGenericType) || this.IsScriptClass) && this.declaration.ContainsExtensionMethods;
                     _lazyContainsExtensionMethods = containsExtensionMethods.ToThreeState();
                 }
 

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

@@ -221,7 +221,7 @@ private void MethodChecks(MethodDeclarationSyntax syntax, Binder withTypeParamsB
                 {
                     diagnostics.Add(ErrorCode.ERR_ExtensionMethodsDecl, location, ContainingType.Name);
                 }
-                else if (!ContainingType.IsStatic || ContainingType.Arity != 0)
+                else if (!ContainingType.IsScriptClass && !(ContainingType.IsStatic && ContainingType.Arity == 0))
                 {
                     // Duplicate Dev10 behavior by selecting the containing type identifier. However if there
                     // is no containing type (in the interactive case for instance), select the method identifier.

src/Compilers/CSharp/Test/Symbol/Symbols/ExtensionMethodTests.cs

@@ -3671,5 +3671,46 @@ static void Main(string[] args)
             Assert.Contains("GetEnumerableDisposable2", symbols);
             Assert.Contains("GetEnumerableDisposable1", symbols);
         }
+
+        [Fact]
+        public void ScriptExtensionMethods()
+        {
+            var source =
+@"static object F(this object o) { return null; }
+class C
+{
+    void M() { this.F(); }
+}
+var o = new object();
+o.F();";
+            var compilation = CreateCompilationWithMscorlib(source, references: new[] { SystemCoreRef }, parseOptions: TestOptions.Script);
+            compilation.VerifyDiagnostics();
+        }
+
+        [Fact]
+        public void InteractiveExtensionMethods()
+        {
+            var parseOptions = TestOptions.Interactive;
+            var references = new[] { MscorlibRef, SystemCoreRef };
+            var source0 =
+@"static object F(this object o) { return 0; }
+var o = new object();
+o.F();";
+            var source1 =
+@"static object G(this object o) { return 1; }
+var o = new object();
+o.G().F();";
+            var s0 = CSharpCompilation.CreateSubmission(
+                "s0.dll",
+                syntaxTree: SyntaxFactory.ParseSyntaxTree(source0, options: parseOptions),
+                references: references);
+            s0.VerifyDiagnostics();
+            var s1 = CSharpCompilation.CreateSubmission(
+                "s1.dll",
+                syntaxTree: SyntaxFactory.ParseSyntaxTree(source1, options: parseOptions),
+                previousSubmission: s0,
+                references: references);
+            s1.VerifyDiagnostics();
+        }
     }
 }