Avoid crash from Script class instantiation (#79879)

Author: jjonescz

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

@@ -5227,16 +5227,14 @@ BoundExpression bindObjectCreationExpression(ObjectCreationExpressionSyntax node
                     case TypeKind.TypeParameter:
                         return BindTypeParameterCreationExpression(node, (TypeParameterSymbol)type, diagnostics);
 
-                    case TypeKind.Submission:
-                        // script class is synthesized and should not be used as a type of a new expression:
-                        throw ExceptionUtilities.UnexpectedValue(type.TypeKind);
-
                     case TypeKind.Pointer:
                     case TypeKind.FunctionPointer:
                         type = new ExtendedErrorTypeSymbol(type, LookupResultKind.NotCreatable,
                             diagnostics.Add(ErrorCode.ERR_UnsafeTypeInObjectCreation, node.Location, type));
                         goto case TypeKind.Class;
 
+                    case TypeKind.Submission:
+                    // script class is synthesized and should not be used as a type of a new expression:
                     case TypeKind.Dynamic:
                     // we didn't find any type called "dynamic" so we are using the builtin dynamic type, which has no constructors:
                     case TypeKind.Array:

src/Scripting/CSharpTest/ScriptTests.cs

@@ -1095,6 +1095,19 @@ public async Task Function_ReturningPartialType_CSharp13()
             Assert.Equal("partial", result.GetType().Name);
         }
 
+        [Fact, WorkItem("https://github.com/dotnet/roslyn/issues/79146")]
+        public void ScriptInstantiation()
+        {
+            var parseOptions = CSharpParseOptions.Default.WithKind(SourceCodeKind.Script);
+            var compilation = CSharpCompilation.CreateScriptCompilation("Test",
+                CSharpSyntaxTree.ParseText("var x = new Script();", parseOptions),
+                [NetStandard20Ref]);
+            compilation.VerifyDiagnostics(
+                // (1,13): error CS8386: Invalid object creation
+                // var x = new Script();
+                Diagnostic(ErrorCode.ERR_InvalidObjectCreation, "Script").WithLocation(1, 13));
+        }
+
         private class StreamOffsetResolver : SourceReferenceResolver
         {
             public override bool Equals(object other) => ReferenceEquals(this, other);