Treat .csx/.vbx as regular source files not script

src/Compilers/CSharp/Test/CommandLine/CommandLineTests.cs

@@ -7677,6 +7677,36 @@ static void Main()
 
             CleanupAllGeneratedFiles(src.Path);
         }
+
+        /// <summary>
+        /// Script compilation should be internal only.
+        /// </summary>
+        [WorkItem(1979, "https://github.com/dotnet/roslyn/issues/1979")]
+        [Fact]
+        public void ScriptCompilationInternalOnly()
+        {
+            const string source = @"System.Console.WriteLine();";
+            var dir = Temp.CreateDirectory();
+            var file = dir.CreateFile("c.csx");
+            file.WriteAllText(source);
+
+            // Compiling script file with internal API should be supported.
+            var compilation = CreateCompilationWithMscorlib(
+                source,
+                sourceFileName: file.Path,
+                parseOptions: new CSharpParseOptions(kind: SourceCodeKind.Script),
+                options: new CSharpCompilationOptions(OutputKind.ConsoleApplication));
+            compilation.VerifyDiagnostics();
+
+            // Compiling with command-line compiler, should not treat .csx as script.
+            var compiler = new MockCSharpCompiler(null, _baseDirectory, new[] { "/nologo", "/preferreduilang:en", file.Path });
+            var outWriter = new StringWriter(CultureInfo.InvariantCulture);
+            int exitCode = compiler.Run(outWriter);
+            Assert.Equal(1, exitCode);
+            Assert.True(outWriter.ToString().Contains("(1,25): error CS1022: Type or namespace definition, or end-of-file expected"));
+
+            CleanupAllGeneratedFiles(file.Path);
+        }
     }
 
     [DiagnosticAnalyzer(LanguageNames.CSharp, LanguageNames.VisualBasic)]

src/Compilers/Core/Portable/CommandLine/CommonCommandLineParser.cs

@@ -771,21 +771,9 @@ internal IEnumerable<string> ResolveRelativePaths(IEnumerable<string> paths, str
             }
         }
 
-        internal CommandLineSourceFile ToCommandLineSourceFile(string resolvedPath)
+        private CommandLineSourceFile ToCommandLineSourceFile(string resolvedPath)
         {
-            string extension = PathUtilities.GetExtension(resolvedPath);
-
-            bool isScriptFile;
-            if (IsInteractive)
-            {
-                isScriptFile = !string.Equals(extension, RegularFileExtension, StringComparison.OrdinalIgnoreCase);
-            }
-            else
-            {
-                isScriptFile = string.Equals(extension, ScriptFileExtension, StringComparison.OrdinalIgnoreCase);
-            }
-
-            return new CommandLineSourceFile(resolvedPath, isScriptFile);
+            return new CommandLineSourceFile(resolvedPath, isScript: false);
         }
 
         internal IEnumerable<CommandLineSourceFile> ParseFileArgument(string arg, string baseDirectory, IList<Diagnostic> errors)

src/Compilers/VisualBasic/Test/CommandLine/CommandLineTests.vb

@@ -7135,6 +7135,35 @@ End Class
             Assert.Contains(CodeAnalysisResources.AnalyzerExecutionTimeColumnHeader, output, StringComparison.Ordinal)
             CleanupAllGeneratedFiles(source)
         End Sub
+
+        ''' <summary>
+        ''' Script compilation should be internal only.
+        ''' </summary>
+        <WorkItem(1979, "https://github.com/dotnet/roslyn/issues/1979")>
+        <Fact>
+        Public Sub ScriptCompilationInternalOnly()
+            Dim source = "System.Console.WriteLine()"
+            Dim dir = Temp.CreateDirectory()
+            Dim file = dir.CreateFile("b.vbx")
+            file.WriteAllText(source)
+
+            ' Compiling script file with internal API should be supported.
+            Dim compilation = CreateCompilationWithMscorlib(
+                <compilation>
+                    <file name="b.vbx"><%= source %></file>
+                </compilation>,
+                parseOptions:=New VisualBasicParseOptions(kind:=SourceCodeKind.Script),
+                options:=New VisualBasicCompilationOptions(OutputKind.ConsoleApplication))
+            compilation.VerifyDiagnostics()
+
+            ' Compiling with command-line compiler, should not treat .vbx as script.
+            Dim cmd = New MockVisualBasicCompiler(Nothing, _baseDirectory, {"/nologo", "/preferreduilang:en", file.Path})
+            Dim output As StringWriter = New StringWriter()
+            cmd.Run(output, Nothing)
+            Assert.True(output.ToString().Contains("error BC30689: Statement cannot appear outside of a method body."))
+
+            CleanupAllGeneratedFiles(file.Path)
+        End Sub
     End Class
 
     <DiagnosticAnalyzer(LanguageNames.VisualBasic)>