csi.exe should emit exception to stderr, not stdout

src/Interactive/CsiCore/Csi.cs

@@ -36,7 +36,7 @@ internal static int Main(string[] args)
             }
             catch (Exception ex)
             {
-                Console.WriteLine(ex.ToString());
+                Console.Error.WriteLine(ex.ToString());
                 return 1;
             }
         }

src/Scripting/CSharpTest.Desktop/CsiTests.cs

@@ -79,7 +79,7 @@ public void ReferenceSearchPaths_LIB()
             var result = ProcessUtilities.Run(CsiPath, "/r:C.dll a.csx", workingDirectory: cwd.Path, additionalEnvironmentVars: new[] { KeyValuePair.Create("LIB", dir.Path) });
 
             // error CS0006: Metadata file 'C.dll' could not be found
-            Assert.True(result.Output.StartsWith("error CS0006", StringComparison.Ordinal));
+            Assert.True(result.Errors.StartsWith("error CS0006", StringComparison.Ordinal));
             Assert.True(result.ContainsErrors);
         }
 

src/Scripting/CSharpTest/CommandLineRunnerTests.cs

@@ -79,6 +79,10 @@ public void Await()
 . select x * x
 Enumerable.WhereSelectArrayIterator<int, int> {{ 9, 16, 25 }}
 > ", runner.Console.Out.ToString());
+
+            AssertEx.AssertEqualToleratingWhitespaceDifferences(
+                @"(1,19): warning CS1998: This async method lacks 'await' operators and will run synchronously. Consider using the 'await' operator to await non-blocking API calls, or 'await Task.Run(...)' to do CPU-bound work on a background thread.",
+                runner.Console.Error.ToString());
         }
 
         [Fact]
@@ -185,6 +189,11 @@ > div(10, 0)
   + Submission#0.div(int, int)
 «Gray»
 > ", runner.Console.Out.ToString());
+
+            Assert.Equal(
+$@"{new System.DivideByZeroException().Message}
+  + Submission#0.div(int, int)
+", runner.Console.Error.ToString());
         }
 
         [Fact]
@@ -211,6 +220,11 @@ > C<string>.div<bool>(10, 0)
   + Submission#0.C<T>.div<U>(int, int)
 «Gray»
 > ", runner.Console.Out.ToString());
+
+            Assert.Equal(
+$@"{new System.DivideByZeroException().Message}
+  + Submission#0.C<T>.div<U>(int, int)
+", runner.Console.Error.ToString());
         }
 
         [Fact]
@@ -241,9 +255,9 @@ public void Args_Interactive2()
 
             runner.RunInteractive();
 
-            AssertEx.AssertEqualToleratingWhitespaceDifferences(
-                $@"error CS2001: Source file '{Path.Combine(AppContext.BaseDirectory, "@arg1")}' could not be found.",
-                runner.Console.Out.ToString());
+            var error = $@"error CS2001: Source file '{Path.Combine(AppContext.BaseDirectory, "@arg1")}' could not be found.";
+            AssertEx.AssertEqualToleratingWhitespaceDifferences(error, runner.Console.Out.ToString());
+            AssertEx.AssertEqualToleratingWhitespaceDifferences(error, runner.Console.Error.ToString());
         }
 
         [Fact]
@@ -389,9 +403,9 @@ public void Script_NonExistingFile()
 
             Assert.Equal(1, runner.RunInteractive());
 
-            AssertEx.AssertEqualToleratingWhitespaceDifferences($@"
-error CS2001: Source file '{Path.Combine(AppContext.BaseDirectory, "a + b")}' could not be found.
-", runner.Console.Out.ToString());
+            var error = $@"error CS2001: Source file '{Path.Combine(AppContext.BaseDirectory, "a + b")}' could not be found.";
+            AssertEx.AssertEqualToleratingWhitespaceDifferences(error, runner.Console.Out.ToString());
+            AssertEx.AssertEqualToleratingWhitespaceDifferences(error, runner.Console.Error.ToString());
         }
 
         [Fact]
@@ -431,9 +445,9 @@ public void Script_BadUsings()
 
             Assert.Equal(1, runner.RunInteractive());
 
-            AssertEx.AssertEqualToleratingWhitespaceDifferences(@"
-error CS0246: The type or namespace name 'Foo' could not be found (are you missing a using directive or an assembly reference?)
-", runner.Console.Out.ToString());
+            const string error = @"error CS0246: The type or namespace name 'Foo' could not be found (are you missing a using directive or an assembly reference?)";
+            AssertEx.AssertEqualToleratingWhitespaceDifferences(error, runner.Console.Out.ToString());
+            AssertEx.AssertEqualToleratingWhitespaceDifferences(error, runner.Console.Error.ToString());
         }
 
         [Fact]
@@ -453,6 +467,10 @@ > nameof(Microsoft.CodeAnalysis)
 (1,8): error CS0234: The type or namespace name 'CodeAnalysis' does not exist in the namespace 'Microsoft' (are you missing an assembly reference?)
 «Gray»
 > ", runner.Console.Out.ToString());
+
+            AssertEx.AssertEqualToleratingWhitespaceDifferences(
+                "(1,8): error CS0234: The type or namespace name 'CodeAnalysis' does not exist in the namespace 'Microsoft' (are you missing an assembly reference?)",
+                runner.Console.Error.ToString());
         }
 
         [Fact]
@@ -574,6 +592,10 @@ > X
 1
 > 
 ", runner.Console.Out.ToString());
+
+            AssertEx.AssertEqualToleratingWhitespaceDifferences(
+                @"(1,7): error CS1504: Source file 'a.csx' could not be opened -- Could not find file.",
+                runner.Console.Error.ToString());
         }
 
         [Fact]
@@ -609,6 +631,10 @@ > ReferencePaths.Add(@""{dir.Path}"")
 C {{ }}
 > 
 ", runner.Console.Out.ToString());
+
+            AssertEx.AssertEqualToleratingWhitespaceDifferences(
+                @"(1,1): error CS0006: Metadata file 'C.dll' could not be found",
+                runner.Console.Error.ToString());
         }
 
         [Fact]
@@ -689,6 +715,10 @@ 1 1
 C {{ }}
 > 
 ", runner.Console.Out.ToString());
+
+            AssertEx.AssertEqualToleratingWhitespaceDifferences(
+                $@"{init.Path}(2,3): error CS1002: ; expected",
+                runner.Console.Error.ToString());
         }
 
         [Fact]

src/Scripting/Core/Hosting/CommandLine/CommandLineRunner.cs

@@ -48,7 +48,7 @@ internal int RunInteractive()
             ErrorLogger errorLogger = null;
             if (_compiler.Arguments.ErrorLogPath != null)
             {
-                errorLogger = _compiler.GetErrorLogger(_console.Out, CancellationToken.None);
+                errorLogger = _compiler.GetErrorLogger(_console.Error, CancellationToken.None);
                 if (errorLogger == null)
                 {
                     return CommonCompiler.Failed;
@@ -106,7 +106,7 @@ private int RunInteractiveCore(ErrorLogger errorLogger)
             var scriptOptions = GetScriptOptions(_compiler.Arguments, scriptPathOpt, _compiler.MessageProvider, diagnosticsInfos);
 
             var errors = _compiler.Arguments.Errors.Concat(diagnosticsInfos.Select(Diagnostic.Create));
-            if (_compiler.ReportErrors(errors, _console.Out, errorLogger))
+            if (_compiler.ReportErrors(errors, _console.Error, errorLogger))
             {
                 return CommonCompiler.Failed;
             }
@@ -176,7 +176,7 @@ private int RunScript(ScriptOptions options, string code, ErrorLogger errorLogge
             }
             catch (CompilationErrorException e)
             {
-                _compiler.ReportErrors(e.Diagnostics, _console.Out, errorLogger);
+                _compiler.ReportErrors(e.Diagnostics, _console.Error, errorLogger);
                 return CommonCompiler.Failed;
             }
         }
@@ -281,7 +281,7 @@ private bool TryBuildAndRun(Script<object> newScript, InteractiveScriptGlobals g
             catch (FileLoadException e) when (e.InnerException is InteractiveAssemblyLoaderException)
             {
                 _console.ForegroundColor = ConsoleColor.Red;
-                _console.Out.WriteLine(e.InnerException.Message);
+                _console.Error.WriteLine(e.InnerException.Message);
                 _console.ResetColor();
 
                 return false;
@@ -324,7 +324,7 @@ private void DisplayException(Exception e)
             try
             {
                 _console.ForegroundColor = ConsoleColor.Red;
-                _console.Out.Write(_objectFormatter.FormatException(e));
+                _console.Error.Write(_objectFormatter.FormatException(e));
             }
             finally
             {
@@ -363,14 +363,14 @@ private void DisplayDiagnostics(IEnumerable<Diagnostic> diagnostics)
                 foreach (var diagnostic in ordered.Take(MaxDisplayCount))
                 {
                     _console.ForegroundColor = (diagnostic.Severity == DiagnosticSeverity.Error) ? ConsoleColor.Red : ConsoleColor.Yellow;
-                    _console.Out.WriteLine(diagnostic.ToString());
+                    _console.Error.WriteLine(diagnostic.ToString());
                 }
 
                 if (errorsAndWarnings.Length > MaxDisplayCount)
                 {
                     int notShown = errorsAndWarnings.Length - MaxDisplayCount;
                     _console.ForegroundColor = ConsoleColor.DarkRed;
-                    _console.Out.WriteLine(string.Format((notShown == 1) ? ScriptingResources.PlusAdditionalError : ScriptingResources.PlusAdditionalError, notShown));
+                    _console.Error.WriteLine(string.Format((notShown == 1) ? ScriptingResources.PlusAdditionalError : ScriptingResources.PlusAdditionalError, notShown));
                 }
             }
             finally

src/Scripting/CoreTest/TestConsoleIO.cs

@@ -17,7 +17,12 @@ public TestConsoleIO(string input)
         }
 
         private TestConsoleIO(Reader reader)
-            : base(output: new Writer(reader), error: new StringWriter(), input: reader)
+            : this(reader, new Writer(reader))
+        {
+        }
+
+        private TestConsoleIO(Reader reader, TextWriter output)
+            : base(output: output, error: new TeeWriter(output), input: reader)
         {
         }
 
@@ -102,5 +107,40 @@ public override void WriteLine()
                 base.WriteLine();
             }
         }
+
+        private sealed class TeeWriter : StringWriter
+        {
+            public override Encoding Encoding => Encoding.UTF8;
+            private readonly TextWriter _other;
+
+            public TeeWriter(TextWriter other)
+            {
+                _other = other;
+            }
+
+            public override void Write(char value)
+            {
+                _other.Write(value);
+                base.Write(value);
+            }
+
+            public override void Write(string value)
+            {
+                _other.Write(value);
+                base.Write(value);
+            }
+
+            public override void WriteLine(string value)
+            {
+                _other.WriteLine(value);
+                base.WriteLine(value);
+            }
+
+            public override void WriteLine()
+            {
+                _other.WriteLine();
+                base.WriteLine();
+            }
+        }
     }
 }