Add `#help` command to csi/vbi

src/Scripting/CSharpTest/CommandLineRunnerTests.cs

@@ -48,6 +48,7 @@ public void Await()
 $@"Microsoft (R) Visual C# Interactive Compiler version {CompilerVersion}
 Copyright (C) Microsoft Corporation. All rights reserved.
 
+Type ""#help"" for more information.
 > async Task<int[]> GetStuffAsync()
 . {{
 .   return new int[] {{ 1, 2, 3, 4, 5 }};
@@ -76,6 +77,7 @@ public void Exception()
 $@"Microsoft (R) Visual C# Interactive Compiler version {CompilerVersion}
 Copyright (C) Microsoft Corporation. All rights reserved.
 
+Type ""#help"" for more information.
 > int div(int a, int b) => a/b;
 > div(10, 2)
 5
@@ -101,6 +103,7 @@ public void Args()
 $@"Microsoft (R) Visual C# Interactive Compiler version {CompilerVersion}
 Copyright (C) Microsoft Corporation. All rights reserved.
 
+Type ""#help"" for more information.
 > foreach (var arg in Args) Print(arg);
 ""arg1""
 ""arg2""
@@ -200,5 +203,29 @@ public void ResponseFile()
                 "System.Text",
             }, arguments.CompilationOptions.Usings.AsEnumerable());
         }
+
+        [Fact]
+        public void HelpCommand()
+        {
+            var runner = CreateRunner(input:
+@"#help
+");
+            runner.RunInteractive();
+
+            Assert.Equal(
+$@"Microsoft (R) Visual C# Interactive Compiler version {CompilerVersion}
+Copyright (C) Microsoft Corporation. All rights reserved.
+
+Type ""#help"" for more information.
+> #help
+Keyboard shortcuts:
+  Enter         If the current submission appears to be complete, evaluate it.  Otherwise, insert a new line.
+  Escape        Clear the current submission.
+  UpArrow       Replace the current submission with a previous submission.
+  DownArrow     Replace the current submission with a subsequent submission (after having previously navigated backwards).
+REPL commands:
+  #help         Display help on available commands and key bindings.
+> ", runner.Console.Out.ToString());
+        }
     }
 }

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

@@ -163,6 +163,8 @@ private int RunScript(ScriptOptions options, string code, string scriptPath, Err
 
         private void RunInteractiveLoop(ScriptOptions options, CancellationToken cancellationToken)
         {
+            _console.Out.WriteLine(ScriptingResources.HelpPrompt);
+
             var globals = new InteractiveScriptGlobals(_console.Out, _objectFormatter);
             globals.Args.AddRange(_compiler.Arguments.ScriptArguments);
 
@@ -207,6 +209,12 @@ private void RunInteractiveLoop(ScriptOptions options, CancellationToken cancell
 
                 string code = input.ToString();
 
+                if (IsHelpCommand(code))
+                {
+                    DisplayHelpText();
+                    continue;
+                }
+
                 Script<object> newScript;
                 if (state == null)
                 {
@@ -329,6 +337,19 @@ private static bool IsTaskAwaiter(Type type)
             return false;
         }
 
+        private static bool IsHelpCommand(string text)
+        {
+            const string helpCommand = "#help";
+            return text != null &&
+                   text.TrimStart().TrimEnd() == helpCommand;
+        }
+
+        private void DisplayHelpText()
+        {
+            _console.Out.Write(ScriptingResources.HelpText);
+            _console.Out.WriteLine();
+        }
+
         private void DisplayDiagnostics(IEnumerable<Diagnostic> diagnostics)
         {
             const int MaxDisplayCount = 5;

src/Scripting/Core/ScriptingResources.Designer.cs

@@ -11,8 +11,8 @@
 namespace Microsoft.CodeAnalysis.Scripting {
     using System;
     using System.Reflection;
-
-
+    
+    
     /// <summary>
     ///   A strongly-typed resource class, for looking up localized strings, etc.
     /// </summary>
@@ -142,6 +142,30 @@ internal class ScriptingResources {
             }
         }
         
+        /// <summary>
+        ///   Looks up a localized string similar to Type &quot;#help&quot; for more information..
+        /// </summary>
+        internal static string HelpPrompt {
+            get {
+                return ResourceManager.GetString("HelpPrompt", resourceCulture);
+            }
+        }
+        
+        /// <summary>
+        ///   Looks up a localized string similar to Keyboard shortcuts:
+        ///  Enter         If the current submission appears to be complete, evaluate it.  Otherwise, insert a new line.
+        ///  Escape        Clear the current submission.
+        ///  UpArrow       Replace the current submission with a previous submission.
+        ///  DownArrow     Replace the current submission with a subsequent submission (after having previously navigated backwards).
+        ///REPL commands:
+        ///  #help         Display help on available commands and key bindings..
+        /// </summary>
+        internal static string HelpText {
+            get {
+                return ResourceManager.GetString("HelpText", resourceCulture);
+            }
+        }
+        
         /// <summary>
         ///   Looks up a localized string similar to Invalid assembly name.
         /// </summary>

src/Scripting/Core/ScriptingResources.resx

@@ -146,4 +146,16 @@
   <data name="CannotSetConstantVariable" xml:space="preserve">
     <value>Cannot set a constant variable</value>
   </data>
+  <data name="HelpPrompt" xml:space="preserve">
+    <value>Type "#help" for more information.</value>
+  </data>
+  <data name="HelpText" xml:space="preserve">
+    <value>Keyboard shortcuts:
+  Enter         If the current submission appears to be complete, evaluate it.  Otherwise, insert a new line.
+  Escape        Clear the current submission.
+  UpArrow       Replace the current submission with a previous submission.
+  DownArrow     Replace the current submission with a subsequent submission (after having previously navigated backwards).
+REPL commands:
+  #help         Display help on available commands and key bindings.</value>
+  </data>
 </root>
\ No newline at end of file