improve kql and sql connection experience

src/Microsoft.DotNet.Interactive.Kql.Tests/KqlConnectionTests.cs

@@ -68,6 +68,65 @@ public async Task It_can_connect_and_query_data()
                                                          e.FormattedValues.Any(f => f.MimeType == HtmlFormatter.MimeType));
     }
 
+    [KqlFact]
+    public async Task It_does_not_add_a_kernel_on_connection_failure()
+    {
+        var cluster = KqlFactAttribute.GetClusterForTests();
+        using var kernel = await CreateKernelAsync();
+        var result = await kernel.SubmitCodeAsync(
+            "#!connect kql --kernel-name KustoHelp --cluster \"invalid_cluster\" --database \"Samples\"");
+
+        result.Events
+            .Should()
+            .ContainSingle<CommandFailed>();
+
+        var kqlKernel = kernel.FindKernelByName("kql-KustoHelp");
+
+        kqlKernel.Should().BeNull();
+    }
+
+    [KqlFact]
+    public async Task It_allows_to_retry_connecting()
+    {
+        var cluster = KqlFactAttribute.GetClusterForTests();
+        using var kernel = await CreateKernelAsync();
+        var result = await kernel.SubmitCodeAsync(
+            "#!connect kql --kernel-name KustoHelp --cluster \"invalid_cluster\" --database \"Samples\"");
+
+        result.Events
+            .Should()
+            .ContainSingle<CommandFailed>();
+
+        result = await kernel.SubmitCodeAsync(
+            $"#!connect kql --kernel-name KustoHelp --cluster \"{cluster}\" --database \"Samples\"");
+
+        result.Events
+            .Should()
+            .NotContainErrors();
+    }
+
+    [KqlFact]
+    public async Task It_gives_error_if_kernel_name_is_already_used()
+    {
+        var cluster = KqlFactAttribute.GetClusterForTests();
+        using var kernel = await CreateKernelAsync();
+        var result = await kernel.SubmitCodeAsync($"#!connect kql --kernel-name KustoHelp --cluster \"{cluster}\" --database \"Samples\"");
+
+        result.Events
+            .Should()
+            .NotContainErrors();
+
+        result = await kernel.SubmitCodeAsync($"#!connect kql --kernel-name KustoHelp --cluster \"{cluster}\" --database \"Samples\"");
+
+        result.Events
+            .Should()
+            .ContainSingle<CommandFailed>()
+            .Which
+            .Message
+            .Should()
+            .Contain("A kernel with name KustoHelp is already present. Use a different value for the kernel-name option.");
+    }
+
     [KqlFact]
     public async Task It_can_store_result_set_with_a_name()
     {

src/Microsoft.DotNet.Interactive.Kql/ConnectKqlCommand.cs

@@ -1,6 +1,7 @@
 // Copyright (c) .NET Foundation and contributors. All rights reserved.
 // Licensed under the MIT license. See LICENSE file in the project root for full license information.
 
+using System;
 using System.CommandLine;
 using System.CommandLine.Invocation;
 using System.Threading.Tasks;
@@ -40,6 +41,14 @@ public ConnectKqlCommand(string resolvedToolsServicePath)
 
         var localName = commandLineContext.ParseResult.GetValueForOption(KernelNameOption);
 
+        var found = context?.HandlingKernel?.RootKernel.FindKernelByName($"kql-{localName}") is not null;
+
+        if (found)
+        {
+            throw new InvalidOperationException(
+                $"A kernel with name {localName} is already present. Use a different value for the {KernelNameOption.Name} option.");
+        }
+
         var kernel = await connector.CreateKernelAsync(localName);
 
         return kernel;

src/Microsoft.DotNet.Interactive.SqlServer.Tests/MsSqlConnectionTests.cs

@@ -70,6 +70,64 @@ public async Task It_can_connect_and_query_data()
                                                          e.FormattedValues.Any(f => f.MimeType == HtmlFormatter.MimeType));
     }
 
+    [MsSqlFact]
+    public async Task It_does_not_add_a_kernel_on_connection_failure()
+    {
+        var connectionString = MsSqlFactAttribute.GetConnectionStringForTests();
+        using var kernel = await CreateKernelAsync();
+        var result = await kernel.SubmitCodeAsync("#!connect mssql --kernel-name adventureworks \"invalid_connection_string\"");
+
+        result.Events
+            .Should()
+            .ContainSingle<CommandFailed>();
+
+        var kqlKernel = kernel.FindKernelByName("sql-adventureworks");
+
+        kqlKernel.Should().BeNull();
+    }
+
+    [MsSqlFact]
+    public async Task It_allows_to_retry_connecting()
+    {
+        var connectionString = MsSqlFactAttribute.GetConnectionStringForTests();
+        using var kernel = await CreateKernelAsync();
+        var result = await kernel.SubmitCodeAsync("#!connect mssql --kernel-name adventureworks \"invalid_connection_string\"");
+
+        result.Events
+            .Should()
+            .ContainSingle<CommandFailed>();
+
+        result = await kernel.SubmitCodeAsync(
+            $"#!connect mssql --kernel-name adventureworks \"{connectionString}\"");
+
+        result.Events
+            .Should()
+            .NotContainErrors();
+    }
+
+    [MsSqlFact]
+    public async Task It_gives_error_if_kernel_name_is_already_used()
+    {
+        var connectionString = MsSqlFactAttribute.GetConnectionStringForTests();
+        using var kernel = await CreateKernelAsync();
+        var result = await kernel.SubmitCodeAsync($"#!connect mssql --kernel-name adventureworks \"{connectionString}\"");
+
+        result.Events
+            .Should()
+            .NotContainErrors();
+
+        result = await kernel.SubmitCodeAsync(
+            $"#!connect mssql --kernel-name adventureworks \"{connectionString}\"");
+
+        result.Events
+            .Should()
+            .ContainSingle<CommandFailed>()
+            .Which
+            .Message
+            .Should()
+            .Contain("\"A kernel with name adventureworks is already present. Use a different value for the kernel-name option.\"");
+    }
+
     [MsSqlFact]
     public async Task null_values_are_preserved_as_null_references()
     {

src/Microsoft.DotNet.Interactive.SqlServer/ConnectMsSqlCommand.cs

@@ -1,6 +1,7 @@
 // Copyright (c) .NET Foundation and contributors. All rights reserved.
 // Licensed under the MIT license. See LICENSE file in the project root for full license information.
 
+using System;
 using System.Collections.Generic;
 using System.CommandLine;
 using System.CommandLine.Invocation;
@@ -43,6 +44,14 @@ public ConnectMsSqlCommand(string resolvedToolsServicePath)
 
         var localName = commandLineContext.ParseResult.GetValueForOption(KernelNameOption);
 
+        var found = context?.HandlingKernel?.RootKernel.FindKernelByName($"sql-{localName}") is not null;
+
+        if (found)
+        {
+            throw new InvalidOperationException(
+                $"A kernel with name {localName} is already present. Use a different value for the {KernelNameOption.Name} option.");
+        }
+
         var kernel = await connector.CreateKernelAsync(localName);
 
         if (connector.CreateDbContext)