Address Copilot review comments for serverlist command

- Use strings.TrimSpace in serverlistCommand for consistency
- Fix test formatting to put each test case on its own line
- Add InstanceName validation before using as map key
- Document :serverlist command in README.md

Author: dlevy-msft-sql

README.md

@@ -155,6 +155,7 @@ switches are most important to you to have implemented next in the new sqlcmd.
 - The new `--driver-logging-level` command line parameter allows you to see traces from the `go-mssqldb` client driver. Use `64` to see all traces.
 - Sqlcmd can now print results using a vertical format. Use the new `--vertical` command line option to set it. It's also controlled by the `SQLCMDFORMAT` scripting variable.
 - `:help` displays a list of available sqlcmd commands.
+- `:serverlist` lists local SQL Server instances discovered via the SQL Server Browser service.
 
 ```
 1> select session_id, client_interface_name, program_name from sys.dm_exec_sessions where session_id=@@spid

pkg/sqlcmd/commands.go

@@ -657,7 +657,7 @@ go [<n>]
 }
 
 func serverlistCommand(s *Sqlcmd, args []string, line uint) error {
-	if len(args) > 0 && args[0] != "" {
+	if len(args) > 0 && strings.TrimSpace(args[0]) != "" {
 		return InvalidCommandError("SERVERLIST", line)
 	}
 	ListLocalServers(s.GetOutput())

pkg/sqlcmd/commands_test.go

@@ -55,8 +55,10 @@ func TestCommandParsing(t *testing.T) {
 		{`:RESET`, "RESET", []string{""}},
 		{`RESET`, "RESET", []string{""}},
 		{`:HELP`, "HELP", []string{""}},
-		{`:help`, "HELP", []string{""}}, {`:SERVERLIST`, "SERVERLIST", []string{""}},
-		{`:serverlist`, "SERVERLIST", []string{""}}}
+		{`:help`, "HELP", []string{""}},
+		{`:SERVERLIST`, "SERVERLIST", []string{""}},
+		{`:serverlist`, "SERVERLIST", []string{""}},
+	}
 
 	for _, test := range commands {
 		cmd, args := c.matchCommand(test.line)

pkg/sqlcmd/serverlist.go

@@ -94,7 +94,10 @@ func parseInstances(msg []byte) msdsn.BrowserData {
 					if len(instanceDict) == 0 {
 						break
 					}
-					results[strings.ToUpper(instanceDict["InstanceName"])] = instanceDict
+					// Only add if InstanceName key exists and is non-empty
+					if instName, ok := instanceDict["InstanceName"]; ok && instName != "" {
+						results[strings.ToUpper(instName)] = instanceDict
+					}
 					instanceDict = map[string]string{}
 					continue
 				}