Establish conn to curret-context if no args given (#261)

sqlcmd when invoked with no arguments, executes in backward compat mode
 and ignores current-context info for establishing connection. This 
commit changes the default behavior to establish connection to the endpoint 
associated with current-context in sqlcmd config file by setting SQLCMDSERVER,
 SQLCMDUSER, SQLCMDPASSWORD as env variables.
If these env variables are already set then their values are not overridden.
This ensures that users can connect to sql server instance pointed by 
current-context if sqlcmd is invoked with no arguments.

Author: apoorvdeshmukh

cmd/modern/main.go

@@ -45,10 +45,32 @@ func main() {
 		cmdparser.Initialize(initializeCallback)
 		rootCmd.Execute()
 	} else {
+		initializeEnvVars()
 		legacyCmd.Execute(version)
 	}
 }
 
+// initializeEnvVars intializes SQLCMDSERVER, SQLCMDUSER and SQLCMDPASSWORD
+// if the currentContext is set and if these env vars are not already set.
+// In terms of precedence, command line switches/flags take higher precedence
+// than env variables and env variables take higher precedence over config
+// file info.
+func initializeEnvVars() {
+	initializeCallback()
+	if config.CurrentContextName() != "" {
+		server, username, password := config.GetCurrentContextInfo()
+		if os.Getenv("SQLCMDSERVER") == "" {
+			os.Setenv("SQLCMDSERVER", server)
+		}
+		if os.Getenv("SQLCMDUSER") == "" {
+			os.Setenv("SQLCMDUSER", username)
+		}
+		if os.Getenv("SQLCMDPASSWORD") == "" {
+			os.Setenv("SQLCMDPASSWORD", password)
+		}
+	}
+}
+
 // isFirstArgModernCliSubCommand is TEMPORARY code, to be removed when
 // we remove the Kong based CLI
 func isFirstArgModernCliSubCommand() (isNewCliCommand bool) {

internal/config/context.go

@@ -75,10 +75,12 @@ func CurrentContext() (endpoint Endpoint, user *User) {
 				}
 			}
 
-			for _, u := range config.Users {
-				if u.Name == *c.User {
-					user = &u
-					break
+			if UserExists(c) {
+				for _, u := range config.Users {
+					if u.Name == *c.User {
+						user = &u
+						break
+					}
 				}
 			}
 		}
@@ -94,6 +96,23 @@ func CurrentContext() (endpoint Endpoint, user *User) {
 	return
 }
 
+// GetCurrentContextInfo returns endpoint and basic auth info
+// associated with current context
+func GetCurrentContextInfo() (server string, username string, password string) {
+	endpoint, user := CurrentContext()
+	server = fmt.Sprintf("%s,%d", endpoint.Address, endpoint.Port)
+	if user != nil {
+		username = user.BasicAuth.Username
+		if user.AuthenticationType == "basic" {
+			password = decryptCallback(
+				user.BasicAuth.Password,
+				user.BasicAuth.PasswordEncrypted,
+			)
+		}
+	}
+	return
+}
+
 // DeleteContext removes the context with the given name from the application's
 // configuration. If the context does not exist, the function does nothing. The
 // function also updates the CurrentContext field in the configuration to the

internal/config/user.go

@@ -5,8 +5,9 @@ package config
 
 import (
 	"fmt"
-	. "github.com/microsoft/go-sqlcmd/cmd/modern/sqlconfig"
 	"strconv"
+
+	. "github.com/microsoft/go-sqlcmd/cmd/modern/sqlconfig"
 )
 
 // AddUser adds a new user to the configuration.
@@ -123,3 +124,9 @@ func userOrdinal(name string) (ordinal int) {
 	}
 	return
 }
+
+// UserExists checks if the current context has a 'user', e.g. a context used
+// for trusted authentication will not have a user.
+func UserExists(context Context) bool {
+	return context.ContextDetails.User != nil && *context.ContextDetails.User != ""
+}