Conditionally Building the Application

To keep the examples in this chapter clear and easier to follow, copy the existing version of the Pomodoro application you built to a new working environment.

This ensures your application source files will match the description provided in this chapter. If you want to continue developing the Pomodoro application in its original directory, make sure you’re changing the appropriate files and adding new files to the correct path relative to the original directory.

We can continue developing our application from the same point. Because we’re using Go modules, we don’t need to take any extra actions. Go modules will resolve the modules to the current directory for us automatically.

Updating the go.mod file

To use our notify package to send out notifications with the Pomodoro app, we add the dependency to the file go.mod under the subdirectory pomo. Also, because our packages are local only, replace the path to the package pointing it to the local directory with its source code, by using the replace directive:

This last step wouldn’t be necessary if the package was available on an external Git repository, as the Go tools would download it when required.

Now we add the notification functionality in the package app, but let’s make it optional. When the users are building the application, it will include the notification by default, but the user can disable it by providing the build tag disable_notification.

To do this, instead of calling package notify directly, we’ll add a helper function send_notification(). By default, this function calls notify and sends out the notification. We’ll also deploy a second version of this function that doesn’t do anything in another file using the build tag disable_notification.

Go accepts multiple build tags for a single file. We separate the tags with spaces to evaluate them with an OR condition, which means Go includes the file if the user provides any of the tags. For an AND condition, we separate the tags with a comma, in which case Go will include the file if the user provides all the tags.

Updating the notification_stub.go file

Let’s use this idea to build the notification integration. First, we add the stub function that does nothing by adding a new file notification_stub.go under the directory pomo/app. We define the condition to include this file in the build by adding the build tags disable_notification and containers, separated ...