Unhide the cursor before exiting for interrupt signals

[zimeg]

Summary

This PR unhides the cursor after an interrupt signal is sent while the spinner is active to prevent the cursor from disappearing in some terminals.

All of the signals listened for before termination are os.Interrupt and a custom syscall.Signal(0x0).

The syscall.Signal(0x0) is used to signal a successful .Stop() of the spinner and can safely be used as a termination signal since it doesn't send an actual signal, it only checks that the current process exists.

Preview

On some terminals, pressing CTRL-C would quit the program without unhiding the cursor. This example is shown with ANSI terminal:

Before changes

before.mov

After changes

after.mov

Reviewers

A small program to test with is ready in this repo to verify various exit codes and conditions in certain cases. Different testing cases are listed in SIGNALS.md if you want to try these yourself!

While multiple signals are noted in the link above, only the interrupt - ^C - is supported in these changes.

[kernel-sanders]

This solves my biggest problem with this library!

Unfortunately, it doesn't compile on Windows: spinner/spinner.go:359:14: undefined: syscall.Kill

[vaaleyard]

@briandowns please consider this

[briandowns]

I'd consider this if it can be achieved without breaking windows and also scoping the change to the code without all of the other updates. It's a fine change but this PR is a bit bloated and breaks too many users.

[zimeg]

Unfortunately, it doesn't compile on Windows: spinner/spinner.go:359:14: undefined: syscall.Kill

@kernel-sanders Thanks for giving this a test run 🙏 I can confirm this was happening with the following commands and have also made changes to fix this in fbe5c85:

$ gh repo clone zimeg/spinners
$ cd spinners
$ GOOS=windows make build

Lot's more learnings about syscall and the strangenesses within, but I'll leave a comment with the important change 📚

I'd consider this if it can be achieved without breaking windows and also scoping the change to the code without all of the other updates. It's a fine change but this PR is a bit bloated and breaks too many users.

@briandowns And thanks for giving this a look 👾 I made a few changes to tidy things with support for Windows, but please do let me know if other changes make sense!

[zimeg]

TIL os.Interrupt is the only signal available across all os packages! Reference 📚 ✨

Instead of checking unique syscall values that might not exist, including SIGQUIT, only the standard interrupt is caught here.

This means the cursor won't be unhidden for all termination signals, but IMO covering the ^C case seems ideal 🤖

[jallard-007]

Why not register a signal handler and pass down context.Context to avoid a hard exit? This would avoid breaking users.