Ignore ANSI sequences when measuring string width

[zimeg]

Summary

Hello! This PR updates the computeNumberOfLinesNeededToPrintStringInternal function to ignore ANSI sequences from the string width measurement since these are not visibly printed to the terminal.

Currently, ANSI sequences are included in this measurement which can cause the computed number of lines to be greater than the actual number of lines needed to print a string. When this happens, previous lines are unexpectedly erased from the screen.

Demo

Before changes

before.mov

After changes

after.mov

Reviewers

The following snippet can be used to demonstrate the erasure behavior on a terminal of width 80:

package main

import (
	"time"

	"github.com/briandowns/spinner"
)

func main() {
	s := spinner.New(spinner.CharSets[9], 100*time.Millisecond)
	s.Suffix = " \x1b[36mHere we are.\x1b[0m Waiting ever so \x1b[1;33mpatiently\x1b[0m as we watch the spinner spin."

	s.Start()
	time.Sleep(2 * time.Second)
	s.Stop()
}

To test these changes, checkout this branch and update your go.mod to include:

replace github.com/briandowns/spinner v1.20.0 => ../path-to-branch/spinner

Notes

• The computeNumberOfLinesNeededToPrintStringInternal function was updated to measure the line count in an iterative manner.
• Tests for the computeNumberOfLinesNeededToPrintStringInternal function were updated to use a table-driven testing approach. New tests were also added for checking expected behavior of strings containing ANSI sequences.

[briandowns]

Thank you for this!

[shinji62]

@briandowns Can we get a new release ? I am impacted by this issues as well.

[briandowns]

All set @shinji62 ! https://github.com/briandowns/spinner/releases/tag/v1.21.0

[shinji62]

Wow that's was fast !

[mwbrooks]

Fantastic, thank you for the release @briandowns! 🙇🏻 🚀

[briandowns]

No prob. :D