Bug

There is a panic slice bounds out of range in ImmediateLineWriter.WritePrefixedLines cause regex.FindAllStringIndex returns byte indexes and we try to match these indexes in slice of runes which is incorrect when input string has 2 byte symbols.

Way to reproduce

windows (git bash)

seq 1 2 | ./rush --immediate-output printf "один123\nдва1234\nтри123\n"

macOS

seq 1 2 | ./rush --immediate-output echo -e "один123\nдва1234\nтри123\n"

or this simple test demonstrates it

package process

import (
	"sync"
	"testing"
)

func TestImmediateLineWriter_WritePrefixedLines(t *testing.T) {
	const inputThatPanics = `один123
два1234
три123
`
	t.Run("panic occurs", func(t *testing.T) {
		lw := &ImmediateLineWriter{
			lock:    &sync.Mutex{},
			numJobs: 2,
		}

		lw.WritePrefixedLines(inputThatPanics, nil)
	})
}

Fix

By removing unnecessary casting input string to []rune: regex.FindAllStringIndex returns byte indexes so we can directly access string parts by these indexes.