Bug Report: Unescape(Escape()) does not return the original string in go/sqlescape

[Maniktherana]

Overview of the Issue

EscapeID for the string a`a returns `a``a` but UnescapeID doesn't reverse it. Currently, it simply returns a``a, removing the outer backticks without halving the ones inside the string.

related: #14987

Reproduction Steps

run this code:

package main

import (
	"fmt"

	"vitess.io/vitess/go/sqlescape"
)

func main() {
	str := "a`a"
	escaped := sqlescape.EscapeID(str)
	unescaped := sqlescape.UnescapeID(escaped)
	unescaped2 := sqlescape.UnescapeID("`a`a`")
	fmt.Printf("String: %s\nEscaped: %s\nUnescaped: %s\nUnescaped2: %s", str, escaped, unescaped, unescaped2)
}

output should be:

String: a`a
Escaped: `a``a`
Unescaped: a``a
Unescaped2: a`a

Binary Version

vtgate version Version: 18.0.3-SNAPSHOT

Operating System and Environment details

- Operating system macOS 14.0
- Kernel version Darwin 23.0.0
- Architecture arm64

Log Fragments

No response

[Maniktherana]

If this is a bug, I'd be happy to patch it while working on tests for go/sqlescape

[systay]

this looks like a real bug. thanks for taking it on!

if possible, make the bug fix into a separate PR. That makes it much easier to back port the fix to earlier releases.