Unquote function panics when an escape character exists in string.

[krum110487]

I found a bug in the function "unquote" where if there is a "\" in the string it fails.
Here is an example of it broken.

func main() {
	example := "'te\\st'"
	s, err := unquote(example)
	if err != nil {
		panic(err)
	}
	fmt.Println(s)
}

func unquote(s string) (string, error) {
	quote := s[0]
	s = s[1 : len(s)-1]
	out := ""
	for s != "" {
		value, _, tail, err := strconv.UnquoteChar(s, quote)
		if err != nil {
			return "", err
		}
		s = tail
		out += string(value)
	}
	return out, nil
}

I just pulled the unquote from the code to test it. I did this to fix it.

func unquote(s string) (string, error) {
	quote := s[0]
	s = s[1 : len(s)-1]
	out := ""
	for s != "" {
		if s[:1] == "\\" {
			out += "\\"
			s = s[1:len(s)]
			continue
		}
		value, _, tail, err := strconv.UnquoteChar(s, quote)
		if err != nil {
			return "", err
		}
		s = tail
		out += string(value)
	}
	return out, nil
}

Basically, the issue is if the string starts with a \, it will error in "UnquoteChar" which is why I am skipping it and manually adding it. Not sure if this is the "Best" approach, but it gets the point around.

It could also be fixed by replacing \\ with \\\\ before processing.

[alecthomas]

There may be a bug, but your test case is not one. In this case:

	example := "'te\\st'"

The Go parser is unquoting the \\, so what Participle sees is \s. If you change this to use backticks, Participle behaves as you would expect because Go is no longer unescaping:

	example := `'te\\st'`

[krum110487]

Why would my example be wrong, I was unquoting text which is sometimes regex which is literally a \s and not \\s and it errored, I know I can escape it, are you saying I have to escape all backslashes in strings by writing my own custom consumer? I would expect the built in unquoting to do fl that instead of erroring.

[alecthomas]

The builtin unquote uses Go's unquoting rules, which doesn't support \s. If you want to support something else you'll need to roll your own.

[krum110487]

The builtin unquote uses Go's unquoting rules, which doesn't support \s. If you want to support something else you'll need to roll your own.

got ya, ok I understand! Thank you for responding. May I recommend an EscapeQuoted String property than, to maybe allow it to work out of the box? Thank you!