Make RegexParseException public

[OskarKlintrot]

I'm trying to validate a regex pattern but I can't catch System.Text.RegularExpressions.RegexParseException since it's internal.

I can solve it by using pattern matching but it feels like a bodge:

private static bool IsValidRegex(string pattern)
{
    if (string.IsNullOrEmpty(pattern))
    {
        return false;
    }

    try
    {
        Regex.Match(string.Empty, pattern);
    }
    catch (Exception ex)
        when (ex is ArgumentException)
    {
        return false;
    }

    return true;
}

[stephentoub]

I'm not clear on the concern. It's documented to throw an ArgumentException:

Exceptions
ArgumentException
A regular expression parsing error occurred.

and it does. You can just catch an ArgumentException.

What's the concern?

[danmoseley]

RegexParseException contains the RegexParseError and the Offset. The ArgumentException contains these (hopefully always) only in the text of the message,.eg

Invalid pattern 'asdfasdf[asdfasdf' at offset 17. Unterminated [] set.

I am actually not sure why it exists as we do not catch it and we do not pull off either of those values from it. We could delete it in favor of using ArgumentException directly, or make it public to expose one or both of these things (note that RegexParseError is internal)

When VS itself squiggles the offset in the regex, I believe it's implemented using a clone of our regex parsing code, and it may be getting the offset out of the RegexParseException rather than parsing the message.

[danmoseley]

But to @stephentoub question -- @OskarKlintrot what are you trying to achieve?

[OskarKlintrot]

I have no clue what I'm doing. I could not get it to work yesterday. Today I noticed I had Common Language Runtime Exceptions set to all so I restored it to default and tried again and then it works just fine! When I select all again it still works! Looks like a PEBKAC or a glitch somewhere yesterday :)

[danmoseley]

I see. It’s still probably worth an issue to discuss exposing the offset. If we don’t, we can probably do some cleanup to remove the type.