String.gsub error

when I attempt to call string.gsub like so:

string.gsub(a_string, "(%a+)%s*(%b())", "any string, table, or function")

It causes the error: vm error: java.lang.ArrayIndexOutOfBoundsException: N, on the line number of the string.gsub call (N is the number of characters in a_string), when a_string both starts and ends with a letter.

This happens whether the '(' and ')' in %b() are escaped or not.

I think it might be a bug, but I'm posting it here in case I'm just doing something wrong.

Interesting. I can reproduce this. I suppose a possible workaround would be to make your own substitution function using string.gmatch or similar, to avoid this issue.

Further investigation suggests that the %bxy pattern is the problematic portion. May I ask what sort of string transformations you're using this for?

I'm matching parentheses to detect functions in my calculator program and catch nonexistent functions, as well as remove any arguments past the number the function takes.

Ah. Well, you may have better luck going through the string a bit more slowly. It might be worth posting a bug report down in the Bugs section, though I think that if this is a bug, it's most likely a bug in LuaJ, so there wouldn't be much that dan200 or Cloudy could do about it.