[1.481] string.find() pattern %b throws Java error unless matched

Say I'm trying to match something like a function call. Here's what I expect to happen (based on Lua's behavior outside Minecraft):

lua> print(string.find("abc(123)", "([%w_]+)(%b())"))
1   8   abc   (123)

lua> print(string.find("abc", "([%w_]+)(%b())"))
nil

But here's what I get in CC:

lua> print(string.find("abc(123)", "([%w_]+)(%b())"))
18abc(123)

lua> print(string.find("abc", "([%w_]+)(%b())"))
lua:1: vm error:
java.lang.ArrayIndexOutOfBoundsException

From what I can tell, using %b in your search pattern always throws that Java error unless a match is found (in which case it does what it's supposed to).

Yep, this is one of the bugs in LuaJ's string library. The workaround is to append a match to the end of the string and discard the match if it's the one you appended. Obviously, this works better when you're ONLY looking for %b() and no other matches, since you can use the numeric returns and check whether or not they're #str + 1 and #str + 2 respectively (given str being the string to match, and the find being run against str.."()").

That worked perfectly to fix a show-stopping bug with my replacement Lua shell. Can't have your shell crashing every time you give the wrong number of parameters to a macro.

Thanks for the workaround Lyqyd!