`pcall` captures errors differently when debugging

[eduardomezencio]

(while writing this report, I messed aroung a little to make sure I was not missing anything stupid and ended up finding a solution, so I'll open a PR myself soon. I still decided to open the issue to document it and reference in the PR)

Normally in lua, when you pass a table to the error function and pcall catches this error, the result returned by pcall is the table itself. When debugging with local-lua the result will be a string. This breaks programs that use these tables for complex error handling. I don't know if this is a known side-effect or "feature" of the debugger, but I couldn't find anything on the docs about this.

I observed this debugging with luajit and with lua5.3. Here's a code to reproduce the problem:

local function f()
  error {'a table', x = true}
end

local success, result = pcall(f)
print(success, result)

If you're debugging, result will be a string, otherwise it will be the table it was supposed to be.