Lua hook-like call AFTER line processing

Question

Lua features hook call BEFORE every processed line. What I need is a call AFTER line is processed, so that I can check for encountered errors and so on. Is there a way to make such kind of call?

Otherwise things get a little bit confusing if error is encountered at the last line of the script. I don't get any feedback.

UPDATE #1 We want to catch both Lua errors and 'our' errors asserted via lua_error(*L) C interface, and Lua should throw correct debug info including the line number where the error occurred.

Using return hook we always get error line number -1, which is not what we want. Using any combination of pcall and any hook setup after lua_error(*L) we get either line number -1, or number of the next executed line, never a correct one.

SOLUTION# We managed to make everything work. The thing was that Lua throws a real C exception after it detects an error, so some of our 'cleaning & finalizing' C code called from Lua operation did not execute, which messed up some flags and so on. The solution was to execute 'cleaning code' right before calling lua_error(...). This is correct and desired Lua behavior as we really want to stop executing the function once lua_error(...) is called, it was our mistake to expect any code would be executed after lua_error(...) call.

Tnx Paul Kulchenko, some of this behavior was found while trying to design a simple example script which reproduces the problem.

Before every processed line <=> before starting and then after every processed line but the last — Deduplicator, Aug 25 '14 at 13:26

lhf · Answer 1 · 2014-08-25T13:05:42.027

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Try setting a return hook: it'll be called after the last line is executed.

edited Aug 25 '14 at 13:05

answered Aug 25 '14 at 12:33

lhf

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Thank you for your answer. I updated the question with some addition info. – ahrvoje Aug 27 '14 at 11:50

score 0 · Answer 2 · answered Aug 26 '14 at 06:18

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I'm not sure debug hook is the best solution for what you are trying to do (or you need to provide more details). If you just need to check for run-time errors, why use debug hooks at all if you can run your code with pcall and get an error message that points to the line number where the error happened (or use xpcall, which also allows you to get a stack trace)? You can combine this with debug.getinfo(func, "L") to get a table whose indexes are valid line numbers for the function.

answered Aug 26 '14 at 06:18

Paul Kulchenko

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We also want to use it for 'our' error asserted via lua_error(*L), and nothing seems to work correctly. I updated the question. – ahrvoje Aug 27 '14 at 11:52
You'll need to come with a simple script that shows the issue. – Paul Kulchenko Aug 27 '14 at 15:40

Lua hook-like call AFTER line processing

2 Answers2