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Lua and Ravi 5.3 Debug Adapter for VSCode

This project aims to provide a debug adapter that allows Microsoft's Visual Studio Code to step through Ravi or Lua 5.3 code.

Debugger in Action


This is work in progress. The basic debugger is working with following features and limitations.

  • Launch a Ravi/Lua 5.3 script and stop on entry
  • Step through code
  • Set breakpoints at line/source level (upto a max of 20 breakpoints)
  • Local variables and variable arguments are shown in the Variables window; number of variables displayed is limited to 250
  • Tables are expanded to first few levels only - expansion limited to 250 elements
  • Lua stdout and stderr are redirected to the debugger
  • The debugger can step into dynamically generated Lua code
  • Support limited to x86-64 Windows 10, Ubuntu and OSX platforms
  • Unlike other Lua debuggers this implementation uses a custom Ravi VM, with extensions to support debugging
  • Various limitations - see list below

Note: This is work in progress so please expect bugs!


You can install the Ravi Debug extension from VSCode Marketplace - search for 'Lua and Ravi 5.3 Debugger'. Pre-built X86 64-bit binaries for Windows 10, OS X Mojave, and Ubuntu 14.04 are included in the installation - note that these do not have JIT enabled.

Issues and Limitations

  • The 'pause' function does not work, i.e. you cannot pause a running script
  • In all cases the number of variables or table entries displayed is truncated to 250 items
  • The stack trace is truncated to 50 items
  • Only upto 20 breakpoints can be set
  • You cannot set a breakpoint against a dynamically generated Lua function
  • You may not be able to debug Lua 5.0, 5.1 or 5.2 scripts - only 5.3 is tested and officially supported
  • Table variables can only be expanded to the first few levels
  • You cannot attach to a script already running somewhere
  • When the debugger runs the Lua Hook is disabled - so the running script is not allowed to modify the hook
  • Evaluating expressions is not supported
  • You cannot modify the variables displayed - the values are readonly
  • If you amend/edit the script being debugged it will not be recognised in the debug session so you will need to start a new session to recognise changes
  • Using LUA_PATH and LUA_CPATH has been tested briefly. When using LUA_CPATH you need to ensure that the native shared libraries are available on the system path; otherwise library dependencies can fail to be loaded.

Recent changes

  • Jul 2021: Updated to fix breaking change in VS Code Debug extension for breakpoints in 1.53 (breaking change in 1.42). Also revised the mechanism for supplying arguments to the script.
  • Jul 2020: Updated Ravi to 1.0 Beta4a
  • Dec 2019: Updated Ravi to latest version, added support for arguments to launch script
  • Feb 2017: Since VSCode 1.8 there is a bug in VSCode that messes up output to stdout - added a workaround for this bug. Details of bug are at issue #17526
  • Feb 2017: The debugger is now synced with Lua 5.3.4
  • Oct 2016: Added support for expanding tables to more than 1 level but still limited to first 4 or 5 levels
  • Oct 2016: Display of variable types - if __name metamethod is defined for user defined types then this is used
  • Oct 2016: Display of variable contents - if __tostring metamethod is defined for user defined types then this is used
  • Oct 2016: Variable type names are passed to VSCode so that these get displayed by the UI

Getting Started

Once you have installed the extension, you will need to setup launch.json as shown in the steps below.

First Launch

Select Ravi Debugger

Configure launch.json

See also

Ravi Programming Language

Implementation Notes

The debugger is a standalone executable that can be invoked by VSCode. VSCode communicates with the debugger via stdin/stdout as per the VSCode debug adapter API which uses JSON messages exchanged between VSCode and the debugger.


VSCode Debug Adapter for Ravi / Lua 5.3



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