Debug HC3 Lua in VS Code — breakpoints included

The HC3 web editor gives you self:debug prints and not much else. flua gives you a real debugger: breakpoints, step over/into, call stacks, and variable inspection — in VS Code, on the QA code you are editing, no changes to the file.

If you ran flua --tool setup (post 1), the launch configurations are already in .vscode/launch.json:

• Flua: Run Current File — run, log in the terminal
• Flua: Run Current File (UI) — run + UI viewer in the browser
• Flua: Debug Current File (mobdebug) — breakpoints, stepping, variables
• Flua: Debug Current File (UI+mobdebug) — the debugger and the viewer together

Press F5 with a .lua file open, or pick a configuration from the Run and Debug panel. Put a breakpoint on any line of onInit, start "Debug Current File (UI+mobdebug)", and VS Code stops there — before anything else runs. You can then step through your QA line by line, hover variables, and watch self, while the UI viewer sits in the browser showing the device you are debugging.

Two flua-specific niceties you get for free:

• The virtual clock pauses while you think. Step slowly through a QA with timers — nothing fires while the debugger is stopped, so the state you are inspecting is exactly the state at the breakpoint, and the run resumes from where you left it.
• You debug against the simulated HC3. api.get, fibaro.call, UI events — everything the QA touches is fake, so a misbehaving QA can never turn the house on and off while you are stepping through it.

Prefer the terminal? No setup needed:

flua --debugger 8172 quickapp.lua

...and attach a debugger client to port 8172 — the same protocol the mobdebug VS Code extension speaks, so the extension works out of the box.

There is also a static check for the quick wins before you even run:

flua --check quickapp.lua   # syntax, --%% directive typos, deprecated APIs

Next post: stop testing one QA at a time — run a whole house full of devices in a single flua process.

flua: https://github.com/jangabrielsson/flua · setup guide: USAGE.md