Use ZeroBrane Studio. (And send the author a donation, no matter how small.)
“Unlike Eclipse and IntelliJ [and Visual Studio Code], it has a small footprint and is fully customizable with Lua. Unlike TextMate and Sublime Text, it includes a remote debugger and a full IDE feature set. Unlike Decoda, it runs on Windows, macOS, and Linux and supports various Lua versions with on-device debugging.”
It is *for* Lua, *in* Lua, can *run* Lua and visually *debug* Lua…
…and it will reliably highlight your code *as* Lua, including warning you about variables that shield others (or that are unshielded globals).
The editor inside it is based on Scintilla, so you already know how to use it.