This extension activates automatically when project's tsconfig.json file has "tstl" key.
transpiling to Lua. The TSTL extension will immediately warn you when this is the case, so that you
discover it at writing-time rather than at compile-time. For example:
Automatic tsconfig.json Schema
In most popular IDEs, you can specify a "$schema" key at the top of a JSON file. Doing this
activates auto-complete and field validation, which makes working with the JSON much easier.
One extra feature of VSCode is that if you happen to be working in a tsconfig.json file without
an explicitly defined "$schema" key, the editor will automatically use
the standard tsconfig schema.