Long story short, documentation for CMake related features in Visual Studio 2017 sucks. It’s scattered among a ton of blog post where most of the code samples are outdated or contain errors. Here is an example launch.vs.json that I’m using for reference:

{
	"version": "0.2.1",
	"defaults": {},
	"configurations": [
		{
			"type": "Debug",
			"project": "CMakeLists.txt",
			"projectTarget": "foo.exe",
			"name": "foo.exe",

			// currentDir and not cwd like we can read in most examples ...
			"currentDir": "${workspaceRoot}",

			// this one is pretty straightforward
			"args": [ "arg0", "arg1" ],

			// env overwrites all the environment variables ...
			// separate vars by a null (\u0000) character. You can use existing env vars, see PATH
			"env": "TEST_ENV=foo\u0000HELLO=World\u0000PATH=${env.PATH};${workspaceRoot}"
		}
	]
}