Issue parsing Mix Standalone path on Windows

[ericsalim]

Environment

• Elixir & Erlang/OTP versions (elixir --version): Elixir 1.13.0 & Erlang/OTP 24
• Operating system: Windows
• How have you started Livebook (mix phx.server, livebook CLI, Docker, etc): Windows Command Line
• Livebook version (use git rev-parse HEAD if running with mix): 0.6.1
• Browsers that reproduce this bug (the more the merrier): N/A
• Include what is logged in the browser console: ERROR!!! [Livebook] "C" does not point to a Mix project
• Include what is logged to the server console: N/A

Current behavior

With Livebook 0.5, Mix Standalone runtime used to work fine. I set my environment variable like below:

SET LIVEBOOK_DEFAULT_RUNTIME=mix:C:/Users/my.name/livebook

After upgrading to the latest version, starting Livebook fails with this error:

ERROR!!! [Livebook] "C" does not point to a Mix project

I believe this is because the latest version adds support for [:FLAGS], messing file path splitting on Windows. Fortunately my Mix project lives on the same drive, so I can use /Users/my.name/livebook. But if my Mix project lives on another drive, then I see this as a blocking issue.

If this is an intended behavior and there's another way to do this, then the documentation should make this clearer.

Expected behavior

I expect either the file path to be parsed correctly, or the documentation to be made clearer.

[jonatanklosko]

One way I see is supporting quotes to resolve ambiguity, but in shell this will require nested quotes like LIVEBOOK_DEFAULT_RUNTIME="mix:'C:/Users/my.name/livebook'", which is not really intuitive. @josevalim any other ideas?

[josevalim]

Only split on the first : and let the runtime specific logic split on it again if necessary. I agree that the quotes are not very helpful, so we probably don’t need to support it.

[jonatanklosko]

The parsing is already runtime-specific

livebook/lib/livebook/config.ex

Lines 318 to 319 in 8f4cafe

	"mix:" <> config ->
	{path, flags} = parse_mix_config!(config)

It's just that there's a genuine ambiguity in mix:PATH[:FLAGS], because PATH may include :.

[josevalim]

Maybe move the flats to be first and we parse the known flags? -- *José Valimhttps://dashbit.co/ <https://dashbit.co/>*

[jonatanklosko]

Actually, the flags can also include a file path, so it's always going to be unrealiable, unless we have a way to implicitly distinguish the parts 🤔

[josevalim]

Ok, so I think we need two vars. LIVEBOOK_DEFAULT_RUNTIME and LIVEBOOK_DEFAULT_RUNTIME_FLAGS.

[jonatanklosko]

For the mix runtime the flags are project path and mix run flags, so we would still need the quotes?

[josevalim]

@jonatanklosko if we are looking at flags, then does it mean we need -- explicitly? If so, we can do this:

First split once on :-- to get the flags bit. Then split on the first :?

[josevalim]

Ok. I actually think we should just check for Windows style paths. Check if we have <<letter, ?:, _::binary>> when letter in ?a..?z or letter in ?A..?Z immediately after "mix:". If you are still worried about false positives, then you can check : is followed by either / or \.

[jonatanklosko]

Yeah, sounds good to me! Theoretically the path could have : anywhere, so either way the delimiter is heuristic-based, but I think it's fine.

[josevalim]

I think in those cases people can use the quotes. But solving the immediate case for windows for be beneficial.