give some error message when using bad directive

[bjornregnell]

Version(s)
0.1.18

Describe the bug
scala-cli should complain if I write bad directives like by mistake replacing using with use after //>

To Reproduce

$ cat main.scala 
//> use scala "3.2.1"
//> use lib "org.jline:jline:3.21.0"

val t = org.jline.terminal.TerminalBuilder.terminal

@main def run = 
  println(s"hello $t")

$ scala-cli run main.scala 
Compiling project (Scala 3.2.1, JVM)
[error] ./main.scala:4:9: value jline is not a member of org
[error] val t = org.jline.terminal.TerminalBuilder.terminal
[error]         ^^^^^^^^^
Error compiling project (Scala 3.2.1, JVM)
Compilation failed

Above nothing is said about that the directive is bad. Instead it goes ahead and compiles and the compile error is not so helpful...

Expected behaviour
I should get some feedback that use is not a valid directive; it would be nice if it proposed something like did you mean 'using' .

[Gedochao]

Hmm... I'm not sure about an error message. //> is still a comment, so I guess it should compile successfully, if it can't be parsed as a using directive...
But yeah, we definitely could print a warning and potentially maybe add an actionable diagnostic.
thoughts?

[bjornregnell]

Yes, warning and actionable diagnostics is the right way. And I agree that it should go ahead and try to compile despite the problem -- but in this case it will not compile as there is a missing dependency. I think scala-cli can and should help with some good output here.

[tgodzik]

@lwronski this would be a pretty neat actionable diagnostic. We should get some levenstein going maybe, which might be helpful in more cases.

[bjornregnell]

See also #266 (comment)

[SethTisue]

I guess this is under the same umbrella. I (and @Izmar, iirc — I may have the wrong user name, apologies if so) were surprised by the following behavior:

% cat S.scala 
//> using option -deprecation
class C
//> using scala 2.13.12
class D

% scala-cli compile S.scala
Compiling project (Scala 3.3.0, JVM)
Compiled project (Scala 3.3.0, JVM)

Note that the second directive was silently ignored. I expected either that the directives could go anywhere, or that I would get a warning.