REPL: display the compiler + Java version on startup

[dwijnand]

before:

scala>                                                                                                                  

after:

Welcome to Scala 3.0.3-RC1-bin-SNAPSHOT-nonbootstrapped-git-2b1b622 (1.8.0_292, Java OpenJDK 64-Bit Server VM).
Type in expressions for evaluation. Or try :help.
                                                                                                                                      
scala> 

which brings 3 in line with Scala 2:

Welcome to Scala 2.13.6 (OpenJDK 64-Bit Server VM, Java 1.8.0_292).
Type in expressions for evaluation. Or try :help.

scala> 

[SethTisue]

apologies to @som-snytt for not festooning this with configuration knobs and levers

[som-snytt]

I will say that trimming the message was one of my early contributions, IIRC. There was back and forth about what to say in one line that is beginner friendly but not annoying. Now we need Seth's other favorite feature, the prompt with version string.

[SethTisue]

Now we need Seth's other favorite feature, the prompt with version string.

😋

[SethTisue]

in case anyone doubts the value of having a banner and including this information:

first, I think it's crucial for beginners to tell them about :help, otherwise the discoverability of all the colon commands is zero

second, about showing the Scala version and JDK version, one could also imagine having an :info command (or some such) to show it, rather than displaying it every time

but by the time a user thinks to run something like :info it's too late. if the time ever even comes, most of the time it won't come. meanwhile they're running the wrong Scala version or the wrong JDK version and don't even realize it, and don't have a reason to check it with :info. or to go through the two-stage process of first trying :help to even find out about :info in the first place... a user won't normally invoke :help without a reason

then maybe they're filing a bug report or asking for help on Gitter, and do they think to tell us what their Scala and JDK versions are? maybe, but if it's right there in the REPL banner it's a lot likelier they'll do that

having it in the banner reminds people that hey, Scala isn't just Scala, it often matters which version you have and what JDK you're running it on

and although we certainly don't want creeping banner bloat, I feel like the Scala 2 style banner is sufficiently brief as not to waste space or be annoying

I may be a bit biased because I happen to be answer-questions-on-Gitter guy and I'm also triage-people's-bug-reports guy :-)

[ekrich]

I do think adding a :info as well would be a good idea. This way you could check if the repl has been open a long time.