REPL: grab bag of tab completion issues/improvements

[SethTisue]

if something is a blocker for some 2.13.x release, remove it from here and give it its own ticket

doc: https://github.com/jline/jline3/wiki/Completion

on the PR Som wrote:

Tried it out. Did Jline completion always tab through alternatives? Some ordinary completion is broken, however, and will need repair.

(Actually I couldn't reproduce: c tab displayed cc and was stuck. Reminiscent of #10914.)

I guess the val c: C used to be shown below the line as an explanatory result?

scala> class C
defined class C

scala> val c = new C
c: C = C@58a7dc4

scala> val c: C // c tab

[SethTisue]

"Completion suggestions have changed when the cursor is midway through an identifier" (scala/scala#8036 (comment))

[SethTisue]

scala/scala#7645 (comment): "I noticed that ^A ^E no longer go to line start/end all the time."

[SethTisue]

I closed scala/scala-dev#698 with scala/scala#8905 but there are still a number of ways the UX could be better; 698 has some commentary with details

[SethTisue]

scala/scala#8905 indicates whether a method is nullary, nilary, or other by showing nothing, (), or (. @lrytz suggested that it ought to insert the parens for you when you chose that completion. I believe JLine does support this through the "suffix" field. Something to try.

[som-snytt]

I just noticed 2.13.6 // print tab completion looked like

scala> 1 + 1 // print
(1).+(1) // : Int(2)

and now it does a weird thing where it does completions but with 2 columns (blank left column) and it prints wrong when highlighting the right column. These are 3 tabs, redrawing the line:

scala> 1 + 1 // print
                       (1).+(1) // : Int(2)
scala> 1 + 1 // print
                       (1).+(1) // : Int(2)
scala> 1 + 1 // print(1).+(1) // : Int(2)
                       (1).+(1) // : Int(2)

This is on WSL, so maybe something else is going on. Or maybe the improvement to regular completions introduced this behavior for // print completion. Not worth a ticket, however.

[som-snytt]

Forgot the umbrella when I #12843 "Show me the parameters"