Status update: STD gives an adequate error message now:
$ viv -c -e '/ : /'
===SORRY!===
Backtrack control ':' does not seem to have a preceding atom to control at
(eval) line 1:
------> / :⏏ /
Parse failed
Rakudo's complaint has changed but is still LTA:
$ perl6-m -e '/ : /'
===SORRY!===
Unrecognized regex metacharacter : (must be quoted to match literally)
at -e:1
------> / :⏏ /
Unrecognized regex metacharacter (must be quoted to match literally)
at -e:1
------> / :⏏ /
expecting any of:
statement list
prefix or term
prefix or meta-prefix
infix stopper
