LTAness with putting space before sig specifier of Callable

[zoffixznet]

There is a host of things here, some of which are probably of the DIHWIDT variety, but maybe some could be improved.

This is on 2018.05-54-g148d7c5.

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Since spaces are needed to unpack stuff like Arrays in signatures, I wrote a thing like this:

$ perl6 -e 'sub (&s :()) {}'
===SORRY!=== Error while compiling -e
Can only use the : invocant marker in the signature for a method
at -e:1
------> sub (&s :()⏏) {}
    expecting any of:
        constraint

The actual signature was longer, so the cursor was pointing in the wrong place, but eventually I realized that it's the extra space in the signature specifier of the Callable that was causing the problem (maybe that can be included in the error as a suggestion to check?)

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However, if you write it that way in places where invocant markers are allowed, you get silence and a signature you did not intend:

$ perl6 -e '.say for :(&s :(), *%_), method (&s :()) {}.signature'
(&s: $ (), *%_)
(&s: $ (), *%_)

Strangelly, though those two signatures gist the same, they smartmatch False:

$ perl6 -e 'say :(&s :(), *%_) ~~ method (&s :()) {}.signature'
False

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Also, there's this crash if you remove the space and make the thingie an invocant:

$ perl6 -e 'say :(&s:():)'
No such method 'multi-invocant' for invocant of type 'Any'
  in block <unit> at -e line 1