From @LLFourn

21​:46 < lizmat> m​: sub a is looser {}
21​:46 <+camelia> rakudo-moar 7e106c​: OUTPUT«===SORRY!=== Error while
compiling /tmp/dyKjMCb7xA␤Can't use unknown
  trait 'is looser' in a sub declaration.␤at
/tmp/dyKjMCb7xA​:1␤ expecting any of​:␤ rw raw
  hidden-from-backtrace hidden-from-USAGE␤ pure
default DEPRECATED i…»
21​:47 < llfourn> 'is looser' is actually in that error message which is a
bit LTA :\
21​:47 < lizmat> m​: sub a is looser(infix​:<+>) {}
21​:47 <+camelia> rakudo-moar 7e106c​: OUTPUT«===SORRY!=== Error while
compiling /tmp/4MtREU_vCv␤Can't use unknown
  trait 'is looser' in a sub declaration.␤at
/tmp/4MtREU_vCv​:1␤ expecting any of​:␤ rw raw
  hidden-from-backtrace hidden-from-USAGE␤ pure
default DEPRECATED i…»
21​:48 < lizmat> llfourn​: that just means it's not finding the correct MMD
candidate
21​:48 < lizmat> llfourn​: I suggest you rakudobug it
21​:48 < llfourn> lizmat​: okie dokes
21​:48 < lizmat> m​: sub a is looser(&infix​:<+>) {}
21​:48 <+camelia> rakudo-moar 7e106c​: ( no output )
21​:49 < llfourn> lizmat​: so I'll rakudobug it as an LTA error?
21​:49 < lizmat> well, yes, because apparently if you give it a Callable
operator, it does work
21​:50 < lizmat> m​: sub is looser(&infix​:<+>) {}

sub a is looser {} #LTA
sub a is looser(infix​:<+>) {} #LTA
sub a is looser(&infix​:<+>) {} # works
sub is looser(&infix​:<+>) {} #LTA