Misprinted domain-free parameters with cohesion attribute

[Andreas Abel]

{-# OPTIONS --cohesion --erasure #-}

import Agda.Builtin.Bool

postulate
  Flat : (@♭ A : Set) → Set

module @0 Bool where
  open module M (@♭ A) (_ : Flat A) = Agda.Builtin.Bool public

This prints the module abstraction as module M @♭ A (_ : Flat A), which does not parse because of missing parenthesis around @♭ A.

Found this bug by reading the code for the printer:

agda/src/full/Agda/Syntax/Concrete/Pretty.hs

Lines 304 to 322 in 1eb3dd8

 instance Pretty NamedBinding where 
   pretty (NamedBinding withH x) = prH $ 
     if | Just l <- isLabeled x -> text l <+> "=" <+> pretty xb 
        | otherwise             -> pretty xb 
  
     where 
  
     xb = namedArg x 
     bn = binderName xb 
     prH | withH     = prettyRelevance x 
                     . prettyHiding x mparens 
                     . prettyCohesion x 
                     . prettyQuantity x 
                     . prettyTactic bn 
         | otherwise = id 
     -- Parentheses are needed when an attribute @... is present 
     mparens 
       | noUserQuantity x, Nothing <- bnameTactic bn = id 
       | otherwise = parens 

This code bit-rotted when cohesion was added in 4a45eb9; the noUserQuantity check became insufficient to check whether there are modalities.

[Andreas Abel]

The original test case for #3945 had the bad printing already:

agda/test/Fail/Issue3945.err

Line 3 in 3a34310

 when checking that the expression λ @♭ a → flat a has type